Search Results (38)

The long-term monoculture of Eucalyptus plantations in southern China has raised ecological concerns, prompting a shift towards mixed-species plantations as a sustainable alternative. This study investigates the mechanisms by which companion tree species enhance soil functionality in subtropical red soil regions. A field experiment compared a pure Eucalyptus (CK) plantation with three mixed-species plantations: Eucalyptus × Mytilaria laosensis (A × M), Eucalyptus × Magnolia hypolampra (A × H), and Eucalyptus × Michelia gioii (A × X). Comprehensive soil analyses were conducted at three soil depths (0–20 cm, 20–40 cm, and 40–60 cm) to assess chemical properties, enzyme activities, and humus components, and soil organic carbon (SOC) molecular structure was characterized by Fourier-Transform Infrared Spectroscopy (FTIR), with the relationships quantified using structural equation modeling (SEM) to test predefined causal hypotheses. The results showed that A × H significantly boosted topsoil fertility (e.g., OM: 46.61 g/kg), while A × M enhanced the recalcitrant organic carbon (ROC: 35.29 g/kg), indicating superior carbon sequestration potential. The FTIR analysis revealed species-specific alterations in SOC chemistry, such as increased aromatic compounds in A × H/A × X. The SEM analysis demonstrated that the latent variable “Humus” (reflected by LOC and ROC) directly and positively influenced the latent variable “Soil Fertility” (reflected by pH, OM, and AP; path coefficient: 0.62). In contrast, the latent variable “Organic Components” (reflected by specific FTIR functional groups) exhibited a significant direct negative effect on “Soil Fertility” (−0.41). The significant pathway from “Organic Components” to “Enzymatic Activity” (0.55*) underscored the role of microbial mediation. The study concludes that mixed plantations, particularly with Mytilaria laosensis (A × M), improve soil health through an “organic input–microbial enzyme response–humus formation” pathway, offering a scientific basis for sustainable forestry practices that balance productivity and ecological resilience. Full article

Monoculture plantations of Eucalyptus in China have raised ecological concerns due to water depletion, soil degradation, and fire risk. Integrating Eucalyptus with Cupressus offers a sustainable approach to improving forest ecosystem health. In this study, we established five forest treatments, pure Eucalyptus (1:0), mixed Eucalyptus–Cupressus at three ratios (2:1, 1:1, and 1:2), and pure Cupressus (0:1), to assess their effects on soil properties, microbial diversity, and metabolomic profiles. Laboratory analyses revealed significant differences in physicochemical soil properties (such as water content (p < 0.05), pH (p < 0.001), organic carbon (p < 0.001), and nitrogen (p < 0.001)) among various groups within the mixed forests. Microbial community investigations highlighted a unique microbial signature in Eucalyptus–Cupressus mixed forests, especially when the tree ratio was 1:2, characterized by a rich (Chao1, p < 0.05) and diverse (Shannon, p < 0.05) array of bacterial taxa. The mixed Eucalyptus–Cupressus forest also exhibited an uplift in microbial communities, bacterial genera such as RB41, and fungal genera including Penicillium, Talaromyces, and Mortierella, which are associated with enhanced organic matter decomposition and nutrient cycling. Interactive networks within microbial communities were revealed through co-occurrence and Spearman correlation analyses, highlighting potential symbiotic relationships and ecological complexities. Metabolomic analysis, coupled with pathway analysis, further illuminated metabolic shifts in the mixed forests, emphasizing alterations in key metabolic pathways such as phenylpropanoid biosynthesis, tyrosine metabolism, arachidonic acid metabolism, and isoquinoline alkaloid biosynthesis. Collectively, these results show that moderately mixed Eucalyptus–Cupressus forests improve soil fertility and microbial multifunctionality, providing a practical model for sustainable and resilient forest management in subtropical regions. Full article

Afforestation substantially promotes vegetation restoration and modifies soil physical, chemical, and biological properties. The integrated effects of soil properties on soil quality, expressed via a composite soil quality index (SQI), remain unclear despite variations among individual properties. Here, five vegetation restoration treatments were selected as follows: (1) barren land (BL, control), (2) disturbed short-rotation Eucalyptus plantation (REP); (3) undisturbed long-term Eucalyptus plantation (UEP); (4) mixed native-species plantation (MF); and (5) natural forest (NF) following >50 years of restoration. Soil physicochemical properties and microbial community compositions were investigated, and soil quality was evaluated by an integrated SQI. Our results showed that vegetation restoration had strong effects on soil physicochemical properties, soil quality, and microbial communities. Most of the soil physicochemical properties exhibited significant differences among treatments. Soil dissolved organic carbon, total nitrogen, and ammonium nitrogen were the three key soil quality indicators. The SQI increased significantly with vegetation recovery intensity. In both UEP and MF, it reached levels comparable to NF, and was higher in UEP than in REP, implying that short-rotation practices impede soil restoration. In addition, microbial biomass (bacteria, fungi, arbuscular mycorrhizal fungi, actinomycetes, and total microbe PLFAs) increased from BL to NF. All plantations exhibited lower microbial biomass than NF, revealing incomplete recovery and a greater sensitivity to soil physicochemical properties. Conversely, the fungi-to-bacteria biomass ratio decreased sequentially (REP > BL > UEP > MF > NF). Strong positive correlations between microbial biomass and the SQI were observed. These results collectively indicate that afforestation with mixed tree species is optimal for rapid soil restoration, and undisturbed long-term monocultures can achieve similar outcomes. These findings highlight that tree species mixtures and reducing disturbance should be taken into consideration when restoring degraded ecosystems in the tropics. Full article

In recent decades, a significant decline in arthropods’ abundance and biodiversity, as a consequence of intensive agricultural practices and reductions in their natural environments, has been observed. While landscape-scale biodiversity studies are well documented in the literature, the impact of field-level agricultural management remains less understood. To address this gap, a sampling of diversity was carried out through Malaise traps on five agricultural surfaces with different management schemes: two characterized by the presence of trees (Populus L. spp. and Eucalyptus spp.), two herbaceous fields in different development stages (flowering Carthamus tinctorius L. and stubble of Triticum aestivum), and one mixed system (an agroforestry plantation composed of Populus L. spp. and Carthamus tinctorius L.). Data collection focused on evaluating the total animal biomass (weight and number) and the richness and evenness components of diversity using Shannon and Simpson indices at the Order level. The sampled arthropods belonged to six Orders of Insecta and one Order of Arachnida. The agroforestry system had a higher total animal biomass, in terms of weight, than the other treatments (61.24% higher than in the eucalyptus system, 58.91% higher than in the wheat stubble, 42.63% higher than in the flowering safflower system, and 11.63% higher than in the poplar plantation), with the number of total arthropods following a similar trend. The results demonstrated that the biomass, richness, and evenness of the collected arthropods varied according to the management practices applied, and higher values were recorded in the agroforestry system. Although preliminary, the findings suggest the suitability of mixed systems for sustaining higher diversity than traditional monoculture management schemes. Full article

Water use strategies reflect the ability of plants to adapt to drought caused by climate change. However, how these strategies change with stand development and seasonal drought is not fully understood. This study used stable isotope techniques (δD, δ¹⁸O, and δ¹³C) combined with the MixSIAR model to quantify the seasonal changes in water use sources and water use efficiency (WUE) of Eucalyptus urophylla S.T.Blake × E. grandis (E. urophylla × E. grandis) at four stand ages (2-, 4-, 9- and 14-year-old) and to identify their influencing factors. Our results showed that the young (2-year-old) and middle-aged (4-year-old) stands primarily relied on shallow soil water throughout the growing season due to the limitations of a shallow root system. In contrast, the mature (9-year-old) and overmature (14-year-old) stands, influenced by the synergistic effects of larger and deeper root systems and relative extractable water (REW), exhibited more flexibility in water use, mainly relying on shallow soil water in wet months, but shifting to using middle and deep soil layer water in dry months, and quickly returning to mainly using shallow soil water in the episodic wet month of the dry season. The WUE of E. urophylla × E. grandis was affected by the combined effect of air temperature (T), vapor pressure deficit (VPD), and REW. WUE was consistent across the stand ages in the wet season but decreased significantly with stand age in the dry season. This suggests that mature and overmature stands depend more on shifting their water source, while young and middle-aged stands rely more on enhanced WUE to cope with seasonal drought stress, resulting in young and middle-aged stands being more vulnerable to drought stress. These findings offer valuable insights for managing water resources in eucalyptus plantations, particularly as drought frequency and intensity continue to rise. Full article

Seasonal droughts induced by climate change pose a significant threat to the normal growth patterns of forests in the subtropical regions of southern China. Therefore, it is crucial to explore the response of tree water use patterns to seasonal drought to maintain tree physiological activities. However, it remains unknown whether changes in dry and wet seasons have an impact on the water use patterns of trees of different ages. In this study, a two-year experiment was conducted in Eucalyptus urophylla × Eucalyptus grandis (hereinafter referred to as Eucalyptus) plantations at three ages (4, 7, and 17 years). Specifically, the water use patterns of Eucalyptus in dry and wet seasons were calculated using hydrogen stable isotopes (including the isotopes in xylem water and 0–150 cm soil layers) coupled with MixSIAR. The results showed that there were notable variations in the proportions of water absorption from different soil layers by Eucalyptus during dry and wet seasons. During the dry season (April 2024), 4-year-old and 7-year-old Eucalyptus primarily utilized water from the 40–90 cm soil layer, while 17-year-old Eucalyptus mainly relied on deep soil water at depths of 60–150 cm, with a utilization ratio of 50.9%. During the wet season (August 2023), the depth of water uptake by Eucalyptus of different ages significantly shifted towards shallow layers, and the trees primarily utilized surface soil water from the 0–60 cm layer, with utilization ratios of 59.9%, 64.8%, and 61.6% for 4-year-old, 7-year-old, and 17-year-old Eucalyptus, respectively. The water sources of Eucalyptus during dry and wet seasons were variable, which allowed Eucalyptus to cope with seasonal drought stress. The differences in the water uptake strategies of Eucalyptus between dry and wet seasons can be attributed to their long-term adaptation to the environment. Our research revealed the differences in the water utilization of Eucalyptus with various ages between dry and wet seasons in subtropical China, providing new insights for a better understanding of the adaptive mechanisms of subtropical forests in response to alterations in water conditions caused by climate change. Full article

Soil microbes are critical in regulating the growth and function of eucalyptus plantations. The mechanisms underlying soil microbial communities’ response to different eucalyptus plantation management practices remain elusive. In this study, we compiled datasets containing 2744 observations across global eucalyptus-planted regions and analyzed the effects of five management practices (i.e., burning, residual removal, fertilization, mixed planting, and controlling planting years) on soil microbial biomass, diversity, and structures. Our results showed that fungal community alpha diversity responds more sensitively to management practices than bacterial community alpha diversity on eucalyptus plantations. Although the implementation of management practices significantly increased the content of most soil nutrients and microbial biomass elements (excluding burning), these practices did not necessarily improve soil microbial biomass and diversity, particularly among fungal communities. Burning, fertilization, and mixing eucalyptus with nitrogen-fixing species significantly decreased the diversity of fungal communities, which were mainly impacted by soil organic carbon and total potassium content. Compared to the four other management practices, mixing eucalyptus with nitrogen-fixing species favored the growth of bacterial communities and the storage of microbial biomass nitrogen, making it the most effective management practice. However, attention should also be paid to the protection of fungal communities. In addition, these management practices significantly changed microbial community structures, which were positively correlated with the microbial biomass elements carbon and nitrogen and, to a lesser extent, soil microbial alpha diversity. Our results highlight the importance of prioritizing mixing eucalyptus with nitrogen-fixing species as a management practice and safeguarding fungal community diversity during its implementation and suggest that microbial diversity development associated with soil organic carbon and potassium contents should be given priority in eucalyptus plantation management. Full article

Mixed-species plantations involving Eucalyptus and Acacia trees are an effective alternative for managing sustainable plantations. In this study, we evaluated the growth, productivity, nutrient return, and soil properties of a mixed Eucalyptus hybrid (Eucalyptus camaldulensis Dehnh. × E. urophylla S.T. Blake; E) and Acacia auriculiformis A. Cunn. ex Benth. plantation (A) and Eucalyptus hybrid and A. auriculiformis plantations. The mixed Eucalyptus hybrid and A. auriculiformis plantation included three ratios at E33:A67, E50:A50, and E67:A33, while the Eucalyptus (E100) and A. auriculiformis (A100) plantations were established on degraded lands in the Had Wanakorn Forestry Research and Student Training Station, Prachuap Khiri Khan province, Thailand. Three replications within a plot size of 20 × 20 m² were designed to plant Eucalyptus hybrid and A. auriculiformis seedlings at a spacing of 2 × 3 m². The diameters at breast height (DBH) and height (H) of the Eucalyptus hybrid and A. auriculiformis were measured and monitored after planting for five years. The aboveground biomass of the five-year-old mixed and monoculture plantations was then estimated. Litterfall production and nutrient return from the mixed and monoculture plantations were measured for three years. In addition, soil samples at depths of 0–5, 5–10, and 10–20 cm were collected to analyze the soil’s chemical properties. Differences in growth, aboveground biomass, litterfall production, nutrient return, and soil properties were analyzed and tested using Tukey’s HSD. The results indicated that both the DBH and H of the Eucalyptus hybrid in the mixed and monoculture plantations were not significantly different (p > 0.05). Similarly, the DBH and H of A. auriculiformis in each treatment were also not significantly different (p > 0.05). However, the DBH and H of the Eucalyptus hybrid were higher than those of A. auriculiformis. The aboveground biomass for the mixed plantation ratios E50:A50, E100, E67:A33, and E33:A67 was not significantly different, while the stem biomass was the highest in E100. Litterfall production was influenced by the proportion of the Eucalyptus hybrid relative to A. auriculiformis, but the monoculture A100 plantation had the highest litter production. The nitrogen return estimated for the mixed plantation was between A100 and E100. Similarly, the total nitrogen in the topsoil (0–5 cm) of the mixed plantation was higher than that in the monoculture E100 plantation. These results indicate that mixing A. auriculiformis with Eucalyptus can improve soil nutrients and nutrient cycling and increase nutrient returns, suggesting that mixed plantations are an effective option for sustainable plantation management and can mitigate the negative environmental impacts of Eucalyptus monocultures. Full article

The growing recognition of mixed Eucalyptus and native broadleaf plantations as a means of offsetting the detrimental impacts of pure Eucalyptus plantations on soil fertility and the wider ecological environment is accompanied by a clear and undeniable positive impact on forest ecosystem functions. Nevertheless, the question of how mixed Eucalyptus and native broadleaf plantations enhance soil multifunctionality (SMF) and the mechanisms driving soil fungal communities remains unanswered. In this study, three types of mixed Eucalyptus and native broadleaf plantations were selected and compared with neighboring evergreen broadleaf forests and pure Eucalyptus plantations. SMF was quantified using 20 parameters related to soil nutrient cycling. Partial least squares path modeling (PLS-PM) was employed to identify the key drivers regulating SMF. The findings of this study indicate that mixed Eucalyptus and native broadleaf plantations significantly enhance SMF. Mixed Eucalyptus and native broadleaf plantations led to improvements in soil properties (7.60–52.22%), enzyme activities (10.13–275.51%), and fungal community diversity (1.54–29.5%) to varying degrees compared with pure Eucalyptus plantations. Additionally, the mixed plantations exhibit enhanced connectivity and complexity in fungal co-occurrence networks. The PLS-PM results reveal that soil properties, fungal diversity, and co-occurrence network complexity directly and positively drive changes in SMF. Furthermore, soil properties exert an indirect influence on SMF through their impact on fungal diversity, species composition, and network complexity. The findings of this study highlight the significant role of mixed Eucalyptus and native broadleaf plantations in enhancing SMF through improved soil properties, fungal diversity, and co-occurrence network complexity. This indicates that incorporating native broadleaf species into Eucalyptus plantations can effectively mitigate the negative impacts of monoculture plantations on soil health and ecosystem functionality. In conclusion, our study contributes to the understanding of how mixed plantations influence SMF, offering new insights into the optimization of forest management and ecological restoration strategies in artificial forest ecosystems. Full article

The glomalin-related soil protein (GRSP) is an important component of soil organic carbon (SOC), which plays an important role in maintaining soil structural stability, soil carbon (C), and nitrogen (N) fixation. However, little is known about the GRSP content in soil and its contribution to soil nutrients in plantations of different tree species. In this study, we determined the soil physicochemical characteristics and GRSP contents in different soil layers of four kinds of plantations, including Acacia mangium (AM), Pinus caribaea (PC), Eucalyptus urophylla (EU), and Magnoliaceae glanca (MG), to address how the plantation types affected the GRSP in different layers of soil in southern China. The results showed that with an increase in soil depth, the GRSP content decreased linearly, and the contribution rate of GRSP to SOC and total nitrogen (TN) in deep soil was 1.08–1.18 times that in surface soil. The tree species significantly affected the vertical distribution of GRSP in soil. Among the four plantations, the conifer species PC had the highest level of GRSP, while the N-fixing species AM had the lowest level. However, SOC, soil capillary porosity (CP), TN, soil water content (SWC), and total phosphorus (TP) were important factors regulating soil GRSP content. Additionally, the regulation effects of soil properties on GRSP were various in surface and deep soil among different plantations. In order to improve soil quality and C sequestration potential, conifer species can be planted appropriately, or conifer species and N-fixing species can be mixed to increase soil nutrient content and enhance soil structure and function in afforestation of southern China. Full article

Soil quality (SQ) pertains to the intricate and ongoing capacity of soil to function as a thriving ecosystem that supports the growth of plants and animals. However, there is a limited understanding of SQ assessment in mixed forest plantations. Therefore, we formulated and tested the hypothesis that the inclusion of a nitrogen-fixing tree species (such as Acacia mangium) improves SQ indicators in mixed treatments involving Eucalyptus trees. To evaluate the changes in SQ, we conducted a field experiment that employed the Soil Management Assessment Framework (SMAF) tool to analyze pure and mixed plantations of Eucalyptus grandis and A. mangium. Soil samples were collected at a depth of 0–20 cm from different treatments, including pure E. grandis without nitrogen fertilization (E), pure A. mangium (A), pure E. grandis with nitrogen fertilization (E + N), and mixed E. grandis and A. mangium (E + A). Sampling took place at 27 and 39 months after planting. We selected seven indicators of SQ: two biological indicators (soil microbial biomass carbon and β-glucosidase enzyme activity), four chemical indicators (soil organic carbon, pH, available phosphorus, and potassium), and one physical indicator (bulk density). By applying the SMAF tool, we determined the SQ scores for each indicator. The results revealed that E + A stands exhibited higher SMAF scores than pure stands, particularly in terms of pH (0.49 and 0.52 at 27 and 39 months, respectively) and phosphorus levels (0.84 and 0.82, at 27 and 39 months), respectively. Forest management practices and the sampling period had the most pronounced impact on biological and chemical indicators. Notably, significant positive correlations were observed between SMAF scores and pH, available phosphorus content, enzymes, soil organic carbon, and microbial biomass in both sampling periods. This study effectively provided novel information that introducing a nitrogen-fixing tree species in combination with eucalyptus trees enhances SQ, as indicated by the SMAF tool, which could reduce the need for external inputs (e.g., mineral fertilizers) by the farmers. Future studies should analyze the effects of A. mangium not only with other E. grandis varieties but also with other forestry essences. Full article

The water holding capacity of forest soil plays a crucial role in ensuring forest productivity, particularly in Eucalyptus urophylla plantations. In this study, we investigated the soil water holding capacity and hydrological properties of Eucalyptus in a subtropical area of Guangxi, China. Different stand ages (five years old, seven years old, and 15 years old) and successive rotations (first, second, and third) of Eucalyptus plantations were compared, with Cunninghamia lanceolata (Chinese Fir) and Pinus massoniana (Pine) plantations serving as references. Soil physical properties, soil hydrological parameters, and litter characteristics were analyzed to assess soil water retention and conservation variations. Our findings revealed that Eucalyptus and Chinese Fir plantation forests exhibit superior soil physical characteristics compared to Pine plantations, resulting in better soil water retention. However, an increase in the age of Eucalyptus plantations significantly diminished the capillary water holding capacity of the soil, despite an increase in surface litter accumulation and litter moisture content. Furthermore, successive rotations led to a notable reduction in soil capillary porosity, soil moisture content, soil saturated permeability, and overall soil water holding capacity. In addition, soil bulk density emerged as a critical factor relating to the hydrological characteristics of Eucalyptus plantation forests. Decreasing soil bulk density in Eucalyptus forests may offer potential for optimizing their water retention function. These results reveal that Eucalyptus management practices significantly alter the hydrological properties of soil through their effects on soil and litter properties, and consequently, stand age, rotation, and species mixing should be given intensive attention in maintaining the maximization of soil water holding capacity. Full article

In recent years, monoculture and multi-rotation successional Eucalyptus plantations have given rise to several environmental issues, including the degradation of soil quality and nutrient imbalance, and the conversion of logging sites to multi-rotation Eucalyptus plantations has attracted considerable attention from the scientists involved. However, the effects of different management strategies on soil extracellular enzyme activities (EEAs) and enzyme stoichiometry (ES) in degraded Eucalyptus plantations are not clear. In this study, we investigated the responses and mechanisms of soil physicochemical properties, microbial biomass, carbon, and nitrogen- and phosphorus-acquiring enzyme activities, as well as the microbial resource requirements of Eucalyptus plantations, under different management strategies. The findings revealed that second-rotation (TWE) and third-rotation (THE) continuous plantings of pure Eucalyptus plantations resulted in significant decreases in soil organic carbon (SOC), total nitrogen (TN) and effective available phosphorus (AP) contents, while soil nutrient contents increased after the introduction of Manglietia glauca to form mixed forests (EM) with Eucalyptus or pure Manglietia glauca (M). Meanwhile, phosphorus-acquiring enzymes significantly increased with successive rotations of Eucalyptus (TWE and THE), while EEA_C:P and EEA_N:P gradually decreased and phosphorus limitation gradually increased compared to that of a native-species-mixed plantation (CK). After the introduction of Manglietia glauca (EM and M), phosphorus-acquiring enzyme activities showed lower levels and there were significant increases in EEA_C:P and EEA_N:P compared to those of continuous plantings of pure Eucalyptus plantations, which reduced microbial phosphorus demand. Moreover, soil nutrients played a more significant role in altering the EEAs and ES than did microbial biomass (0–10 cm: 72.7% > 53.3%, 10–20 cm: 54.5% > 32.6%). The results showed that EM and M improved soil fertility quality conditions and alleviated soil nutrient phosphorus limitations for soil microorganisms. Therefore, the introduction of Manglietia glauca, either to form mixed forests with Eucalyptus or in rotation with Eucalyptus, can be used as technical means for the conversion of multi-rotation successive Eucalyptus plantations. Full article

The soils of Eucalyptus pure plantations and Eucalyptus–Castanopsis fissa mixed plantations were studied using soil column leaching experiments with acid solutions to mimic the effects of acid rain on the soils. This helped researchers learn more about how soil base ions react to acid deposition and their ability to protect the soil from excessive acidity under pure and mixed-species plantations. The results showed that acid rain leaching increased the leaching loss, desorption, and desorption rate of soil base ions while decreasing the soil pH value, adsorption, and adsorption rate of soil base ions. The soil pH value and the leaching loss ranges of K⁺, Na⁺, and Mg²⁺ were all greater in the pure plantations than in the mixed plantations, while the leaching range of Ca²⁺ was greater in the mixed plantation than in the pure plantations. In the two types of plantations, the adsorption rates of Ca²⁺ and Na⁺ in the mixed plantations were higher than in the pure plantations, while K⁺ and Mg²⁺ showed higher adsorption rates in the pure plantations than in the mixed plantations. Therefore, soil pH and base ions were greatly affected by the pH value of acid rain. Compared with the pure plantations, the establishment of Eucalyptus–Castanopsis fissa mixed plantations can slow soil acidification and leaching of K⁺, Na⁺, and Mg²⁺ and contribute to the adsorption of Ca²⁺ and Na⁺, which is beneficial for the soil nutrient fixation of Eucalyptus plantations. The mixed plantations were found to increase the exchange reaction between H⁺ and base ions, thereby improving the acid buffer performance of the soil. This, in turn, helped to mitigate the decline in soil fertility. Therefore, establishment of Eucalyptus–Castanopsis fissa mixed-species plantations can slow down the impact of acid rain on soil acidification in artificial plantation land to a certain extent and play an important role in optimizing the plantation structure of Eucalyptus stands and maintaining their productivity. Full article

The extracellular enzyme activity (EEA) and enzymatic stoichiometry (EES) of soil are useful indicators of shifts in soil nutrition and microbial resource requirements. Nevertheless, it is uncertain how the limitation of soil microbial nutrients is altered by a Eucalyptus plantation mixed with a N₂-fixing tree species. Our study examined the microbial nutrient limitation in two plantations: a pure Eucalyptus plantation (PP) and a mixed plantation (Eucalyptus and Erythrophleum fordii, MP) in rhizosphere and non-rhizosphere soils, beginning with two indicators, soil EEA and EES. In this study, the soil EEA was considerably (p < 0.05) greater in the MP contrasted to the PP, and the enzyme C:N:P ratios of the PP (1.12:1:1.10) and MP (1.07:1:1.08) both diverged from the global average EEA (1:1:1), and the deviation degree of the PP was greater. The results of the vector analysis demonstrated that the vector angle (VA) and vector length (VL) were considerably (p < 0.05) smaller in the MP contrasted to the PP. In comparison to the PP, the MP had a considerably (p < 0.05) poorer carbon quality index (CQI). Additionally, both microbial and soil properties have a considerable impact on soil EEA and EES, according to variance partitioning analysis (VPA) and redundancy analysis (RDA). In summary, our results show that the restriction of microorganisms on C and P in rhizosphere soils is usually weaker than that in non-rhizosphere soils and that the addition of N₂-fixing tree species to Eucalyptus plantations can lessen but not completely remove the restriction of soil microorganisms on C and P. Future management practices involving mixed plantations with N₂-fixing trees species could help decrease microbial nutrient limitation and promote sustainable plantations. Full article