The sulfur cycle is one of the geochemical element cycles in which microorganisms play a key driving role. The microbial function of soil S cycling in response to desert degradation, however, remains largely unknown. We used metagenomics to analyze the characteristics of microbial communities and their functional genes involved in the S cycles under natural water gradients with three typical halophytes shrubs in the Ebinur Lake Basin Desert, China. Our results showed that the rhizosphere effect, water gradient, and halophyte type played a major role in shaping the S cycle. On the whole, in the rhizosphere type and low water environment, the functional genes involved in the S cycle had high abundance, and the SOX system in Alhagi sparsifolia had a high expression level. In the S cycle network structure, as the soil water content decreased, the complexity in S gene networks increased, showing the characteristics of clustering and high connectivity. Indicates the strengthening mode in microbial interactions with the water content. Interestingly, the negative correlation of the network changed with the water content, and there was more competition among communities under the low water gradient and more cooperation under the high water gradient. Through the correlation between environmental factors and the network, nitrate (NO 3 −) and soil available S (AS) constrained most S gene ecology networks. The key species involved in the S cycle were halophilic microorganisms. These results can enhance the understanding of soil S biogeochemical processes and contribute to the mitigation of desertification by improving soil conservation.
Long-term monitoring of ice-dammed lake development are important for understanding the process of lake storage and outburst. Based on remote sensing observations for the period 1972-2020, we obtained so far the most detailed reconstruction of the filling and drain of Kyagar lake, a typical annually ice-dammed lake in the north Karakoram. We show that annually repeated lake filling-drains were detected by satellite observations during two periods:1996 to 2009 and 2015 to 2020, while between 2009 and 2015 none obvious outburst occurred. These two intermitted periods with regular annual cycles of lake outburst were likely related to the long-term cycle of glacier surge dynamics, which show two remarkable surge-induced terminus accelerations during 1995-1997 and 2014-2016. Following each surge, the maximum lake areas were decreased by about 33% from 1996-2009 and by about 88% from 2015-2020. With climate warming and the thinning of the ice-dam, the storage capacity of glacial lake will likely continue decrease in the future, and the risk of lake outburst flood thus somehow decrease. Repeated drainage following filling exacer-bates the depletion of material at the glacier terminal, leading to the cessation of storage and creating the conditions for the next glacial surge to occur, thus creating a long-term cycling process. Together with the uncertainty and intensified climate changes, it suggests that a close monitoring of the glacial lake development and glacier dynamics would be still important.
Soil is the largest carbon reservoir in terrestrial ecosystems, and thus minor changes in it can dramatically affect atmospheric CO 2 concentrations. The fragile ecological environment in the northwestern arid zone of China is susceptible to natural and anthropogenic disturbances, which lead to variations in structure and function of the ecosystem, as well as carbon source–sink dynamics. In this study, digital soil maps of soil organic carbon stocks (SOCS) were produced at a 90-m resolution for two periods (the 1980s and 2010s) based on historical soil profile data and a random forest model. The results showed that the prediction accuracy for SOCS in the topsoil (0–30 cm) was superior to that of the subsoil (30–100 cm). Among them, the mean annual evapotranspiration, normalized difference vegetation index during the growing season, multi-year mean temperature, and clay content were the main environmental factors affecting the spatial distribution of SOCS. In the past 30 years, the SOCS of the northwestern arid zone have decreased by 585.50 Tg, with a mean decline of 19.52 Tg C yr -1. The changes in SOCS caused by land-use conversion and reductions in SOCS were further shown to be attributable to grassland desertification and agricultural reclamation. These findings are valuable for exploring the carbon cycle in terrestrial ecosystems in the context of global climate change and for achieving China’s goal of carbon neutrality.
Despite straw application within rice agriculture being widely practiced, both in China and globally, there remain few studies on the maize straw substituted for chemical fertilizers. In this study, maize straw substituted for chemical fertilizers to a double-cropping rice field and compared the effects of medium (MS 9,600 kg·ha−1·year−1) and high (HS 19,200 kg·ha−1·year−1) application on rice yield and soil characteristics with that of the application of single chemical fertilizers (CF) over a period of 1982 to present. The yields of late and early rice increased by 42.66 and 25.04% in 2019 and 2020, respectively. The soil bulk density of MS and HS decreased significantly by 15.94 and 33.35% compared with that of CF, whereas total soil porosity increased significantly by 9.46 and 20.17%, respectively. Long-term straw application significantly improved the soil stable aggregates content (> 0.25 mm). Straw application increased soil urease, protease, alkaline phosphatase (ALP), acid phosphatase (ACP) and catalase activities, microbial biomass carbon (C), microbial biomass nitrogen (N), and soil nutrients content compared with CF, especially HS. Correlation analysis showed that double-cropping rice yield was highly significantly correlated with soil bulk density, total porosity, catalase, microbial biomass C, microbial biomass N, and available P. In conclusion, maize straw substituted for chemical fertilizers not only makes rational use of straw resources, but also improves soil characteristics to improve crop yield.
There is currently a lack of evidence surrounding changes in the health of riparian zones under different land-use patterns within mega-reservoirs and around dams. Scientific evidence for the quantitative effects of stress indicators is vague and varies significantly among reservoirs and dams worldwide. In this study, we used a field-based approach to evaluate riparian health changes—influenced by pressure indicators—across 274 transects from three land-use areas (rural, rural–urban transitional, and urban) in the Three Gorges Dam Reservoir (TGDR) in China during 2019. Multivariate statistical techniques were applied to test for riparian zone changes under these variant land-use patterns. Our results showed that 13 pressure indicators significantly influenced 27 health indicators (including parameters for habitat, plant cover, regeneration, erosion, and exotics) of the riparian zones from the three land-use areas differently. Our results also showed that parameters for plant cover, erosion, and exotics were major contributors within the selected riparian health indicators, whereas land-use designs, farming systems, and pollutant activity variables were the pressure indicators with the strongest impact. Pearson correlation (with r ranging from -0.731 to 0.989) showed that urban transects exhibited the strongest comparative interaction, whereas rural–urban transitional transects formed the weakest association. Furthermore, the agglomerative hierarchical cluster analysis revealed similarities between rural and rural–urban transitional sites while confirming substantial dissimilarity in urban locations. These comprehensive and relevant results provide essential information for reservoir administrators to implement functional changes suited to TGDR land-use scenarios.
Quinoa (Chenopodium quinoa), a herbaceous annual, has been widely cultivated in recent years because of its high nutritional value and strong tolerance to abiotic stresses. The study was conducted at two planting densities (LD, 10 plants/m2; HD, 65 plants/m2) on ameliorated coastal mudflats in Jiangsu Province, China (118° 46′ E, 32° 03′ N). The results showed soil salinity and organic matter were higher in the HD than LD treatment, and salinity of the rhizosphere soil was higher than that of the non-rhizosphere soil. Quinoa grown in HD was taller, with thicker stalks and lower yields per plant, but higher yield per unit area. Amplicon sequencing showed that Proteobacteria, Bacteroidota and Acidobacteria were the dominant bacterial phyla. Regarding the rhizosphere soil, the Shannon index was higher in the HD than LD, and Proteobacteria and Bacteroidota were more abundant in the HD treatment. Fifty-one differential metabolites were identified by metabolomic assays, belonging to 14 annotated metabolic pathways. S-adenosylmethionine was the most abundant and up-regulated metabolite (fold change >1.67), and was more abundant in the roots from the LD than HD treatment. Docosahexaenoic acid was more abundant in the HD than LD treatment, and was down-regulated metabolite. In conclusion, planting density was an important factor affecting quinoa yield; compared with unplanted soil, planting quinoa at low density increased the content of the important metabolite S-adenosylmethionine in the root system of quinoa, and high density cultivation of quinoa increased soil salinity and microbial abundance and diversity.
Secondary forest restoration can alter terrestrial ecosystem processes and potentially impact subsurface carbon dynamics. However, the effects of long-term forest restoration on the soil microbial metabolic activity remain unclear. So, the aim of this study was to explore the response of soil microbial metabolism to forest restoration. Among them, the soil basal respiration (BR), microbial quotient ( qMB), and metabolic quotient ( qCO 2) were studied. This study investigated a natural vegetation restoration sequence approximately ~160 years after farmland abandonment on the central Loess Plateau, China, corresponding to five vegetation restoration stages including farmland, grassland, shrubland, pioneer forests, and climax forests. The results showed that BR and qCO 2 were increased following forest restoration, whereas qMB showed the opposite trend. Forest restoration also increased the activities of β-1,4-glucosidase and β-D-cellobiosidase. Restoration age, litter traits such as nitrogen, cellulose and lignin decomposition rates, dissolved organic carbon contents, fungi and bacteria composition were also important indicators affecting microbial metabolic activities. Long-term forest restoration can change soil microbial community structure, reduce carbon mineralization efficiency, improve soil microbial carbon utilization efficiency, and promote soil organic carbon accumulation.
Soil salinity is a serious threat in arid and semi-aridagro-ecosystem of India,which is directly influenced the soil physical properties. Therefore, understanding the dynamic nature of salinity is key to implement suitable management practices for improving the fertility of saline soils. In this context, field experiments were conducted in saline soil, comprising five treatments of control (no amendments and chemical fertilizer), recommended dose nitrogen, phosphorus and potassium (N-P-K) fertilizers @ 60:30:30 kg ha-1 (100 % RDF), rice straw compost (RSC) @ 14 Mg ha-1, gypsum enriched compost (GEC) @ 14 Mg ha-1, and municipal solid waste compost @16 Mg ha-1 (MSWC) for three consecutive years (2012 to 2015). Results revealed that composts and chemical fertilizer application in saline soil had brought significant improvement in soil organic carbon (SOC), soil aggregate stability indices, soil water retention, transmission characteristics, and pore size distribution. This improvement in soil physical properties imparted into better soil physical environment and significant reduction in soil salinity (75%) was reported with application of MSWC. Multivariate analysis indicated that mean weight diameter (MWD) and retension pores (RP) were the main two soil physical properties that help to reduce soil salinity. Improved soil environment in compost amendated treatments broght significantly higher grain yield of mustard and pearl millet was observed with MSWC as compared to control. Organic amendments significantly improved the soil physical environment.
Microbiota play essential roles in nitrogen (N) cycling in freshwater river ecosystems. However, microbial functional groups associated with N cycling (especially denitrification) in freshwater rivers under anthropogenic disturbance are still poorly understood. Here, we studied the impacts of different land-use types on denitrification-related microbial communities in Weihe River, Hanjiang River, and their tributaries, in the Qinling Mountains, China. The major land-use types in the three river areas were divided into natural (forest, shrub, grassland, and open water) and anthropogenic (agricultural and urbanized land) types. A landscape survey of microbiota in the river water and sediment was carried out with extensive sample sources based on deep 16S rRNA gene sequencing, which yielded operational taxonomic units for predicting functional groups. With increases in proportions of agricultural and urbanized land areas, electrical conductivity, total N, ammonium-N, and nitrate-N all increased in water samples. Conversely, microbial diversity exhibited a decreasing trend in water samples, whereas the relative abundance of denitrification-related functional groups increased, with increases in the proportions of agricultural and urbanized land areas. The relative abundances of denitrification- and human-related microbial functional groups in sediment samples were distinctively higher in Weihe River (mainly under agriculture and urbanization), when compared with those of Hanjiang River and Qinling tributaries (dominated by forests). The results indicate that anthropogenic land-use types, such as agricultural and urbanized land, result in simple microbial community structure and stimulate microbe-mediated denitrification in freshwater rivers.
Abstract: Land systems in drylands have been experiencing increasing conflicts among different land functions due to ecological vulnerability and growing demands. The improvement of one function is often at the cost of other functions, which causes trade-offs of functions. Understanding land multifunctionality and its trade-offs are prerequisites to alleviate land use conflicts and achieve land sustainability. But research often cannot well address the fuzziness and uncertainty within assessments, and neglect the nonlinear feature when quantifying the trade-offs. Taking the Heihe River Basin (HRB), a typical arid ecologically vulnerable area in China, as the study area, we applied the set pair analysis (SPA) to develop a novel framework for assessing land multifunctionality at a fine scale from the production-living-ecological angle. We then utilized the constraint line fitted with segmented quantile regression to identify the trade-offs among land functions and understand the bidirectional interaction between land systems. The results showed that the overall land multifunctionality in HRB showed an upward trend during 2000-2015, and especially the production and living functions had a larger magnitude. We used the coupling coordination degree to comprehensively indicate the interaction and found that the degree was high in the south and low in the north, which was mainly controlled by ecological function. The effects of different drivers on land functions showed nonlinear characteristics, and thresholds existed for some influencing factors. Our research provides reliable and detailed information to coordinated the development of land systems, which is helpful for sustainable land use and territorial spatial planning.
Mitigating soil nutrient depletion and increasing utilization efficiency is a prerequisite of sustainable agriculture. Therefore, a field experiment was carried out for 2 years in the midland agroecology of Ethiopia, to identify soil amendment types that can improved soil nitrogen (N) and phosphorus (P) balances at the same time maximize utilization efficiency and profitability under teff cultivation. Using RCBD with three replications, the soil amendments applied on the degraded acidic farmland plots were polyacrylamide (PAM = 40 kg ha−1), biochar (B = 8 t ha−1), lime (L = 4 t ha−1), gypsum (G = 5 t ha−1), PAM+B, PAM+L, PAM+G, and a control. N and P inflows from (atmospheric deposition, biological fixation, and fertilizers), and outflows by (water erosion, leaching, gaseous emissions, and harvested products) were monitored in the 24 plots via NUTrient MONitoring model. Results showed that all of the applied soil amendments improved nutrient balances (by 8–134%) compared with the control. Of the measured outflows, harvested products (43–60%) and water erosion (14–31%) were the major contributors to N depletion, followed by leaching (15–23%) and gaseous emissions (11–13%). Among the applied soil amendments, PAM+L appreciably reduced P loss from water erosion by 61% and N losses from erosion, leaching, and emissions by 55%, 10%, and 3%, respectively, and increased N use efficiency by 31% compared to control plot. Moreover, PAM+L provided a net benefit much higher compared with others. Thus, application of PAM+L would be an effective strategy to combat nutrient depletion and foster crop production in dryland agriculture.
As the important coal bases in northwestern China, the hydrological and ecological environment of Ordos, northern Shaanxi (Shanbei) and Shanxi Province has attracted more and more attention. Terrestrial water storage anomaly (TWSA) and precipitation, as important hydrological elements, play an important role in the distribution and growth of vegetation. In this paper, the Gravity Recovery and Climate Experiment (GRACE) satellite data, Tropical Rainfall Measuring Mission (TRMM) precipitation data, and the Remote Sensing Ecological Index (RSEI) were used to analyze the spatial-temporal changes and coupling relationships of TWSA, precipitation and ecological environment from 2002 to 2020. The numerical results showed the TWSA in the study area has a decreasing trend and the rates are -6.19mm/a, -7.67mm/a and -16.92mm/a for Ordos, Shanbei and Shanxi Province, respectively. On the contrary, the precipitation appeared an increasing trend and the rates are 0.35mm/a, 0.63mm/a and 0.18mm/a for these three sub-regions. It is found that the precipitation is not the main factor causing the variation of TWSA, but the coal mining activities and artificial irrigation activities, which is especially clear in the Taihang Mountains in eastern of Shanxi Province. The ecological environment has been improving, and TWSA and precipitation are the important hydrological factors causing this change. Precipitation is the main reason for improving the ecological environment in three sub-regions on a seasonal scale, especially in summer. The research results are helpful to understand the impact of hydrological changes on the ecological environment, which play an important role in environmental governance in coal mining areas.
Desert expansions can cause tremendous losses to human well-being. However, the process of shifting from the non-desert state to the desert state, a representation of a system regime shift, remains unclear on the global scale. Clarifying the underpinning pattern, predictors and signals of this process is of great value in advancing understanding of both ecosystem resilience and sustainable developments. Here, we combine the climate classification map and long-term observational land cover data to assess the global desert distribution and its changes from 2000 to 2019. The identified desert areas cover approximately 7.53% of the global land in the past two decades. Only approximately 16.03% of these deserts shows expanding trends, especially in countries such as Tunisia, Tajikistan and Peru. After assessing 26 climatic, ecological and socioeconomic factors that could potentially modify desert expansion rates, vegetation cover diversity was identified as the strongest predictor in both hot and cold deserts, followed by cattle density in hot deserts and desert size in cold deserts. In addition, pronounced high fluctuation in satellite vegetation productivity and flickering between land cover states could serve as two signals for desert conversion and fast expansion, respectively. Our results provide not only a long-term overview of global desert changing patterns but also possible guidance for constraining desert expansion.
Implementation of the Natural Forest Protection Project and Grain for Green Programme in China has promoted forest restoration, increased productivity, and enhanced the carbon stocks. However, few studies have characterized temporal and spatial variation in productivity and ecological stability in planted and natural forests and evaluated the factors driving such variation. In this study, we used 1399 permanent forest plots to identify change patters in the productivity and temporal stability of above-ground biomass (AGB) and evaluated the factors driving these changes in planted and natural forests in Sichuan Province, China. The mean temporal stability of AGB was higher for natural forest than for planted forest from 1979 to 2017; While, the productivity of planted forest was higher. The stability decreased at a rate of -0.013 yr-1 in entire natural forest and -0.011 yr-1 in planted forests, and the productivity of natural forest decreased significantly over time, with a slope of -0.0065 Mg ha-1 yr-1 per calendar year. Altitude, latitude, annual precipitation, and stand age dominated variability in the productivity and AGB stability of natural forest. Richness, tree density, and stand age were the determinants of productivity and stability in planted forest. Our results suggest that selective thinning and enriching species richness and forest stand age can effectively balance the productivity and biomass temporal stability of planted forests. Older natural forests still need to be strictly protected under climate change.
Despite sustained global efforts to avoid, reduce, and reverse land degradation, estimates of land degradation nationally and regionally vary considerably. Land degradation reduces agricultural productivity, impacts the provision of vital ecosystem services, and disproportionately affects vulnerable populations. The 2030 Agenda for Sustainable Development, through Sustainable Development Goal (SDG) 15.3, sets out to achieve land degradation neutrality (LDN) by improving the livelihoods of those most affected and building resilience in areas affected by or at risk from degradation. The United Nations Convention to Combat Desertification (UNCCD) leads the charge in creating a spatially-explicit framework for monitoring and reporting on LDN goals that countries can integrate into their land planning policies. However, it remains difficult to operationalize the integration of biophysical indicators of land degradation with climatic and socio-economic indicators to assess the impact of land degradation on vulnerable populations. We present an integrative framework that demonstrates how freely available global geospatial datasets can be leveraged through an open-source platform (Trends.Earth) to simplify and operationalize monitoring and reporting on progress towards achieving LDN. Then, we summarize a suite of datasets and approaches that can be used to understand and quantify the socio-ecological interactions between drought, land degradation and population exposed to desertification, land degradation and drought (DLDD). We discuss how improvements in Earth Observation (EO) datasets and algorithms will allow UNCCD land-based progress sub-indicators (changes in primary productivity, land cover, soil organic carbon, drought, and population exposure) to be computed at enhanced spatial resolutions.
Organic materials are essential to increase soil organic carbon (SOC). However, it is unclear whether C sequestration is primarily affected by the form of organic materials or soil types. Wheat straw, tobacco straw, and their derived biochars were added to acidic soil, saline soil and calcareous soil in the same C concentration and incubated for 30, 90, and 180 days, respectively. The contents of humic substances (HS), the structural characteristic of SOC, and enzyme activities were investigated. The results revealed that both biochar-C and crop straw-C were mainly sequestered in humin (HU) across all soil types. Moreover, humic acid (HA) levels increased in straw treatments but not in biochar treatments. The cluster analysis and principal components analysis showed that HU had a significantly positive correlation with SOC. The aryl C of SOC increased in biochar treatments, while phenolic C and O-alkyl C of SOC increased in straw treatments. A positive correlation was found between aromatic C and SOC concentration, as well as between polyphenol oxidase activity and O-alkyl C. The formation of O-alkyl C was affected by polyphenol oxidase activity. These findings suggest that the form of organic materials and microbial activity, rather than soil types, influence the formation of HS and functional groups of SOC. Soil amended with biochar can sequester more recalcitrant C while also increasing the hydrophobicity of SOC.
Planting Robinia pseudoacacia in water-limited regions can promote soil and water conservation and improve ecological service function. However, it can also cause the formation of below-ground dried soil layers (DSLs), causing land degradation and tree mortality. To ascertain the spatial-temporal dynamics and recovery processes of DSLs, we monitored the deep soil water content (SWC) to a depth of 500 cm at 27 sites on a typical R. pseudoacacia forest (planted in 2003) hillslope from 2017–2020, and calculated the evaluation indices of DSLs based on plant and soil criteria. We found that, compared to plant criterion identified-DSLs, the degree of soil criterion identified-DSLs was more severe, although the spatial-temporal characteristics were similar. Severe soil desiccation was identified in the forest as 79% of the 500 cm profile drying out below 101 cm. During the study period, the mean thickness of DSLs and mean SWC within DSLs were 397 cm and 9.0%, respectively, and the quantitative index of DSLs reached level III (> 0.51, severe DSLs). All DSL indices demonstrated weak or moderate variability in space and strong variability in time. Interestingly, two rainfall events triggered DSL disappearance at seven sites, indicating the possibility of DSL recovery under heavy rainfall. Possible mechanisms explaining the DSLs recovery phenomenon were linked with continued rainfall, micro-topography, soil texture, individual root characteristics, and their interactions. This information is helpful for soil water management and land development in planted forests and for reclaiming DSLs under similar conditions.
The objective was to know the effect of amendments and mulch (pine woodchips) on three planted autochthonous species in two substrates six years after the beginning of the restoration. But because this kind of mulch contained pine cones, pine seedlings appeared after the first year of the restoration; new objectives were added to the initial one: to know if organic amendments influence pine growth among planted vegetation, and if there were competition among planted species, opportunistic species and pines. Essential soil parameters, plant cover and diversity and pine growth were measured and statistically processed with correlation analyses, ANOVA and Detrended Correspondence Analysis. Six years after restoration organic amendments, applied all over the plots contributed significantly to explain the differences on the tested variables. The combined effects of the two substrates and the two organic amendments effectively enhanced soil properties recovery, but they also facilitated the establishment and entry of new species in addition to planted vegetation, driving a differential plant development. The number of pines, as well as their coverage, depended on the interaction between the amendment and the substrate: a) only one amendment favoured the pines and b) the way the amendment works depended on the substrate. Planted vegetation cover and total plant cover from amended plots doubled that of control plots. Results indicate the potential suitability of organic amendments, pine chips mulch and derived opportunistic species for restoring post-mining areas.