Loess Plateau Of China Research Articles

Long-Term Nutrient Cycle in Improved Grain Yield of Dryland Winter Wheat (Triticum aestivum L.) under Hydrological Process of Plant Ecosystem Distribution in the Loess Plateau of China.

Precipitation is the major cause of crop yield variation in rainfed agriculture production in the Loess Plateau. As over fertilization is economically and environmentally undesirable, and crop yield and the resulting returns for N input are uncertain when rainfall variability is high, optimizing N management according to precipitation during fallow season is vital for efficient crop water use and high yield in dryland rainfed farming systems. Results show that the nitrogen treatment rate of 180 treatment significantly increased the tiller percentage rate, and the leaf area index at anthesis, the jointing anthesis, anthesis maturity dry matter, and nitrogen accumulation was closely related to yield. N150 treatment compared to N180 treatment significantly increased the percentage of ear-bearing tiller by 7%, dry substance accretion from jointing to anthesis by 9%, and yield by 17% and 15%, respectively. Our study has important implications for the assessment of the effects of fallow precipitation, as well as for the sustainable development of dryland agriculture in the Loess Plateau. Our results indicate that adjusting N fertilizer inputs based on summer rainfall variation could enhance wheat yield in rainfed farming systems.

Deep soil water use of old-aged vegetation (17- to 36-year stand age) after the formation of dried soil layers based on in situ monitoring

Study regionXindiangou Watershed in Suide, the Loess Plateau, China Study focusDeep soil water (DSW) is gradually depleted as vegetation stand age increases, resulting in dried soil layers (DSLs) in the Loess Plateau in China. However, it is unclear whether old-aged vegetation continues to use DSW under DSLs. This study monitored soil water five times (2001, 2005, 2006, 2007, 2020) in the deep profile for three common vegetation types [Pinus tabuliformis Carr. (P. tabuliformis), Caragana korshinskii Kom. (C. korshinskii), Platycladus orientalis L. Franco (P. orientalis)] planted in 1985. In 2020, we measured soil water content, root characteristics, and soil particle composition to investigate DSW status and the influencing factors. New hydrologic insights for the regionSoil water in the 2–10 m soil layer did not significantly differ from 17- to 36-year stand for the three vegetation types (p < 0.05), indicating that old-aged vegetation no longer used DSW with a strong soil desiccation index in 2–10 m. P. tabuliformis (23- to 36-year stand) used DSW in the 17–22 m with an average consumption of 11.6 mm year–1, while old-aged C. korshinskii did not use DSW. DSW under long-term depletion correlated significantly with clay content. This study showed unfavorable DSW resources for water use under old-aged vegetation, with further measures to conduct selective thinning or complementary planting considered to alleviate the DSW deficit.

Do Ecological Restoration Projects Undermine Economic Performance? A Spatially Explicit Empirical Study in Loess Plateau, China

Exploring the complex relationship between ecological restoration and economic development is valuable for decision makers to formulate policy for sustainable development. The large-scale environmental restoration program—Grain for Green—was mainly implemented in the Loess Plateau of China to improve the soil retention service. However, whether this world-famous program affects local economic development has not been fully explored. In this study, using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model and spatializing the gross domestic product (GDP) based on the remotely sensed nightlight data, we explored the tradeoff between environment (i.e., soil retention service) and economy (i.e., GDP) for the Loess Plateau in a spatially explicit way. We found that the soil retention service increased prominently over the past 40 years, especially after implementing the Grain for Green project. Meanwhile, the GDP increased about nine-fold over the past four decades from 4.52 to 40.29 × 107 USD. A win–win situation of soil retention and economic development was achieved in the Loess Plateau of China, particularly in the loess gully and loess hilly gully regions of the Loess Plateau. The win–win situation of soil retention and economic development was as a result of the Grain for Green program, the optimization of industrial structure, and the increase in non-agriculture employment. Compared with previous studies, more spatial information was available for the Loess Plateau in this study, which is more valuable to policymakers.

Productivity variation and stability of intensive forage‐winter wheat cropping systems on the Loess Plateau, China

AbstractIntegrating forage crops into the continuous winter wheat (Triticum aestivum L.) cropping system can be used for increasing rural population income and maintaining grain production on the Loess Plateau. The objective of this study was to comprehensively evaluate economic yield (EYyield), dry matter yield (DMyield), crude protein yield (CPyield), wheat equivalent yield (WEyield), and food equivalent yield (FEUyield) when incorporating annual forages (oat [Avena sativa L.], soybean [Glycine max L.], and vetch [Vicia sativa L.]) into the traditional fallow‐winter wheat system from a 4‐year (2016–2020) experiment on the Loess Plateau of China. Results showed that incorporating annual forages into the continuous wheat system significantly increased system productivity. Among the four growing seasons, average system DMyield values for fallow‐winter wheat (F‐W), oat‐winter wheat (O‐W), soybean‐winter wheat (S‐W), and vetch‐winter wheat (V‐W) were 10348.52, 13854.15, 14679.94, and 12185.29 kg ha−1, respectively. The average wheat EYyield values were 3777.82, 3115.19, 4020.76, and 3180.71 kg ha−1, respectively. The average forage DMyield values were 0.00, 5497.19, 4284.64, and 2817.50 kg ha−1, respectively. The S‐W system had the highest DMyield and CPyield (1350.10 kg ha−1), and also had DMyield with the smallest variation (CV = 15.21%). The O‐W, S‐W, and V‐W systems produced FEUyield values that were 48.67%, 68.46%, and 30.53%, respectively, greater than the F‐W system. When considering market prices and yields, the S‐W system increased wheat gain yield and had the highest WEyield (6607.90 kg ha−1). Therefore, in consideration of forage quality, winter wheat production, and system productivity, we recommend the S‐W system for local farmers on the Loess Plateau.

Characteristics of the Water Consumption Components of Winter Wheat Fields and Their Effects on the Loess Plateau under Climate Change: An Example at Xifeng Station, Gansu, China

Understanding the components of water consumption plays a critical role in agricultural management in arid regions. This study aimed to analyze the characteristics of the components of the water consumption of winter wheat on the Loess Plateau in China to investigate their effects on yield and water use efficiency (WUE). Winter wheat observation data were collected from 1981 to 2020 at the Xifeng Agrometeorological Station on the Loess Plateau. The results show that over the past 40 years, the average water consumption of the winter wheat fields was 315 mm, but there were large differences between years. The soil water was first converted from precipitation (P) during the growing season, accounting for 69.4%, and then consumed via soil water storage (ΔW) in the fallow period, accounting for 30.6%. The yield of winter wheat varied from 1057 to 6914 kg·ha−1. The correlation between winter wheat yield and P during the growth period was stronger than the correlation between winter wheat yield and ΔW. The average WUE was 11.0 kg·ha−1·mm−1 from 1981 to 2020, with the highest value of 13.7 kg·ha−1·mm−1 occurring in the 2010s and the lowest value of 9.6 kg·ha−1·mm−1 occurring in the 2000s. The WUE was positively correlated with P (p &lt; 0.01) during the growth period and negatively correlated with ΔW (p &lt; 0.05). Therefore, P can increase yield and WUE more effectively than ΔW. These findings provide a theoretical basis for the efficient utilization of water resources on the Loess Plateau and the sustainable development of dry farming.

Integrated mulching and nitrogen management strategies influence carbon footprint and sustainability of wheat production on the Loess Plateau of China

Integrated mulching and nitrogen management strategies influence carbon footprint and sustainability of wheat production on the Loess Plateau of China

Structural, functional properties of protein and characteristics of tofu from small-seeded soybeans grown in the Loess Plateau of China.

The structural, functional properties of protein isolated from small-seeded soybeans were investigated and characteristics of tofu were studied. Small-seeded soybean protein had obvious α', α, β, acidic and basic subunits bands and two endothermic peaks (76.02-76.63℃ and 91.94-94.25℃). Small-seeded black soybean protein isolates (SBSPI) had more β-sheet (31.90-33.54%) structure, while small-seeded yellow soybean protein isolates (SYSPI) had more α-helix (18.89-20.72%) structure. SYSPI had higher fluorescence intensity (839.10-847.80) than SBSPI (482.70-565.10). SBSPI exhibited higher surface hydrophobicity (939.51-1252.75) and water absorption capacity (8.07-8.50g/g). Tofu made from small-seeded yellow soybeans had higher yield (549.46-560.23g/100g soybean) and was brighter (L*, 74.61-77.48) and more yellowish (b*, 14.83-14.95) in color. Tofu made from Fugu small-seeded black soybean (FGSBS) had the highest hardness (178.52g), adhesiveness (-25.77g.sec), chewiness (87.45g) and resilience (0.26), signifying a more compact structure.

Differential Responses of Soil Microbial N-Cycling Functional Genes to 35 yr Applications of Chemical Fertilizer and Organic Manure in Wheat Field Soil on Loess Plateau

Fertilization changes nitrogen (N)-cycling processes and associated microbial communities in agricultural ecosystems. However, the long-term responses of N-cycling potential and microbial functional genes to different fertilization sources remain unclear. Soil samples were collected to a depth of 20 cm under winter wheat applied annually with N fertilizer (NF), organic manure (OM), N fertilizer plus organic manure (NM), and a control without fertilization (CK) for 35 yr, and they were analyzed for microbial functional genes involved in soil N cycling using metagenome sequencing in the Loess Plateau of China. Soil N fractions were greater with OM and NM than NF and CK. The total abundances of N-cycling genes were 9.3% (p &lt; 0.05) greater with NM than CK, and 8.2% (p &lt; 0.05) and 12.2% (p &lt; 0.01) higher with OM and NM than NF, respectively. Compared to CK, OM and NM increased the abundance of genes associated with nitrification, denitrification, dissimilatory nitrate reduction, and assimilatory nitrate reduction, but decreased the abundance of genes related to organic N metabolism. However, NF increased the abundance of genes involved in nitrification. Both OM and NM also enhanced the relative abundance of Proteobacteria carrying N-cycling genes but reduced those of Firmicutes and Cyanobacteria. Soil organic carbon, total N, and potential carbon mineralization were the dominant factors affecting the abundances of N-cycling genes. Long-term application of OM and NM can promote N cycling by enhancing gene abundance due to increased soil organic matter and microbial biomass compared to NF and CK.

Divergent response of soil microbes to environmental stress change under different plant communities in the Loess Plateau

Soil microorganisms play a crucial role in the proper functioning and stability of grassland ecosystems, and are influenced by the nutrient acquisition strategies of their host plants. The Loess Plateau in China, is known for its severe soil erosion and distinctive loess deposits, with soil nutrient levels declining from southeast to northwest. However, little is known about the relative effects of different host plants on soil microbial communities under different environmental stress in the Loess Plateau. We investigated the microbial community within soil profiles (0–100 cm) under two types of grasses community (Agropyron cristatum and Stipa spp.) with different drought tolerances, which are widely distributed in three different climate regions of the Loess Plateau. The diversity, composition, community assembly, and predicted functions of the bacterial and fungal community were evaluated. We discovered that the climate-plant-soil microbe interactions were the most significant factor affecting the community composition of bacteria and fungi on the regional scale. In addition, the effects of edaphic factors (e.g., soil organic carbon [SOC], total nitrogen [TN], and total phosphorus [TP]) on the soil bacterial and fungal communities increased from the warm-temperate to the desert steppe environment. Furthermore, the microbial community and assembly processes were driven by TP content of Agropyron grass, which is more resistant to environmental stress, while the soil of Stipa grass was driven by SOC. This may have occurred because the soil microbes in the Agropyron grassland had a stronger ability to utilize refractory organic matter thus reducing dependence on SOC, compared to soil microbes in the Stipa grassland. Collectively, our results show that the soil microbes recruited by the different plant communities responded differently in microbial composition, assembly, and functions to adapt the environmental stress change.

Long-Term Chemical and Organic Fertilization Differently Affect Soil Aggregates and Associated Carbon and Nitrogen in the Loess Plateau of China

Fertilizer sources may have variable effects on soil aggregation, aggregated-associated C and N, and wheat yield. A 34-year field experiment was performed to evaluate the influences of chemical and organic fertilization on soil aggregates and associated carbon and nitrogen under winter wheat in a Cumulic Haplustoll of the Loess Plateau, China. Treatments included unfertilized control (CK), inorganic N fertilizer (NF), inorganic P fertilizer (PF), inorganic N and P fertilizer (NP), organic manure (M), inorganic N fertilizer plus manure (NM), inorganic P fertilizer plus manure (PM), and inorganic N plus P fertilizers plus manure (NPM). Compared to CK, long-term fertilization significantly increased the proportion of soil macro-aggregates, mean weight diameter (MWD), and geometric mean diameter (GMD), but decreased the proportion of micro-aggregates and fractal dimension, especially fertilizer plus manure. Compared to CK, manure treatments (M, NM, PM, and NPM) had a better improvement on soil organic carbon (SOC), soil total nitrogen (STN), particle organic C, and microbial biomass C in all aggregates than the fertilizer alone. The SOC in different aggregates increased with the increased aggregate size, which was because the larger aggregates formed by the binding of the smaller aggregates and organic matter. PON increased in NM and NPM, and MBN was more sensitive to N fertilizer. The C/N ratio in bulk soil and aggregates decreased with fertilization, especially in fertilizer with manure and in macro-aggregates. The improved soil structure was related to the increased SOC and STN, which was proved by the positive correlations among SOC and STN with macro-aggregates and MWD. A correlation analysis also showed that the contribution rate of SOC and STN in macro-aggregates was positively associated with the macro-aggregate and stability. Therefore, the sequestration of C and N in soil was related to aggregate size and was mainly affected by larger aggregates. The results demonstrated that fertilizer with manure improved the soil structure and fertility better than fertilizer alone, thus increasing crop yield.

Effects of plastic film mulching and legume rotation on soil nutrients and microbial communities in the Loess Plateau of China

BackgroundPotato (Solanum tuberosum L.) continuous cropping causes the decrease of tuber yield, deterioration of quality and soil degradation in the semi-arid area. These negative effects can generally be mitigated by legume rotation and mulching. However, little is known about how can mulching and legume rotation alleviate the above damage through altering soil environment.MethodsA field experiment was conducted to investigate changes in soil properties and microbial community in response to legume rotation and mulching under six planting patterns: potato continuous cropping without film mulching (PC), potato continuous cropping with film mulching (PCF), potato–broad bean rotation without film mulching (R1), potato–broad bean rotation with film mulching (R1F), potato–pea rotation without film mulching (R2) and potato–pea rotation with film mulching (R2F).ResultsCompared with the PC, the R1F and R2F had significantly enhanced the contents of alkaline nitrogen (AN), available phosphorus (AP), available potassium (AK), total carbon (TC) and total nitrogen (TN), but reduced soil pH and electrical conductivity (EC). The Shannon index of fungi in R1F and R2 was significantly higher than other treatments. The dominant bacterial and fungal phyla of each treatment was Proteobacteria and Ascomycota. R1, R1F, R2 and R2F enhanced the relative abundance of metabolic fungi and altered key differential microbial species. Soil EC, AN and AK were major factors influencing the soil bacterial and fungal communities.ConclusionOverall, the study demonstrated that potato-broad bean/pea rotation with mulching can be adopted as the preferred cropping systems to alleviate potato continuous cropping obstacles through enhancing soil fertility and regulating soil microbial communities in the semi-arid of Loess Plateau, China.Graphical

Multi-Perspective Analysis of Land Changes in the Transitional Zone between the Mu Us Desert and the Loess Plateau in China from 2000 to 2020

The transition zone between the Mu Us Sandy Land and the Loess Plateau is considered an ecologically fragile area. However, significant changes in land use have occurred in the past few decades due to changes in land policies and the implementation of major national ecological projects. Despite this, there is still a lack of clear investigation into the impact of these changes on the landscape structure and ecological health of the area. This study utilizes high-resolution annual land use data from China, along with multi-index models and algorithms, to comprehensively analyze regional land use changes, landscape patterns, and the ecological environment’s quality. Through a comprehensive analysis of various factors, including changes in quantity, transformation in land types, spatial dynamics, landscape structure, and ecological quality, we aim to provide a better understanding of the complex interactions between land use and ecological systems in this area. The research results indicate that: (1) Since 2000, 9057.4 km2 of land in the study area has undergone changes. The grassland area has the largest increase, the forest area has the fastest growth rate, while cropland and barren land have decreased to varying degrees, and impervious surface has slightly expanded. (2) The movement trajectory of the center of gravity for different land types is closely related to human activities such as land development and utilization, as well as ecological restoration. Land changes have resulted in an escalation of landscape fragmentation, a reduction in landscape diversity, and a decline in the uniform distribution of different types. (3) Ecological land is the key to improving the ecological environment. The increase in ecological land area in the study area has led to an improvement in the quality of the ecological environment. The net contribution rate of land change to ecological improvement reaches 1.99%. The analysis methods and perspectives used in this study can be applied to other similar studies. The study’s findings enhance the understanding of how land and vegetation changes affect the ecological environment in this crucial area. They are of great significance in guiding the development and utilization of land resources and the implementation of ecological environment projects.

Carbon and nitrogen footprints of apple orchards in China's Loess Plateau under different fertilization regimes

To comprehensively understand the effects of different fertilization regimes on carbon sequestration and greenhouse gas (GHG) emissions in apple orchard production systems, we assessed the carbon (C) emissions and nitrogen (N) losses along with the life cycle assessment (LCA) to quantify the carbon footprint (CF) and nitrogen footprint (NF) under different fertilization regimes in the Loess Plateau, China. The field experiment was comprising four N fertilizer regimes such as i) single inorganic fertilizer with 800 kg N ha−1 (N800); ii) single inorganic fertilizer with 400 kg N ha−1 (N400); iii) inorganic and organic fertilizers each with 200 kg N ha−1 (N200+O200) as well as without N fertilizer treatment as control (CK). Data regarding the soil organic carbon (SOC), nitrate N (NO3−–N), ammonium N (NH4+–N) and emissions of carbon oxide (CO2) and nitrous oxide (N2O) were measured. Organic fertilizer substitution (OFS) boosted SOC while decreased NO3−–N and NH4+–N concentrations. The cumulative CO2 emissions and emission factors (EFs) of N2O did not change significantly amongst fertilization strategies; however, as compared to N800, N400 and N200+O200 significantly reduced N2O emissions by 41.8%–45.7% and 43.5%–46.6% respectively. The NF was dominated by N residues (73.0%–97.4%) and organic fertilizer (24.37%), with a significant difference detected between N400 and N200+N200 treatments. Meanwhile, compared to inorganic plots, OFS significantly reduced CF (345.9%–368.0%), which was influenced by SOC sequestration. The CF from N plots in apple orchard was dominated by fertilizer (21.7%–39.6%), pesticides (4.3%–6.2%) and N2O (5.6%–11.8%). In addition, our results were further supported by a meta-analysis with 22 published studies, which showed that organic fertilizer and chemical fertilizer + organic fertilizer significantly reduced regional CF by 388.8% and 78.2%, respectively. However, regional NF ranged from 441.4 kg N-eq ha−1 to 453.9 kg N-eq ha−1, with no significant difference between fertilizer strategies. Therefore, reducing the amount of N fertilizer and partial OFS is a viable long-term strategy for mitigating climate change through C sequestration, reduction of N residues, and GHG mitigation, which could be beneficial to low C apple production in the Loess Plateau, China.

Predicting the interrill erosion rate on hillslopes incorporating soil aggregate stability on the Loess Plateau of China

The Water Erosion Prediction Project (WEPP) model is a physical process-based model that can predict both interrill and rill erosion on hillslopes. The interrill erodibility (Ki) is quantified by the soil particle size distribution, which is a key parameter in WEPP model. However, the important effects of soil structure on soil erodibility are ignored, which seriously affects the prediction accuracy of the model. In this study, simulated rainfall experiments (60, 90, 120 mm h−1) were performed to improve the prediction equation of interrill erosion incorporating the aggregate instability index (As). Rare earth elements (REEs) were employed as tracers to distinguish interrill and rill erosion on slopes in a box (2 m long, 0.5 m wide, 0.4 m deep) with gradients of 10°, 20° and 30°. The Le Bissonnais method was used to determine the soil aggregate stability. The results showed that aggregate stability played a crucial role in interrill erosion under similar runoff rates. The improved equation contains four parameters, As, runoff rate (q), rainfall intensity (I) and slope gradient (Sf), with a coefficient of determination (R2) of 0.81 and model efficiency (ME) of 0.79. This equation exhibits greatly improved efficiency in estimating the interrill erosion rate compared to the WEPP model. Furthermore, a new equation incorporating the As, flow velocity (v), flow depth (h) and hydraulic gradient (J) was developed, with R2 of 0.90 and ME of 0.89. This study provides a deeper understanding of the mechanism of interrill erosion and improves upon the physical process-based soil erosion model.

LAI‐based reduction in growth of semiarid grasslands and its responses to climate change on China's Loess Plateau

AbstractUnderstanding the response of vegetation growth to climate change can provide key information for predicting future ecosystem dynamics. Over the past 6 years, the semiarid regions of the Loess Plateau in China have experienced a transition from wet to dry years, but little is known about the response of grass growth to this change. Thus, this study aimed to analyze and evaluate the effect of climate change on grass growth. Using observed climate data and leaf area index (LAI) data obtained with hemispherical photography from 2016 to 2021, we investigated changes in trends of five climatic factors, including precipitation (P), temperature (T), relative humidity (RH), wind speed (WS), and solar radiation (Rs), and their impact on the growth of alfalfa (Medicago sativa) and Stipa bungeana plantations in the semiarid area of the Loess Plateau. The results showed a tendency to become colder in spring and drier in summer and autumn. In response, LAI tended to decrease in alfalfa and S. bungeana plots with interannual variation rates of 0.21 year−1 and 0.12 year−1, respectively. Additionally, linear regression methods showed that P had the greatest effect on LAI of two grasslands during the growing season (R2 &gt; 0.84, p &lt; 0.01), followed by RH and T (0.30 &lt; R2 &lt; 0.50, p &lt; 0.01), a negative effect of WS (R2 = 0.36, p &lt; 0.01), and no significant effect of Rs on LAI were found. Conversely, the path analysis indicated that Rs and P were the largest decision coefficients affecting the monthly LAI of alfalfa and S. bungeana, respectively, due to the different time‐to‐peak LAI and root growth depth of these two grass species. This study can provide theoretical support for ecological restoration and system management of semiarid grasslands.

Regulation of soil water and nitrate by optimizing nitrogen fertilization and the addition of manure based on precipitation: An 8-year field record

Optimizing fertilization strategies to improve water utilization efficiency and obtain higher crop yields and low nitrate leaching is essential for balancing food security and environmental risks in the rain-fed area of the Loess Plateau. The eight consecutive years (2014–2022) field experiment followed a split-plot design, and the experimental factors were nitrogen application rate (N0, N75, N150, N225, and N300) and manure application rate (M0 and M1). In general, (1) the relationships between nitrogen application rate and grain yield (GY), crop N uptake and water utilization efficiency (WUE) followed a quadratic curve. Compared with chemical fertilizer alone (NPK), chemical fertilizer plus manure (MNPK) significantly increased the annual average grain yield by 28.5%, 18.3%, 8.9%, 6.9% and 4.2% at the N application rate of N0, N75, N150, N225 and N300. (2) The nitrate accumulation (SNA) in the same soil layer increased with the nitrogen application rate. The residue nitrate will increase dramatically when the N application rate exceeds 150 kg ha-1. The peaks of SNA gradually moved to the deeper layer with increasing years of fertilization. The total soil nitrate accumulation (TSNA) of NPK was significantly higher than that of MNPK in dry and normal years, but the opposite was true in wet years. The total soil water storage (TSWS) decreased and then increased with the N application rate, and the annual average TSWS of the MNPK treatments was 3.9% less than that of the NPK treatments. (3) The addition of manure significantly increased the annual average moisture storage rate (MSR) during the fallow season by 4.6%. The GY in dry and normal years was more dependent on MSR than that in wet years. In terms of the long-term effects, the MSR contributes more to GY than growing season precipitation (GSP), and the high MSR caused by manure application reduced TSNA and TSWS by promoting crop growth. The results showed that M1N150 could obtain a high grain yield while maintaining low nitrate residue. Taken together, this study emphasized the importance of optimizing nitrogen fertilizer management and cattle manure application in combination with precipitation types to ensure food production and reduce negative environmental effects in the rain-fed area of the Loess Plateau in China.

Spatio-Temporal Patterns of NDVI and Its Influencing Factors Based on the ESTARFM in the Loess Plateau of China

The Loess Plateau is ecologically vulnerable. Vegetation is the key factor in ecological improvement. The study of the distribution patterns of vegetation and its impact factors has important guiding meaning for ecological construction in the region. The existing single sensor cannot provide long-term and high-resolution data. We established data of NDVI with a great spatial resolution by fusing the GIMMS NDVI and the MODIS NDVI based on the ESTARFM. Furthermore, we analyzed the variation in NDVI under different topographies and its response to climatic factors and human activities in the Loess Plateau. The results manifested that: (1) The fused NDVI by the ESTARFM had a high correlation with the MODIS NDVI and can be used in subsequent studies. (2) The multi-year average NDVI of this region ranged from 0.027 to 0.973, which is specifically low in the northwest and high southeast. The NDVI manifested an upward trend in the last 31 years. Its growth rate was 0.0036/a (p &lt; 0.01). Spatially, the area with an upward trend of NDVI accounted for 89.48% of the plateau. (3) For topography, the larger area with the extremely significant upward of NDVI was found at elevations of 500–1500 m, with slopes of 6–15°. The larger area with the extremely significant downward trend of NDVI was found at an elevation of higher than 3000 m, with a slope of greater than 35°. (4) The response of the NDVI to the climatic factors manifested a significant spatial heterogeneity. The temperature had a more significant impact on NDVI than precipitation. (5) Human activities contributed more to NDVI than climatic factors (65.22% for human activities and 34.78% for climatic factors). Among them, the area with a high contribution of human activities to NDVI increase was consistent with the area where the GGP was implemented. The distribution of areas with high contribution of human activities to NDVI decrease was in line with that of the provincial capital cities. The results served as the theoretical foundation for assessing the efficacy of environmental stewardship and for optimizing ecological restoration measures.

Cropland-to-shrubland conversion reduces soil water storage and contributes little to soil carbon sequestration in a dryland area

The conversion of croplands to shrublands is a common approach used to control soil erosion in the drylands of the Loess Plateau in China and affects the soil, water, and carbon cycles. Knowledge of the soil water content (SWC) and soil organic carbon (SOC) content in response to land-use change is essential for optimizing revegetation strategies and improving ecosystem services. This study investigated the distribution characteristics of the SWC and SOC content for the 0–500 cm soil layer in 11 croplands and 39 shrublands planted on a former cropland over 50 years ago. The coupled and trade-off relationship between soil water consumption and carbon fixation in the shrubland soil was also analyzed. The results showed that the SOC content and SWC of the shrublands and croplands varied with soil depth, but their distribution patterns were similar under both land-use types. Planting shrubs on slopes reduced the SWC but did not significantly enhance the SOC content, indicating that cropland-to-shrubland conversion results in excessive soil water depletion without increasing carbon fixation in the soil. Additionally, both the SOC content and SWC of the shrublands varied significantly with slope positions (p < 0.05) and showed intermediate coordination levels across the entire slope. Moreover, the SOC content provided higher benefits than SWC, where the foot slope showing a relatively higher coupling coordination degree and a lower trade-off than other slope positions. These results suggest that shrubs provide a limited contribution to improve SOC stocks in the drylands of the Loess Plateau and that reductions in deep soil water under cropland-to-shrubland conversion require consideration when planning future ecological restoration measures. To improve ecosystem services (carbon sequestration and soil conservation) without compromising water resources in the drylands of the Loess Plateau or similar regions worldwide, it is necessary to fully consider the slope position and the trade-off between the SWC and SOC content.

Paleotopography-constrained numerical modeling of loess landform evolution

Numerical modeling of landform evolution is the key to understanding the formation of land surfaces. However, landform evolution occurs under certain initial topographic conditions, while existing landform evolution models often use a plane or a randomly produced surface to establish the initial topographic conditions. This misunderstanding of the initial topographic conditions causes the landform evolution results to deviate greatly from the real terrain. Therefore, the initial topographic conditions must be reconstructed and integrated into the current numerical landform evolution model. In this paper, the Loess Plateau of China was selected as a typical sample area. The paleotopography was reconstructed and integrated into the numerical landform evolution model. Based on the evolutionary mechanism of loess landforms, modules of surface erosion, matter diffusion and precipitation were selected to construct a numerical model of loess landform evolution. Moreover, randomly produced terrain was used as the initial conditions during the landform evolution process and compared with the paleotopography-constrained evolution results. In addition, the results of the landform evolution process were evaluated with different terrain factors, and the uncertainty of the model was assessed by comparing different model conditions. The results show that, due to the control of paleotopography, the evolution results can maintain the main morphological structure of valleys in the loess landscape. Without considering the paleotopography, a large difference exists between the evolution results and the true ground terrain. These results show that paleotopography is an important feature of loess landform evolution modeling and is indispensable for reasonably expressing the process of landform evolution. Finally, the numerical modeling of loess landform evolution with the consideration of paleotopography can not only help to achieve a better understanding of the loess landform evolution process but also provide a reference for feature dependent landform evolution modeling in different landform applications.

Partitioning and integrating of plant traits and phylogeny in assessing diversity along secondary forest succession in Loess Plateau of China.

Assessing plant diversity during community succession based on plant trait and phylogenetic features within a community (alpha scale) and among communities (beta scale) could improve our understanding of community succession mechanism. However, whether changes of community functional diversity at alpha and beta scale are structured by different traits and whether integrating plant traits and phylogeny can enhance the ability in detecting diversity pattern have not been studied in detail. Thirty plots representing different successional stages were established on the Loess Plateau of China and 15 functional traits were measured for all coexisting species. We first analyzed the functional alpha and beta diversity along succession by decomposing species trait into alpha and beta components and then integrated key traits with phylogenetic information to explore their roles in shaping species turnover during community succession. We found that functional alpha diversity increased along successional stages and was structured by morphological traits, while beta diversity decreased during succession and was more structured by stoichiometry traits. Phylogenetic alpha diversity showed congruent pattern with functional alpha diversity because of phylogenetic conservation of trait alpha components (variation within community), while beta diversity showed incongruent pattern due to phylogenetic randomness of trait beta components (variation among communities). Furthermore, only integrating relatively conserved traits (plant height and seed mass) and phylogenetic information can raise the detecting ability in assessing diversity change. Overall, our results reveal the increasing niche differentiation within community and functional convergence among communities with succession process, indicating the importance of matching traits with scale in studying community functional diversity and the asymmetry of traits and phylogeny in reflecting species ecological differences under long-term selection pressures.