To accurately quantify the contributions of climate change and human activities to net primary productivity (NPP) on the Loess Plateau, we used MODIS products, meteorological data, land use data, and the partial derivative method to analyze spatiotemporal variations and driving mechanisms of NPP from 2000 to 2020. Results showed that NPP increased significantly during 2000-2020, with an average annual growth rate of 6.76 g C·m-2·a-1. The NPP growth rate during 2000-2009 (7.99 g C·m-2·a-1) was higher than that from 2010 to 2020 (5.85 g C·m-2·a-1). In 83.3% area of the Loess Plateau region, the spatial variation of NPP exhibited an extremely significant upward trend, with only a small portion showing non-significant change or a declining trend. The increase in vegetation NPP on the Loess Plateau was synergistically driven by climate change and human activities, where precipitation was the dominant climatic factor, with 96.5% of the regional NPP positively correlated with precipitation. Temperature promoted NPP overall, while solar radiation exhibited a distinct meridional zonality in its correlation with NPP. Driven by combined climate and human activities, regional vegetation NPP increased significantly but with a decelerated growth rate, indicating a shift from rapid restoration to stable and sustainable development. Our findings would provide theoretical support for vegetation restoration on the Loess Plateau.

Revealing the spatial distribution mechanism of the coupling effect between soil water and salt is essential for managing saline-alkali farmland. This study utilized the multifractal method to analyze soil water and salt under varying water content levels in arid saline-alkali farmland. Soil samples were collected on the second (S1), fifth (S2), eighth (S3), eleventh (S4), and fourteenth (S5) days after a rainfall event. The findings showed that a significant decrease in soil water content, contrasting with an increase in soil salt content throughout the soil layers post-rainfall. As water content decreased, the spatial variability of soil water initially increased from S1-3 and then decreased, while the spatial variability of soil salt decreased. The spatial distribution between soil water and salt exhibited a high correlation at S3-4 (with relative water content of soil ranging from 0.52 to 0.75) due to their coupling effect. However, soil salt was unevenly leached by rainfall at high water content levels (S1-2) and precipitated at low water content levels (S5), resulting in low spatial variability correlations between soil water and salt. This study elucidated the coupling process of soil water and salt, identifying their spatiotemporal distribution mechanism in dryland agricultural areas.

Investigating the spatial distribution characteristics of the interaction between soil salinity and moisture is crucial in revealing moisture–salinity interaction in semi-arid farmland. The sampling of soil was performed on the second (S1), fifth (S2), eighth (S3), eleventh (S4), and fourteenth (S5) days after the erosive rainfall. The multifractal method was used to analyze spatial distribution parameters of soil moisture and salinity under the different stages. The findings showed that the soil moisture content decreased from 22.44% to 12.73%, while the salinity increased from 0.71 to 1.18 g kg–1 after the rainfall. As the amount of moisture in the soil decreased, the variability in the distribution of moisture initially increased from S1 to S3 and then decreased, while the salinity content also decreased. The spatial distribution of soil moisture and salinity content showed a strong correlation at S3 to S4 (with the relative water content of soil ranging from 0.52 to 0.75), indicating a significant coupling effect in these stages. However, the distribution of soil salinity was not uniform under high moisture content conditions (S1 to S2), as it was leached unevenly by rainfall, and under low moisture content conditions (S5), it precipitated, resulting in a low correlation between the spatial distribution of soil moisture and salinity content. This research has provided insight into the coupling dynamics of soil moisture and salinity content, revealing the mechanisms governing their spatial distribution in dryland agricultural regions.

Revealing trade-off and synergistic relationships among ecosystem services plays a key role in ensuring a stable ecosystem for long-term development. It is the crucial precondition for realizing watershed protection and high-quality development. The variations in land use during 1990–2020 are investigated by taking the typical areas for returning farmland to forests as an example. The spatiotemporal distributions of six key ecosystem services, namely carbon storage, water yield, net primary productivity (NPP), soil conservation, habitat quality, and forest recreation are quantified by the InVEST model and statistical data. We also uncover the spatial difference in the ecosystem in Loess Plateau, located in northern Shaanxi, with hot spot analysis and probe the trade-off and synergistic correlations among the investigated ecosystem services. The results show that: (1) the farmland decreased dramatically. On the contrary, the forests and orchards increased significantly. (2) During the same period, carbon storage and habitat quality increased, and water yield, NPP, soil conservation, and forest recreation initially declined, but subsequently rose to higher values than that in 1990. All these services in the southeastern part of the research area surpass those found in the northwest. (3) The ecosystem services relationships in northern Shaanxi are mainly characterized by synergistic correlations, which became stronger from 1990 to 2020. The trade-off effects mainly occur among the water yield and other ecosystem services and are distributed in the west and north of the investigated area. Based on these findings, this work provides scientific principles for improving the ecological environment and enhancing the resource sustainability of the study area.

Microplastics (MPs) is a major threat to agroecosystems. Their accumulation and impacts should be evaluated to advance our understanding of soil function and health. Uncovering the role of cascade effects in regulating crop growth is crucial to understanding the link between MPs disturbance and environmental functions. Therefore, we aimed to assess how the cascade changes between (non-) biological factors and functional traits of maize regulate the response of maize growth to MPs in different nutrient soil environments. We found that soil dehydration induced by MPs may disrupt the balance of the physiological status of maize, negatively affect photosynthetic performance, and enhance competition among organisms for limited nutrients. However, root-responsive nutrient cues with a high degree of tectonic freedom allowed adaptive phenotypic plasticity to occur, masking the negative effects of MPs. In nutrient-rich soil environments, moderate and high intensity (>0.5 %) MPs disturbances initiated root nutrient foraging activities, and maize tended to decrease its cost of investing in root construction, i.e., increasing specific root length (SRL) to promote its own growth. The growth of maize was mainly characterized by increases in the belowground biomass (BGB, 7.11 to 20.81 g) and aboveground biomass (AGB, 61.11 to 118.26 g). Our study suggests that a cascade effect between environmental factors initiated by MPs and the functional architecture of the maize root system drives maize to regulate its growth by responding to nutrient cues. These findings will help to ensure food security, formulate environmental risk management policies and protect soil health, especially in the context of future agriculture.

Arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (expressing the nifH gene) play an important role in maintaining plant growth and soil function, and the reconstruction and restoration of vegetation and degraded ecosystems should focus on these communities and the links between them. However, little is known about changes in these taxa and their interactions during the natural recovery of abandoned land. Here, we investigated the changes in and interactions between AMF and nifH gene-expressing bacteria in farmland (S1), grassland (S2), shrubland (S3), pioneer forests (S4), and climax forests (S5) as five typical stages of vegetation succession on the Loess Plateau, China. We found that vegetation succession significantly influenced the diversity of AMF and nifH communities. With the progression of secondary succession, the diversity of AMF increased from farmland to pioneer forest communities, and decreased in the climax vegetation, while the diversity of the nifH community first decreased and then gradually increased. The community structures of the AMF and nifH communities differed significantly between the five vegetation types. Specifically, the AMF community structure changed significantly during the later stages of succession, while the N-fixing bacteria community tended to be stable during late succession. The interactions between AMF and nifH bacteria gradually increased from the farmland to shrub stages but tended to weaken from the shrub to climax forest stages. Therefore, the relationships between microbial communities during the early and middle stages of vegetation succession following land abandonment on the Loess Plateau are mainly cooperative and mutually beneficial, while competition likely intensifies during later successional stages. Furthermore, we found that soil microbial biomass, enzyme activity, and total phosphorus content were the main drivers of microbial community changes. Overall, this study complements current understanding of the changes and interrelationships of AMF and N-fixing bacteria during vegetation succession in areas prone to soil erosion, and provides new insights into the natural recovery of degraded ecosystems as driven by soil microbial communities.

目的:研究黄土丘陵地区温室内环境因子变化对香菇子实体生长的影响,确定特定区域条件下温室香菇出菇期环境因子的适宜范围,为该地区香菇科学栽培提供一定依据.方法:以"七河九号"香菇菌株为研究对象,在延安市河庄坪镇万庄村温室内典型位置安装传感器,连续测量记录环境因子参数,系统分析香菇出菇期温室内不同位置的环境因子变化规律和香菇子实体经济性状指标,并对二者进行相关性分析.结果:1)温室温度在15～30℃,温度略高的炎热天气应降温,控制温度为15～25 ℃.2)相对湿度为40％～82％,相对湿度过低,可采用微喷设备控制相对湿度在80％～90％.3)CO2浓度为400～600 μmol/mol,可通过揭苫管理调控.4)光照强度为0～4000lx,光照过强,需增加遮阳网层数,控制光照强度为500～1 000lx.5)阳面近地层位置更适合香菇生长,相对湿度和光照强度是影响香菇子实体生长的主要因素,应着重管理水分和光照.

[Objective]Part of the newly cultivated farmland formed by the"Gully Control and Land Reclamation"project is facing the risk of soil salinization in the loess hilly region.The spatial distribution characteristics of soil water and salt and their influencing factors were studied for preventing and controlling soil salinization,and promoting sustainable utilization of newly cultivated land.[Methods]A typical area of newly cultivated land was selected,and six experimental plots were established along a gully head to the gully mouth,with sampling points numbered sequentially from 1 to 6.The grid method was used to obtain soil samples from the 0-20 and 20-40 cm layers in each plot.The multifractal method was used to analyze the spatial distribution characteristics of soil water and salt.[Results]Soil water content and salt content gradually decreased from the gully head to the gully mouth.The mean soil water contents and salt contents at sampling points 1,2,and 3 were 17.6％ and 0.81 g/kg,respectively,which were 23.0％ and 14.1％ higher than the respective values at sampling points 4,5,and 6.Meanwhile,the multifractal parameters D1 of soil water and salt at sampling points 1,2,and 3 were less than the respective values at sampling points 4,5,and 6.ΔD values showed the opposite result,indicating that the spatial variability of soil water and salt at sampling points 1,2,and 3 were higher.The depth of groundwater influence was the main reason for increased accumulation of salt in the surface soil at sampling points 1,2,and 3(p＜0.05).The terrain characteristic was also an important reason(p＜0.05).The narrow terrain was not conducive to drainage,was prone to waterlogging,and exhibited exacerbated salt accumulation.In addition,sampling points 1,2,and 3 may be invaded by slope runoff and sediment with high salt content that increased soil water,salt content,and variability in the area.[Conclusion]The depth of groundwater influence,terrain characteristics,and slope runoff sediment were important reasons for the high soil water content,salt content,and their spatial variability at sampling points 1,2,and 3 in newly cultivated farmland.Thus,newly cultivated farmland near the gully head location would be a key area for preventing soil salinization in the future.

It is important to study the mechanisms associated with the spatial distribution of soil water and salt to control soil salinization and promote the sustainable development of farmland. Six plots in a slight farmland with different spatial locations were selected to determine the spatial distribution of soil water and salt and their correlation using the multifractal method. Each plot was applied using the grid method (15 m × 15 m, 3600 m2), where each sampling site was located at the center point coordinates. The 0–20 and 20–40 cm soil layers were sampled.The spatial variability of the soil water and salt were 1.41 and 1.73 fold higher in the upstream farmland than in the downstream farmland. The spatial variability of the soil water and salt was significantly correlated. In addition, the spatial variability of the soil water and salt significantly correlated in the 0–20 and 20–40 cm layers. The spatial distribution of both soil water and salt in the entire soil layer had similar characteristics at this sampling scale. Our results provide a theoretical basis to study the interactive mechanisms associated with the distribution of soil water and salt.

[Objective] The characteristics of land use transformation of Gaoxigou village, Mizhi County, Shaanxi Province, an ecological demonstration village under the rapid development of urbanization were studied in order to provide reference for the sustainable development of rural productive-living-ecological space in the Loess Plateau region of Northern Shaanxi Province. [Methods] The dynamic attitude of land use and land use transfer matrix were used to analyze the spatial characteristics of productive-living-ecological space at Gaoxigou village from 1953 to 2022. Combined with field research, the spatial pattern evolution characteristics and corresponding spatial governance optimization strategies were analyzed. [Results] ① from 1953 to 2022, the production space of Gaoxigou village decreased, while the living space and ecological space increased. From 1953 to 1973, the ecological space changed the most, the green space increased from 12.07 hm2 to 100.33 hm2, the other ecological space decreased from 12.07 hm2 to 100.33 hm2, and the production space gradually decreased from 145.67 hm2 to 110.07 hm2. From 1986 to 2022, the production space decreased by 42.4 hm2, the living space increased by 5 hm2, and the ecological space increased by 37.39 hm2. ② From 1986 to 2022, the transformation of productive-living-ecological space at Gaoxigou village reflected in the increase of green space and rural living space, and the decrease of agricultural production space, other ecological space and water ecological space. There were 67.83 hm2 of agricultural production space and 59.95 hm2 of other ecological space transformed into green space, and part of green space ecological space transformed into agricultural production space and rural living space, with the transfer area of 21.20 hm2 and 3.22 hm2, respectively. ③ To solve the problem of insufficient production space efficiency, Gaoxigou village adopt the measures to change the cultivation method of wide planting and low harvest, greatly increase the grain yield, change the single agricultural production situation, and realize the coexistence of multiple business modes; In response to the low quality of living space, Gaoxigou village had taken measures to strengthen infrastructure, build new homes, and encourage young people to go out and engage in other industries. In view of the serious damage to ecological space, measures have been taken to control soil erosion, return farmland to forest or grassland, build tourism culture and promote ecological scenery. [Conclusion] According to the main problems of early productive-living-ecological space, Gaoxigou village made appropriate optimization strategies to improve the utilization rate of land, expand the area of forest and grass, so that the green ecological space reached 80%. The efficient development of agriculture, forestry and animal husbandry, and the overall improvement of production, life and ecology make Gaoxigou village an ecological demonstration representative of the loess hilly region.

Arbuscular mycorrhizal fungi (AMF) influence plant nitrogen/phosphorus (N/P) by modifying plant N and P uptake, which further affects plant stoichiometric N/P homeostasis. Plant species and community stoichiometric N/P homeostasis can impact plant species and community stability, respectively, in response to variations of soil N and P availabilities. We investigated interspecific plant interactions via AMF in regard to plant and soil microbial N/P stoichiometry across different soil N and P availabilities induced by N and P addition (0 mg N kg−1, 25 mg N kg−1, 50 mg N kg−1, 30 mg P kg−1 and 100 mg P kg−1). We selected one dominant (Bothriochloa ischaemum; C4 grass) and one subordinate (Lespedeza davurica; legume) species in a natural grassland climax community. We examined how AMF influences stoichiometric N/P homeostasis in monoculture and mixed culture systems, and the resulting consequences for temporal stability of plant species and community in response to variations in soil N and P availability.The AMF mitigated the P limitation of soil microbial communities and decreased the degree of stoichiometric N/P homeostasis of host plants in monoculture. Through their resource‐scavenging and soil organic matter mineralisation functions, AMF enhances plant ‘luxury consumption', promoting species stability in monoculture in response to soil N and P availability variations. Compared with plants in monoculture, the interaction between B. ischaemum and L. davurica via AMF increased shoot N/P under soil N‐poor conditions, leading to an enhanced degree of stoichiometric N/P homeostasis in both plant species, especially the legume.Our results suggest that interspecific plant interaction between C4 grass and legume mediated by AMF confers an advantage in complementarity in plant N acquisition under N‐poor conditions, leading to increased stability of plant communities and better maintenance of subordinate species (legume) in response to soil N deficiency.

以陕北地区典型乡村——榆林市米脂县高西沟村为例,探究其在水土保持措施下土地利用景观格局变化及驱动因素,对黄土丘陵区水土保持、景观格局优化、美丽乡村建设和生态可持续发展具有指导意义.基于高西沟 1986 年、2004 年、2022 年遥感影像,借助 ArcGIS、ERDAS和 FRAGSTATS等软件,运用动态度、转移矩阵、景观格局指数对土地利用变化进行分析,并对其驱动因素展开探讨.结果表明:(1)林地和草地是高西沟的主导地类,约占区域总面积的 80%,耕地、未利用地呈减少趋势,水域和建设用地无较大变化;土地利用综合动态度逐渐降低,土地利用变化趋于平稳.(2)研究区林地转入面积最为显著,主要由耕地转入,林地整体增加 112 hm2;而耕地主要由草地转入,未利用地则向草地转出.(3)林地为高西沟土地利用景观格局中的最大优势斑块,且破碎程度最高,研究区各景观类型斑块形成较为稳定的连接,景观连通性较好;整体景观格局演变分散,各景观类型的面积差距越来越大,优势景观明显,整体破碎程度高.(4)高西沟土地利用变化受水土保持、产业结构和相关政策影响.水土保持是高西沟耕地减少、未利用地开发和林草大面积增加的主要驱动因素,产业结构调整和国家政策与财力资助是高西沟土地利用景观格局优化的辅助影响因素.

[目的]探寻城镇化快速发展条件下作为生态示范村的陕西省米脂县高西沟村的土地利用转型特征,为陕北黄土高原地区的乡村"三生"空间可持续发展提供参考.[方法]通过土地利用动态度、土地利用转移矩阵分析高西沟 1953-2022 年的"三生"空间特征,并结合实地调研对村域多年"三生"空间格局演变特征及对应的空间治理优化策略展开分析.[结果]①1953-2022 年,高西沟生产空间呈减小趋势,生活空间和生态空间呈增大趋势.1953-1973 年,生态空间变化幅度最大,绿地生态空间从 12.07 hm2 增加到100.33 hm2,其他生态空间从 12.07 hm2 减小到 100.33 hm2,生产空间逐渐减小,从 145.67 hm2 减小到110.07 hm2.1986-2022 年,生产空间减少了 42.4 hm2,生活空间增加了 5 hm2,生态空间增加了37.39 hm2.②1986-2022 年,高西沟"三生"空间转型体现在绿地生态空间和农村生活空间的增加,农业生产空间、其他生态空间和水域生态空间的减少.有 67.83 hm2 的农业生产空间和 59.95 hm2 的其他生态空间转化为绿地生态空间,而部分绿地生态空间转化为农业生产空间和农村生活空间,其转移面积分别为21.20 和 3.22 hm2.③高西沟针对生产空间效益不足的问题,采取改变广种薄收的耕种方式,大幅提高粮食产量,改变单一的农业生产状况,实现多种经营模式并存的举措;针对生活空间品质低下的问题,采取全力抓牢基建,量力新建家园,鼓励青年外出,从事其他产业的举措;针对生态空间破坏严重的问题,采取控制水土流失,退耕还林还草,打造旅游文化,推广生态风光的举措.[结论]根据早期"三生"空间的主要问题,高西沟做出适宜的优化策略,提高土地利用率,扩大林草面积,使绿地生态空间达到 80％.农林牧的高效发展,生产、生活、生态的全面改善,使高西沟成为黄土丘陵区的生态示范代表.

Soil and water conservation practices, governance processes, and governance effects can be regarded as elements that constitute a unique coupling system. In order to understand the operation of this coupling system, a structural equation model was used to determine the coupling paths and intensities based on field research data collected from 193 local households in Changting County, China during 2021. The results showed that the elements within the coupling system remained unchanged and the coupling state was steady, with the same coupling path directions in 2010 and 2020. However, the intensities of the coupling paths varied with different path coefficients, where they followed the order of: governance process (0.99) > governance effect (0.57) > coupling state (–0.39) in 2010; and governance process (0.94) > coupling state (0.92) > governance effect (0.17) in 2020. We conclude that although the elements were optimized to a certain extent during the evolution of the coupling system, the lack of harmony among ecological resources and industries detrimentally affected the dynamics of the coupling system. Thus, the government should focus on the harmonious development of ecological resources and the integration of industries to facilitate the high-quality development of ecological civilization.

[Objective] Clarifying the ecological economic basis of Progress Leading to Victory and its relationship with soil and water conservation can further promote the high-quality control of soil and water loss in Changting County on the achieved control effect of soil and water loss. [Methods] Based on the need of the coupling relationship between the eco-economic system in which human needs are in the stage of transforming from the later stage of life development to the stage of physical and mental health needs, it is clear that it is inevitable to put forward the idea of Progress Leading to Victory, and the theory and practice of sustainable development, the integration of eco-economy and economic ecology have laid a theoretical and practical foundation for the emergence of Progress Leading to Victory. Through the mechanism of action of Progress leading to Victory on soil and water conservation, it is revealed that the elements of advance regulating the control process of soil and water loss, the elements of victoryregulating the control effect of soil and water loss. [Results] The mutual promotion of soil and water conservation and Progress Leading to Victory can realize the high-quality development of soil and water conservation and promote the construction of regional ecological civilization. [Conclusion] This research can promote the high-quality development of soil and water conservation at a higher starting point, and promote the control of soil and water loss and the construction of ecological civilization to continuously achieve new results in Changting County.

Water shortage and soil salinization in gully farmland comprising sediment deposited farmland (SF) and excavated farmland (EF) have become a widespread concern in the loess hilly region. A two-year field experiment was conducted to assess the soil water content (SWC) and salt content (SSC) and their effect on the spring maize yield and water use efficiency in SF and EF. Eight treatments comprising flat cropping without mulching (1), ridge planting without mulching (2), ridge planting with plastic mulching (3), and ridge planting with straw mulching (4) were tested in the SF and EF plots, respectively. The results showed that the yield was higher in SF than EF, whereas the water use efficiency was significantly higher in EF because the bottom water flux was 117.4% higher in SF than EF (P < 0.01). A significant positive correlation was found between the average SWC and yield (P < 0.01), thereby indicating that the yield was severely limited by the SWC. Thus, the higher water use efficiency in EF has important implications for alleviating water scarcity during agricultural production in this region. The risk of soil salinization was decreased greatly by treatment 3 where the SSC was decreased in EF and SF were 0.09 g kg–1 and 0.08 g kg–1, respectively. In addition, treatment 3 had the most significant impacts on the yield and water use efficiency. Our study provided appropriate land type and effective tillage measure for the sustainable development in dryland agricultural areas.

BACKGROUND Limited and erratic precipitation with inefficient irrigation scheduling often leads to an unstable crop yield and low water-use efficiency (WUE) in semi-arid and semi-humid regions. A 2-year field experiment was conducted to evaluate the effect of three irrigation strategies (conventional irrigation (CK), full-drip irrigation (FI), based on crop evapotranspiration and precipitation forecast, and deficit drip irrigation (DI) (75% FI)) on photosynthetic characteristics, leaf-to-air temperature difference ( increment T), grain yield, and the WUE of summer maize. RESULTS The results showed that the daily average net photosynthetic rate (Pn) of DI and FI increased by 25.4% and 25.8% at jointing stage in 2018, and 26.3% and 26.5% at grain-filling stage in 2019 compared with CK, respectively. At jointing stage in 2018 and grain-filling stage in 2019, the transpiration rate (Tr) of DI was significantly lower than that of FI (P < 0.05) but there was insignificant difference in Pn value (P > 0.05). The increment T between 12:00-14:00 of DI and FI was significantly lower than that of CK at jointing stage in 2018 and grain-filling stage in 2019 (P < 0.05). The 2-year average grain yields of DI and FI were 11.4 and 11.5 t ha(-1), which increased by 32.4% and 32.8% compared with CK, respectively. The WUE of DI was 2.82 kg m(-3), which was 17.9% and 33.8% higher than that of FI and CK, respectively. CONCLUSION Deficit drip irrigation based on crop evapotranspiration and precipitation forecast improves crop WUE and maintains high grain yields in semi-arid and semi-humid regions. (c) 2021 Society of Chemical Industry.

Soil salinization and water deficits in gully consolidation farmland including excavated farmland (EF) and sediment deposited farmland (SF) have become an increasing concern in the Loess Hilly region, China. However, the responses of different farmland types and tillage‐mulching practices on soil salt content (SSC) and water use efficiency (WUE) have not been widely studied in this region. Thus, we conducted a two‐year field experiment to assess the soil water content (SWC) and SSC and their effect on the spring maize yield and WUE under different tillage‐mulching practices in EF and SF. Eight treatments incorporating flat cropping without mulching (FC), ridge planting without mulching (RP), ridge cropping with straw mulching (SM), and ridge cropping with plastic mulching (PM) were applied to EF and SF plots, respectively. Our results indicated that the yield of spring maize was limited by SWC (p < 0.01). Although EF had a low yield of spring maize compared to SF, it had the highest WUE (p < 0.01), which was mainly due to the lower groundwater consumption. Meanwhile, the average SSC was significantly lower in EF than in SF (p < 0.01). PM had the highest SWC (14.9%) and significantly reduced the accumulation of SSC (−0.09 g kg−1), thereby improving spring maize yield (12,200 kg ha−1) and WUE (1.71 kg m−3) (p < 0.05). These results suggested that EF with PM is optimal for groundwater conservation, decreasing the risk of soil salinization, and improving WUE and maize yield in dryland agricultural areas.

Soil physical properties (SPP) are considered to be important indices that reflect soil structure, hydrological conditions and soil quality. It is of substantial interest to study the spatial distribution of SPP owing to the high spatial variability caused by land consolidation under various land restoration modes in excavated farmland in the loess hilly area of China. In our study, three land restoration modes were selected including natural restoration land (NR), alfalfa land (AL) and maize land (ML). Soil texture composition, including the contents of clay, silt and sand, field capacity (FC), saturated conductivity (Ks) and bulk density (BD) were determined using a multifractal analysis. SPP were found to possess variable characteristics, although land consolidation destroyed the soil structure and decreased the spatial autocorrelation. Furthermore, SPP varied with land restoration and could be illustrated by the multifractal parameters of D1, ΔD, Δa and Δf in different modes of land restoration. Owing to multiple compaction from large machinery in the surface soil, soil particles were fine-grained and increased the spatial variability in soil texture composition under all the land restoration modes. Plough numbers and vegetative root characteristics had the most significant impacts on the improvement in SPP, which resulted in the best spatial distribution characteristics of SPP found in ML compared with those in AL and NR. In addition, compared with ML, Δa values of NR and AL were 4.9- and 3.0-fold that of FC, respectively, and Δa values of NR and AL were 2.3- and 1.5-fold higher than those of Ks, respectively. These results indicate that SPP can be rapidly improved by increasing plough numbers and planting vegetation types after land consolidation. Thus, we conclude that ML is an optimal land restoration mode that results in favorable conditions to rapidly improve SPP.

Net primary productivity (NPP) of grassland is a key link and important part of the ecosystem's carbon cycle. We estimated the changes of NPP in grasslands of the Loess Plateau with unchanged land use types during 2000-2015 and analyzed its responses to the variation of main climate factors (annual precipitation, annual heavy rainfall, annual effective rainfall days, annual average temperature, annual maximum temperature, annual minimum temperature) using piecewise linear regression and Pearson correlation analysis. The driving factors of grassland NPP were further analyzed by pixel-by-pixel with boosted regression tree analysis. The results showed that annual mean grassland NPP in the Loess Plateau showed an increasing trend during the study period, with 51.3% of the total grassland area showing a significant increasing trend. The average increase rate of annual mean NPP declined from 15.23 g C·m-2·a-1 in 2000-2004 to 3.58 g C·m-2·a-1 in 2004-2015. There was a significant positive correlation between grassland NPP and precipitation, but negative correlation with temperature factors. Annual precipitation was the dominant climatic factor affecting NPP of the whole study area with the highest relative importance. Annual maximum temperature was the dominant driving force of grassland NPP of central Loess Plateau, while annual minimum temperature mainly affected the growth of grassland in high-altitude area of the western Loess Plateau.