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Article

Nutrient Element Stocks and Dynamic Changes in Stump–Root Systems of Eucalyptus urophylla × E. grandis

by
Zhushan Xie
1,
Xiang Liang
1,
Haiyu Liu
1,
Xiangsheng Deng
1 and
Fei Cheng
1,2,*
1
Guangxi Colleges and Universities Key Laboratory for Cultivation and Utilization of Subtropical Forest Plantation, College of Forestry, Guangxi University, Nanning 530004, China
2
Guangxi Key Laboratory of Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning 530004, China
*
Author to whom correspondence should be addressed.
Forests 2024, 15(1), 1; https://doi.org/10.3390/f15010001
Submission received: 9 November 2023 / Revised: 10 December 2023 / Accepted: 12 December 2023 / Published: 19 December 2023
(This article belongs to the Section Forest Ecology and Management)
Browse Figures
Versions Notes

Abstract

:
Stump–root systems consist of aboveground stumps and underground coarse roots after timber harvesting. Stump–root systems are the primary source of coarse woody debris (CWD) in plantations, and they play a crucial role in the material cycle, energy flow, and biodiversity of Eucalyptus plantation ecosystems. However, there is limited knowledge about the changes in elemental stock within this CWD type during decomposition. To address this gap, we conducted a study on Eucalyptus urophylla × E. grandis stump–root systems at various times (0, 1, 2, 3, 4, 5, and 6 years) after clearcutting. Our aim was to investigate the stock changes in eight elements (K, Ca, Mg, S, Fe, Mn, Cu, and Zn) within the stumps and coarse roots over time and their decay levels, and we analyzed the relationship between elemental stocks and the physical, chemical, and structural components of stump–root systems. Our findings revealed the following: (1) The majority of each element’s stock within the stump–root system was found in the coarse roots. The elemental stocks in both stumps and coarse roots decreased as time passed after clearcutting and as decay progressed. (2) Notably, the elemental stocks in stumps and coarse roots were significantly higher than in other treatments during the initial 0–2 years after clearcutting and at decay classes I and II. In terms of elemental stocks, stumps from all clearcutting times or decay classes had the highest K stock, followed by Ca and Fe. Mg, Mn, and S stocks were lower than the first three, while Zn and Cu stocks were very low. The ordering of elemental stocks from high to low in the stump–root systems generally aligned with that of the coarse roots. (3) The residual rates of K, Mg, and Mn stocks in the stump–root systems fit the negative exponential model well. It took approximately 1 to 3.5 years for a 50% loss of the initial stocks of these elements and 5 to 10 years for a 95% loss. (4) The large amount of biomass in the stump–root system is the long-term nutrient reservoir of plantations, and any factor related to biomass loss affects the magnitude and duration of the nutrient reservoir, such as N, P, stoichiometric ratios, density, water-holding capacity, and hemicellulose. These findings contribute to a better understanding of the nutrient elemental dynamics and ecological functions of stump–root systems in Eucalyptus plantations.

1. Introduction

Coarse woody debris (CWD) is an essential component of forest ecosystems, both in terms of structure and function. Due to its significant quantity and slow turnover, CWD plays a crucial role in nutrient release and long-term forest productivity, as well as maintaining ecosystem integrity and ecological processes [1,2]. Previous studies on CWD have mainly focused on standing dead trees, fallen logs, and large branches, primarily in natural forests or forests at higher latitudes or altitudes [3,4,5,6]. In intensively managed plantations, the main type of CWD is often stump–root systems left after logging [7,8,9,10]. Stump–root systems consist of aboveground stumps and underground coarse roots after timber harvesting. In plantation ecosystems, their biomass is very large, much higher than in natural forest ecosystems. For instance, Debeljak et al. found that the underground biomass in Slovenian plantations ranged from 40.0 t/hm2 to 48.2 t/hm2, while natural forests only had 2.0 t/hm2 to 22.8 t/hm2 [11]. Typically, the aboveground biomass of stump–root systems only represents a small portion of the total CWD biomass of plantation ecosystems, with the coarse roots being the main component [3]. However, excavating the underground part is labor-intensive, time-consuming, and costly [12,13,14]. This hinders our in-depth understanding of coarse root decomposition and nutrient release in plantations [7,8,15,16].
Stump–root systems are a long-term nutrient source in plantation ecosystems [1,3,7,8,9,13,17,18,19,20,21,22,23]. For example, Palviainen et al. studied the changes in C, N, P, K, Ca, and Mg content and storage during the stump–root system decomposition of three tree species in southern Finland over 40 years, and found that stump–root systems alleviated the nutrient loss caused by water-soil erosion after clearcutting [7,8]. Yue et al. also found that stump–root systems of larch had a positive impact on the P content and availability in the area surrounding the systems [24]. Stumps and coarse roots can significantly increase the total carbon, nitrogen, and phosphorus content of the soil through decomposition, as has been revealed in previous studies [15,16,18]. The release of nutrients from stumps and coarse roots during decomposition can increase the total P content of topsoil by approximately 50% [16]. However, these studies did not involve the dynamic changes in element stock. In addition, temperature and precipitation significantly affect the turnover of stump–root systems [25], and different tree species also result in obvious differences in the physicochemical characteristics of stump–root systems [26], but the specific impact of these factors on the element stock and release of stump–root systems in plantations has not yet been clarified.
Eucalyptus plantations are the largest type of artificial forest in southern China’s provinces. In Guangxi province alone, the plantation area reaches 5.4 million hectares, resulting in a significant amount of stump–root system biomass [10]. However, due to long-term continuous planting and improper management, the soil fertility of Eucalyptus plantations has degraded, leading to a decline in productivity. Although the nutrient content is not as high as that of fallen leaves and fine roots, stump–root systems’ high biomass and strong resistance to decomposition make them a long-term nutrient reservoir for Eucalyptus plantations [1,3,27,28,29]. However, our current knowledge regarding the nutrient storage of stump–root systems in Eucalyptus plantations, the release patterns of nutrient elements over time, and the factors that influence them remains limited.
Our previous study analyzed C, N, P, and their stoichiometric ratios in Eucalyptus stumps and coarse roots [10], whereas K, Ca, Mg, S, Fe, Mn, Cu, and Zn are likewise nutrients essential for plant growth. For example, K plays a vital role in maintaining cell osmotic balance, carbohydrate metabolism, protein synthesis, stomatal regulation, and enhancing plant stress resistance. Ca contributes to cell wall formation, acts as a messenger in cell division and elongation, regulates ion channels, and aids in the formation and development of the xylem. Mg is essential for chlorophyll production, nucleic acid and protein synthesis, phosphorylation, and the formation and development of the xylem [30]. S is involved in protein and secondary metabolite synthesis, supports the function of oxidoreductases, and is a key component of lignin. Fe is a component of chlorophyll, and is involved in the cell’s electron transport chain, DNA synthesis, nitrogen metabolism, and the synthesis of antioxidant enzymes [31]. Mn binds to proteins in Photosystem II, regulates protein and amino acid synthesis, and influences nitrogen absorption and transport. Cu is a component of photosynthetic enzymes, contributing to the photosynthetic electron transport chain and chloroplast development, and is a vital part of superoxide dismutase. Zn plays a crucial role in catalyzing photosynthesis, is essential for DNA synthesis and stability as well as cell division, and influences plant hormone synthesis and regulation [32]. However, little is known about their distribution in Eucalyptus stumps and coarse roots and the dynamics of the stocks during decomposition. This will hinder our understanding of the role of stumps and coarse roots in the maintenance of plantations.
Therefore, this study investigated eight element stocks in aboveground stumps and underground coarse roots with different decomposition years and decay degrees. The aim is to reveal the important role of stump–root systems in alleviating nutrient deficiency in Eucalyptus plantations and provide references for their proper management. Previous studies have shown that underground coarse root systems account for more than 80% [10] of the total biomass of stump–root systems. Here, we hypothesizes that due to the relatively stable underground environment, the residual rates of various elements in underground coarse roots are higher than that of aboveground parts, resulting in higher stock of various elements and total storage in underground coarse roots compared to stumps.

2. Materials and Methods

2.1. Study Site

The study site of this research was located on the State-owned Guangming Mountain Forest Farm (108.17° E, 23.70° N), Mashan County, Guangxi province, China (Figure 1). The elevation of the forest farm ranges from 200 to 400 m, and the terrain is characterized by low hills. The climate is a southern humid subtropical monsoon climate, with an average annual temperature of 21.8 °C. The extreme high and low temperatures are approximately 39 °C and 2 °C, respectively. The frost-free period is about 344 days, and the average annual precipitation can reach 1722.5 mm. The monsoon characteristics are obvious, with a clear distinction between dry and rainy seasons. The rainfall is concentrated from May to September, while from October to March of the following year, the rainfall is significantly less.
In November 2021, six E. urophylla × E. grandis plantations and one felling blank were selected as the study sites. The six plantations were clearcut and replanted in 2015, 2016, 2017, 2018, 2019, and 2020, with ages for plantations and decomposition years for stump–root systems since clearcutting ranging from 6 years to 1 year. The felling blank site was logged in 2021 and has not been replanted yet, with an age and time since logging of 0. The profiles of the seven sites are shown in Table 1.
The distance between each site was 2–5 km, and the site conditions were basically similar. The soils were ultisols (laterite) produced from sandstone, and the understory vegetation of the sites was dominated by Miscanthus floridulus, Rubus cochinchinensis, Melastoma candidum, Blechnum orientale, Pteris semipinnata, Dicranopteris linearis, Urena lobata, and Bidens pilosa.

2.2. Plot Setup and Field Survey

Four 20 m × 30 m plots were randomly set up at each site, resulting in a total of 28 plots. Each repeated plot in each site had a similar understory microenvironment. The distance between the plots was no less than 50 m.
A survey was conducted on all aboveground stumps of the systems in each plot. The stump height and diameter at a distance of 10 cm above the ground were measured using a measuring tape and recorded. The decay level of stump–root systems was classified based on the aboveground stumps, using a modified CWD classification system (Table S1) [17], combined with wood hardness, color, and presence of epiphytes [10] (Figure 2).

2.3. Sample Collection

Based on the survey results of the aboveground stumps, the distribution of stump decay levels within each plot was preliminarily determined, and then, the stump–root systems were excavated [33]. At least 3 stump–root systems were excavated for each decay level in each plot. During excavation, starting from the aboveground stumps, the excavation was carried out along the direction of the root system until the entire stump–root system was dug out. Efforts were made to maintain the integrity of the root system, especially the coarse roots with a diameter of 1 cm or more, which account for more than 90% of the underground biomass of the stump–root systems [34]. After excavation, the stump–root systems were cut into aboveground stumps and underground coarse roots from the base of the stumps using a chainsaw. After removing attached soil and gravel, the fresh weight of the stumps and coarse roots was measured and recorded.
For stumps with decay grades of I, II, and III, a disk with a thickness of 5 cm was cut at a distance of 5~10 cm from the top using a chainsaw. For ones with decay grades of IV and V, a loose wooden sample of at least 500 g was cut using a knife. Since thinner roots decompose faster, this study uniformly cut root segments with a diameter of 5 cm and a length of 30 cm from the small end of the roots to ensure comparability between different samples. Each sample was placed in a separate sealed bag and labeled accordingly. A total of 128 stump–root systems were excavated for this study, with 128 aboveground stumps and 128 belowground coarse roots collected. After transportation to the laboratory, all samples were pre-processed.
Sample volume was determined using the drainage method. Sample density (Tables S4 and S6) was obtained by dividing the dry mass by the volume. The dry weights were calculated based on the moisture content. To obtain the stump and coarse root biomass yield (per hectare), the arithmetic mean of the weighted stump and coarse root biomass (dry matter) was multiplied by the number of stumps per hectare (Table 1). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) content were determined using an ANKOM A2000i automated fiber analyzer (ANKOM Technology, Macedon, NY, USA). The acid-washed lignin (ADL) content was determined according to the method described by Trofymow et al. [35]. Finally, the cellulose, hemicellulose, and lignin content (Tables S4 and S6) of the samples was calculated using the following equations:
H e m i c e l l u l o s e = N D F − A D F
C e l l u l o s e = A D F − A D L
L i g n i n = A D L − a s h c o n t e n t

2.4. Nutrient Element Determination

Six stumps and coarse roots samples from each decay class were used to determine the chemical composition of wood samples. For each decay class, the measured sample was a mixture of at least three subsamples. The stumps and coarse roots were dried at 65 °C until constant weight, and then, preliminarily crushed with a grinder and further ground with a mill. The obtained powder was sieved through a 60-mesh sieve. We accurately weighed 1 g (FA1004, Shanghai Sunny Hengping Scientific Instrument Co., Ltd., Shanghai, China, accuracy ± 0.0001 g) of stump or coarse root powder samples, which were separately digested with H2SO4-H2O2 (Nanning Lantian Experimental Equipment Co., Ltd., Nanning, China) [36] and HNO3-HClO4 (Nanning Lantian Experimental Equipment Co., Ltd., Nanning, China) [36,37]. The H2SO4-H2O2 digestion solution was used for potassium (K) determination by the flame photometer (FP6410, INESA-A, Shanghai, China) method [36]. The HNO3-HClO4 mixed acid digestion solution was used for calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) determination by atomic absorption spectrophotometer (Z-2000, HITACHI, Tokyo, Japan) [36,38], and sulfur (S) determination by the spectrophotometric turbidity method (Z-2000, HITACHI, Tokyo, Japan).

2.5. Statistics and Data Analysis

The product of the content (Table S9) of an element in a specific clearcutting year or decay class of stumps and the biomass (Tables S2 and S3) of the corresponding clearcutting year or decay class of stumps is the stock of that element in that year or decay class of stumps. The calculation of elemental stock in coarse roots is also the same. The elemental stock of stump–root systems is the sum of the element stocks in stumps and coarse roots.
We conducted data analysis using SPSS 25.0. The t-test was employed to compare the differences in the inventory of the same elements between stumps and coarse roots at the same time or under the same decay treatment. Before performing a One-way ANOVA, the Bartlett test for homogeneity of variances was conducted. If p > 0.05, the variances were equal among different treatments, and One-way ANOVA was performed. If not, a square root transformation of the data was followed by another Bartlett test. If the data remained inhomogeneous, a non-parametric test (Kruskal–Wallis test) was conducted. When variances were homogeneous, One-way ANOVA was performed. If p < 0.05, there was a significant difference among treatments in the One-way ANOVA or Kruskal–Wallis test, and a post hoc Tukey test was applied. If p > 0.05, there was no significant difference among treatments.
The impact of stump–root system characteristics on elemental stocks was explored using Pearson correlation analysis. Using the Olson negative exponential model [39] to fit the change in residual elemental stock of stump–root systems, the model is as follows:
y = A e − k t
In the model, y represents the percentage, which is the ratio of the initial elemental stock (at year 0 after logging) to the stock at a certain year after logging. A and k are model parameters, and t represents the time after logging. Using Origin 2023 for model fitting, we calculated the parameters A and k, and estimated the time required (T0.5 and T0.95) for the element to lose 50% and 95% of its initial stock, respectively.
SPSS 25.0 (IBM Corp., Armonk, NY, USA) was used for Pearson correlation analysis, the research area map was drawn using ArcGIS 10.8 (ESRI, Redlands, CA, USA), and all figures were plotted using Origin 2023 (OriginLab Corp., Northampton, MA, USA).

3. Results

3.1. Distribution of Elemental Stocks in Stump–Root Systems

T-tests revealed an uneven distribution of elemental stocks between stumps and coarse roots of the same clearcutting time or decay class. For the same decay class, the stock of each element in the coarse roots accounted for more than 70% of the total stock of the corresponding element in the whole stump–root system (Table S8). For the same clearcutting age, coarse roots accounted for 77.80% to 97.35% of the total stocks of the corresponding element in the entire stump–root systems (Table S10). Compared to stumps, significantly higher average stocks of a particular element were found in coarse roots within 0–6 years after clearcutting or across five decay classes (Figure S1). The total stocks of the eight elements in coarse roots were also significantly higher than those in stumps for a specific year or decay class (Figure 3I).
The stocks of the eight elements in stumps decreased as the year after clearcutting increased (Figure 3). Stumps exhibited significantly higher element stocks within 0–2 years compared to subsequent years. The total stocks of the eight elements in coarse roots also decreased with the passage of time. Coarse roots showed significantly higher stocks of seven elements within 0–2 years, but Fe did not differ significantly over the years. The total stocks of the eight elements in coarse roots also decreased as the years after clearcutting increased, particularly within 0–3 years.
Both stumps and coarse roots exhibited declining stocks of all eight nutrients with increasing decay class. Element stocks in decay classes I and II were significantly higher in both stumps and coarse roots compared to the other decay classes. The total stocks of all eight elements in stumps and coarse roots also decreased with increasing decay class (Figure 4).
Considering that coarse roots accounted for the majority of the total elemental stocks in the stump–root systems, the changes in specific elemental stocks and total stocks in the stump–root systems with time or decay class were similar to those observed in coarse roots.
The stumps and coarse roots of all clearcutting years or decay classes showed the highest stocks of K, followed by Ca and Fe, while exhibiting lower stocks of Mg, Mn, and S. The stocks of Zn and Cu were found to be very low. The ranking of elemental stocks varied with years after clearcutting or decay class. However, except for year 0 after clearcutting and decay class I, the ranking order of elemental stocks in the stump–root system was consistent with that of coarse roots.

3.2. Residual Rates of Elemental Stocks in Stump–Root Systems

3.2.1. Dynamics of Residual Rates of Elemental Stock

The residual rates of the eight elements in stumps and coarse roots exhibited a consistent downward trend as the number of years after clearcutting increased. Specifically, the residual rate of each element experienced a rapid decline within the first 3 years after clearcutting, with most elements reaching less than 50% of the residual rate within this timeframe (Figure 5). Coarse roots, which accounted for over 70% of the stump–root systems in terms of elemental stocks, total elemental stocks, and biomass, demonstrated similar patterns of change to the overall stump–root systems with regard to these three indicators (Figure S2).

3.2.2. Fitting of Residual Rates of Elemental Stock

The R2 values of the Olson model indicated that stumps were better fitted for the residual rate dynamics of K, Mg, S, and Mn stocks. Ca and Fe were also reasonably fitted, while Cu and Zn showed the poorest fit. Coarse roots showed a similar pattern, with better fits for K, Mg, and Mn stocks, followed by Ca and S. Cu and Zn were again the worst fitted. Unfortunately, the model could not accurately fit the residual rate dynamics of Fe stocks in coarse roots.
The loss constants revealed that K and Mg stocks in stumps had higher loss rates, indicating faster depletion compared to Ca, S, Fe, and Mn. Similarly, K and S stocks in coarse roots also had higher loss rates, followed by Ca, Mg, and Mn. The loss constants also indicated that stumps lost K, Ca, Mg, and Mn stocks faster than coarse roots, while the opposite was true for S (Table 2).
The K, Mg, Ca, and Mn stocks of stumps took 1.413~3.427 and 5.167~9.823 years to lose 50% and 95% of their initial stocks, respectively. This was faster than coarse roots, which took 1.725~4.463 and 5.789~14.199 years for the same losses. Stumps lost 50% of their S stocks in 2.703 years, which was slower than coarse roots (0.934 years). However, stumps took 9.572 years to lose 95% of their S stocks, which was also slower than coarse roots (5.382 years).

3.3. Relationship between Elemental Stocks and Stump–Root System Factors

The Pearson correlation analysis revealed a significant positive correlation between stump biomass and the eight elemental stocks. With the exception of S, Fe, and Zn, the content of other stump elements exhibited a significant positive correlation with their respective stocks. Although the correlation between the C content in the stumps and elemental stocks was not significant, the N and P contents displayed a significant positive correlation with most elemental stocks. Furthermore, the stocks of the three lignocellulose components in the stumps exhibited a significant positive correlation with all eight elemental stocks. Density demonstrated a significant positive correlation with the various elemental stocks, while water-holding capacity exhibited a significant negative correlation with them, excluding Cu and Zn. Additionally, the C/N, C/P, and lignin/N of stumps displayed a significant negative correlation with the elemental stocks, excluding Cu, while the N/P had a significant negative correlation with these stocks, excluding Ca, Fe, and Cu. The stump biomass was significantly positively correlated with the N and P contents and stocks, lignocellulose stock, and hemicellulose content and density. It was significantly negatively correlated with the S and Zn contents, water-holding capacity, and chemical stoichiometry ratios (Figure 6).
Coarse root biomass was positively correlated with all of the elemental stocks other than Fe. All eight elemental contents in coarse roots were positively correlated with their stocks. C content had no significant correlation with the stocks, but N and P contents were positively correlated with most elemental stocks. The stocks of lignocellulose components in coarse roots were positively correlated with all of the stocks other than Fe and Zn. Coarse root density was negatively correlated with the stocks of Ca, Mn, and Cu, while water-holding capacity was positively correlated with the stocks of all elements other than Ca and Fe. Coarse root C/N, C/P, and lignin/N were negatively correlated with all of the elemental stocks other than Fe, while N/P was only negatively correlated with the stocks of Mg, S, and Zn. Coarse root biomass was positively correlated with N and P contents and stocks and lignocellulose stocks, and negatively correlated with Fe content, density, C/N, C/P, and lignin/N (Figure 6).

4. Discussion

4.1. Nutrient Element Stocks in Stump–Root Systems

The nutrient element stocks in the stump–root systems reflect the abundance or scarcity of nutrient elements in the forest stand per unit area. These stocks also determine the long-term nutrient supply for forest growth, which, in turn, influences the nutrient material cycle and energy flow in plantation ecosystems. In this study, we discovered that Eucalyptus trees retain a significant amount of nutrients in the stands after clearcutting. We also found that all eight elements tested were detectable in the stumps and coarse roots of the E. urophylla × E. grandis stump–root systems at various stages of decomposition. Generally, as the years after clearcutting and decay classes increased, the nutrient element stocks in the stump–root systems decreased. This decrease in elemental stocks over time may be due to the loss of biomass, particularly in the aboveground portion, which was more susceptible to rapid biomass loss under the external environment. Although the stocks were higher in the underground part compared to the aboveground part, indicating slower biomass loss in the underground environment, an overall decreasing trend was observed. Regardless of whether it was above or below ground, the nutrient elements generally followed the following pattern: major elements (K) > moderate elements (Ca, Mg, S) > trace elements (Fe, Mn, Cu, Zn). This pattern aligns with the different nutrient requirements for forest growth and is evident during the decomposition phases of the stump–root systems.
The size of nutrient pools in stump–root systems can vary greatly depending on latitude, climate, and tree species. A study conducted in southern Finland at low altitudes focused on the dynamics of elemental stocks in stumps of three commonly found tree species in plantations. The results showed that after 0–40 years of harvesting, Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) stumps were enriched in N, P, and Mg, while silver birch (Betula pendula) stumps were enriched in N, P, Ca, and Mg during specific time periods. However, in the remaining years, the stumps released these elements at varying rates. The element enrichment in Norway spruce and Scots pine stumps was found to be stronger compared to silver birch stumps [7,8].
In contrast, this study found that the stumps and coarse roots of Eucalyptus showed a significantly faster decline in element stocks compared to the Finnish stumps. This difference may be attributed to variations in climatic conditions and landforms [25,40]. Additionally, Eucalyptus stumps did not exhibit enrichment in several of the aforementioned elements, but were able to become enriched in Fe and Cu during 3–6 years after clearcutting. Coarse roots also showed a clear trend of Fe enrichment during this period, while the stumps showed a general trend of Fe release in the 0–6 years after clearcutting. Red soils, which are rich in Fe, have high Fe content that is difficult to leach. The content of Fe in the soil is usually higher than that in roots, and there is an exchange of elements between CWD and the soil [41,42,43,44]. Therefore, the apparent accumulation of Fe stocks in coarse roots may be due to the entry of soil Fe into these roots. Stumps, on the other hand, are not significantly affected by soil Fe as they are not in direct contact with the soil. However, the reason for the slow increase in Cu reserves 3–6 years after clearcutting is not well understood, and its smaller stock capacity may lead to significant fluctuations in response to both biotic and abiotic factors [45,46]. It is hypothesized that the activity of white-rot fungi could be one potential cause. As decomposition progresses, higher decay-resistant extractive concentrations in heartwood can lead to the accumulation of resistant compounds and more difficult-to-decompose substances, such as lignin, in the stump–root systems [9]. The microbial community in stump–root systems becomes dominated by fungi [47], and white-rot fungi require Cu ions for lignin degradation. Therefore, it is possible that the microbial community of stump–root systems absorbs Cu from the soil [48,49,50,51].
Limited knowledge exists regarding the impact of the nutrient pool in stump–root systems on the growth of subsequent Eucalyptus plantations. Previous studies have shown that the roots of C. lanceolata significantly increase soil total N and P concentrations in the surrounding area. Additionally, they have a minor effect on total K concentration, which is not statistically significant. These findings are closely tied to the years following clearcutting [41]. In mixed larch–ash (Fraxinus mandshurica Rupr.) forests, the decayed stump–root systems of larch trees in decay class IV significantly influences soil P concentration in the surrounding area up to a depth of 40 cm, with the maximum impact reaching 75 cm. However, in pure larch (Larix olgensis Henry) forests, only the soil P concentration in the top 10 cm is significantly affected, with the maximum impact reaching 35 cm [24]. Currently, when reforesting continuous Eucalyptus plantations in China, seedlings are typically planted between two stump–root systems with a space of 2 m × 3 m. Our study reveals that the stump–root systems lose a substantial portion of their initial total nutrient elements, particularly the essential elements, within the first two years after logging. Since most newly planted seedlings are situated far from the stump–root systems, the nutrients released from the decomposition of the stump–root systems may be lost due to water-soil erosion before the new roots expand into the area influenced by the stump–root systems. Therefore, further research is necessary to investigate the extent to which the Eucalyptus stump–root systems affect the soil area and to understand the mechanisms of nutrient retention and transport in both the stump–root system and the soil.

4.2. Residual Rates of Nutrient Stocks in Stump–Root Systems

This study observed that the initial stocks of the eight elements were rapidly released within the first 3 years after clearcutting, followed by a slower rate of change. During this initial period, stumps released more than half of their initial reserves of seven elements, including 75% of the initial reserves of K and Mg. Coarse roots also released more than half of their initial stocks of six elements within the first 3 years after clearcutting, with K, S, Mg, and Zn exceeding 2/3 of their initial stocks. Other elements, except for Fe, also released a significant portion of their initial stocks within the first 3 to 4 years after clearcutting. It is worth noting that previous studies have shown that Eucalyptus leaves release most of their nutrient stocks within 1 year after harvesting [52], but this study found that the Eucalyptus stump–root systems can continue to release nutrient stocks for several years to more than 10 years. This suggests that even after the depletion of nutrients from leaves, the stump–root systems can still replenish nutrients to the stands, thereby mitigating nutrient deficits in Eucalyptus plantations [7,8,53].
The pattern of stocks for large and medium elements in this study can be better predicted using a negative exponential model, which may be attributed to the fast turnover of material in the subtropical region [25]. However, the release migration process of trace elements from the stump–root systems is influenced by numerous factors, and small changes in any of these factors can significantly impact the release [25,40,54,55,56,57,58,59,60]. Therefore, further research is needed to gain a deeper understanding of the pattern of trace element release.
Model predictions indicate that coarse roots lost S stock at a faster rate compared to stumps, while Ca, Mg, and Mn stocks were lost faster in stumps than in coarse roots. K stock was lost at a comparable rate in both stumps and coarse roots, and Ca stock took the longest time to be lost. Specifically, coarse roots lost 50% of their initial stocks of K, Mg, and S within two years after clearcutting, and this rate of release was significantly faster than the rate of biomass loss from coarse roots [10]. Similarly, the dynamics of residual rates of S stock in Eucalyptus stumps differed significantly from the dynamics of residual rates of biomass in stumps. This suggests that there is some correlation between stump–root system biomass and nutrient element losses, but predicting the dynamics of nutrient element contents and stocks in specific stump–root systems will require targeted measurements and analyses.

4.3. Factors Influencing Elemental Stocks in Stump–Root Systems

The dynamics of elemental stocks in stump–root systems are influenced by a combination of biotic and abiotic factors, both internal and external [25,40,54,55,56,57,58,59,60]. The elemental stock is the product of content and its corresponding biomass. Therefore, the content and biomass directly affect elemental stocks [7,8]. In this study, the elemental stocks in the stumps and coarse roots were usually influenced by both biomass and elemental contents. The lignocellulose contents in the stumps and coarse roots did not have a significant relationship with the elemental stocks. However, we observed a significant positive correlation between the lignocellulose and elemental stocks, further illustrating the significant impact of biomass on elemental stocks.
The dynamics of elemental stocks in stump–root systems are somewhat synergistic with the dynamics of lignocellulose stocks [61]. Lignin, cellulose, and hemicellulose are the main structural components of Eucalyptus stump–root systems [10], and they constitute the main body of biomass. Generally, as CWD decomposes, cellulose and hemicellulose decrease, while lignin relatively increases [10,62]. The reason is that cellulose and hemicellulose are relatively simple carbon-containing high-molecular-weight polymers, so they are more likely to be exposed to microorganisms and decomposed. Their loss naturally accompanies the loss of biomass. Although lignin is also rich in carbon, it is relatively difficult to degrade due to the presence of benzene rings, resulting in its enrichment during decomposition. Additionally, microbial metabolites may form lignin analogs during plant decomposition, which also causes the lignin content to increase with decomposition. At the same time, the cell lysates of the wood residues are degraded and form cavities, and this leads to lower density. Increased connectivity within the stump–root systems facilitates water and air movement as well as microbial invasion, which promotes nutrient transport within the systems and release to the surrounding environment [16,63,64,65,66]. This also explains the significant positive correlation between biomass and the density of stump–root systems during the decay process, as well as the significant negative correlation with water-holding capacity, further explaining the relationships between elemental stocks and both density and water-holding capacity. It can be seen that the large biomass for stump–root systems serves as a long-term nutrient reservoir in artificial forests, and any factors that regulate biomass loss will affect the size and duration of the nutrient reservoir.
The stoichiometric ratios of stumps and coarse roots were significantly negatively correlated with the elemental stocks. We speculate that the stoichiometric ratios primarily act on elemental stocks through their influence on biomass. Our previous study explored C, N, P, and their related stoichiometric ratios in stumps and coarse roots; the results showed that as decomposition progressed, the C content of stumps and coarse roots showed an upward trend, but the N and P contents showed an “enrichment-release” and a “released” state, respectively [9]. It should also be noted that the first 0–3 years of stump–root system decomposition had abundant elemental stocks, including high levels of N and P, resulting in smaller C/N, C/P, N/P, and lignin/N, which were beneficial for the decomposition of stumps and coarse roots [21,67,68]. However, as decomposition progressed, the N and P were consumed, leading to an increase in these stoichiometric ratios, while the elemental stocks remained at lower levels due to biomass loss. This explains the negative correlation between the stoichiometric ratios and most elemental stocks. Additionally, the lack of a close relationship between C and elemental stocks suggests that the negative correlation between the stoichiometric ratios and elemental stocks is mainly related to N and P contents.
In summary, there are numerous closely related biotic and abiotic factors that drive the complex ecological processes of stump–root system decomposition and elemental release [47,69]. Understanding the mechanisms behind these factors is crucial for gaining a deeper understanding of stump–root system decomposition and element release, as well as for improving nutrient management in Eucalyptus plantations.

5. Conclusions

This study investigated the stock changes in eight elements within E. urophylla × E. grandis stumps and coarse roots over time and their decay levels, and analyzed the relationship between elemental stocks and stump–root system characteristics. The results suggested the following: (1) Coarse roots play a significant role in storing a substantial amount of each element within entire stump–root systems. Nutrient stocks in stumps and coarse roots decreased as the time and decay class increased after clearcutting. (2) Nutrient stocks in stumps and coarse roots were significantly higher within 0–2 years and decay classes I and II. Stumps of all clearcutting times or decay classes had the highest K stock, followed by Ca and Fe, with lower stocks of Mg, Mn, and S, and very low stocks of Zn and Cu. The ranking of elemental stocks in the stump–root system generally matched that of coarse roots. (3) The time required for a 50% loss of the initial K, Mg, and Mn stocks of these elements ranged from about 1 to 3.5 years, while a 95% loss took about 5–10 years. (4) The large amount of biomass in the stump–root system is the long-term nutrient reservoir of plantations, and any factor related to biomass loss affects the magnitude and duration of the nutrient reservoir, such as N, P, stoichiometric ratios, density, water-holding capacity, and hemicellulose. Our study sheds light on the changes in elemental stocks within Eucalyptus stump–root systems during decomposition. These findings contribute to a better understanding of the nutrient elemental dynamics and ecological functions of stump–root systems in Eucalyptus plantations.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/f15010001/s1, Figure S1: Average stocks of nutrient elements in Eucalyptus stumps and coarse roots during 0–6 years of decomposition time; Figure S2: Changes in sum of 8 elemental stocks and biomass of Eucalyptus stumps and coarse roots during 0–6 years of decomposition time; Table S1: Description of stumps decay classes; Table S2: Biomass of Eucalyptus stumps, coarse roots and stump-root systems during 0–6 years of decomposition time; Table S3: Biomass of Eucalyptus stumps, coarse roots and stump-root systems with different decay classes; Table S4: Changes in density, WHC (water-holding capacity), cellulose, lignin and hemicellulose of Eucalyptus stumps with different decomposition times and decay classes; Table S5: Changes in C content, N content, P content, C/N, C/P, N/P and Lignin/N of Eucalyptus stumps with different decomposition times and decay classes; Table S6: Changes in density, WHC (water-holding capacity), cellulose, lignin and hemicellulose of Eucalyptus coarse roots with different decomposition times and decay classes; Table S7: Changes in C content, N content, P content, C/N, C/P, N/P and Lignin/N of Eucalyptus coarse roots with different decomposition times and decay classes; Table S8: Changes in nutrient element stocks of Eucalyptus stumps, coarse roots and stump-root systems with different decay classes (mean ± S.E.); Table S9: Changes in nutrient contents of Eucalyptus stumps and coarse roots during 0–6 years of decomposition time (mean ± S.E.); Table S10: Changes in nutrient stocks in Eucalyptus stumps, coarse roots and stump-root systems during 0–6 years of decomposition time (mean ± S.E.).

Author Contributions

Sample determination, data analysis, and paper writing, Z.X.; sample determination and data analysis, X.L.; survey and sample collection, H.L. and X.D.; experimental design, sample survey, sample collection, and paper modification, F.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the National Natural Science Foundation of China under grant number 32160359 for the project “Characteristics of microbial communities during decomposition of underground coarse roots of Eucalyptus stumps”.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Marañón-Jiménez, S.; Castro, J. Effect of decomposing post-fire coarse woody debris on soil fertility and nutrient availability in a Mediterranean ecosystem. Biogeochemistry 2013, 112, 519–535. [Google Scholar] [CrossRef]
  2. Dai, Z.H.; Trettin, C.C.; Burton, A.J.; Jurgensen, M.F.; Page-Dumroese, D.S.; Forschler, B.T.; Schilling, J.S.; Lindner, D.L. Coarse woody debris decomposition assessment tool: Model development and sensitivity analysis. PLoS ONE 2021, 16, 0251893. [Google Scholar] [CrossRef]
  3. Didion, M.; Abegg, M. Tree stumps—An important but undervalued dead wood pool. Ann. For. Sci. 2022, 79, 34. [Google Scholar] [CrossRef]
  4. Woodall, C.; Rondeux, J.; Verkerk, H.; Ståhl, G. Estimating dead wood during national forest inventories: A review of inventory methodologies and suggestions for harmonization. Environ. Manag. 2009, 44, 624–631. [Google Scholar] [CrossRef]
  5. Dossa, G.; Schaefer, D.; Zhang, J.L.; Tao, J.P.; Cao, K.F.; Corlett, R.T.; Cunningham, A.B.; Xu, J.C.; Cornelissen, J.; Harrison, R.D. The cover uncovered: Bark control over wood decomposition. J. Ecol. 2018, 106, 2147–2160. [Google Scholar] [CrossRef]
  6. Shorohova, E.; Kapitsa, E.; Kuznetsov, A.; Kuznetsova, S.; Lopes De Gerenyu, V.; Kaganov, V.; Kurganova, I. Coarse woody debris density and carbon concentration by decay classes in mixed montane wet tropical forests. Biotropica 2022, 54, 635–644. [Google Scholar] [CrossRef]
  7. Palviainen, M.; Finér, L.; Laiho, R.; Shorohova, E.; Kapitsa, E.; Vanha-Majamaa, I. Carbon and nitrogen release from decomposing Scots pine, Norway spruce and silver birch stumps. For. Ecol. Manag. 2010, 259, 390–398. [Google Scholar] [CrossRef]
  8. Palviainen, M.; Finér, L.; Laiho, R.; Shorohova, E.; Kapitsa, E.; Vanha-Majamaa, I. Phosphorus and base cation accumulation and release patterns in decomposing Scots pine, Norway spruce and silver birch stumps. For. Ecol. Manag. 2010, 260, 1478–1489. [Google Scholar] [CrossRef]
  9. Deng, X. Stump Biomass of Eucalyptus Plantations and Physical, Chemical and Structural Component Characteristics of Stumps. Master’s Thesis, Guangxi University, Nanning, China, 2022. [Google Scholar]
  10. Deng, X.; Liang, X.; Shen, L.; Liu, H.; Yang, M.; Zeng, M.; Liang, M.; Cheng, F. Decomposition and nutrient dynamics of stumps and coarse roots of Eucalyptus plantations in southern China. Ann. For. Sci. 2023, 80, 30. [Google Scholar] [CrossRef]
  11. Debeljak, M. Coarse woody debris in virgin and managed forest. Ecol. Indic. 2006, 6, 733–742. [Google Scholar] [CrossRef]
  12. Gora, E.M.; Sayer, E.J.; Turner, B.L.; Tanner, E. Decomposition of coarse woody debris in a long-term litter manipulation experiment: A focus on nutrient availability. Funct. Ecol. 2018, 32, 1128–1138. [Google Scholar] [CrossRef]
  13. Guo, L.; Chen, J.; Cui, X.H.; Fan, B.; Lin, H. Application of ground penetrating radar for coarse root detection and quantification: A review. Plant Soil 2013, 362, 1–23. [Google Scholar] [CrossRef]
  14. Resh, S.C.; Battaglia, M.; Worledge, D.; Ladiges, S. Coarse root biomass for Eucalyptus plantations in Tasmania, Australia: Sources of variation and methods for assessment. Trees 2003, 17, 389–399. [Google Scholar] [CrossRef]
  15. Błońska, E.; Kacprzyk, M.; Spólnik, A. Effect of deadwood of different tree species in various stages of decomposition on biochemical soil properties and carbon storage. Ecol. Res. 2017, 32, 193–203. [Google Scholar] [CrossRef]
  16. Hope, G.D. Changes in soil properties, tree growth, and nutrition over a period of 10 years after stump removal and scarification on moderately coarse soils in interior British Columbia. For. Ecol. Manag. 2007, 242, 625–635. [Google Scholar] [CrossRef]
  17. Carmona, M.R.; Armesto, J.J.; Aravena, J.C.; Pérez, C.A. Coarse woody debris biomass in successional and primary temperate forests in Chiloé Island, Chile. For. Ecol. Manag. 2002, 164, 265–275. [Google Scholar] [CrossRef]
  18. Sucre, E.B.; Fox, T.R. Decomposing stumps influence carbon and nitrogen pools and fine-root distribution in soils. For. Ecol. Manag. 2009, 258, 2242–2248. [Google Scholar] [CrossRef]
  19. Yang, H.; Ciais, P.; Chave, J.; Huang, Y.; Ballantyne, A.P.; Yu, K.; Berzaghi, F.; Wigneron, J. Coarse woody debris are buffering mortality-induced carbon losses to the atmosphere in tropical forests. Environ. Res. Lett. 2021, 16, 011006. [Google Scholar] [CrossRef]
  20. Idol, T.W.; Figler, R.A.; Pope, P.E.; Ponder, F. Characterization of coarse woody debris across a 100 year chronosequence of upland oak-hickory forests. For. Ecol. Manag. 2001, 149, 153–161. [Google Scholar] [CrossRef]
  21. Benoist, A.; Houle, D.; Bradley, R.L.; Bellenger, J. Evaluation of biological nitrogen fixation in coarse woody debris from Eastern Canadian boreal forests. Soil Biol. Biochem. 2022, 165, 108531. [Google Scholar] [CrossRef]
  22. Ortiz, C.A.; Hammar, T.; Ahlgren, S.; Hansson, P.; Stendahl, J. Time-dependent global warming impact of tree stump bioenergy in Sweden. For. Ecol. Manag. 2016, 371, 5–14. [Google Scholar] [CrossRef]
  23. Keyser, T.L.; Loftis, D.L. Stump sprouting of 19 upland hardwood species 1 year following initiation of a shelterwood with reserves silvicultural system in the southern Appalachian Mountains, USA. New For. 2015, 46, 449–464. [Google Scholar] [CrossRef]
  24. Yue, Y.; Men, X.L.; Sun, Z.H.; Chen, X.W. Effects of Larix olgensis henry stumps and coarse roots on phosphorus fractions and availability in plantation microsite soils. Forests 2022, 13, 2166. [Google Scholar] [CrossRef]
  25. Carvalhais, N.; Forkel, M.; Khomik, M.; Bellarby, J.; Jung, M.; Migliavacca, M.; Mu, M.; Saatchi, S.; Santoro, M.; Thurner, M.; et al. Global covariation of carbon turnover times with climate in terrestrial ecosystems. Nature 2014, 514, 213–217. [Google Scholar] [CrossRef]
  26. Herrmann, S.; Bauhus, J. Effects of moisture, temperature and decomposition stage on respirational carbon loss from coarse woody debris (CWD) of important European tree species. Scand. J. For. Res. 2013, 28, 346–357. [Google Scholar] [CrossRef]
  27. de Souza Kulmann, M.S.; de Jesus Eufrade-Junior, H.; Dick, G.; Schumacher, M.V.; de Azevedo, G.B.; Azevedo, G.T.D.O.S.; Guerra, S.P.S. Belowground biomass harvest influences biomass production, stock, export and nutrient use efficiency of second rotation Eucalyptus plantations. Biomass Bioenergy 2022, 161, 106476. [Google Scholar] [CrossRef]
  28. Eufrade-Junior HD, J.; Leonello, E.C.; Spadim, E.R.; Rodrigues, S.A.; Azevedo, G.B.D.; Guerra, S.P.S. Stump and coarse root biomass from eucalypt forest plantations in a commercial-scale operation for bioenergy. Biomass Bioenergy 2020, 142, 1–7. [Google Scholar] [CrossRef]
  29. Gominho, J.; Lourenço, A.; Miranda, I.; Pereira, H. Chemical and fuel properties of stumps biomass from Eucalyptus globulus plantations. Ind. Crops Prod. 2012, 39, 12–16. [Google Scholar] [CrossRef]
  30. Gielen, S.; IBatlle, J.V.; Vincke, C.; Van Hees, M.; Vandenhove, H. Concentrations and distributions of Al, Ca, Cl, K, Mg and Mn in a Scots pine forest in Belgium. Ecol. Model. 2016, 324, 1–10. [Google Scholar] [CrossRef]
  31. Prieto, I.; Querejeta, J.I. Simulated climate change decreases nutrient resorption from senescing leaves. Glob. Chang. Biol. 2020, 26, 1795–1807. [Google Scholar] [CrossRef]
  32. Ågren, G.I.; Weih, M. Plant stoichiometry at different scales: Element concentration patterns reflect environment more than genotype. New Phytol. 2012, 194, 944–952. [Google Scholar] [CrossRef] [PubMed]
  33. Addo-Danso, S.D.; Prescott, C.E.; Smith, A.R. Methods for estimating root biomass and production in forest and woodland ecosystem carbon studies: A review. For. Ecol. Manag. 2016, 359, 332–351. [Google Scholar] [CrossRef]
  34. Kaarakka, L.; Vaittinen, J.; Marjanen, M.; Hellsten, S.; Kukkola, M.; Saarsalmi, A.; Palviainen, M.; Helmisaari, H. Stump harvesting in Picea abies stands: Soil surface disturbance and biomass distribution of the harvested stumps and roots. For. Ecol. Manag. 2018, 425, 27–34. [Google Scholar] [CrossRef]
  35. Trofymow, J.A.; Moore, T.R.; Titus, B.; Prescott, C.; Morrison, I.; Siltanen, M.; Smith, S.; Fyles, J.; Wein, R.; Camiré, C.; et al. Rates of litter decomposition over 6 years in Canadian forests: Influence of litter quality and climate. Can. J. For. Res. 2002, 32, 789–804. [Google Scholar] [CrossRef]
  36. Sahrawat, K.L.; Ravi Kumar, G.; Rao, J.K. Evaluation of triacid and dry ashing procedures for determining potassium, calcium, magnesium, iron, zinc, manganese, and copper in plant materials. Commun. Soil Sci. Plant Anal. 2002, 33, 95–102. [Google Scholar] [CrossRef]
  37. Zheljazkov, V.D.; Warman, P.R. Comparison of three digestion methods for the recovery of 17 plant essential nutrients and trace elements from six composts. Compos. Sci. Util. 2002, 10, 197–203. [Google Scholar] [CrossRef]
  38. Ashagrie, Y.; Zech, W.; Guggenberger, G. Transformation of a Podocarpus falcatus dominated natural forest into a monoculture Eucalyptus globulus plantation at Munesa, Ethiopia: Soil organic C, N and S dynamics in primary particle and aggregate-size fractions. Agric. Ecosyst. Environ. 2005, 106, 89–98. [Google Scholar] [CrossRef]
  39. Palviainen, M.; Finér, L. Decomposition and nutrient release from Norway spruce coarse roots and stumps—A 40-year chronosequence study. For. Ecol. Manag. 2015, 358, 1–11. [Google Scholar] [CrossRef]
  40. Berhe, A.A.; Barnes, R.T.; Six, J.; Marín-Spiotta, E. Role of soil erosion in biogeochemical cycling of essential elements: Carbon, nitrogen, and phosphorus. Annu. Rev. Earth Planet. Sci. 2018, 46, 521–548. [Google Scholar] [CrossRef]
  41. Kappes, H.; Catalano, C.; Topp, W. Coarse woody debris ameliorates chemical and biotic soil parameters of acidified broad-leaved forests. Appl. Soil Ecol. 2007, 36, 190–198. [Google Scholar] [CrossRef]
  42. Wiebe, S.A.; Morris, D.M.; Luckai, N.J.; Reid, D.E.B. The influence of coarse woody debris on soil carbon and nutrient pools 15 years after clearcut harvesting in black spruce—Dominated stands in northwestern Ontario, Canada. Écoscience 2014, 21, 11–20. [Google Scholar] [CrossRef]
  43. Johnson, D.W.; Todd, D.E., Jr.; Trettin, C.F.; Mulholland, P.J. Decadal Changes in Potassium, Calcium, and Magnesium in a Deciduous Forest Soil. Soil Sci. Soc. Am. J. 2008, 72, 1795–1805. [Google Scholar] [CrossRef]
  44. Shorohova, E.; Kapitsa, E.; Ruokolainen, A.; Romashkin, I.; Kazartsev, I. Types and rates of decomposition of Larix sibirica trees and logs in a mixed European boreal old-growth forest. For. Ecol. Manag. 2019, 439, 173–180. [Google Scholar] [CrossRef]
  45. Marañón-Jimenez, S.; Castro, J.; Fernández-Ondoño, E.; Zamora, R. Charred wood remaining after a wildfire as a reservoir of macro- and micronutrients in a Mediterranean pine forest. Int. J. Wildland Fire 2013, 22, 681–695. [Google Scholar] [CrossRef]
  46. Arnstadt, T.; Hoppe, B.; Kahl, T.; Kellner, H.; Krüger, D.; Bauhus, J.; Hofrichter, M. Dynamics of fungal community composition, decomposition and resulting deadwood properties in logs of Fagus sylvatica, Picea abies and Pinus sylvestris. For. Ecol. Manag. 2016, 382, 129–142. [Google Scholar] [CrossRef]
  47. Deng, X.; Cheng, F.; Li, M.; He, P.; Shen, L.; Liu, H. Effect of different decay classes of Eucalyptus stump substrates on microbial resource limitation and carbon-use efficiency. Plant Soil 2022, 478, 651–669. [Google Scholar] [CrossRef]
  48. Arnstadt, T.; Hoppe, B.; Kahl, T.; Kellner, H.; Krüger, D.; Bässler, C.; Bauhus, J.; Hofrichter, M. Patterns of laccase and peroxidases in coarse woody debris of Fagus sylvatica, Picea abies and Pinus sylvestris and their relation to different wood parameters. Eur. J. For. Res. 2016, 135, 109–124. [Google Scholar] [CrossRef]
  49. Garavaglia, S.; Teresa Cambria, M.; Miglio, M.; Ragusa, S.; Iacobazzi, V.; Palmieri, F.; D’Ambrosio, C.; Scaloni, A.; Rizzi, M. The structure of Rigidoporus lignosus laccase containing a full complement of copper ions, reveals an asymmetrical arrangement for the T3 copper pair. J. Mol. Biol. 2004, 342, 1519–1531. [Google Scholar] [CrossRef]
  50. Hafner, S.D.; Groffman, P.M. Soil nitrogen cycling under litter and coarse woody debris in a mixed forest in New York State. Soil Biol. Biochem. 2005, 37, 2159–2162. [Google Scholar] [CrossRef]
  51. Gómez-Brandón, M.; Ascher-Jenull, J.; Bardelli, T.; Fornasier, F.; Fravolini, G.; Arfaioli, P.; Ceccherini, M.T.; Pietramellara, G.; Lamorski, K.; Sławiński, C.; et al. Physico-chemical and microbiological evidence of exposure effects on Picea abies—Coarse woody debris at different stages of decay. For. Ecol. Manag. 2017, 391, 376–389. [Google Scholar] [CrossRef]
  52. Alvarez, E.; Fernández Marcos, M.L.; Torrado, V.; Fernández Sanjurjo, M.J. Dynamics of macronutrients during the first stages of litter decomposition from forest species in a temperate area (Galicia, NW Spain). Nutr. Cycl. Agroecosystems 2008, 80, 243–256. [Google Scholar] [CrossRef]
  53. Herrmann, S.; Bauhus, J. Nutrient retention and release in coarse woody debris of three important central European tree species and the use of NIRS to determine deadwood chemical properties. For. Ecosyst. 2018, 5, 22. [Google Scholar] [CrossRef]
  54. Klockow, P.A.; D’Amato, A.W.; Bradford, J.B.; Fraver, S. Nutrient concentrations in coarse and fine woody debris of Populus tremuloides Michx.-dominated forests, northern Minnesota, USA. Silva Fenn. 2014, 48, 962. [Google Scholar] [CrossRef]
  55. Saunders, M.R.; Fraver, S.; Wagner, R.G. Nutrient concentration of down woody debris in mixedwood forests in central Maine, USA. Silva Fenn. 2011, 45, 197–210. [Google Scholar] [CrossRef]
  56. Dhiedt, E.; De Keersmaeker, L.; Vandekerkhove, K.; Verheyen, K. Effects of decomposing beech (Fagus sylvatica) logs on the chemistry of acidified sand and loam soils in two forest reserves in Flanders (northern Belgium). For. Ecol. Manag. 2019, 445, 70–81. [Google Scholar] [CrossRef]
  57. Cornwell, W.K.; Cornelissen JH, C.; Allison, S.D.; Bauhus, J.; Eggleton, P.; Preston, C.; Scarff, F.; Weedon, J.; Wirth, C.; Zanne, A. Plant traits and wood fates across the globe: Rotted, burned, or consumed. Glob. Chang. Biol. 2009, 15, 2431–2449. [Google Scholar] [CrossRef]
  58. Błońska, E.; Kempf, M.; Lasota, J. Woody debris as a substrate for the growth of a new generation of forest trees. For. Ecol. Manag. 2022, 525, 120566. [Google Scholar] [CrossRef]
  59. Bonanomi, G.; Zotti, M.; Cesarano, G.; Sarker, T.C.; Saulino, L.; Saracino, A.; Idbella, M.; Agrelli, D.; Ascoli, R.; Rita, A.; et al. Decomposition of woody debris in Mediterranean ecosystems: The role of wood chemical and anatomical traits. Plant Soil 2021, 460, 263–280. [Google Scholar] [CrossRef]
  60. Filipiak, M.; Sobczyk, L.; Weiner, J. Fungal Transformation of Tree Stumps into a Suitable Resource for Xylophagous Beetles via Changes in Elemental Ratios. Insects 2016, 7, 13. [Google Scholar] [CrossRef]
  61. Fukasawa, Y.; Katsumata, S.; Mori, A.S.; Osono, T.; Takeda, H. Accumulation and decay dynamics of coarse woody debris in a Japanese old-growth subalpine coniferous forest. Ecol. Res. 2014, 29, 257–269. [Google Scholar] [CrossRef]
  62. Romashkin, I.; Shorohova, E.; Kapitsa, E.; Galibina, N.; Nikerova, K. Substrate quality regulates density loss, cellulose degradation and nitrogen dynamics in downed woody debris in a boreal forest. For. Ecol. Manag. 2021, 491, 119143. [Google Scholar] [CrossRef]
  63. Fukasawa, Y. Fungal succession and decomposition of Pinus densiflora snags. Ecol. Res. 2018, 33, 435–444. [Google Scholar] [CrossRef]
  64. Fontaine, S.; Barot, S.; Barré, P.; Bdioui, N.; Mary, B.; Rumpel, C. Stability of organic carbon in deep soil layers controlled by fresh carbon supply. Nature 2007, 450, 277–280. [Google Scholar] [CrossRef] [PubMed]
  65. Baldrian, P. Forest microbiome: Diversity, complexity and dynamics. FEMS Microbiol. Rev. 2017, 41, 109–130. [Google Scholar] [CrossRef] [PubMed]
  66. Pastorelli, R.; Paletto, A.; Agnelli, A.E.; Lagomarsino, A.; De Meo, I. Microbial communities associated with decomposing deadwood of downy birch in a natural forest in Khibiny Mountains (Kola Peninsula, Russian Federation). For. Ecol. Manag. 2020, 455, 117643. [Google Scholar] [CrossRef]
  67. Gorgolewski, A.; Rudz, P.; Jones, T.; Basiliko, N.; Caspersen, J. Assessing Coarse Woody Debris Nutrient Dynamics in Managed Northern Hardwood Forests Using a Matrix Transition Model. Ecosystems 2020, 23, 541–554. [Google Scholar] [CrossRef]
  68. Hellsten, S.; Helmisaari, H.; Melin, Y.; Skovsgaard, J.P.; Kaakinen, S.; Kukkola, M.; Saarsalmi, A.; Petersson, H.; Akselsson, C. Nutrient concentrations in stumps and coarse roots of Norway spruce, Scots pine and silver birch in Sweden, Finland and Denmark. For. Ecol. Manag. 2013, 290, 40–48. [Google Scholar] [CrossRef]
  69. Fukasawa, Y.; Osono, T.; Takeda, H. Dynamics of physicochemical properties and occurrence of fungal fruit bodies during decomposition of coarse woody debris of Fagus crenata. J. For. Res. 2009, 14, 20–29. [Google Scholar] [CrossRef]
Forests 15 00001 g001
Figure 1. Location map. The green part is the jurisdiction of Nanning City, Guangxi, the light pink part is the jurisdiction of Mashan County, the green dot is the location of Guangming Mountain Forest Farm.
Figure 1. Location map. The green part is the jurisdiction of Nanning City, Guangxi, the light pink part is the jurisdiction of Mashan County, the green dot is the location of Guangming Mountain Forest Farm.
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Figure 2. Excavation and weighing of Eucalyptus stumps and coarse roots at study sites [10].
Figure 2. Excavation and weighing of Eucalyptus stumps and coarse roots at study sites [10].
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Figure 3. K (A), Ca (B), Mg (C), S (D), Fe (E), Mn (F), Cu (G), Zn (H) stocks and total stocks of eight elements (I) in stumps, coarse roots, and stump–root system at different decomposition times (mean ± S.E.). Different lowercase letters on the same line indicate significantly different (p < 0.05) means for different decomposition times within the stump, coarse root, or stump–root system.
Figure 3. K (A), Ca (B), Mg (C), S (D), Fe (E), Mn (F), Cu (G), Zn (H) stocks and total stocks of eight elements (I) in stumps, coarse roots, and stump–root system at different decomposition times (mean ± S.E.). Different lowercase letters on the same line indicate significantly different (p < 0.05) means for different decomposition times within the stump, coarse root, or stump–root system.
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Figure 4. K (A), Ca (B), Mg (C), S (D), Fe (E), Mn (F), Cu (G) and Zn (H) stocks in stumps, coarse roots, and stump–root system at different decay classes (mean ± S.E.). Different lowercase letters on the same line indicate significantly different (p < 0.05) means for different decay classes within the stump, coarse root, or stump–root system.
Figure 4. K (A), Ca (B), Mg (C), S (D), Fe (E), Mn (F), Cu (G) and Zn (H) stocks in stumps, coarse roots, and stump–root system at different decay classes (mean ± S.E.). Different lowercase letters on the same line indicate significantly different (p < 0.05) means for different decay classes within the stump, coarse root, or stump–root system.
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Figure 5. Changes in K (A), Ca (B), Mg (C), S (D), Fe (E), Mn (F), Cu (G), Zn (H) and sum of eight elements (I) stocks and biomass (J) of Eucalyptus stumps, coarse roots, and stump–root system during 0–6 years of decomposition time. Residual percentages for elemental stocks, sum of 8 elemental stocks, and biomass indicate ratio of decomposition time relative to 0 years.
Figure 5. Changes in K (A), Ca (B), Mg (C), S (D), Fe (E), Mn (F), Cu (G), Zn (H) and sum of eight elements (I) stocks and biomass (J) of Eucalyptus stumps, coarse roots, and stump–root system during 0–6 years of decomposition time. Residual percentages for elemental stocks, sum of 8 elemental stocks, and biomass indicate ratio of decomposition time relative to 0 years.
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Figure 6. Pearson correlation for biomass, elemental contents, stoichiometric ratios, lignocellulose, density, water-holding capacity, and elemental stocks of stumps (A) and coarse roots (B). KS, K stock; CaS, Ca stock; MgS, Mg stock; SS, S stock; FeS, Fe stock; MnS, Mn stock; CuS, Cu stock; ZnS, Zn stock; CC, C content; NC, N content; PC, P content; KC, K content; CaC, Ca content; MgC, Mg content; SC, S content; FeC, Fe content; MnC, Mn content; CuC, Cu content; ZnC, Zn content; LC, lignin content; CeC, cellulose content; HCC, hemicellulose content; WHC, water-holding capacity.
Figure 6. Pearson correlation for biomass, elemental contents, stoichiometric ratios, lignocellulose, density, water-holding capacity, and elemental stocks of stumps (A) and coarse roots (B). KS, K stock; CaS, Ca stock; MgS, Mg stock; SS, S stock; FeS, Fe stock; MnS, Mn stock; CuS, Cu stock; ZnS, Zn stock; CC, C content; NC, N content; PC, P content; KC, K content; CaC, Ca content; MgC, Mg content; SC, S content; FeC, Fe content; MnC, Mn content; CuC, Cu content; ZnC, Zn content; LC, lignin content; CeC, cellulose content; HCC, hemicellulose content; WHC, water-holding capacity.
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Table 1. Characteristics of the experimental sites.
Table 1. Characteristics of the experimental sites.
Decomposition Time (Year)0123456
Year of replanting-202020192018201720162015
DBH (cm)-4.5813.213.615.316.7
TH (m)-4.710.513.517.518.520.5
Density of plantation (tree·ha−1)-166716671667166716671667
NSH1506163713501343103710811332
Distribution by decay classes of stumpsIIIIII, IVIII, IVIV, VIV, VV
Diameter of stump at 10 cm above ground (cm)22.920.922.424.924.522.621.6
DBH is diameter at breast height; TH is tree height; NSH is number of stumps per hectare. - indicates that there are no data at this location. All sites had a sandy loam soil texture, were well drained, and were replanted with the same tree species.
Table 2. Negative exponential decay model between remaining nutrients and time for Eucalyptus stumps, coarse roots, and stump–root system.
Table 2. Negative exponential decay model between remaining nutrients and time for Eucalyptus stumps, coarse roots, and stump–root system.
ElementTypeRegression EquationR2KT0.5 (Years)T0.95 (Years)
KStumpy = 118.904e−0.613t0.6680.6131.4135.167
Coarse rooty = 132.837e−0.566t0.6820.5661.7255.789
CaStumpy = 142.448e−0.305t0.5840.3053.4279.823
Coarse rooty = 128.042e−0.211t0.5160.2114.46314.199
MgStumpy = 102.824e−0.490t0.8370.491.4726.114
Coarse rooty = 77.415e−0.375t0.6130.3751.8487.989
SStumpy = 116.399e−0.313t0.6370.3132.7039.572
Coarse rooty = 81.062e−0.518t0.4950.5180.9345.382
FeStumpy = 124.305e−0.318t0.5760.3182.8689.421
Coarse root-----
MnStumpy = 105.329e−0.358t0.8310.3582.0838.369
Coarse rooty = 146.183e−0.306t0.640.3063.5099.791
CuStumpy = 89.853e−0.205t0.2760.2053.41314.615
Coarse rooty = 115.900e−0.246t0.2820.2462.86612.179
ZnStumpy = 80.906e−0.180t0.2480.182.67816.644
Coarse rooty = 54.487e−0.138t0.0390.1385.02221.71
“-” indicates that the model cannot fit the loss of nutrient stocks.
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Xie, Z.; Liang, X.; Liu, H.; Deng, X.; Cheng, F. Nutrient Element Stocks and Dynamic Changes in Stump–Root Systems of Eucalyptus urophylla × E. grandis. Forests 2024, 15, 1. https://doi.org/10.3390/f15010001

AMA Style

Xie Z, Liang X, Liu H, Deng X, Cheng F. Nutrient Element Stocks and Dynamic Changes in Stump–Root Systems of Eucalyptus urophylla × E. grandis. Forests. 2024; 15(1):1. https://doi.org/10.3390/f15010001

Chicago/Turabian Style

Xie, Zhushan, Xiang Liang, Haiyu Liu, Xiangsheng Deng, and Fei Cheng. 2024. "Nutrient Element Stocks and Dynamic Changes in Stump–Root Systems of Eucalyptus urophylla × E. grandis" Forests 15, no. 1: 1. https://doi.org/10.3390/f15010001

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