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Article

Monthly Dynamical Patterns of Nitrogen and Phosphorus Resorption Efficiencies and C:N:P Stoichiometric Ratios in Castanopsis carlesii (Hemsl.) Hayata and Cunninghamia lanceolata (Lamb.) Hook. Plantations

by
Yaoyi Zhang
,
Jing Yang
,
Xinyu Wei
,
Xiangyin Ni
and
Fuzhong Wu
*
Key Laboratory for Humid Subtropical Eco-Geographical Processes of the Ministry of Education, School of Geographical Sciences, Fujian Normal University, Fuzhou 350007, China
*
Author to whom correspondence should be addressed.
Forests 2022, 13(9), 1458; https://doi.org/10.3390/f13091458
Submission received: 30 August 2022 / Revised: 8 September 2022 / Accepted: 8 September 2022 / Published: 10 September 2022
(This article belongs to the Special Issue Carbon and Nutrient Transfer via Above and Belowground Litter in Forests)
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Abstract

:
Trees can resorb nutrients to preserve and reuse them before leaves fall, which could efficiently adapt to environmental changes. However, the nutrient requirements of trees in different months with seasonal climate changes are often neglected. In this study, we selected plantations of an evergreen broadleaf tree (Castanopsis carlesii (Hemsl.) Hayata) and a coniferous tree (Cunninghamia lanceolate (Lamb.) Hook.) in the subtropics. The monthly dynamics of leaf nitrogen (N) and phosphorus (P) resorption efficiencies and C:N:P stoichiometric ratios were checked along a growing season from April to October 2021. Trees in both plantations exhibited efficient N and P resorption but with significant monthly variations. The N and P resorption efficiencies in the Cunninghamia lanceolata plantation ranged from 34.26% to 56.28% and 41.01% to 54.85%, respectively, and were highest in September. In contrast, N and P resorption efficiencies in the Castanopsis carlesii plantation ranged from 11.25% to 34.23% and 49.22% to 58.72%, respectively, and were highest in July. Compared with the Cunninghamia lanceolata, the C:N of the Castanopsis carlesii plantation was significantly lower, while its C:P was significantly higher in May and September. The Castanopsis carlesii plantation was strongly limited by P (the N:P ratios in mature leaves were higher than 20), whereas the Cunninghamia lanceolata plantation might be limited by both N and P (the N:P ratios in mature leaves were between 10 and 20). In addition, the statistical analyses revealed that temperature and precipitation were significantly associated with N and P resorption efficiencies, but the relationships were controlled by forest types. These findings highlight that efficient resorption of N and P may be beneficial in regulating nutrient limitation and balance in subtropical forest ecosystems. These results contribute to the understanding of N and P utilization strategies of trees and provide a theoretical basis for vegetation management in the subtropics.

1. Introduction

Nutrient resorption is a process by which plants transfer nutrients from senescent organs to fresh tissues [1,2,3]. It is an important strategy for trees to conserve and use nutrients efficiently and profoundly affects several key processes in ecosystems, such as plant nutrient uptake, ecochemical balance, and carbon cycling [4,5,6]. The efficiency of this nutrient transfer (nutrient resorption efficiency) can be quantified by the percentage reduction in nutrient content between mature and senescent leaves [7,8,9]. However, nutrients that are not transferred from senescent leaves fall to the ground with withered leaves and are recycled in the ecosystem after the withered leaves are decomposed. Therefore, the final nutrient content in senescent leaves can also be used as an indicator of nutrient resorption (nutrient resorption proficiency) [7], which reflects the extent of nutrient transfer from leaves [7,8]. However, it is well known that trees often have various nutrient requirements to satisfy the growing need with monthly climate changes [10,11,12], but the dynamical patterns of nutrient resorption are often neglected.
Temperature and precipitation are important drivers for regulating the nutrient utilization of trees [13,14,15]. Previous studies have shown that P resorption efficiency increases with increasing average annual temperature and average annual precipitation, while N resorption efficiency decreases [16]. However, other studies have suggested that N and P resorption efficiencies decrease with increasing average annual temperature or average annual precipitation [17,18]. Most of these studies were limited to large regional scales, and differences in the species selected as well as the sampling months may contribute to the uncertainty of the results. Currently, even less is known about the dynamics of leaf resorption of forest trees in response to seasonal climate changes. Given the importance of resorption for plants and ecosystems, more data are needed to clarify this issue so that we can incorporate nutrient resorption into models of plant responses to climate changes [19].
The trees with different functional types also develop various nutrient resorption strategies [8,20,21]. A meta-analysis proposed that the P resorption efficiency was higher in coniferous plantations than in broadleaf plantations, while the N resorption efficiency has no significant difference [22]. Consistent results were also observed in many natural forests [21,23]. However, a study in the karst ecosystems of Southwestern China documented that coniferous trees have a lower P resorption efficiency and a higher N resorption efficiency than broadleaf trees [24]. The differences in nutrient resorption among functional types of forests remain uncertain.
In addition, element stoichiometry focuses on the interactions and balances among elements [25,26,27]. Element stoichiometric balance exerts an essential role in species development, community structure, and adaptation to environmental stresses [28,29]. Specifically, C:N:P stoichiometric ratios of plants can reveal the nutrient utilization and relative nutrient limitation [30,31]. At present, C:N:P stoichiometric ratios have been evaluated at both global and regional scales, and vary with several factors such as plant functional types [2,8], soil nutrients [5,6,32], and climate changes [33,34], which can provide theoretical support for the management and conservation of forest.
Compared to other regions at the same latitude, the subtropical region of China nurtures vast humid subtropical forests [35]. In recent years, amounts of natural broadleaf evergreen forests in the region have been replaced by large areas of mono-structured plantations to meet the needs of economic development [36]. More than 60% of China’s plantations are located in warm and humid subtropical regions [37]. However, N and P in subtropical forest soils are highly susceptible to leaching out of the ecosystem by rainfall [18], thus limiting plant growth. Therefore, the N and P resorption strategies of subtropical plants may be more important compared to other regions. The Cunninghamia lanceolate (Lamb.) Hook. is an important fast-growing tree for afforestation in subtropical regions, accounting for 17.3% of total plantations in China [38]. Castanopsis carlesii (Hemsl.) Hayata is one of the most typical trees of evergreen broadleaf forests in subtropical regions of China [39]. The results in studying the nutrient resorption and C:N:P stoichiometric characteristics in Castanopsis carlesii and Cunninghamia lanceolata plantations can help to understand the nutrient use strategies of subtropical forests.
Therefore, to understand the dynamics of nutrient use strategies in response to changes in temperature and precipitation in different plantations, we investigated the C, N, and P contents and stoichiometric ratios in mature and senescent leaves and nutrient resorption of Cunninghamia lanceolata plantation and Castanopsis carlesii plantation in a typical subtropical region, where both plantations have similar climates and land-use histories. We hypothesized that N and P resorption and C:N:P stoichiometric ratios in the leaves may vary significantly with forest types and are regulated by seasonal climate changes. Our objectives were to determine (i) what are the differences of nutrient resorption and C:N:P stoichiometric ratios between the two plantations, and (ii) whether and how nutrient resorption strategies were influenced by monthly temperature and precipitation dynamics. These results can provide further insights into a better understanding of nutrient cycling and ecological processes in different forest plantations in the subtropics and provide a theoretical basis for the management of plantations.

2. Materials and Methods

2.1. Study Site

The study site was located in Fujian Sanming Forest Ecosystem National Observation and Research Station, China (26°19′ N, 117°36′ E), in the southeast of the Wuyishan National Nature Reserve and northwest of the Daiyun Mountains. The area is dominated by low hills, with an average elevation of 300 m and a slope of 25–45°. The climate is maritime subtropical monsoonal, with an average annual temperature of 19.3 °C and an annual precipitation of 1610 mm from 1960 to 2019, with about 80% of the rainfall occurring between March and August [40]. The soils were developed from granite and can be classified as Hapludults under the Ultisols order according to the United States Department of Agriculture Soil Taxonomy. The soil pH is 4.38 [37,38]. Before 1958, the area was covered by natural broadleaf forests dominated by Castanopsis carlesii [41]. However, as the demand for timber for construction increased, the natural forests were gradually logged and replaced by plantations (mainly Castanopsis carlesii and Cunninghamia lanceolata).
In 2011, six 20 m × 20 m plots were set up in a randomized group design in a natural forest of Castanopsis carlesii formed in 1976, including two treatments, a Castanopsis carlesii plantation and a Cunninghamia lanceolata plantation (Table 1), with three replicates in each plantation [40]. We investigated in 2021 when both plantations were 10 years old and in a rapid growth stage with high nutrient demand.

2.2. Sampling and Chemical Analysis

At the end of each month from April to October 2021, five trees with similar height and diameter at breast height were selected in each replicate sample plot to collect the mature leaves. A total of 15 trees from each plantation were collected. The green mature leaves of Castanopsis carlesii were collected in the Castanopsis carlesii plantation, while the green needles on the second or third node branches were collected in the Cunninghamia lanceolata plantation. The collected mature leaves were placed in moist self-sealing bags and brought back to the laboratory through an insulated box (internal temperature < 4 °C) [42]. In addition, senescent leaves were also collected at the end of each month. Three separate 0.7 m × 0.7 m nylon mesh frames were set up in each replicate sample plot in the Castanopsis carlesii plantation. The fresh leaf litter of Castanopsis carlesii in nylon mesh frames was selected as senescent leaf samples. Because of the persistence effect, the needle litter of branches of Cunninghamia lanceolata can retain on the trunk for many years [43], and so the newly senescent brownish-yellow needles on the trees were collected as senescent needle samples in the Cunninghamia lanceolata plantation. In addition, soil samples were collected at a depth of 0–20 cm in the Castanopsis carlesii plantation and the Cunninghamia lanceolata plantation to assess the chemical composition in August 2021. During the sampling period, three tipping bucket rainfall barrels were placed in a non-forested area near the sample plots for automatic recording of precipitation. A temperature logger was also placed in the non-forested area for recording air temperature (Figure 1).
The collected mature and senescent leaves were dried in an oven at 65 °C for more than 72 h to a constant weight. Afterward, the dried samples were ground with a grinder (Tube Mill 100 control) and sieved through 100 mesh. The soil samples were air dried and also sieved through 100 mesh. The C and N contents of leaves and soil were determined using an elemental analyzer (Elemental Analyzer Vario EL III, Langenselbold, Germany) [37]. The P content of leaves and soil was determined using a continuous flow analyzer (SAN++, SKALAR, Holland) after the preparation of the solution, to be measured by H2SO4-HClO4 decoction [44].

2.3. Calculation and Analysis

To eliminate the error caused by the loss of leaf mass during senescence in the calculation of the nutrient resorption efficiency (NuRE) during leaf senescence, we used the following formula [9,43]:
NuRE = 1 − N u s e n e s c e n t N u m a t u r e M L C F × 100
where Numature and Nusenescent are the nutrient contents on a mass basis in mature and senescent leaves (mg·g−1), respectively; and MLCF is the mass loss correction factor used to compensate for the loss of leaf mass during senescence (specifically the ratio of the dry mass of senescent leaves to the dry mass of mature leaves).
The nutrient resorption proficiency (NuRP) is expressed directly as the nutrient contents in senescent leaves [7]. Furthermore, the amount of nutrient changes during leaf senescence was calculated by subtracting the nutrient contents of mature leaves from the nutrient contents of senescent leaves.
The C:N, C:P, and N:P ratios were determined using the C, N, and P contents in each leaf sample. The C:N:P stoichiometric ratios were calculated as mass ratios. The normality and chi-squareness of the data were checked and transformed if necessary. A two-way analysis of variance (two-way ANOVA) was used to test the effects of forest type and sampling time on leaf element contents, resorption efficiencies, and stoichiometric ratios. A one-way analysis of variance (one-way ANOVA) and Tukey’s multiple comparison test were used to analyze the differences between plantations at the P < 0.05 level. Pearson correlation was used to determine the correlations among leaf nutrient contents, stoichiometric ratios, resorption and temperature, and precipitation. The above analyses were performed using SPSS 23.0 (IBM SPSS, Chicago, IL, USA).

3. Results

3.1. Carbon, Nitrogen, and Phosphorus Contents in Mature and Senescent Leaves

The contents of C, N, and P in mature and senescent leaves mostly differed significantly between plantations and varied with months (Figure 2). The C content in the mature leaves of the Cunninghamia lanceolata plantation was lower in April and May than of the Castanopsis carlesii plantation, but higher at subsequent times (Figure 2a). During the growing season, the N content in both mature and senescent leaves of the Cunninghamia lanceolata plantation was significantly lower than that of the Castanopsis carlesii plantation (Figure 2c,d). The P content in mature leaves of the Cunninghamia lanceolata plantation was significantly higher than that of the Castanopsis carlesii plantation in May and September, and this pattern was more pronounced in senescent leaves (Figure 2e,f).
Leaf N and P contents in both plantations decreased markedly during leaf senescence, and the dynamical patterns of decrease differed significantly between plantations (Figure 3). The N content decreased significantly more in the Cunninghamia lanceolata plantation than in the Castanopsis carlesii plantation in May, while it was significantly less than in the Castanopsis carlesii plantation in July (Figure 3a). In contrast, the P content decreased significantly more in the Cunninghamia lanceolata plantation than in the Castanopsis carlesii plantation in April and September, while it was significantly less than in the Castanopsis carlesii plantation in June, July, and October (Figure 3b).

3.2. Nitrogen and Phosphorus Resorption Efficiencies in the Leaves of Castanopsis carlesii and Cunninghamia lanceolata Plantations

Dynamical patterns of N and P resorption efficiencies differed significantly between plantations (Figure 4). The N resorption efficiencies of the Cunninghamia lanceolata plantation and the Castanopsis carlesii plantation varied from 34.26% to 56.28% and from 11.25% to 34.23%, respectively (Figure 4a). The N resorption efficiency of the Cunninghamia lanceolata plantation was significantly lower than that of the Castanopsis carlesii plantation in July but higher in most months. In contrast, the P resorption efficiencies of the Cunninghamia lanceolata plantation and the Castanopsis carlesii plantation varied from 41.01% to 54.85% and from 49.22% to 58.72%, respectively (Figure 4b). The P resorption efficiency of the Cunninghamia lanceolata plantation was significantly lower than that of the Castanopsis carlesii plantation in most sampling months.

3.3. Carbon, Nitrogen, and Phosphorus Stoichiometric Ratios in Mature and Senescent Leaves

The C:N, C:P, and N:P ratios in mature leaves varied from 31.39 to 61.24, from 753.09 to 1022.54, and from 14.57 to 28.92 during the investigation period, respectively (Figure 5). Forest types displayed a significant effect on C:N in mature leaves (Figure 5a). The C:N of mature leaves in the Cunninghamia lanceolata plantation was significantly higher than that of the Castanopsis carlesii plantation in all months. The C:P of mature leaves varied with time, and the variation patterns varied significantly between plantations (Figure 5c). The C:P of mature leaves in the Cunninghamia lanceolata plantation was significantly lower than that in the Castanopsis carlesii plantation in May and September, but higher in October. The N:P of mature leaves also differed significantly between plantations (Figure 5e). Compared to the Castanopsis carlesii plantation, the Cunninghamia lanceolata plantation had significantly lower mature leaf N:P.
The C:N, C:P, and N:P of senescent leaves varied from 34.45 to 110.42, from 1292.61 to 2060.64, and from 14.50 to 49.94, respectively. Forest types exhibited a significant effect on the C:N:P stoichiometric ratios in senescent leaves (Figure 5). The C:N of senescent leaves in the Cunninghamia lanceolata plantation was significantly higher than that of the Castanopsis carlesii plantation in all sampling months (Figure 5b). In contrast, C:P and N:P in senescent leaves of the Cunninghamia lanceolata plantation were significantly lower than that of the Castanopsis carlesii plantation (Figure 5d,f).

3.4. Correlation of Nutrient Contents, Resorption Efficiencies, and Stoichiometric Ratios with Climatic Factors

In the Castanopsis carlesii plantation, the temperature was significantly negatively correlated with senescent leaf P content and significantly positively correlated with leaf PRE (Figure 6). Precipitation was significantly negatively correlated with leaf NRE, PRE, mature leaf N and P contents, and senescent leaf C:N and significantly positively correlated with senescent leaf N, mature leaf C:N, and C:P. In the Cunninghamia lanceolata plantation, the temperature was significantly negatively correlated with leaf NRE, PRE, senescent leaf C:N, and C:P, and significantly positively correlated with senescent leaf N content (Figure 7). Precipitation was significantly positively correlated with senescent leaf P content.

4. Discussion

The results here partially supported our hypothesis that the dynamical patterns of N and P resorption and C:N:P stoichiometric ratios of in leaves vary significantly with forest types and are regulated by seasonal climate changes. We found that N and P resorption efficiencies in the Castanopsis carlesii plantation were higher in the middle of the growing season than in the Cunninghamia lanceolata plantation, and lower in the early and late growing season. Moreover, the P-limited Castanopsis carlesii plantation exhibited better P resorption, while the Cunninghamia lanceolata plantation limited by both N and P showed similar levels of N and P resorption. These findings revealed that plant growth limitation could have a dominant role in controlling nutrient resorption [23,24]. We also found that temperature and precipitation were significantly associated with N and P resorption, but this relationship differed between forest types, implying that adaptive nutrient use strategies respond to the change of the external environment and ultimately to plant development and growth [16,22].
Resorption is one of the important nutrient conservation strategies to improve plant nutrient utilization, playing a key role in several ecosystem processes such as species competition, nutrient return, and decomposition of leaf litter [1,18]. We found that the N and P resorption characteristics in the two plantations were significantly different (Figure 4). Compared to the Castanopsis carlesii plantation, the Cunninghamia lanceolata plantation showed higher NRE and NRP but lower PRE and PRP (Figure 2 and Figure 4). These results indicated that the Castanopsis carlesii plantation could be generally more efficient and proficient in resorbing P, while the Cunninghamia lanceolata plantation could be better at resorbing N. This is in agreement with findings on coniferous and broadleaf trees in subtropical karst regions [24]. The higher soil N content in the Cunninghamia lanceolata plantation may also be due to the fact that the needles require less N and that most of the N is obtained through resorption rather than root uptake, hence the higher N retained in the soil. In addition, PRE was higher than NRE in both plantations. This result is consistent with the average NRE (49.1%) and PRE (51.0%) of plants in Eastern China [23]. The possible reasons are the general lack of P in soils in subtropical regions and the differences in the relative amounts of N and P leached from leaves [45,46]. Therefore, subtropical trees might survive in P-deficient ecosystems by increasing P resorption.
Plant nutrient resorption may exhibit seasonal dynamics in response to environmental changes [13,14,15]. The dynamical patterns of N and P resorption efficiencies in response to seasonal climate changes differed significantly between the two plantations (Figure 4). In the Castanopsis carlesii plantation, N and P resorption efficiencies were significantly negatively correlated with precipitation, and P resorption efficiency was significantly positively correlated with temperature (Figure 6). The possible reason is that as a broad-leaved evergreen species, Castanopsis carlesii has a large leaf area [47]. Higher precipitation may lead to abnormal senescence of Castanopsis carlesii leaves and leaching of nutrients from the leaves, which results in lower nutrient resorption efficiencies [48]. In addition, it has been suggested that elevated temperatures may delay the leaf senescence in broadleaf trees, which may prolong the time to retransfer P in leaves, resulting in higher P resorption efficiency [49,50,51]. In the Cunninghamia lanceolata plantation, N and P resorption efficiencies were significantly negatively correlated with temperature, but not with precipitation (Figure 7). This indicates that the nutrient resorption of Cunninghamia lanceolata is more regulated by temperature than precipitation. In some studies, a higher temperature may aggravate the degree of membrane lipid peroxidation in leaf cells, thereby accelerating leaf senescence, leading to a shorter time for nutrient retransfer and lower nutrient resorption [52,53]. This may explain the negative relationship between nutrient resorption efficiencies and temperature in the Cunninghamia lanceolata plantation. Differences in the responses of N and P resorption efficiencies to temperature and precipitation between plantations also supports our hypothesis.
Ecological stoichiometric ratios can usually reflect the growth and nutrient utilization status of plants [25,54]. In this study, mature leaf C:N was significantly higher in the Cunninghamia lanceolata plantation than in the Castanopsis carlesii plantation. This might be attributed to the higher C content as well as the lower N content in the Cunninghamia lanceolata plantation. Previous studies have observed that coniferous trees tend to have high amounts of resins, waxes, and tannins. These substances are rich in C, which help to increase the C content and C:N in leaves [16,24]. In addition, we found that the C:P in mature leaves varied with time, and these variation patterns varied significantly between plantations (Figure 5). Previous studies have shown that plants need more rRNA to synthesize the required proteins during high growth periods and that increased rRNA leads to an increase in P content [6,55,56]. The Mature leaf C:P in Cunninghamia lanceolata plantation was significantly lower in April, May, and September than in Castanopsis carlesii plantation, and higher in other months (Figure 5). This indicated that the growth rate of the Cunninghamia lanceolata plantation may be higher in the early and late growing season and lower in the middle of the growing season compared to that of the Castanopsis carlesii plantation. In addition, resorption causes changes in leaf nutrient contents by transferring nutrients to other active tissues before leaf drop, thus it may be an important process affecting the seasonal dynamics of leaf stoichiometric ratios [24]. In the present study, NRE and PRE were higher in the early and late growing season and lower in the middle of the growing season in the Cunninghamia lanceolata plantation compared to the Castanopsis carlesii plantation. This suggested that trees in subtropical forests might meet the nutrient demands of a high growth rate by increasing nutrient resorption.
The availability of N and P tends to limit plant growth and community composition in terrestrial ecosystems, so leaf N:P is widely used to assess the nutrient limitation of plants [28]. In this study, the leaf N:P ratios differed significantly between two plantations, but changed less over time (Figure 5), which did not support our hypothesis. The theory of dynamic equilibrium believes that organisms can control many of their characteristics, especially nutrient balance so that the internal environment will not change drastically with changes in the external environment [55]. The leaf N:P in the two plantations showed a certain degree of homeostasis, which might be the result of the long-term adaptation of different subtropical plants to the environment, or, might be related to its strong ability to maintain homeostasis [57,58]. Therefore, it is speculated that the difference in leaf N:P of trees in different plantations is more determined by the genetic characteristics of the species itself. In addition, a study proposed that the plant growth of terrestrial plants was N-limited when mature leaf N:P is less than 10, and P-limited when N:P is more than 20 [28]. Our results suggested that the Castanopsis carlesii plantation was strongly P-limited (average N:P of 27.23), whereas the Cunninghamia lanceolata plantation was both N and P-limited (average N:P of 16.24). The stronger P limitation in the Castanopsis carlesii plantation compared to the Cunninghamia lanceolata plantation may explain its more efficient P resorption. These findings implied that N and P resorption might be adapted to the nutrient limitation status of plants. In subtropical low-nutrient habitats, Castanopsis carlesii and lanceolata plantations may maintain leaf N:P relative stability as much as possible by regulating nutrient resorption. This is consistent with previous findings [58,59].

5. Conclusions

In conclusion, there were marked monthly dynamics of leaf N and P resorption and C:N:P stoichiometric ratios in both Castanopsis carlesii and Cunninghamia lanceolata plantations, but the dynamic patterns differed significantly between forest types. Due to the limitation of P, the Castanopsis carlesii plantation had a higher P resorption efficiency than its N resorption efficiency, and exhibited a higher N and P resorption in the middle of the growing season to meet the nutrient requirements of the rapid growth period. In contrast, the Cunninghamia lanceolata plantation displayed similar levels of N and P resorption due to the co-limitation of N and P and showed higher N and P resorption in the early and late growing season. Furthermore, the correlation showed that the N and P resorption efficiencies displayed strongly significant correlations with temperature and precipitation in both plantations. The results here could further clarify the differences in the dynamics of N and P utilization strategies between different functional plantations and help to understand the nutrient cycling processes in the subtropical forest ecosystems.

Author Contributions

F.W. and X.N. designed the experiments; Y.Z., J.Y., and X.W. collected and examined the samples; Y.Z. analyzed the data and drafted the manuscript; F.W. revised the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (32171641, 32101509 and 32022056).

Data Availability Statement

Not applicable.

Acknowledgments

We wish to thank the Fujian Sanming Forest Ecosystem National Observation and Research Station for their support and all those who have helped us in the field sampling and experiments.

Conflicts of Interest

The authors declare no conflict of interest.

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Forests 13 01458 g001 550
Figure 1. Monthly average air temperature and precipitation during the experiment. Each column represents the average value of three replicates (n = 3). Error bars represent standard errors (SE).
Figure 1. Monthly average air temperature and precipitation during the experiment. Each column represents the average value of three replicates (n = 3). Error bars represent standard errors (SE).
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Figure 2. C, N and P contents in mature (a,c,e) and senescent leaves (b,d,f). Each scatter represents the average value of the three replicates (n = 3). Error bars represent standard errors (SE). The p values show the results from repeated measures ANOVA testing for the effect of forest type over time. ns: not significant. Asterisks denote significant differences between forest types: * p < 0.05, ** p < 0.01, *** p < 0.001.
Figure 2. C, N and P contents in mature (a,c,e) and senescent leaves (b,d,f). Each scatter represents the average value of the three replicates (n = 3). Error bars represent standard errors (SE). The p values show the results from repeated measures ANOVA testing for the effect of forest type over time. ns: not significant. Asterisks denote significant differences between forest types: * p < 0.05, ** p < 0.01, *** p < 0.001.
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Figure 3. Changes in N (a) and P contents (b) during leaf senescence. Each column represents the average value of the three replicates (n = 3). Error bars represent standard errors (SE). The p values show the results from repeated measures ANOVA testing for the effect of forest type over time. Asterisks denote significant differences between forest types: * p < 0.05, ** p < 0.01, *** p < 0.001.
Figure 3. Changes in N (a) and P contents (b) during leaf senescence. Each column represents the average value of the three replicates (n = 3). Error bars represent standard errors (SE). The p values show the results from repeated measures ANOVA testing for the effect of forest type over time. Asterisks denote significant differences between forest types: * p < 0.05, ** p < 0.01, *** p < 0.001.
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Figure 4. Leaf N (a) and P (b) resorption efficiencies. NRE: Nitrogen resorption efficiency, PRE: Phosphorus resorption efficiency. Each column represents the average value of the three replicates (n = 3). Error bars represent standard errors (SE). The p values show the results from repeated measures ANOVA testing for the effect of forest type over time. Asterisks denote significant differences between forest types: * p < 0.05, ** p < 0.01. The dotted line represents the 50% threshold.
Figure 4. Leaf N (a) and P (b) resorption efficiencies. NRE: Nitrogen resorption efficiency, PRE: Phosphorus resorption efficiency. Each column represents the average value of the three replicates (n = 3). Error bars represent standard errors (SE). The p values show the results from repeated measures ANOVA testing for the effect of forest type over time. Asterisks denote significant differences between forest types: * p < 0.05, ** p < 0.01. The dotted line represents the 50% threshold.
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Figure 5. C:N, C:P, and N:P ratios in mature (a,c,e) and senescent leaves (b,d,f). Each scatter represents the average value of the three replicates (n = 3). Error bars represent standard errors (SE). The p values show the results from repeated measures ANOVA testing for the effect of forest type over time. ns: not significant. Asterisks denote significant differences between forest types: * p < 0.05, ** p < 0.01, *** p < 0.001.
Figure 5. C:N, C:P, and N:P ratios in mature (a,c,e) and senescent leaves (b,d,f). Each scatter represents the average value of the three replicates (n = 3). Error bars represent standard errors (SE). The p values show the results from repeated measures ANOVA testing for the effect of forest type over time. ns: not significant. Asterisks denote significant differences between forest types: * p < 0.05, ** p < 0.01, *** p < 0.001.
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Figure 6. Correlation of nutrient contents, resorption efficiencies, and stoichiometric ratios with climatic factors in the Castanopsis carlesii plantation. NRE: N resorption efficiency; PRE: P resorption efficiency; Cm: C content in mature leaves; Nm: N content in mature leaves; Pm: P content in mature leaves; Cs: C content in senescent leaves; Ns: N content in senescent leaves; Ps: P content in senescent leaves. C:Nm: C:N in mature leaves; C:Pm: C:P in mature leaves; N:Pm: N:P in mature leaves; C:Ns: C:N in senescent leaves; C:Ps: C:P in senescent leaves; N:Ps: N:P in senescent leaves. T: Temperature; P: Precipitation. Asterisks indicate significant correlations among indicators. * p < 0.05, ** p < 0.01, *** p < 0.001. The same is below.
Figure 6. Correlation of nutrient contents, resorption efficiencies, and stoichiometric ratios with climatic factors in the Castanopsis carlesii plantation. NRE: N resorption efficiency; PRE: P resorption efficiency; Cm: C content in mature leaves; Nm: N content in mature leaves; Pm: P content in mature leaves; Cs: C content in senescent leaves; Ns: N content in senescent leaves; Ps: P content in senescent leaves. C:Nm: C:N in mature leaves; C:Pm: C:P in mature leaves; N:Pm: N:P in mature leaves; C:Ns: C:N in senescent leaves; C:Ps: C:P in senescent leaves; N:Ps: N:P in senescent leaves. T: Temperature; P: Precipitation. Asterisks indicate significant correlations among indicators. * p < 0.05, ** p < 0.01, *** p < 0.001. The same is below.
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Figure 7. Correlation of nutrient contents, resorption efficiencies, and stoichiometric ratios with climatic factors in the Cunninghamia lanceolata plantation. Asterisks indicate significant correlations among indicators. * p < 0.05, ** p < 0.01, *** p < 0.001.
Figure 7. Correlation of nutrient contents, resorption efficiencies, and stoichiometric ratios with climatic factors in the Cunninghamia lanceolata plantation. Asterisks indicate significant correlations among indicators. * p < 0.05, ** p < 0.01, *** p < 0.001.
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Table
Table 1. The characteristics of the two plantations.
Table 1. The characteristics of the two plantations.
ParametersCastanopsis carlesii PlantationCunninghamia lanceolata Plantation
Tree age (year)1010
Slope (°)3233
Stand density (plant·ha−1)24002860
Average tree height (m)8.77 ± 0.1711.30 ± 0.37
Average breast diameter (cm)9.93 ± 0.6214.80 ± 0.28
Soil C (mg·g−1)23.83 ± 0.56 27.02 ± 0.27
Soil N (mg·g−1)1.54 ± 0.03 1.79 ± 0.04
Soil P (mg·g−1)0.19 ± 0.000.19 ± 0.00
Values are meant ± standard errors (n = 3).
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Zhang, Y.; Yang, J.; Wei, X.; Ni, X.; Wu, F. Monthly Dynamical Patterns of Nitrogen and Phosphorus Resorption Efficiencies and C:N:P Stoichiometric Ratios in Castanopsis carlesii (Hemsl.) Hayata and Cunninghamia lanceolata (Lamb.) Hook. Plantations. Forests 2022, 13, 1458. https://doi.org/10.3390/f13091458

AMA Style

Zhang Y, Yang J, Wei X, Ni X, Wu F. Monthly Dynamical Patterns of Nitrogen and Phosphorus Resorption Efficiencies and C:N:P Stoichiometric Ratios in Castanopsis carlesii (Hemsl.) Hayata and Cunninghamia lanceolata (Lamb.) Hook. Plantations. Forests. 2022; 13(9):1458. https://doi.org/10.3390/f13091458

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Zhang, Yaoyi, Jing Yang, Xinyu Wei, Xiangyin Ni, and Fuzhong Wu. 2022. "Monthly Dynamical Patterns of Nitrogen and Phosphorus Resorption Efficiencies and C:N:P Stoichiometric Ratios in Castanopsis carlesii (Hemsl.) Hayata and Cunninghamia lanceolata (Lamb.) Hook. Plantations" Forests 13, no. 9: 1458. https://doi.org/10.3390/f13091458

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