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Microorganisms, the major decomposers of plant residues, are crucial for soil nutrient cycling. Living grass mulching effectively alters microbial community structure and promotes nutrient cycling. However, its consistency with mulching ages and growth periods remains unclear. Therefore, this study aims to clarify the dynamic characteristics of microbial communities and enzyme activities across different mulching ages. In this study, high-throughput sequencing technology was used to investigate bacterial and fungal community evolution in three mulching treatments with Vicia villosa for 8 years (VV_8), 4 years (VV_4), and clean tillage in a citrus orchard. This study covered three growth periods (citrus-grass: spring sprouting to budding period [SSBP], fruit swelling to withering period [FSWP], and fruit maturity to seeding period [FMSP]). The results showed that VV_4 and VV_8 treatments increased bacterial and fungal alpha diversity as well as the activities of nitrogen (N), carbon (C), and phosphorus cycling enzymes. C-cycling enzyme activity was the primary key factor driving changes in microbial diversity across growth periods. Under leguminous green mulching, bacteria alpha diversity increased the most during FSWP, while fungi increased the most during FMSP. Additionally, the relative abundance of Ascomycota and Basidiomycota significantly increased during the FSWP and FMSP, reaching 63.65-73.80 % and 79.73-84.51 %, respectively. With increasing mulching ages, the structural stability and synergistic effects of microorganisms were correspondingly enhanced. Furthermore, available nutrients determined microbial community evolution, with N availability being a key factor influencing microbial diversity, especially fungal diversity. In conclusion, as mulching ages increase, improved nutrient availability gradually enhances microbial diversity, synergistic interactions, and nutrient cycling functions, with copiotrophic taxa occupying a key position in the microbial network. FSWP is a critical turning point for enhancing microbial activity and C-cycling function. This study offers theoretical support for developing microbial regulation strategies to improve soil quality in orchard management practices., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A large amount of stable soil organic matter (SOM) is derived from microbial necromass, which can be assessed by quantifying amino sugar biomarkers. Pinus massoniana Lamb. Plantations are widely distributed in China and play a vital role in forest carbon sequestration. However, the patterns of soil microbial residue remain poorly understood. In this study, amino sugars were used to characterize patterns of soil microbial residues at three soil depths (0-10, 10-20, and 20-30 cm) in P. massoniana plantations of different ages (young, middle-aged, near-mature, mature, and over-mature; denoted as YG, MD, NM, MT, and OM, respectively). In the topsoil (0-10 cm), the total nitrogen (TN) content of the OM forest was the highest, whereas the soil organic carbon (SOC) content of the MT forest was the highest. Consistent with changes in SOC and TN, total microbial residue content decreased with increasing soil depth. However, the total microbial residues C to SOC contribution increased considerably with increasing depth, suggesting that more SOC was derived from microbial residues in the subsoil than that from the topsoil. The fungal residue C to SOC contribution was higher than that of bacterial residue C. Total amino sugar content in the topsoil increased with increasing age, and MT and OM had a significantly higher content than that of other forests. At all soil depths, SOC and TN content predominantly determined microbial necromass, whereas soil microbial biomass content predominantly determined microbial necromass in the topsoil; soil pH predominantly determined microbial necromass in the 10-20 cm soil layer; and soil pH and Ca 2+ content were the primary factors in the soil layer below 20 cm. The study provides valuable insights into controls of microbial-derived organic C could be applied in Earth system studies for predicting SOC dynamics in forests., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Inc.)

Drought would significantly influence the forest soils through changing the litterfall production and decomposition process. However, comprehensive in situ studies on drought effects in subtropical forests, especially in bamboo forests, have rarely been conducted. Here, we conducted a throughfall exclusion experiment with a rainfall reduction of ~80% in moso bamboo (Phyllostachys edulis) forests to investigate effects of drought on litter quantity, quality, soil microbial and enzyme activities, and soil nutrients across two years in subtropical China. We observed that throughfall exclusion (TE) treatment significantly decreased soil moisture by 63% compared to ambient control treatment (CK). Drought significantly decreased the annual litterfall in the second treatment year, and the leaf litter decomposition rate (-30% relative to CK) over 2 years of decomposition. TE treatment significantly decreased net release rate of litter carbon (C) and the amount of litter nitrogen (N) immobilization during a 360-day decomposition period, leading an increased litter C: N ratio in TE compared to CK. There was a distinct difference in soil microbial community composition between TE and CK treatments, showing higher bacteria biomass in TE but no difference in fungal biomass between TE and CK. Structural equation modelling revealed that drought decreased the contribution of litter quantity to soil nutrients but increased that of litter quality and soil microbial community to soil nutrients. Our results suggest that increasing drought events in subtropical China will directly reduce litterfall quantity and quality on the one hand, and alter the soil enzyme activities and microbial composition on the other hand, all of which will consequently decrease litter decomposition rate, soil nutrient availability, growth rate and productivity, leading to changes in the functioning and services of subtropical bamboo forests., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Soil physiochemical properties are critical to understanding forest productivity and carbon (C) finance schemes in terrestrial ecosystems. However, few studies have focused on the effects of the soil physiochemical properties on the productivity in planted forests. This study was therefore conducted at 113 sampling plots located in planted Masson pine forests across subtropical China to test what and how the aboveground net primary productivity (ANPP) would be explained by the soil physiochemical properties, stand attributes, and functional traits using regression analysis and structural equation modelling (SEM). Across subtropical China, the ANPP ranged from 1.79 to 14.04 Mg ha -1 year -1 among the plots, with an average value of 6.05 Mg ha -1 year -1 . The variations in ANPP were positively related to the stand density, root phosphorus (P) content and soil total P content but were negatively related to the stand age, root C:P and N:P ratios. Among these factors, the combined effects of stand density, stand age and soil total P content explained 35% of the ANPP variations. The SEM results showed the indirect effect of the soil total P content via the root P content and C:P ratio on the ANPP and indirect effects of other soil properties (e.g., pH, clay, and bulk density) via the soil total P content and root functional traits (e.g., root P, C:P, and N:P) on the ANPP. By considering all possible variables and paths, the best-fitting SEM explained only 11-13% of the ANPP variations, which suggested that other factors may be more important in determining the productivity in planted forests. Overall, this study highlights that soil total P content should be used as a key soil indicator for determining the ANPP in planted Masson pine forests across subtropical China, and suggests that the root functional traits mediate the effects of soil properties on the ANPP., Competing Interests: Declaration of competing interest None., (Copyright © 2022. Published by Elsevier B.V.)

Establishing forest plantations is an important solution to the growing conflict between an increasing human population and mounting pressure to protect the natural forests, as plantations also harbor great potential for providing multiple ecosystem services (ESs). However, because of the trade-offs between multiple ESs and the conflicts between different stakeholders, the sustainable management of plantations has been exceedingly challenging. Especially in recent years, with China's emphasis on ecological civilization construction and sustainable development, forestry departments have begun to focus on long-term ecological benefits, which conflict with farmers' attention to short-term economic gains. In this study, we quantified 15 field-based ES indicators from the data measured in Chinese fir (Cunninghamia lanceolata) plantations aged 4 to 32 years. Corresponding to the concerns of two different stakeholders (forestry departments and farmers), we calculated ES-multifunctionality with different thresholds under four management scenarios: equal weight, production only, production multifunctionality, and supporting multifunctionality. Our results suggested pronounced stand age effects on both individual ESs and ES-multifunctionality of plantations. For individual ESs, stand age had a greater impact on provisioning services than on supporting services. High degree of trade-offs existed between plantation provisioning ESs and soil nutrient supporting ESs, and between water relevant ESs and the other ESs. With respect to ES-multifunctionality, the values under different scenarios were all augmented with stand age, but to differing degrees. The values for supporting multifunctionality were higher than those of production multifunctionality and production only before 21 years of stand development, but completely reversed once the fir plantations reached an age of 25 years. Finally, several stage-based plantation management recommendations are proposed to minimize conflicts between different stakeholders. Our results combined measures of temporal stability and multifunctionality, thereby providing valuable and timely insight into the multifunctional stability of plantations represented by Chinese fir., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Biochar addition to soil is increasing worldwide, the effect of combined application of biochar and nitrogen (N) fertilizer on soil respiration is still unknown. Understanding of the interactive effects of biochar and N fertilizer addition on temperature sensitivity of soil respiration and temporal dynamics of soil CO 2 emissions in forest ecosystems remains limited. We conducted a full factorial experiment with biochar (B 0 , B 1 and B 2 with 0, 5 and 20 t·ha -1 , respectively) and N fertilizer addition (N 0 and N 1 with 0 and 50 kg·ha -1 NH 4 NO 3 , respectively) as factors, to study their effects on soil respiration rate, temperature sensitivity (Q 10 ), soil available nutrients, and their relations in moso bamboo plantations in subtropical China from April 2014 to April 2016. We found that, irrespective of biochar addition rate, N fertilization increased Q 10 on the one hand, and irrespective of N fertilization rate, lower application rate of biochar resulted in a higher Q 10 , on the other hand. In spite of increased Q 10 , combined application of biochar and N decreased soil respiration rate in both growing season and non-growing season, as well as the annual cumulative soil CO 2 emissions. Annual cumulative soil CO 2 emissions were found to be significantly positively correlated with soil total nitrogen (STN) (p = 0.028) in 0-10 cm soil layer, and with soil ammonium (NH 4 + ) (p = 0.000) and soil microbial biomass carbon (MBC) (p = 0.000) in both 0-10 cm and 10-20 cm soil layer. The present study suggests that the combined application of biochar and N fertilizer can be widely used in subtropical forest ecosystems where soil N is limited, because it increases soil fertility and, at the same time, decreases soil CO 2 emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The variations in net primary productivity (NPP) and its controls are critical to understand the mechanisms that maintain ecosystem services under ongoing climate change and human activities. However, such knowledge is still incomplete in ecotone areas where plant species may reach their physiological thresholds. Our study quantified the variations in NPP and its controls resulting from interannual climate variations and human activities in the Qilian Mountain region (QLMR), an ecotone zone in central Asia. To achieve this goal, three indexes, including actual NPP (ANPP), potential NPP (PNPP), and human-induced NPP (HNPP), and their variations during 2001-2012 were estimated by combining the Carnegie-Ames-Stanford approach and a residual trend method. The results showed that the average PNPP, HNPP and ANPP values across the whole QLMR increased at rates of 4.71, 3.08, and 1.63 g C m - 2  yr - 1 , respectively. The ANPP increased in 66.8% of the area during 2001-2012. The impacts of climate variations and human activities on NPP varied across the ecotone zone, vegetation types and altitudinal gradient. Climate-derived impacts caused the ANPP to increase in over 53% of the area in all vegetation ecosystems except forests. Climate variations were expected to account for most of the changes in ANPP in high-altitude zones (above 3500 m), while the impacts of human activities on ANPP were concentrated mainly in mid- and low-elevation zones. Our results suggest that increasing precipitation is a dominant factor underlying the increase in ANPP in such semiarid regions, while human activity is the primary reason for declines in NPP even if there is vegetation restoration. To improve the functions of vegetation ecosystems in such ecotones, a holistic strategy that combines spatially distinct measures is urgently needed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Vegetation recovery is a promising strategy to mitigate soil loss risk across different landscapes and human disturbance levels. Uncertainties still exist in the impacts of forest restoration on soil erosion with respect to complicated terrain condition and land-use/cover pattern, especially in mountainous reservoir areas undergoing intensive human activities. Here, we assess the effects of forest restoration on controlling soil erosion in the Three Gorges Reservoir area (TGRA), China. The Revised Universal Soil Loss Equation and time-series data were used to estimate soil erosion and its changes in 2001-2015. The slope of soil erosion at a pixel level was estimated to determine the responses of soil erosion to forest restoration. The results indicate that the conversion of cropland to forest was the dominated land use/cover transformation process in the TGRA from 2001 to 2015. The mean annual soil erosion rate in the TGRA decreased, with an annual drop rate of 1.28%. Changes in the soil erosion rate presented significant spatial variations, with a significant decrease (1.09 t∙ha -1 ∙yr -1 ) in the terrain slope zones between 25° and 35°, where intensive forest restoration occurred. Within various land transformation processes, the slope of the mean soil loss rate was the highest (slope = 0.71, P < 0.01) in afforestation areas. Our findings reveal that forest restoration can effectively reduce soil erosion in mountainous reservoir areas, but there are significant variations in the various vegetation recovery processes with the time-lag effect and across elevational gradient. Although most forest restorations occurred in steep slope areas, slope steepness is still the dominated factor in the spatial variation of soil erosion in the TGRA. We suggest forest landscape restoration to fill the scale gap between soil erosion and forest restoration in hilly reservoir areas such as the TGRA., (Copyright © 2019 Elsevier B.V. All rights reserved.)

To determine whether mixed plantations can improve nutrient cycling and to elucidate the mechanisms of such effects, a field litterbag experiment with seven treatments involving Pinus massoniana (P.), Cupressus funebris (C.) and Quercus variabilis (Q.) litter in equal mass proportions (pure litter; pairwise combinations; and the combination of all three species) was conducted in a Pinus massoniana plantation in the region of the Three Gorges Reservoir, China. We measured mass loss and the release of C, N and P from the litter treatments and assessed the effects of mixing litter in each sampling phase and for various decomposition periods. At the end of the study, the mass loss and release of C, N and P among the treatments relative to their initial contents ranged from 47.6% to 62.8%, 59.5% to 75.2%, 63.5% to 78.2% and 58.9% to 72.6%, respectively. Primary mass loss and nutrient release occurred during a phase with high temperatures and precipitation, and decomposition was closely correlated with the initial lignin/N ratio and N concentration. Compared with the decay values of Quercus litter, mixing litter increased N release by 1.2% for the P. + Q. and C. + Q. combinations and increased P release by 3.0-6.3% for the three litter mixture combinations. Additionally, the P. + Q. and C. + Q. two-species mixtures exhibited greater decay than the three-species mixture. Mixing the two coniferous species (P. + C.) also increased decomposition. Furthermore, positive nonadditive mass loss occurred after incubation for 240 d, and mixing effects on the nonadditive release of C, N and P occurred immediately in 60 d incubations in all treatments. In conclusion, mixing these three species or two of species can improve material cycling in plantations, and Quercus appears to be a priority candidate for mixed planting with Pinus and/or Cupressus., (Copyright © 2018. Published by Elsevier B.V.)

Quantifying soil respiration (R s ) and its components [autotrophic respiration (R a ) and heterotrophic respiration (R h )] in relation to forest management is vital to accurately evaluate forest carbon balance. Thus, R s , R a , and R h were continuously monitored from November 2013 to November 2016 in Pinus massoniana forests subjected to four different management practices in China. We hypothesized that understory removal and thinning decrease R a and R h and thus R s , and these decreases will change with time following UR and thinning. Mean values of R s , R a , and R h in light thinned plots (LT=15% of tree basal area thinned) and heavily thinned plots (HT=70% of tree basal area thinned) were significantly higher than in control (CK) and understory removal plots (UR). The annual R h /R s ratio ranged from 58% to 70% across all treatments, and this ratio was significantly higher in HT and LT than in UR and CK. Only HT significantly increased soil temperature. Soil temperature could better explain R h (R 2 =0.69-0.96) than R a (R 2 =0.51-0.86). HT and LT increased Q 10 for both R a and R h , except for R h in UR. Soil moisture content (W; %) was significantly higher in HT than in other treatments, but W had limited effects on soil respiration in that rain-rich subtropical China. This result suggests that global warming alone, or in combination with clear-cutting or canopy tree thinning will markedly increase soil heterotrophic respiration and thus the total soil CO 2 emission. To get firewood for local people and to reduce soil CO 2 emissions under global warming, canopy trees are needed to be protected and understory shrubs may be allowed to be used in the subtropical China., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Soil organic carbon (SOC) is an important component of the global carbon pool. It is a critical indicator of soil quality. We studied SOC content (SOCC) and SOC density (SOCD) of the Three Gorges Reservoir (TGR) area in China. Soil samples from 306 sites across the study area were assessed for SOCC, SOCD and bulk density. Total SOC stocks in the TGR area were estimated at 5.82×10 -1 Pg. We examined relationships between SOCC and SOCD, and the environmental and land-use/land-cover (LULC) variables. The plow layer (0-0.3m) had a significantly higher mean SOCC (20.6gkg -1 ) than the subsoil layer (16.5gkg -1 ); elevation, LULC, soil type and soil thickness were the most influential factors affecting SOCC in the plow layer. In the subsoil layer, elevation and soil thickness were dominant in determining SOCC and SOCD. To study the spatial variability of SOC, we used statistical modeling and GIS-based techniques to map the distribution of SOCC and SOCD of the study area. Both SOCC and SOCD in the plow layer showed patchy distribution and were positively correlated with elevation and vegetation coverage. Spatial variability of SOCD in the subsoil layer showed a gradual transition between LULC categories. The lower SOCC of farmland appeared to be related to the repeated removal of agricultural produce from the land. Preservation of permanent vegetation cover and changing of the traditional farming practices will help to improve SOC stock and increase soil productivity in the TGR area., (Copyright © 2017 Elsevier B.V. All rights reserved.)