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Forest management changes the physical environments and nutrient dynamics and then regulates the forest productivity. Soil phosphorus (P) availability is critical for productivity in tropical and subtropical forests. However, it was still poorly understood how soil P content and fraction respond to various forest management practices in these regions. Here, we measured the soil total P, available P, and Hedley’s P fractions, including inorganic and organic P (Pi and Po), in subtropical pine plantations treated with understory removal (UR), non-dominant species thinning (NDST) and dominant species thinning (DST) after nine years. Compared to plantations without management (CK), treatments such as UR, NDST, and DST decreased soil total P at 0–10 cm and soil available P at 0–10 cm and 10–20 cm. Increases in resin-Pi, NaOH-Pi, and C.HCl-Pi resulted in a higher total Pi in 0–10 cm (p < 0.05) in treated plots (UR, NDST, and DST) than in CK plots. UR, NDST, and DST treatments increased NaHCO3-Po and NaOH-Po (p < 0.05) but decreased C.HCl-Po at a depth of 0–10 cm. Regardless of management treatments, soil total P, available P, and P fractions in 0–10 cm showed higher contents than those in 10–20 cm. There were positive relationships between total P and total Po (p < 0.01) and between available P and total Pi. There were also positive relationships between total P, available P, NaHCO3-Pi, and NaOH-Pi (p < 0.05). In conclusion, forest management such as UR, NDST, and DST decreased soil total P and available P, and transforming soil P fractions to available P will meet the P demand following management in the pine plantations of subtropical China.

Rapid urbanization has affected ecosystem stability, and the construction of ecological security patterns (ESPs) can rationally allocate resources and achieve ecological protection. Priority evaluation of critical areas can maximize the benefits of ecological protection, which is crucial for sustainable urban development. However, most prior studies have focused on assessing individual elements of the ESP, rarely considering both the protection priority of ecological sources and corridors. We constructed ESPs for the Wuhan Metropolitan Area (WMA) from 2000 to 2020 and evaluated the priority of ecological sources and corridors for protection. The findings indicated that high-level ecological sources exhibited higher overall landscape connectivity and ecosystem service values with lower patch fragmentation. The average area proportions of primary, secondary, and tertiary ecological sources in 2000, 2010, and 2020 were 41.11%, 23.03%, and 29.86%, respectively. High-level ecological corridors had shorter lengths and offered higher comprehensive ecosystem service values. The total length of secondary corridors exceeded that of primary corridors by 1951.19 km, 650.39 km, and 2238.18 km in 2000, 2010, and 2020, respectively. Primary corridors, which connected fragmented and isolated sources, should have their ecological land percentage increased to enhance connectivity. Secondary corridors connected two independent and distant sources, providing the basis for ecological protection in the intervening area, whose surrounding habitats should be protected. This study identifies the ecological protection priority and offers a theoretical basis and practical reference for balancing urban development with ecological protection.

IntroductionAtmospheric nitrogen (N) deposition can impact the levels of soil organic carbon (SOC) and total nitrogen (total N) by altering the soil N availability. However, the effect of N input on the mineralization of SOC and total N in various soil aggregate size fractions requires further clarification.MethodsThe soil samples were collected from a Pinus massoniana plantation situated in the Three Gorges Reservoir Area of China. Over a period of three years, the soils from the plantation were subjected to four different levels of nitrogen addition (0 [N0], 30 [N30], 60 [N60], and 90 [N90] kg N ha−1 yr−1). The impact of N addition on the mineralization of SOC and total N in aggregates was evaluated through an incubation experiment, encompassing four aggregate sizes (2000 − 8000, 1000 − 2000, 250 − 1000, and < 250 μm).ResultsThe < 250 μm fraction showed the highest levels of cumulative C mineralization, while the lowest levels were observed in the 2000 − 8000 μm fraction. Compared to the < 250 um fraction, a drop of 9 − 21% in cumulative C mineralization was observed in the 2000 − 8000 μm fraction, indicating that soil aggregates enhance the stability of C in the soil. Cumulative N mineralization levels were consistently at their lowest in the 2000 − 8000 μm fraction, indicating aggregates reducing mineralization-related N loss. Adding N to forest soil samples led to a reduction in cumulative C mineralization. In contrast, an opposite trend was observed in the cumulative N mineralization after adding N in microaggregates. Nitrification was the main contributor to net N mineralization. SOC and total levels increased in response to N30 and N60. N addition leads to an increase in the weight ratio of the 1000 − 2000 μm fraction. Moreover, N90 was linked to decreases in microbial biomass C and N.DiscussionThese findings confirm that the structural characteristics of soil aggregates play a crucial role in sequestering organic carbon and total N sequestration in the presence of N deposition, while highlighting N loss from the soil caused by N input.

The construction of ecological security pattern (ESP) is an effective way to ensure regional ecological security. Although the method of constructing the regional ESP based on ecosystem services (ESs) has been widely recognized and applied, the spatial characteristics of ESs supply–demand mismatch has not been well included into ESP construction. We constructed a regional ESP framework connecting demand sources and ecological sources from the perspective of ESs supply–demand mismatch. Taking the Wuhan urban agglomeration (WUA), findings indicated distinct spatial aggregations of ecological sources and demand sources due to the supply–demand mismatch of ESs. Ecological sources (12,406.29 km2 or 21.42%) were primarily located in the south and north of WUA, while demand sources (1,191.26 km2 or 2.07%) were concentrated mainly in the central. Two types of corridors jointly ensured regional ecological security. A total of 86 supply–supply corridors in the north ensured the supply ability of ESs by connecting ecological sources, while 35 supply–demand corridors in the south alleviated the supply–demand mismatch of ESs. The targeted implementation of ecological governance based on the corridor types provides a new approach to coordinate the mismatch of ESs supply–demand and enhance ecological security. However, 63.38 km2 of pinch points, recognized as high-flow areas within the corridors, primarily comprised fragmented landscapes, and barriers covering 99.67 km2 obstructed corridor flow, notably surrounding the demand sources. These regions should be prioritized for ecological conservation. Overall, this research framework provides a reliable scientific basis for configuring spatial landscape patterns and developing ecological strategies in urban agglomerations.

As a key component of terrestrial ecosystems, soil interacts directly with aboveground vegetation. Evaluating soil quality is therefore of great significance to comprehensively explore the interaction mechanism of this association. The purpose of this study was to fully understand the characteristics of aboveground vegetation, soil quality, and their potential coupling relationship among different forest types in Hunan Province, and to provide a theoretical basis for further exploring the mechanisms underlying soil–vegetation interactions in central China. We have set up sample plots of five kinds of forests (namely broad-leaved forest, coniferous forest, coniferous broad-leaved mixed forest, bamboo forest, and shrub forest) in Hunan Province. To explore the differences of vegetation characteristics and soil physical and chemical properties among the five stand types, variance analysis, principal component analysis, and regression analysis were used. Finally, we explored the coupling relationship between soil quality and aboveground vegetation characteristics of each forest. We found that there were significant differences in soil quality among the forest types, ranked as follows: shrub forest > bamboo forest > broad-leaved forest > mixed coniferous and broad-leaved forest > coniferous forest. In general, there was a negative correlation between vegetation richness and soil quality in the broad-leaved forest and the shrub forest, but they showed a positive correlation in the coniferous forest, the mixed coniferous and broad-leaved forest, and the bamboo forest. As a necessary habitat condition for aboveground vegetation, soil directly determines the survival and prosperity of plant species. These results indicated that for vegetation–soil dynamics in a strong competitive environment, as one aspect wanes the other waxes. However, in a weak competitive environment, the adverse relationship between vegetation and soil is less pronounced and their aspects can promote.

Increasing atmospheric nitrogen (N) deposition has a profound impact on the ecosystem functions and processes. Fine root decomposition is an important pathway for the reentry of nutrients into the soil. However, the effect of N addition on root decomposition and its potential mechanism is not well understood with respect to root branch orders. In this study, we conducted a 30-month decomposition experiment of fine roots under different concentrations of N addition treatments (0, 30, 60, and 90 kg N ha-1 year-1, respectively) in a typical Pinus massoniana plantation in the Three Gorges Reservoir Area of China. In the early stage of decomposition (0−18 months), N addition at all concentrations promoted the decomposition of fine roots, and the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were increased by 13.54%, 6.15% and 7.96% respectively. In the late stage of decomposition (18−30 months), high N addition inhibited the decomposition of fine root, and the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were decreased by 58.35%, 35.43% and 47.56% respectively. At the same time, N addition promoted the release of lignin, carbon (C), N, and phosphorus (P) in the early-stage, whereas high N addition inhibited the release of lignin, C, N, and the activities of lignin-degrading enzyme (peroxidase and polyphenol oxidase) in the late-stage. The decomposition constant (k) was significantly correlated with the initial chemical quality of the fine roots and lignin-degrading enzyme activities. The higher-order (order 3–4 and order 5–6) fine roots decomposed faster than lower-order (order 1–2) fine roots due to higher initial cellulose, starch, sugar, C concentrations and higher C/N, C/P, lignin/N ratios and lower N, P concentrations. In addition, low N (30 kg N ha-1 year-1) treatments decreased soil organic matter content, whereas high N (90 kg N ha-1 year-1) treatment had the opposite effect. All the N treatments reduced soil pH and total P content, indicating that increased N deposition may led to soil acidification. Our findings indicated that the effect of N addition on decomposition varied with the decomposition stages. The decomposition difference between the lower-order and higher-order fine roots were controlled strongly by the initial chemical quality of the fine roots. This study provides new insights into understanding and predicting possible changes in plant root decomposition and soil properties in the future atmospheric N deposition increase scenarios.

Evaluating the environmental effects on soil phosphorus (P) availability is the key to understanding P cycling and regulating forest productivity. However, what and how environmental factors affect soil P availability in regional plantation ecosystems remains unclear. The study evaluated the effects of climatic factors, nitrogen deposition rate, stand attributes, litter characteristics, and soil-associated properties on soil P availability in Masson pine plantations across subtropical China using stepwise regression and structural equation modelling (SEM) analyses. At the 0–20 cm and 20–40 cm soil depths, soil total P ranged from 0.24 to 0.43 g kg−1 and from 0.24 to 0.48 g kg−1, respectively. Similarly, soil available P varied from 0.35 to 7.55 mg kg−1 and from 0.14 to 4.34 mg kg−1, respectively. Soil total and available P had high values in the eastern and northern distribution areas of subtropical China. Soil total P linearly decreased with an increase in bulk density, clay and pH but linearly increased with an increase in DBH. These four factors had a similar contribution (15.5–35.1 %) to soil total P. Soil available P linearly decreased with an increase in bulk density and clay. The relative contribution of clay (48.1–75.7 %) to soil available P was higher than that of bulk density (16.2–33.5 %). Soil total P decreased during the initial 30 years of plantations and then increased. But other variables (e.g., climate, nitrogen deposition, and litter) had no significant impacts on soil P. Overall, the SEM explained 35.4 % and 28.1 % of soil available P variations at the 0–20 cm and 20–40 cm soil depths, respectively, and revealed that clay had strong total effects (β = -0.526 and −0.396) on the soil available P. These results reveal the dominant roles of soil texture (especially clay) in affecting soil P availability in Masson pine plantations and suggest that extending the rotation period benefits soil P recovery in pine plantation ecosystems of subtropical China.

The Three Gorges Dam (TGD) plays a vital role in the hydropower supply of China, which has a substantial impact on the riparian zones along the Yangtze River. Knowledge about how riparian soil properties respond to such changes remains limited. To explore how water regulation disturbs the status of soil nutrients in the riparian zone, a long-term monitoring program was implemented at sites with secondary shrubland (SB) and abandoned farmland (AFD). A total of 288 composite soil samples collected from the two riparian areas were investigated. Compared with 2009, long-term flooding changed the distribution of soil organic matter (SOM) and available phosphorus (AP) contents in various soil layers. The fluctuation of the water level reduced the SOM content, which the range of SOM variation was greater in the early stage of submergence. In 2018, the SOM content in the 10–20 cm at 155–165 m above sea level (a.s.l.) of the AFD was 9.46 g/kg, which reduced by 74.30% compared with 2019. In all the 0–10 cm soil layer, except for 145–155 (a.s.l.) in the AFD plot, soil total nitrogen contents in 2018 were significantly higher than those in 2009. Compared with 2009, the soil AP content in the 10–20 cm layer at 145–155 m (a.s.l.) of SB decreased by 90.90% in 2018. The total potassium (TK) content of AFD increased from 2009 to 2015 but decreased in 2018. However, the soil TK content in 2018 was significantly higher than that in 2009. In AFD, soil pH increased from 2009 to 2015 and reached a maximum value (8.21). In 2018, the pH value of some soil samples showed a downward trend but was always significantly higher than during 2009. Moreover, according to the redundancy analysis, the elevation, soil layer, and flood cycle could explain 56.64% of the changes in soil properties. Our study demonstrates that dam operation was an indirect driver for the changes in the temporal dynamics of soil nutrients, providing a reference for the management of the TGD.

Adult cardiac hypoxia as a crucial pathogenesis factor can induce detrimental effects on cardiac injury and dysfunction. The global transcriptome and translatome reflecting the cellular response to hypoxia have not yet been extensively studied in myocardium. In this study, we conducted RNA sequencing (RNA-seq) and ribosome profiling technique (polyribo-seq) in rat heart tissues and H9C2 cells exposed to different periods of hypoxia stress in vivo and in vitro. The temporal gene-expression profiling displayed the distinction of transcriptome and translatome, which were mainly concentrated in cell apoptosis, autophagy, DNA repair, angiogenesis, vascular process, and cardiac cell proliferation and differentiation. A large number of genes such as GNAI3, SEPT4, FANCL, BNIP3, TBX3, ESR2, PTGS2, KLF4, and ADRB2, whose transcript and translation levels are closely correlated, were identified to own a common RNA motif “5′-GAAGCUGCC-3′” in 5′ UTR. NCBP3 was further determined to recognize this RNA motif and facilitate translational process in myocardium under hypoxia stress. Taken together, our data show the close connection between alterations of transcriptome and translatome after hypoxia exposure, emphasizing the significance of translational regulation in related studies. The profiled molecular responses in current study may be valuable resources for advanced understanding of the mechanisms underlying hypoxia-induced effect on heart diseases.

China has made tremendous efforts in forest restoration (FR), and has established ambitions to govern its fragile ecosystem and improve green welfare until 2035. However, debate still exists over whether FR can simultaneously improve ecosystem services and enhance livelihoods. In this paper, we test the impacts of forest restoration on key ecosystem services and livelihoods via a case study of Badong County in the TGRA, China. The Revised Universal Soil Loss Equation and Carnegie-Ames-Stanford Approach were used to evaluate the soil erosion rate (SER) and net primary productivity (NPP), and we analyzed livelihoods through 520 surveys. Our results revealed that forestland increased significantly from 45.34% to 69.63% during 1990–2015. The annual average SER significantly dropped from 67.01 to 51.18 t·ha−1·yr−1 during 2001–2015, and the annual average NPP increased from 547.12 gC·m−2·a−1 in 2000 to 609.81 gC·m−2·a−1 in 2015. However, the afforestation area offered disadvantages when compared with the persisting forest area in SER and NPP. Households in ecologically fragile areas have equal opportunities in, among others, infrastructure and government policies, but their income and living conditions are often heterogeneous. The per capita income and area of residence improved under FR. Nonetheless, the inequality in per capita income between participating households (PHs) and nonparticipating households (NPHs) increased. Compared with NPHs, PHs lost more cropland, and agricultural income, and more PH householders were forced to find new livelihood activities. These inequalities are not conducive to the sustainable development of FR. Accordingly, we recommend that restoration efforts should focus on forest quality and habitat availability improvement in the persisting forest area and afforestation area, and on new reforestation programmes where appropriate. The government should provide sustainable and science-based ecological subsidies and help PHs obtain alternative livelihood activities, which contribute to higher household income and poverty alleviation.

Analyzing the molecular and physiological processes that govern the uptake and transport of nitrogen (N) in plants is central to efforts to fully understand the optimization of plant N use and the changes in the N-use efficiency in relation to changes in atmospheric N deposition changes. Here, a field experiment was conducted using the ectomycorrhizal fungi (EMF), Pisolithus tinctorius (Pt) and Suillus grevillei (Sg). The effects of N deposition were investigated using concentrations of 0 kg·N·hm−2a−1 (N0), a normal N deposition of 30 kg·N·hm−2a−1 (N30), a moderate N deposition of 60 kg·N·hm−2a−1 (N60), and a severe N deposition of 90 kg·N·hm−2a−1 (N90), with the goal of examining how these factors impacted root activity, root absorbing area, NH4+ and NO3− uptake kinetics, and the expression of ammonium and nitrate transporter genes in Pinus massoniana seedlings under different levels of N deposition. These data revealed that EMF inoculation led to increased root dry weight, activity, and absorbing area. The NH4+ and NO3− uptake kinetics in seedlings conformed to the Michaelis–Menten equation, and uptake rates declined with increasing levels of N addition, with NH4+ uptake rates remaining higher than NO3− uptake rates for all tested concentrations. EMF inoculation was associated with higher Vmax values than were observed for non-mycorrhizal plants. Nitrogen addition resulted in the upregulation of genes in the AMT1 family and the downregulation of genes in the NRT family. EMF inoculation under the N60 and N90 treatment conditions resulted in the increased expression of each of both these gene families. NH4+ and NO3− uptake kinetics were also positively correlated with associated transporter gene expression in P. massoniana roots. Together, these data offer a theoretical foundation for EMF inoculation under conditions of increased N deposition associated with climate change in an effort to improve N absorption and transport rates through the regulation of key nitrogen transporter genes, thereby enhancing N utilization efficiency and promoting plant growth. Synopsis: EMF could enhance the efficiency of N utilization and promote the growth of Pinus massoniana under conditions of increased N deposition.

The process of rapid urbanization has been causing non-negligible disturbances to our ecosystems, which has aggravated the mismatch between ecosystem service (ES) supply and demand. A clear understanding of the relationship between the ES supply–demand mismatch and urbanization is crucial as it could have a lot of significance for implementing ecological compensation and conservation action. Although a large number of studies have explored this problem, previous studies have focused primarily on the spatial mismatching of the ESs, and only a few studies have considered the spatial relationship between the ES supply–demand mismatch and urbanization at the watershed scale. Taking the Yangtze River Economic Belt (YREB) as an example, this study quantitatively assesses the supply and demand of five ESs, including carbon sequestration, water retention, soil conservation, food production, and recreational opportunity. The bivariate Moran’s I method was used to analyze and visualize the spatial correlation between the ES supply–demand mismatch and urbanization. The results indicate that both the total supply and the total demand of the five ESs increased, while the increasing rate of total demand was higher than the total supply of the ESs; this resulted in a significant spatial mismatch between the supply and demand of the ESs from 2000 to 2020. There is also a negative spatial correlation between the ES supply–demand and urbanization, while the results of local spatial clustering have obvious spatial heterogeneity. The metropolis and its surrounding counties are mostly the ES supply and demand deficit area, but some surrounding counties have managed to transform a deficit into a surplus. These results indicate that urbanization has a certain interference on the mismatch of the ES supply and demand, and this interference is not irreversible. Moreover, this study provides a reliable reference for government management in the context of balancing urbanization and the ecosystem.

Restoring degraded lands is now a global priority for conservation, and world leaders even made positive commitments to do so as part of the Bonn Challenge. Forest Landscape Restoration, which focuses on improving ecological functioning, biodiversity conservation and human livelihoods was introduced to meet these restoration goals. However, the restoration can be carried out only after a series of evaluations. One such evaluation is that of land for its suitability for forest landscape restoration and has become the basis for successful restoration of forest landscapes. A land suitability assessment method for forest landscape restoration is therefore fundamental. This study introduces a matter-element model-based methodology to assess land suitability for forest landscape restoration. The case study was evaluated in terms of altitude, slope, aspect, soil depth, soil type, and nutrient status of soil, all of which greatly influence the type of vegetation and plant growth. The results showed that the main factors influencing forest restoration in Zigui were altitude, slope, and soil depth. Roughly 100 km2 are suitable for restoration in Zigui County, accounting for about 60% of the theoretical recoverable area, a little more than one-third of which consists of slopes steeper than 25° and approximately 16% consists of slopes between 15° and 25°. The area under low quality forest land is a little over 40 km2, that under low quality garden land is roughly 15 km2, and that under sloping cultivated land is 40 km2. Evaluating the suitability of land for restoration can serve as a basis for forest-restoration projects and structural adjustments in shelter forests in this fragile area. Specifically, this method of evaluation can be replicated on different spatial and temporal scales and represents a new framework for evaluating the suitability of land for restoration of forests in other regions as well.

The effects of temperature and precipitation on tree growth of given species may vary across its distribution range. To determine how temperature and precipitation influence tree radial growth, we conducted a dendrochronology-based meta-analysis using a network of 113 tree-ring width chronologies of Pinus massoniana trees from the geographical range of the species in southern China. Our results revealed that the difference in the sensitivity of P. massoniana growth to temperature and precipitation was not observed in the entire tree species distribution and each sub-region (all P > 0.05), indicating that there are similarities with respect to the effects of temperature and precipitation on P. massoniana growth among different regions. January–March temperature (T1–3), June–August temperature (T6–8), and July–September precipitation (P7–9) were the key climate signals influencing P. massoniana growth. T1–3 and P7–9 generally enhanced tree growth, whereas T6–8 lead to a decrease in tree growth. Sites with significant negative correlations between tree-ring width index (RWI) and T1–3 showed a northward shift (P 0.05), indicating that high summer temperatures are widespread climate stressors for this species. The growth-climate relationship was determined by combinations of both temperature and precipitation condition of the sampling sites. Temperature seasonality, temperature annual range, and mean temperature of driest quarter of the sampling sites were major contributors to this relationship. These findings have crucial implications for predicting tree growth, introducing the selection of appropriate provenance for afforestation, as well as for climate reconstruction at the regional scale.

It has been indicated that doxorubicin (Dox) can induce some unwanted cardiotoxicity through different signaling pathways. In the present study, calycosin-PEG-PPG-PEG copolymer nanomicelles were developed and well-characterized by different techniques. Afterwards, the protective effects of calycosin-triblock copolymer nanomicelles against Dox-stimulated cardiotoxicity in H9C2 cardiomyocytes were explored by viability, reactive oxygen species (ROS), and reactive nitrogen species (RNS) assays. Also, the expression of ERp57, p53, Bax, and Bcl-2 at both mRNA and protein levels were assessed by qPCR and western blot , respectively. It was seen that synthesized calycosin-triblock copolymer nanomicelles had a size of around 20–30 nm with good colloidal stability, sustained drug release and improved dissolution rate. Also, it was shown that calycosin-triblock copolymer nanomicelles can mitigate Dox-induced cardiotoxicity through a remarkable reduction in ROS and RNS generation. Also, it was found that calycosin-triblock copolymer nanomicelles resulted in the downregulation of Bax and p53 and overexpression of Bcl-2 and ERp57 at both mRNA and proteins levels and these protective effects were inhibited in the presence of ERp57-siRNA silencing. Therefore, this study may provide useful information about the development of drug-loaded nanomicelles for mitigation of Dox-induced toxicity.

To better understand the soil carbon dynamics and cycling in terrestrial ecosystems in response to environmental changes, we studied soil respiration, litter decomposition, and their relations to soil temperature and soil water content for 18-months (Aug. 2010-Jan. 2012) in three different-aged Pinus massoniana forests in the Three Gorges Reservoir Area, China. Across the experimental period, the mean total soil respiration and litter respiration were 1.94 and 0.81, 2.00 and 0.60, 2.19 and 0.71 µmol CO2 m(-2) s(-1), and the litter dry mass remaining was 57.6%, 56.2% and 61.3% in the 20-, 30-, and 46-year-old forests, respectively. We found that the temporal variations of soil respiration and litter decomposition rates can be well explained by soil temperature at 5 cm depth. Both the total soil respiration and litter respiration were significantly positively correlated with the litter decomposition rates. The mean contribution of the litter respiration to the total soil respiration was 31.0%-45.9% for the three different-aged forests. The present study found that the total soil respiration was not significantly affected by forest age when P. masonniana stands exceed a certain age (e.g. >20 years old), but it increased significantly with increased soil temperature. Hence, forest management strategies need to protect the understory vegetation to limit soil warming, in order to reduce the CO2 emission under the currently rapid global warming. The contribution of litter decomposition to the total soil respiration varies across spatial and temporal scales. This indicates the need for separate consideration of soil and litter respiration when assessing the climate impacts on forest carbon cycling.

Cover crops improve soil fertility in orchard ecosystems, however, the response of soil microbial metabolism to fruit tree interactions with cover legumes at different stages of the life cycle remains uncertain, thereby limiting our understanding of the mechanisms that regulate nutrient cycling in orchards with cover crop management. Here, the characteristics of microbial energy (carbon, C) and nutrient (nitrogen, N or phosphorus, P) metabolism in the citrus rhizosphere and bulk soil in orchards were analyzed with two managements, that is, smooth vetch (Vicia villosa Roth var. glabresens Koch) cover and clean tillage, using an extracellular enzymatic stoichiometry model. Microbial C limitation was significantly reduced by cover during the vetch growing season owing to the resulting higher plant root C and soil organic C content. Competition for N between plants and microbes in the bulk soil might lead to significant microbial N limitation in covered orchards during the vetch-decomposition season, presumably owing to a significant increase in citrus root N and a concomitant decrease in bulk soil total N. Partial least squares path modeling showed that citrus root nutrient contents negatively affected microbial C limitation, while soil nutrients negatively affected microbial relative nutrient limitation in covered orchards. Conversely, both effects were reversed by tillage. Smooth vetch cover mitigated microbial C limitation, and the microbial relative N/P limitation was also influenced by the life state of smooth vetch. Our study highlights the importance of changes in microbial metabolism driven by seasonal nutrient dynamics for understanding soil nutrient cycling and optimizing cover-legumes management in orchards. [ABSTRACT FROM AUTHOR]