Abstract:[Objective] The karst and non-karst areas in Southwest China are interlaced with strong spatial heterogeneity. Assessing the spatial differentiation and storage of soil organic carbon (SOC) in this region at the county scale is of great significance for achieving regional "dual carbon" goals. [Methods] Taking Wenshan County, a typical karst county in southeast Yunnan Province, as an example, we employed a grid sampling method to conduct the spatial differences in SOC content and storage in top soil(0-20 cm) and deep soil(0-200 cm). Furthermore, we used the semi-variogram function and geographical detector to analyze the impact of external environmental factors on the spatial differentiation of SOC. [Results] The average SOC content in the top soil and deep soil was 17.80 g/kg and 5.18 g/kg respectively, with a total storage of 3770.89×104 t. The distribution pattern revealed higher SOC content in the topsoil of the western region and lower in the central and northern regions, while the deep soil exhibits higher SOC content in the central and western regions and lower in the northeastern region in Wenshan County. In non-karst areas, the SOC content in the topsoil and deep soil was 20.88 g/kg and 6.12 g/kg, respectively, which was 27.94% and 32.75% higher (P<0.01) than in karst areas. The semi-variogram model indicates that the nugget effect value of SOC ranges from 14.62% to 59.93%, indicating that structural factors dominate the spatial differentiation of SOC in Wenshan County. According to the analysis of the geographical detector, temperature and altitude are the main controlling factors affecting SOC in the top soil layer in karst areas. As the temperature decreases and the altitude increases, the SOC content in Wenshan County shows an increasing trend. However, the SOC content in karst areas is generally lower than that in non-karst areas due to their lower altitudes, severe rocky desertification, and relatively poor vegetation growth. For the deep soil, precipitation is the main controlling factor affecting SOC in karst areas. The leaching effect caused by precipitation may combine dissolved calcium with organic matter to form humic acid calcium, promoting the accumulation of SOC in deep soil. In non-karst areas, stratigraphic chronology plays a leading role. The soil developed from Permian basalt parent material may have higher soil clay and macro-aggregate contents, which helps to maintain the physical protection and stability of SOC in deep soil. [Conclusion] This study will provide a reference for the precise assessment of SOC and the regulation of soil carbon pools in the southwestern karst region.

Abstract:Abstract: [Objective] The contents of soil carbon (C), nitrogen (N) and phosphorus (P) along with their stoichiometric ratios, were changed due to the varying nutrient uptake and utilization strategies among various tree species plantations, which in turn affected soil microbial activity. However, whether soil microorganisms adapt to these changes by adjusting their biomass and extracellular enzyme stoichiometric ratios remains uncertain. This study aims to explore the effects of various tree species plantation on soil-microbe-exoenzyme C:N:P stoichiometric ratios and to investigate the correlations among soil-microbe-exoenzyme stoichiometry. [Methods] we conducted an investigation into the contents of C, N and P, as well as microbial biomass C (Cmic), N (Nmic), P (Pmic), and the activities of C (β-1,4-glucosidase + β-D-cellosidase, BG + CBH), N (N-acetyl-β-glucosaminidase, NAG), and P (acid phosphatase, ACP) acquiring extracellular enzymes for microorganisms at depths 0-40 cm in four native tree species plantations. These plantations include conifers Pinus massoniana, deciduous broad-leaved Liquidambar formosana, evergreen broad-leaved Schima superba, and Elaeocarpus decipiens, located in the hilly region of central Hunan province and share a common soil development and management history. [Results] (1) Different tree species plantations significantly affected soil C, N, P content, microbial biomass, extracellular enzyme activity, Cmic:Nmic:Pmic and EEAC:N:P. Cmic:Pmic ratios in the P. massoniana plantations and the L. formosana plantations were significantly higher than those in the S. superba plantations and the E. decipiens plantations, indicating that microorganisms compete with plants for soil available P and a low utilization rate of soil P, especially evident in the L. formosana plantation. NAG and EEAN:P in the S. superba plantations were the highest, suggesting that the microorganism was obviously limited by N. ACP in the E. decipiens forest was higher, EEAC:N and EEAC:P were also higher than those in other tree species plantations, while EEAN:P was the lowest, indicating that the microorganisms were most restricted by C and P. (2) There were no significant correlation between soil C:N:P and microbial biomass, extracellular enzyme C:N:P, while only Cmic:Nmic and EEAC:N, Cmic:Pmic and EEAC:P showed significant negative correlation, indicating no covariance between soil C:N:P and microbial biomass C:N:P. There was a significant positive correlation between soil C:N:P and C:Pimb, a significantly negatively correlation between Cmic:Nmic:Pmic and C:N:Pimb, and a significant positive correlation between C:Nimb and EEAC:N, which confirmed the influence of C, N and P differences between soil and microorganisms on the stoichiometric ratio of extracellular enzymes. (3) Existing biomass of litter layer had significant effects on soil C, N, P content, Pmic, Cmic:Pmic, Nmic:Pmic, BG+CBH, NAG, and EEAC:P. [Conclusion] By influencing the contents of soil C, N and P, plantations composed of different tree species modulated microbial biomass and extracellular enzyme activity. Microorganisms can adapt to diverse nutrient limitations by regulating their biomass C:N:P ratios and synthesizing specific extracellular enzymes, thereby substantiating the microbial resource allocation theory.

Abstract:[Objective] Acid hydrolyzed soil organic carbon fractions are important in soil, and their changes of contents will affect soil microbial community composition.To study the response of acid hydrolyzed soil organic carbon fractions and soil microbial communities to different logging residue treatments. [Methods] Three treatments of residue removed (R), residue burnt (RB) and residue retained (RR) were applied to a Chinese fir plantation in the Castanopsis kawakamii Nature Reserve in Sanming Fujian, and soils in different soil layers (0-10 cm, 10-20 cm) were collected three years after planting young Chinese fir to study acid hydrolyzed soil organic carbon fractions (labile fraction Ⅰ, Ⅱ and recalcitrant fraction) and microbial community. [Results] (1) Different logging residue treatments had no significant effect on acid hydrolyzed soil organic carbon fractions in the 0-10 cm soil layer (p>0.05). In the soil layer of 10-20 cm, the content of labile fraction Ⅰ (LP Ⅰ) was significantly higher in the RR (7.2 g·kg-1) and R (6.8 g·kg-1) treatments than in the RB (4.7 g·kg-1) treatment, and the contents of labile fraction II ( LP II, 1.06 g·kg-1) and recalcitrant fraction (RP, 3.59 g·kg-1) in the RB treatment were significantly lower than those in the R treatment (1.32 g·kg-1 and 7.79 g·kg-1, respectively) (p<0.05). The contents of acid hydrolyzed soil organic carbon fractions in the 0-10 cm soil layer of the RB treatment were all significantly higher than those in the 10-20 cm soil layer (p<0.05). (2) The microbial biomass carbon content of the RB treatment in the 0-10 cm soil layer (335.1 mg·g-1) was significantly lower than that of the RR (540 mg·g-1) and R (453.7 mg·g-1) treatments(p<0.05), but there was no significant difference in soil microbial biomass nitrogen in each soil layer between the different treatments (p>0.05). Soil microbial biomass phosphorus content and total PLFAs in two soil layers were significantly higher in RR treatment than in RB treatment (p<0.05). In the 0-10 cm soil layer, the F:B ratio was significantly higher in RB treatment than in RR and R treatments, while GP:GN ratio was significantly higher in RR treatment than in RB and R treatments (p<0.05). (3) There were significant positive correlations between acid hydrolyzed soil organic carbon fractions and total microbial biomass and PLFAs content of each microbial taxon (p<0.05). [Conclusion] Retention of logging residue treatments facilitated the maintenance of different soil organic carbon fractions at high levels and had a positive effect on soil microbial biomass and soil microbial community composition. This study is of great significance for taking reasonable management measures of Chinese fir plantations and improving soil productivity.

Abstract:[Objective] As the largest apple producing area in China, the Loess Plateau has faced the problems of aging apple trees and simplification of varieties in recent years. In addition, in order to ensure national food security, many orchards in the Loess Plateau have been converted into farmland. In order to explore the change rule and influencing factors of soil saturated hydraulic conductivity ( Ks ) after returning orchard to farmland. [Methods] In this study, mature apple orchards ( AO ) and orchards with different tillage years ( 2a, 4a, 6a, 10a ) in the Loess Plateau were selected as the research objects, and the original farmland ( CK ) was used as the control. The Ks and soil basic properties of 0-200 cm in different plots were measured. Pearson correlation analysis and structural equation model were used to analyze the response characteristics and influencing factors of Ks after returning orchard to farmland in the Loess Plateau. [Results] With the increase of returning years, the average soil water content, clay and silt content in 0-200 cm of farmland showed a decreasing trend. The average sand content showed an increasing trend. The order of Ks mean values in different plots is 2.25±1.19 cm/h(6a)＞1.60±0.71 cm/h(AO)＞1.49±0.29 cm/h(4a)＞1.46±0.44 cm/h(2a)＞1.40±0.40 cm/h(CK)＞1.04±0.61 cm/h(10a). On the whole, with the increase of returning years, the average value of Ks increased first and then decreased. With the increase of soil depth, Ks in different plots showed a decreasing trend. The direct influencing factors of Ks were soil bulk density and organic matter content, and the indirect influencing factors were tillage years and soil depth. [Conclusion] The research results can provide theoretical support for the response law of soil water movement to land use change in loess tableland area, and provide scientific basis for promoting the prevention and control of soil erosion and the rational use of land in this area.

Abstract:[Objective]Degradation of purple soil is critical, water loss is serious, and it is difficult to increase and sequester carbon in the soil. In order to explore the impact of carbon source addition on the carbon sequestration of purple soil farmland。[Methods]Purple soil slope cropland in Sichuan Province was selected as the study. Six treatments were set up on 10° purple soil slopes: no fertilization (CK), fertilizer + straw returning (T1), fertilizer + straw biochar (T2), fertilizer + cow dung (T3), fertilizer + organic soil matrix (T4), fertilizer + biochar cow dung and mushroom slag compost (T5), each treatment was repeated 3 times. Analyze the change characteristics of runoff, sediment and carbon content under rainfall and different carbon sources.[Results]The results showed that (1) rainfall over 30 mm and short-term heavy rainfall (16.1 mm·h-1) could lead to surface runoff. The addition of carbon sources notably decreased surface runoff. In comparison with the CK , the flow reduction benefits of T2, T3, and T5 reached 38.64%, 38.61%, and 62.95%, respectively. The sediment erosion in different treatments was observed to follow the order: T1>T4>CK>T2>T3>T5, with the highest reduction of 58.99% compared to the CK . (2) The loss of organic carbon through surface runoff was primarily attributed to sediment organic carbon, which accounted for 67.47~90.43% of the total organic carbon loss. Treatments T2, T3, and T5 were effective in reducing the migration of organic carbon, resulting in a total organic carbon loss reduction of 21.74%, 19.40%, and 49.28%, respectively, compared to the CK treatment. Furthermore, the carbon fractions of T5 treatment, including dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), dissolved total carbon (DTC), and sediment organic carbon, exhibited a reduction in migration fluxes by 70.88%, 70.92%, 37.52%, and 60.07%, respectively, compared to the CK treatment. (3) PLS-PM showed that the C sequestration of soil organic carbon was influenced to varying degrees by rainfall characteristics, soil physicochemical properties, and the addition of different carbon sources.[Conclusion]Carbon sources (T2, T3, T5) reduces the total amount of organic carbon loss. T5 processing organic carbon sequestration stock increases, T2 and T3 reduce the loss of each carbon component of surface runoff, while its organic carbon sequestration stock decreases. It shows that the addition of carbon source can increase the carbon content and reduce the carbon migration, but that the solid stock is reduced, which needs to be verified by long-term experiments. This study holds significant importance in enhancing the fertility of purple soil, maintaining soil carbon balance, and reducing soil carbon loss.

Abstract:[Objective]The●present●study●attempted●to●investigate●the●combined●effect●of●crop●cover●and●crop●management●practices●on●preventing●soil●loss●and●improving●the●accuracy●of●C-factor estimation.[Methods]●Six●millet●plots●with●different●treatments,（i.e.,●crop●plot●(C1),●crop-roughness●plot●(C2),●crop-crust●plot●(C3),●bare●plot●(B1),●roughness●plot●(B2),●crust●plot(B3))●were●established●and●the●soil●loss●at●four●growth●stage●was●determined●by●simulated●rainfall.●The●C●factor●was●calculated●using●soil●loss●ratio●(SLR).●The●major●factors●affecting●SLR●were●also●analyzed●and●their●correlations●with●SLR●were●then●regressed●through●numerical●simulation●using●MATLAB.●Subsequently●the●SLR●estimation●models●designed●for●soil●erosion●prediction●on●the●Loess●Plateau●could●be●built.●Finally,●the●C●factor●could●be●calculated●using●the●proposed●SLR●estimation●model●combined●with●the●distribution●curve●of●rainfall●erosivity.[Results]●Surface●roughness●and●soil●crust●can●reduce●soil●loss●in●crop●plot.●Compared●with●,●the●mean●decreasing●of●●and●●was●21%,●16.5%,●respectively.●The●model●formulas●of●crop●plot,●crop-roughness●plot,●crop-crust●plot●were●obtained,●through●validating●by●field●soil●and●water●loss●data●conducted●at●Chunhua●county,●the●model●formulas●can●achieve●accurate●prediction,●the●estimated●C●values●for●the●whole●growth●stage●were●0.30,●0.25,●0.25,●respectively,●with●the●Nash●coefficients●were●0.96,●0.87,●0.75,●respectively.[Conclusion]●These●results●could●provide●some●insights●for●estimating●C●values●at●national●scales.

Abstract:[Objective] In order to explore the difference of precipitation characteristics for multisource precipitation products and their applicability for runoff simulation in an alpine basin on the Tianshan Mountains. [Methods] A comparative analysis of the spatiotemporal characteristics of precipitation is conducted in the upper reaches of the Manas River Basin, based on the datasets CN05.1, GPM, AIMERG, CMFD, and ERA5. Subsequently the accuracy of different products is evaluated based on observed precipitation, and their applicability for runoff simulation is assessed by means of HBV hydrological model. [Results] The spatial pattern for all the precipitation products is characterized by the increase and then decrease from the north to south, whereas only AIMERG and CMFD are able to display higher precipitation in the glacier area. Consistent seasonal variation are detected, but large difference in summer precipitation are shown. At summer, ERA5 is twice as much as CN05.1, and GPM is lower than the other precipitation products. GPM underestimates the monthly precipitation, especially in winter and spring (64%～76%). While the monthly precipitation is overestimated by CMFD, ERA5 and AIMERG. The overestimation of ERA5 is the most serious, especially in summer and autumn (134%～206%), and CMFD slightly overestimates the monthly precipitation. AIMERG has the higher correlation with the observed monthly precipitation and greater critical success index in both rainy season and the non- rainy season. AIMERG, CMFD and CN05.1 have the greatest ability to reproduce daily runoff, with the higher NSE (0.81～0.82) and lower relative error (＜6%). Moreover, the former two products show higher performance in reproducing extreme runoff when compared with CN05.1.[Conclusion] AIMERG and CMFD show great potential in runoff simulation of the upper Manas River. The results can serve as data references for runoff simulation and soil erosion prevention research in the Tianshan region, where meteorological data is limited.

Abstract:[Objective] To explore the transpiration characteristics of common trees and their response to meteorological factors in karst slope secondary forest. [Methods] Heat diffusion probe method (TDP) was used to monitor Broussonetia papyrifera, Koelreuteria paniculata, Triadica sebifera, Ailanthus altissima, Melia azedarach, Toona sinensis, and Rhus chinensis in Puding Karst Ecosystem Observation and Research Station of Chinese Academy of Sciences, and to study the relationship between tree transpiration characteristics and meteorological factors. [Results] (1) The average daily transpiration of Broussonetia papyrifera, Koelreuteria paniculata, Triadica sebifera, Ailanthus altissima, Melia azedarach, Toona sinensis, and Rhus chinensis were: (4 409.97±3 260.63) g/d, (6 611.27±5 629.57) g/d (3 956.32±2498.50) g/d (2984.98±2039.09) g/d (6 300.25±4 637.71) g/d, (780.69±738.80) g/d, (2320.73)±1717.18) g/d.(2) The fluid flow rates of Broussonetia papyrifera, Koelreuteria paniculata, Triadica sebifera, Ailanthus altissima, Melia azedarach, Toona sinensis, and Rhus chinensis were the highest in sunny days, followed by cloudy days, and the lowest in rainy days. (3) The influence of atmospheric temperature (T) and saturation water vapor pressure difference (VPD) on Broussonetia papyrifera, Koelreuteria paniculata, Triadica sebifera, Ailanthus altissima, Melia azedarach, Toona sinensis, and Rhus chinensis under sunny weather was the greatest, followed by relative humidity (RH) and total irradiance (Eg). [Conclusion] The transpiration of common trees in secondary forest of karst slope is limited by special water environment. Different deciduous trees have different water use strategies, and the liquid flow rate is mainly affected by VPD and Eg.

Abstract:[Objective] To investigate the characteristics of runoff-phosphorus loss hysteresis relationship under different rainfall types. [Methods] This study focused on the Menglianggu small watershed in the rocky mountainous area of northern China. Using data from 32 rainfall events recorded between 2010 and 2012, C-Q (concentration-discharge) loops and Pearson correlation analysis were applied. [Results] (1) During torrential rain, a large amount of phosphorus was released after soil saturation, causing the phosphorus concentration peak to lag behind the runoff peak. In the case of heavy rain, dissolved phosphorus was released from nearby sources, while particulate phosphorus was transported from distant sources to the runoff. During moderate rain, the transport of DIP (dissolved inorganic phosphorus), PP (particulate phosphorus), and TP (total phosphorus) was mainly influenced by surface runoff, whereas DP (dissolved phosphorus) was affected by soil and sediment. Light rain showed rapid transport of dissolved phosphorus and slower transport of particulate phosphorus. (2) The C-Q loops of phosphorus transfer exhibited various patterns during the runoff process. PP and TP often showed a clockwise lag, accounting for 18%~23%, mainly due to the strong scouring of surface runoff. The counterclockwise lag appeared in 12%~18% of the phosphorus components, resulting from the slow release of soil phosphorus and the resuspension of riverbed sediments. DP loss mainly exhibited a figure-eight positive loop, accounting for 16%, while DIP loss showed a figure-eight negative loop, accounting for 19%. Linear lags were less frequent, and complex lags ranged between 31% and 45%. (3) Under torrential and heavy rain conditions, DIP and DP had weak or negative correlations with runoff (Q), attributed to the rapid surface scouring, which caused particulate phosphorus to be more easily lost, while dissolved phosphorus was adsorbed by the soil or diluted by the runoff. In moderate rain, the appropriate runoff scouring force enhanced the releases of dissolved phosphorus. In light rain, runoff primarily transported particulate phosphorus attached to loose soil particles. PP and TP were consistently highly correlated across different rainfall types, indicating that TP mainly originates from PP. [Conclusion] The Menglianggu watershed needs to be protected against phosphorus loss for different rainfall conditions.

Abstract:[Objective] To explore the spatial and temporal evolution of soil erosion, driving factors and the interaction between driving factors in Anshun City, a karst area in southwest China, which can help the management of rock desertification and soil and water resources in the area. [Methods] The optimised RUSLE model was used to estimate soil erosion in Anshun City from 2005 to 2020, while the Random Forest Model (RF) was used to reveal the driving factors of soil erosion, and to estimate the effects of driving factor interactions on soil erosion in Anshun City from 2005 to 2020. [Results] (1) from 2005 to 2020, soil erosion in Anshun City generally shows that low-intensity soil erosion is distributed in the central, southeastern and eastern regions, while high-intensity soil erosion is distributed in the northern and southwestern regions. From the time point of view, soil erosion in Anshun City as a whole shows a trend of improvement, most of the areas of soil erosion grade mainly from high to micro-intensity erosion transfer, but there are local areas of erosion exacerbation phenomenon. (2) Rocky desertification has a greater impact on soil erosion in Anshun. The soil erosion intensity of Anshun is positively correlated with rocky desertification in the area accounting for 59.3% of the total area, which is highly correlated. Soil erosion with the increase of rocky desertification intensity shows the trend of increasing and then decreasing. (3) The most important land use types in Anshun City where soil erosion occurs are forest land, arable land and grassland, and the overall rate of soil erosion is in the order of forest land < grassland < arable land. (4) The analysis of the driving factors of soil erosion showed that the vegetation cover and management factor had the strongest explanatory power for the spatial and temporal dynamics of soil erosion in the study area, followed by the factor of soil and water conservation measures and the intensity of rock desertification. The results of driver interaction showed that the interaction between vegetation cover and management factor and soil and water conservation measures factor was the dominant factor, and the top ranked interactions all had the participation of vegetation cover and management factor. [Conclusion] Soil erosion intensity in Anshun City showed an overall trend of improvement from 2005 to 2020, but there was an increase in erosion in some areas. Vegetation cover, rock desertification intensity and land use have the strongest influence on soil erosion in Anshun City. Therefore, the future soil and water management process needs to focus on vegetation cover, rock desertification intensity and land use changes.