N-fixing tree species promote the chemical stability of soil organic carbon in subtropical plantations through increasing the relative contribution of plant-derived lipids

Biodiversity experiments have shown that soil organic carbon(SOC)is not only a function of plant diversity,but is also closely related to the nitrogen(N)-fixing plants.However,the effect of N-fixing trees on SOC chemical stability is still little known,especially with the compounding effects of tree species diversity.An experimental field manipulation was established in subtropical plantations of southern China to explore the impacts of tree species richness(i.e.,one,two,four and six tree species)and with/without N-fixing trees on SOC chemical stability,as indicated by the ratio of easily oxidized organic carbon to SOC(EOC/SOC).Plant-derived C components in terms of hydrolysable plant lipids and lignin phenols were isolated from soils for evaluating their relative contributions to SOC chemical stability.The results showed that N-fixing tree species rather than tree species richness had a significant effect on EOC/SOC.Hydrolysable plant lipids and lignin phenols were negatively correlated with EOC/SOC,while hydrolysable plant lipids contributed more to EOC/SOC than lignin phenols,especially in the occurrence of N-fixing trees.The presence of N-fixing tree species led to an increase in soil N availability and a decrease in fungal abundance,promoting the selective retention of certain key components of hydrolysable plant lipids,thus enhancing SOC chemical stability.These findings underpin the crucial role of N-fixing trees in shaping SOC chemical stability,and therefore,preferential selection of N-fixing tree species in mixed plantations is an appropriate silvicultural strategy to improve SOC chemical stability in subtropical plantations.

Effects of desert plant communities on soil enzyme activities and soil organic carbon in the proluvial fan in the eastern foothills of the Helan Mountain in Ningxia,China

It is of great significance to study the effects of desert plants on soil enzyme activities and soil organic carbon(SOC)for maintaining the stability of the desert ecosystem.In this study,we studied the responses of soil enzyme activities and SOC fractions(particulate organic carbon(POC)and mineral-associated organic carbon(MAOC))to five typical desert plant communities(Convolvulus tragacanthoides,Ephedra rhytidosperma,Stipa breviflora,Stipa tianschanica var.gobica,and Salsola laricifolia communities)in the proluvial fan in the eastern foothills of the Helan Mountain in Ningxia Hui Autonomous Region,China.We recorded the plant community information mainly including the plant coverage and herb and shrub species,and obtained the aboveground biomass and plant species diversity through sample surveys in late July 2023.Soil samples were also collected at depths of 0–10 cm(topsoil)and 10–20 cm(subsoil)to determine the soil physicochemical properties and enzyme activities.The results showed that the plant coverage and aboveground biomass of S.laricifolia community were significantly higher than those of C.tragacanthoides,S.breviflora,and S.tianschanica var.gobica communities(P<0.05).Soil enzyme activities varied among different plant communities.In the topsoil,the enzyme activities of alkaline phosphatase(ALP)andβ-1,4-glucosidas(βG)were significantly higher in E.rhytidosperma and S.tianschanica var.gobica communities than in other plant communities(P<0.05).The topsoil had higher POC and MAOC contents than the subsoil.Specifically,the content of POC in the topsoil was 18.17%–42.73%higher than that in the subsoil.The structural equation model(SEM)indicated that plant species diversity,soil pH,and soil water content(SWC)were the main factors influencing POC and MAOC.The soil pH inhibited the formation of POC and promoted the formation of MAOC.Conversely,SWC stimulated POC production and hindered MAOC formation.Our study aimed to gain insight into the effects of desert plant communities on soil enzyme activities and SOC fractions,as well as the drivers of SOC fractions in the proluvial fan in the eastern foothills of the Helan Mountain and other desert ecosystems.

Spatial-temporal variations and driving factors of soil organic carbon in forest ecosystems of Northeast China

Forest soil carbon is a major carbon pool of terrestrial ecosystems,and accurate estimation of soil organic carbon(SOC)stocks in forest ecosystems is rather challenging.This study compared the prediction performance of three empirical model approaches namely,regression kriging(RK),multiple stepwise regression(MSR),random forest(RF),and boosted regression trees(BRT)to predict SOC stocks in Northeast China for 1990 and 2015.Furthermore,the spatial variation of SOC stocks and the main controlling environmental factors during the past 25 years were identified.A total of 82(in 1990)and 157(in 2015)topsoil(0–20 cm)samples with 12 environmental factors(soil property,climate,topography and biology)were selected for model construction.Randomly selected80%of the soil sample data were used to train the models and the other 20%data for model verification using mean absolute error,root mean square error,coefficient of determination and Lin's consistency correlation coefficient indices.We found BRT model as the best prediction model and it could explain 67%and 60%spatial variation of SOC stocks,in 1990,and 2015,respectively.Predicted maps of all models in both periods showed similar spatial distribution characteristics,with the lower SOC in northeast and higher SOC in southwest.Mean annual temperature and elevation were the key environmental factors influencing the spatial variation of SOC stock in both periods.SOC stocks were mainly stored under Cambosols,Gleyosols and Isohumosols,accounting for 95.6%(1990)and 95.9%(2015).Overall,SOC stocks increased by 471 Tg C during the past 25 years.Our study found that the BRT model employing common environmental factors was the most robust method for forest topsoil SOC stocks inventories.The spatial resolution of BRT model enabled us to pinpoint in which areas of Northeast China that new forest tree planting would be most effective for enhancing forest C stocks.Overall,our approach is likely to be useful in forestry management and ecological restoration at and beyond the regional scale.

Soil Organic Carbon Pool and Its Influencing Factors in Rubber Planted Forest Ecosystem at Different Ages in West Hainan Province

In this research,the contents of organic carbon in soil profiles in rubber forests in west of Hainan were measured and storage quantity of oganic carbon was estimated.The results indicated that contents of organic carbon in soils of ecosystem of rubber forests at different ages were 6.20-14.36 g/kg;organic carbon in soils of rubber forests reduced upon soil depth;the contents differed signigicantly in soils at 0-60 cm in rubber forest at 33 a,but differed little in soils in rubber forests at other ages;the contents were of significant differences in soils in rubber forests at different ages;organic carbon concentrated in soils at 0-30 cm;the storage quantities of organic carbon in rubber forests at 5,10,19 and 33 a were 76.85,74.48,81.74 and 85.31 t/hm^2.Climate,soil property,accumualtion and decomposition of fallen materials,forest age and management are dominant factors influencing accumulation of organic carbon in soils of rubber forest.

Long-term light grazing does not change soil organic carbon stability and stock in biocrust layer in the hilly regions of drylands

Livestock grazing is the most extensive land use in global drylands and one of the most extensive stressors of biological soil crusts(biocrusts).Despite widespread concern about the importance of biocrusts for global carbon(C)cycling,little is known about whether and how long-term grazing alters soil organic carbon(SOC)stability and stock in the biocrust layer.To assess the responses of SOC stability and stock in the biocrust layer to grazing,from June to September 2020,we carried out a large scale field survey in the restored grasslands under long-term grazing with different grazing intensities(represented by the number of goat dung per square meter)and in the grasslands strictly excluded from grazing in four regions(Dingbian County,Shenmu City,Guyuan City and Ansai District)along precipitation gradient in the hilly Loess Plateau,China.In total,51 representative grassland sites were identified as the study sampling sites in this study,including 11 sites in Guyuan City,16 sites in Dingbian County,15 sites in Shenmu City and 9 sites in Ansai District.Combined with extensive laboratory analysis and statistical analysis,at each sampling site,we obtained data on biocrust attributes(cover,community structure,biomass and thickness),soil physical-chemical properties(soil porosity and soil carbon-to-nitrogen ratio(C/N ratio)),and environmental factors(mean annual precipitation,mean annual temperature,altitude,plant cover,litter cover,soil particle-size distribution(the ratio of soil clay and silt content to sand content)),SOC stability index(SI)and SOC stock(SOCS)in the biocrust layer,to conduct this study.Our results revealed that grazing did not change total biocrust cover but markedly altered biocrust community structure by reducing plant cover,with a considerable increase in the relative cover of cyanobacteria(23.1%)while a decrease in the relative cover of mosses(42.2%).Soil porosity and soil C/N ratio in the biocrust layer under grazing decreased significantly by 4.1%–7.2%and 7.2%–13.3%,respectively,compared with those under grazing exclusion.The shifted biocrust community structure ultimately resulted in an average reduction of 15.5%in SOCS in the biocrust layer under grazing.However,compared with higher grazing(intensity of more than 10.00 goat dung/m2),light grazing(intensity of 0.00–10.00 goat dung/m2 or approximately 1.20–2.60 goat/(hm2•a))had no adverse effect on SOCS.SOC stability in the biocrust layer remained unchanged under long-term grazing due to the offset between the positive effect of the decreased soil porosity and the negative effect of the decreased soil C/N ratio on the SOC resistance to decomposition.Mean annual precipitation and soil particle-size distribution also regulated SOC stability indirectly by influencing soil porosity through plant cover and biocrust community structure.These findings suggest that proper grazing might not increase the CO_(2) release potential or adversely affect SOCS in the biocrust layer.This research provides some guidance for proper grazing management in the sustainable utilization of grassland resources and C sequestration in biocrusts in the hilly regions of drylands.

Impacts of Rice Field Winter Planting on Soil Organic Carbon and Carbon Management Index

To tackle with the problem of prevailing farmland abandonment in winter,5 treatments includes Chinese milk vetch-double cropping rice(CRR),rape-double cropping rice(RRR),garlic-double cropping rice(GRR),winter crop multiple cropping rotation(ROT),winter fallow control(WRR)were set up.By measuring soil total organic carbon,active organic carbon and its components and calculating the soil carbon pool management index in 0~15 cm and 15~30 cm soil layers in the early and late rice ripening stage.The effects of different winter planting patterns on the changes of soil organic carbon and carbon pool management index were discussed.In order to provide theoretical basis for the optimization and adjustment of winter planting pattern of double cropping rice field in the middle reaches of Yangtze River.The results showed that soil total organic carbon,active organic carbon and its components in different winter cropping patterns were increased,and ROT and CRR treatments were more beneficial to the accumulation of soil total organic carbon,active organic carbon and its components as well as the improvement of soil carbon pool management index,which should be preferred in the adjustment of cropping patterns.

Soil Organic Carbon Contents and Stocks in Coastal Salt Marshes with Spartina alterniflora Following an Invasion Chronosequence in the Yellow River Delta,China

Plant invasion alters the fundamental structure and function of native ecosystems by affecting the biogeochemical pools and fluxes of materials and energy. Native(Suaeda salsa) and invasive(Spartina alterniflora) salt marshes were selected to study the effects of Spartina alterniflora invasion on soil organic carbon(SOC) contents and stocks in the Yellow River Delta. Results showed that the SOC contents(g/kg) and stocks(kg/m^2) were significantly increased(P < 0.05) after Spartina alterniflora invasion of seven years, especially for the surface soil layer(0–20 cm). The SOC contents exhibited an even distribution along the soil profiles in native salt marshes, while the SOC contents were gradually decreased with depth after Spartina alterniflora invasion of seven years. The natural ln response ratios(Ln RR) were applied to identify the effects of short-term Spartina alterniflora invasion on the SOC stocks. We also found that Spartina alterniflora invasion might cause soil organic carbon losses in a short-term phase(2–4 years in this study) due to the negative Ln RR values, especially for 20–60 cm depth. And the SOCD in surface layer(0–20 cm) do not increase linearly with the invasive age. Spearman correlation analysis revealed that silt + clay content was exponentially related with SOC in surface layer(Adjusted R^2 = 0.43, P < 0.001), suggesting that soil texture could play a key role in SOC sequestration of coastal salt marshes.

Changes in soil organic carbon of terrestrial ecosystems in China:A mini-review

The present study provides an overview of existing literature on changes in soil organic carbon(SOC) of various terrestrial ecosystems in China.Datasets from the literature suggest that SOC stocks in forest,grassland,shrubland and cropland increased between the early 1980s and the early 2000s,amounting to(71±19) Tg·a-1.Conversion of marshland to cropland in the Sanjiang Plain of northeast China resulted in SOC loss of(6±2) Tg·a-1 during the same period.Nevertheless,large uncertainties exist in these estimates,especially for the SOC changes in the forest,shrubland and grassland.To reduce uncertainty,we suggest that future research should focus on:(i) identifying land use changes throughout China with high spatiotemporal resolution,and measuring the SOC loss and sequestration due to land use change;(ii) estimating the changes in SOC of shrubland and non-forest trees(i.e.,cash,shelter and landscape trees);(iii) quantifying the impacts of grassland management on the SOC pool;(iv) evaluating carbon changes in deep soil layers;(v) projecting SOC sequestration potential;and(vi) developing carbon budget models for better estimating the changes in SOC of terrestrial ecosystems in China.

Changes in cropland topsoil organic carbon with different fertilizations under long-term agro-ecosystem experiments across China's Mainland

Topsoil soil organic carbon(SOC) data were collected from long-term Chinese agro-ecosystem experiments presented in 76 reports with measurements over 1977 and 2006.The data set comprised 481 observations(135 rice paddies and 346 dry croplands) of SOC under different fertilization schemes at 70 experimental sites(28 rice paddies and 42 dry croplands).The data set covered 16 dominant soil types found in croplands across 23 provinces of China's Mainland.The fertilization schemes were grouped into six categories:N(inorganic nitrogen fertilizer only),NP(compound inorganic nitrogen and phosphorus fertilizers),NPK(compound inorganic nitrogen,phosphorus and potassium fertilizers),O(organic fertilizers only),OF(combined inorganic/organic fertilization) and Others(other unbalanced fertilizations such as P only,K only,P plus K and N plus K).Relative change in SOC content was analyzed,and rice paddies and dry croplands soils were compared.There was an overall temporal increase in topsoil SOC content,and relative annual change(RAC,g kg-1 yr-1) ranged -0.14-0.60(0.13 on average) for dry cropland soils and -0.12-0.70(0.19 on average) for rice paddies.SOC content increase was higher in rice paddies than in dry croplands.SOC increased across experimental sites,but was higher under organic fertilization and combined organic/inorganic fertilizations than chemical fertilizations.SOC increase was higher under balanced chemical fertilizations with compound N,P and K fertilizers than unbalanced fertilizations such as N only,N plus P,and N plus K.The effects of specific rational fertilizations on SOC increase persisted for 15 years in dry croplands and 20 years in rice paddies,although RAC values decreased generally as the experiment duration increased.Therefore,the extension of rational fertilization in China's croplands may offer a technical option to enhance C sequestration potential and to sustain long-term crop productivity.

Increased soil organic carbon storage in Chinese terrestrial ecosystems from the 1980s to the 2010s

Soil stores a large amount of the terrestrial ecosystem carbon (C) and plays an important role in maintaining global C balance. However, very few studies have addressed the regional patterns of soil organic carbon (SOC) storage and the main factors influencing its changes in Chinese terrestrial ecosystems, especially using field measured data. In this study, we collected information on SOC storage in main types of ecosystems (including forest, grassland, cropland, and wetland) across 18 regions in China during the 1980s (from the Second National Soil Survey of China, SNSSC) and the 2010s (from studies published between 2004 and 2014), and evaluated its changing trends during these 30 years. The SOC storage (0-100 cm) in Chinese terrestrial ecosystems was 83.46 ± 11.89 Pg C in the 1980s and 86.50 ± 8.71 Pg C in the 2010s, and the net increase over the 30 years was 3.04 ± 1.65 Pg C, with an overall rate of 0.101 ± 0.055 Pg C yr-1. This increase was mainly observed in the topsoil (0-20 cm). Forests, grasslands, and croplands SOC storage increased 2.52 ± 0.77, 0.40 ± 0.78, and 0.07 ± 0.31 Pg C, respectively, which can be attributed to the several ecological restoration projects and agricultural practices implemented. On the other hand, SOC storage in wetlands declined 0.76 ± 0.29 Pg C, most likely because of the decrease of wetland area and SOC density. Combining these results with those of vegetation C sink (0.100 Pg C yr-1), the net C sink in Chinese terrestrial ecosystems was about 0.201 ± 0.061 Pg C yr-1, which can offset 14.85%-27.79% of the fossil fuel C emissions from the 1980s to the 2010s. These first estimates of soil C sink based on field measured data supported the premise that China’s terrestrial ecosystems have a large C sequestration potential, and further emphasized the importance of forest protection and reforestation to increase SOC storage capacity.

Spatial Distribution of Surface Soil Organic Carbon Density and Related Factors along an Urbanization Gradient in Beijing

Urban surface soil has a unique set of structures and processes that affect surface soil organic carbon density(SOCdensity) and its spatial variations. Using Beijing as a case study, and assisted by field investigations and experiments, we analyzed the spatial distribution of SOCdensity in different land use types and functional regions, and assessed associated factors such as urbanization level, the physiochemical properties of soil and plant configurations. The present study aims to provide useful information about the mechanisms driving soil organic carbon and climate change in developing and developed areas in urbanized regions like Beijing. Results indicate that P is the main factor positively influencing SOCdensity in most regions. Because of the specific interference directly related to human beings in urban areas, with decreases in the urbanization level, more physiochemical factors of soil can influence SOCdensity. SOCdensity under grasses is not significantly different from that under other plant compositions. Urbanization processes decrease the heterogeneity of the spatial pattern of SOCdensity in most land use types, but increased its contents when the area reached a developed level in Beijing. More factors related to human interference and spatial variation of surface soil carbon storage, especially under impervious land in urban areas, should be considered in future studies.

Moso bamboo expansion decreased soil heterotrophic respiration but increased arbuscular mycorrhizal mycelial respiration in a subtropical broadleaved forest

Moso bamboo(Phyllostachys Pubescens)expansion into adjacent forests has been widely reported to affect plant diversity and its association with mycorrhizal fungi in subtropical China,which will likely have significant impacts on soil respiration.However,there is still limited information on how Moso bamboo expansion changes soil respiration components and their linkage with microbial community composition and activity.Based on a mesh exclusion method,soil respirations derived from roots,arbuscular mycorrhizal(AM)mycelium,and free-living microbes were investigated in a pure Moso bamboo forest(expanded),an adjacent broadleaved forest(nonexpanded),and a mixed bamboo-broadleaved forest(expanding).Our results showed that bamboo expansion decreased the cumulative CO_(2)effluxes from total soil respiration,root respiration and soil heterotrophic respiration(by 19.01%,30.34%,and 29.92%on average),whereas increased those from AM mycelium(by 78.67%in comparison with the broadleaved forests).Bamboo expansion significantly decreased soil organic carbon(C)content,bacterial and fungal abundances,and enzyme activities involved in C,N and P cycling whereas enhanced the interactive relationships among bacterial communities.In contrast,the ingrowth of AM mycelium increased the activities ofβ-glucosidase and N-acetyl-β-glucosaminidase and decreased the interactive relationships among bacterial communities.Changes in soil heterotrophic respiration and AM mycelium respiration had positive correlations with soil enzyme activities and fungal abundances.In summary,our findings suggest that bamboo expansion decreased soil heterotrophic respiration by decreasing soil microbial activity but increased the contribution of AM mycelial respiration to soil C efflux,which may potentially increase soil C loss from AM mycelial pathway.

Effects of vegetable oil residue after soil extraction on physical-chemical properties of sandy soil and plant growth

Vegetable oil has the ability to extract polycyclic aromatic hydrocarbons(PAHs)from contaminated sandy soil for a remediation purpose,with some of the oil remaining in the soil.Although most of the PAHs were removed,the risk of residue oil in the soil was not known.The objective of this study was to evaluate the effects of the vegetable oil residue on higher plant growth and sandy soil properties after soil extraction for a better understanding of the soil remediation.Addition of sunflower oil and column ex...

2005-2020年中国西北干旱区典型生态系统土壤有机碳密度数据集

土壤有机碳库是陆地生态系统碳库中最大、最为活跃的部分,在全球碳循环过程和全球气候变化中起着重要的作用。中国西北旱区位于欧亚大陆的腹地,生态系统极其脆弱,对气候变化的响应也极为敏感,是近年来众多学者关注的热点地区,土壤有机碳储量估算以及空间分布特征日益成为该区域的研究焦点之一,但是数据共享不足与实测数据相对缺乏是造成研究结果不确定性的重要因素。在收集中国生态系统研究网络(CERN)位于中国西北六省区的农田、荒漠、草地生态系统野外科学观测研究站土壤长期观测数据的基础上,通过筛选、质量控制后,采用有机碳估算模型计算生成了中国西北干旱区典型生态系统土壤有机碳密度数据集。本数据集涵盖了11个站点2005-2020年各类长期观测样地的表层(0-20 cm)和剖面分层土壤有机碳密度数据,以期为中国西北干旱区土壤碳储量估算和碳循环过程研究提供有价值的实测数据。

陕北中部黄土区不同种植年限水稻田有机碳矿化对温度的响应

为了探讨陕北中部黄土区不同种植年限水稻田有机碳矿化对温度的响应,以陕北南泥湾水稻种植基地不同种植年限(3、30、78 a)的稻田土壤为研究对象,基于室内35 d培养试验与矿化动态模型研究方法,解析温度对土壤有机碳矿化的影响。结果表明:土壤有机碳累积矿化量和矿化速率均表现为78 a水稻田>30 a水稻田>3 a水稻田>玉米田。土壤累积矿化量、矿化速率、潜在可矿化有机碳含量(C 0)和潜在可矿化有机碳占总有机碳的比值(C 0/SOC)均表现为30℃处理>20℃处理>10℃处理。水稻田矿化累积量均表现为10℃处理(2015.14 mg·kg^(-1))显著低于20℃(2799.20 mg·kg^(-1))和30℃处理(3078.47 mg·kg^(-1))(P<0.05),但20℃与30℃处理之间无显著差异。玉米田累积矿化量在不同培养温度间没有达到显著差异水平。0~20 cm土层累积矿化量是20~40 cm土层的1.18倍。供试土壤在温度从10℃升高到20℃时的温度系数(Q 10)值(1.38)均高于从20℃升高到30℃时的Q 10值(1.14),土层间的Q 10值大小关系为0~20 cm>20~40 cm。潜在可矿化有机碳含量C 0与总有机碳、易氧化有机碳及溶解性有机碳含量之间均呈正相关关系,C 0与微生物生物量碳含量间呈正相关关系但未能达到显著水平。C 0/SOC随水稻种植年限的增加而降低,说明土壤有机碳的固存能力随水稻种植年限的增加而增强。

渭北地区不同种植年限苹果园土壤有机碳分布特征

目的探究种植年限对苹果园土壤有机碳含量及其分布特征的影响,为提高果园土壤肥力,增加果园产量提供参考依据。方法以渭北地区种植年限为5 a,10 a,15 a和20 a的苹果园为研究对象,利用重铬酸钾外加热方法测定苹果园土壤有机碳含量。结果(1)随着种植年限的增加,土壤有机碳含量的总体平均值呈现出先下降后上升的变化趋势,且不同年限之间差异性显著(P<0.05),其中,5 a苹果园中有机碳含量最高,为6.83 g/kg。(2)在距树干0.5 m,1 m,1.5 m水平方向上,除5 a果园土壤外,距树干越近,土壤有机碳含量越高。除15 a果园土壤外,不同种植年限果园土壤有机碳含量在距树干0.5 m,1 m,1.5 m处的变化趋势差异显著(P<0.05)。(3)垂直剖面上,在0~40 cm土层深度范围内,不同种植年限苹果园土壤有机碳含量波动幅度较大,随着土层深度的增加,有机碳含量呈减少趋势,此外,5 a苹果园土壤有机碳含量在200~320 cm深度显著增加。结论渭北地区不同种植年限苹果园土壤有机碳含量随着种植年限的增加,呈现出先下降后上升的变化趋势。水平方向上,不同种植年限果园在近干处有机碳含量高,对果园有机碳赋存的影响更大。垂直方向上,有机碳含量集中在浅层土壤,呈现出表聚特征。

积雪变化对陆地生态系统植被特征和土壤碳氮过程的影响

在季节性积雪地区,冬季气候变暖导致积雪变薄、积雪不连续、融雪提前及雪盖面积缩小等现象。然而相较于氮沉降、增温、降水变化等全球变化因子,目前尚缺乏积雪因子对陆地生态系统过程和功能影响的系统报道。为加深人们对积雪特征变化生态后果的认知,综述了积雪深度和融雪时间变化对植被物候和群落组成、凋落物分解、土壤碳氮过程、温室气体排放和土壤微食物网(土壤动物和微生物)的影响。由于模拟积雪变化手段不同和复杂的气候、土壤背景,生态系统各要素对积雪特征变化的响应规律存在较大的分异和不确定性。例如,在未来气候变暖导致积雪变薄和融雪提前情景下,植被物候提前,生长季延长,导致生产力增加和凋落物数量增加,禾草比例减少导致凋落物质量增加,早春温度高刺激微生物活性,凋落物分解速率高,促进土壤碳氮周转过程。但积雪减少和融雪提前导致的早春低温和夏季干旱也可能引起植被生产力下降,凋落物数量减少质量降低,土壤微生物活性低,分解速率低,从而减缓碳氮周转过程。此外,积雪特征变化对植被特征和土壤碳氮过程影响相关研究目前还存在以下问题:1)积雪深度和融雪时间对生态系统的影响是否存在交互效应仍缺乏关注,且积雪变化对后续生长季是否存在持续效应也不明确;2)积雪因子对植被、土壤碳氮动态过程和土壤生物的影响,各生态要素研究相对较为独立;3)积雪变化引起对土壤地化循环过程影响的微生物驱动机制缺乏组学数据支撑;4)缺乏遥感手段反演各类影响生态系统功能和过程的积雪参数。应加强植被群落-土壤碳氮过程-土壤微食物网生态关联研究、基于基因组学的土壤微生物群落组成和生态功能研究和遥感相关技术研究,以期为发展积雪生态学提供参考。

中国稻田生态系统固碳效应模拟研究

【目的】研究稻田生态系统固碳量的动态变化,为制定与推广耕地固碳减排措施提供依据。【方法】基于3年稻田受控试验数据,校验生物地球化学脱氮—分解作用(denitrification-decomposition,DNDC)模型,并估算2018—2020年间中国稻田生态系统的固碳量;分析稻田生态系统土壤及作物固碳量的时空分布,评估农田生态系统在实现“碳中和”中的贡献。【结果】DNDC模型模拟的水稻产量及土壤有机碳含量与田间观测结果一致性较高(相关系数均大于等于0.77,平均绝对误差和归一化均方根误差均小于13%);2018—2020年中国水稻固碳总量为523.29 Tg,作物对总固碳量的贡献率达97%以上。江西、湖南、广东和广西的双季稻固碳能力较强,而云南、浙江和海南的相对较弱。单季稻固碳量分布呈现北高南低的空间分布特征,其中黑龙江、江苏和湖北的固碳量较高。湖南、福建、江西和广西的双季稻固碳量大于单季稻,双季稻固碳量占总固碳量的60%以上。【结论】DNDC模型可用于模拟稻田生态系统的碳收支,中国稻田生态系统是重要的碳汇,且呈现出较强的空间异质性。

黑土区保护性耕作土壤有机碳动态的模型模拟研究

【目的】保护性耕作是恢复和提高土壤肥力的重要措施,土壤有机碳在保持土壤肥力、维持作物生长与保护土壤环境方面具有非常重要的作用。然而,目前国内仍然缺少研究长期耕作的监测平台,因此采用模型的方法有助于研究长期保护性耕作下土壤有机碳的动态。【方法】依托东北黑土地保护性耕作长期定位试验地,选取免耕(NT)、秋翻(MP)、垄作(RT)3种处理下的土壤为研究对象,优化过程模型(RothC、AMG模型)与统计模型(MLPNN模型)的结构与参数,对比模拟长期保护性耕作下土壤有机碳储量的动态变化,评估不同模型对保护性耕作土壤有机碳动态模拟与预测的效果,并揭示东北黑土有机碳对保护性耕作的长期响应及其影响因素。【结果】优化有机碳在模型中各碳库的分配系数后,RothC与AMG模型模拟误差显著降低。保护性耕作实施的前11年(2001—2012),RothC与AMG过程模型对土壤有机碳的动态变化模拟效果没有显著差异,说明过程模型复杂的结构对持续时间相对较短的试验模拟效果没有显著影响,统计模型MLPNN的模拟结果与过程模型相似,验证了统计模型在田块与样地等小空间尺度内的应用效果。未来100年RothC与AMG模型预测的MP处理土壤有机碳变化趋势相同,但RothC模型预测结果得出,NT与RT处理土壤有机碳表现出先增长后达到平衡的趋势,但AMG模型模拟的结果却是有机碳一直处于增长趋势,这可能与土壤碳饱和效应与耕作处理的影响有关。RothC与AMG模型对碳投入都具有很高的灵敏度,但对气候因素与土壤因素变化的响应却存在差异。【结论】模型模拟长期保护性耕作土壤有机碳动态时需要因地制宜选择合适的预测模型。在预测保护性耕作土壤有机碳的短期变化时可以采用结构较为简单的AMG过程模型;在进行长期预测时,可以采用结构较为复杂的RothC模型。在特定条件下,统计模型MLPNN在田块与样地等小空间尺度上对土壤有机碳的模拟与过程模型具有相近的效果。

典型黑土带玉米农田土壤微生物群落地理分布及驱动因素

探究东北黑土带土壤微生物群落的地理分布格局及其驱动因子,对于有效和可持续地管理这一宝贵的土地资源具有重要的学术价值。本文以东北典型黑土带玉米农田的耕层土壤为研究对象,采集了来自黑龙江省、吉林省和辽宁省24个样点72个土壤样本。利用磷脂脂肪酸(Phospholipidfattyacid,PLFA)技术定量描述土壤微生物群落结构,运用随机森林和层次分割分析等机械学习算法深入解析环境因子对微生物地理分布的相对贡献。研究发现,典型黑土带玉米农田土壤总微生物和各微生物类群的生物量呈现随纬度自南向北增加的空间分布格局;土壤有机碳(SOC)和土壤全氮(TN)不仅是驱动微生物生物量纬度分布格局的主要因素,也是影响微生物群落组成最重要的因素。SOC和TN还与其他环境因子,特别是与土壤粘粒含量(CC)之间存在耦合关系,共同影响东北黑土带土壤微生物群落组成。