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Abstract Cropland on steep slopes is crucial for smallholders to maintain food security and their livelihoods, but the social‐ecological predicament on global steeply sloped cropland is largely overlooked and remains unclear. Here we find that global steeply sloped cropland supports ∼168 million people's livelihoods. Large disparities in population pressure on steeply sloped cropland exist across the development spectrum, among which lower‐middle‐income countries have the highest population density (∼222 per km2) and low‐income countries have the largest population growth rate (∼62.1% from 2000 to 2020). Moreover, inhabitants of steeply sloped cropland, especially those belonging to low‐income countries, are marginalized from public services and face more environmental pressure represented by severe soil erosion and low cropland productivity. Our findings imply that residents of steeply sloped cropland deserve more attention to eradicate global poverty and inequality.

Non-point source nitrogen loss poses a risk to sustainable aquatic ecosystems. However, non-point sources, as well as impaired river segments with high nitrogen concentrations, are difficult to monitor and regulate because of their diffusive nature, budget constraints, and resource deficiencies. For the purpose of catchment management, the Bayesian maximum entropy approach and spatial regression models have been used to explore the spatiotemporal patterns of non-point source nitrogen loss. In this study, a total of 18 sampling sites were selected along the river network in the Hujiashan Catchment. Over the time period of 2008–2012, water samples were collected 116 times at each site and analyzed for non-point source nitrogen loss. The morphometric variables and soil drainage of different land cover types were studied and considered potential factors affecting nitrogen loss. The results revealed that, compared with the approach using the Euclidean distance, the Bayesian maximum entropy approach using the river distance led to an appreciable 10.1% reduction in the estimation error, and more than 53.3% and 44.7% of the river network in the dry and wet seasons, respectively, had a probability of non-point source nitrogen impairment. The proportion of the impaired river segments exhibited an overall decreasing trend in the study catchment from 2008 to 2012, and the reduction in the wet seasons was greater than that in the dry seasons. High nitrogen concentrations were primarily found in the downstream reaches and river segments close to the residential lands. Croplands and residential lands were the dominant factors affecting non-point source nitrogen loss, and explained up to 70.7% of total nitrogen in the dry seasons and 54.7% in the wet seasons. A thorough understanding of the location of impaired river segments and the dominant factors affecting total nitrogen concentration would have considerable importance for catchment management.

A large amount of soil loss is caused by a small number of extreme events that are mainly responsible for the time compression of geomorphic processes. The aim of this study was to analyze suspended sediment transport during extreme erosion events in a mountainous watershed. Field measurements were conducted in Wangjiaqiao, a small agricultural watershed (16.7 km(2)) in the Three Gorges Area (TGA) of China. Continuous records were used to analyze suspended sediment transport regimes and assess the sediment loads of 205 rainfall-runoff events during a period of 16 hydrological years (1989-2004). Extreme events were defined as the largest events, ranked in order of their absolute magnitude (representing the 95(th) percentile). Ten extreme erosion events from 205 erosion events, representing 83.8% of the total suspended sediment load, were selected for study. The results of canonical discriminant analysis indicated that extreme erosion events are characterized by high maximum flood-suspended sediment concentrations, high runoff coefficients, and high flood peak discharge, which could possibly be explained by the transport of deposited sediment within the stream bed during previous events or bank collapses.

Abstract: This research integrated the Revised Universal Soil Loss Equation (RUSLE) and the soil statistical analysis with RS and GIS techniques to quantify soil and nutrients loss risk. The Letianxi [...]

Jiangsu Province, located between northern China and southern China, is a typically mixed area of conventional and three-line hybrid rice without Oryza rufipogon Griff. and Oryza nivara S. D. Sharma & Shastry. In the recent decade, occurrence of weedy rice rapidly increased year by year since it was found and reported from 2000. The recent cloning of the CMS-WA gene (wild abortive cytoplasmic male sterility) makes it possible to design a marker specific for the gene for testing large quantities of weedy rice samples in a single assay by polymerase chain reaction (PCR). Through performing a BLAST search in the National Center for Biotechnology Information (NCBI) database using the sequence of the CMS-WA gene cloned from ZS97A as a reference, the major difference between threeline hybrid rice and conventional rice cultivars was found in the 287 to 439 bp region of the CMS-WA gene. A specific marker, WA7, was designed and evaluated for this region of the CMS-WA gene. This marker, in combination with RED4, a specific marker for the Rc red pericarp gene, was used to distinguish weedy rice, threeline hybrid rice, and conventional rice in a single PCR assay. A total of 1232 accessions of weedy rice collected from 63 locations in Jiangsu Province, China, were evaluated using the red pericarp and CMS-WA DNA markers. Only four accessions from three locations were found positive for the CMS-WA gene, accounting for just 4.76 and 0.32% of all locations and accessions, respectively. These results indicate that the three-line hybrid is likely a source but not the major source of weedy rice in Jiangsu Province. [ABSTRACT FROM AUTHOR]

It is crucial for effective water resource management in a watershed that the relationship between land use changes and baseflow. This study quantifies the influence of land use changes on the baseflow dynamics using a hydrological model and partial least-squares (PLS) regression in the Upper Du Watershed (8961 km2), China. Our study suggests that forest can be a major factor with a negative impact on the baseflow. Additionally, farmland and urban land have second-order negative effects on the baseflow dynamics. Baseflow increases when forest is replaced by farmland because the evapotranspiration (ET), associated with baseflow recession, is weaker and shorter in duration in the farmland than in the forest. The conversion of forest to urban land increases baseflow owing to the presence of non-contributing impervious surfaces in urban areas, which prevents the urban land from intercepting the baseflow discharge. These results indicate that the baseflow dynamics are closely associated with varying land use types within a watershed. Thus, this study is intended to provide a deeper understanding of the baseflow processes and useful quantitative information on land use factors in watersheds, enabling more informed decision-making in forest and watershed management. [ABSTRACT FROM AUTHOR]

Seed germination is a central component of plant life history. To investigate the proposed role of seed size on germination strategy in plant communities, a semifield experiment was conducted in alpine meadow of the Qinghai-Tibetan Plateau, China. Interspecies relationships of seed mass and seed germination characteristics were studied under semifield conditions with different light availability. Light availability and seed mass had significant effects on final germination percentage and time to germination for studied species. There was a significant negative correlation between the strength of light required for germination and seed mass. Fifteen study species (e.g. Ligularia przewalskii, Artemisia sieversiana Willd, Tripolium vulgare Ness. and Saussurea morifolia Chen) exhibited a synchronous germination strategy. Seeds from large-seeded species, such as Dracocephalum ruyschiana, Laniophlomis rotate (Benth.) and Salvia przewalskii Maxim., were less likely to require light for germination than those of small-seeded species, such as A. sieversiana Willd, Senecio diversipinnus Ling and Saussurea mongolica (Franch.). We propose that germination strategies of small-seeded species are well suited to unpredictable environmental variation in this alpine grassland community. In this study we examined interspecies relationships for seed mass and seed germination characteristics in 20 alpine forbs under semifield conditions with different light availability. There was a significant negative correlation between the strength of light required for germination and seed mass. Seeds from large-seeded species were less likely to require light for germination than those of small-seeded species. Germination strategies of small-seeded species are well suited to unpredictable environmental variation in this alpine grassland community. [ABSTRACT FROM AUTHOR]

Purpose: It has been suggested that above and belowground interactions produce important feedbacks in natural ecosystems. It is necessary to study the relationships between aboveground plant functional group traits and belowground biomass and soil chemical properties in natural grasslands. Materials and methods: In a field study, four natural alpine meadows dominated by different plant functional groups were selected. We assigned the plant species to one of two functional groups: the grasses functional group (GFG) or the forbs functional group (FFG). The aboveground GFG and FFG biomass and total belowground biomass were measured. At the same time, for each sampling quadrat, soil pH, soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), and available phosphorus (AP) were determined. Results and discussion: GFG-dominated meadows had significantly higher total belowground biomass, SOM, TN, TP, AN, and AP than FFG-dominated meadows. Correlation analyses showed that total belowground biomass (to a depth of 30 cm) and soil nutrient contents were significantly and positively correlated with the GFG biomass proportion, but negatively correlated with the FFG biomass proportion. Conclusions: There were significant positive correlations among above and belowground biomass and the soil chemical properties studied. The GFG proportion may thus be an indicator of soil chemical properties in the studied meadow types. This implies that natural increases in, or introduction of more, GFG species in FFG-dominated meadows may improve soil nutrient conditions. This study provides the basis of understanding for future studies on plant-soil interactions and feedbacks in grassland ecosystems. [ABSTRACT FROM AUTHOR]

Land use and land cover change is gaining recognition as a key driver of environmental change. Rapid change of land use has occurred in the red soil hilly region of southeast China in the past three decades due to rural land reform, population pressure and rapid economic growth. In this paper, land use change and its impacts on environmental quality of Xianning County were investigated using technologies of remote sensing (RS), geographic information systems (GIS), and spatial principal components analysis (SPCA). It was indicated that the area of paddy field and upland decline rapidly while the area of woodland, horticulture farm and residential land increased sharply between 1978 and 2002. The driving forces probably were land use policy of the State government, structural adjustment of agricultural sectors and implementation of environmental conservation measures. Based on the assessment of environmental implications of land use practices, the environmental quality of some land use types (i.e. Woodland, sparse woodland, and paddy field) tended to improve, while horticulture farms, water body, and residential land showed a deterioration trend of environmental quality during 1978–2002. Perhaps the most significant finding of this study is that environment appears a negative tendency in the study area from 1991 to 2002, because little attention has been paid to the status and management of agricultural lands, which account for a substantial proportion of total land area. Therefore, for further improving environment in red soil hilly region in China, urgent action is required to improve the advisory services support to farmers on new tillage practices, soil and water conservation practices, raising the efficiency of fertilizer and manure use. [ABSTRACT FROM AUTHOR]