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Soil relative water concentration is one of the most important influences on crop growth and the diversity and composition of microorganisms in the crop rhizosphere. This study investigates the influences of soil relative water concentration on CO2 flux and rhizospheric microbial diversity in maize crops. Plots of maize were given different irrigation treatments; namely, control (natural precipitation) and low, medium, and high sprinkling irrigation quotas (achieving soil relative water contents of 55.0–65.0%, 65.0–75.0%, and 75.0–85.0%, respectively). Compared with controls, CO2 uptake increased with soil relative water concentration, mainly during the tasseling, pustulation, and mature growth stages. In addition, the richness and evenness of the bacterial and archaeal communities in the soil matrix increased with soil relative water concentration. However, the diversity of fungal communities had an inverse trend compared with that of bacterial and archaeal communities, which resulted from dry-wet cycling promoted the diversity of fungal diversity. The relative abundances of most dominant bacteria and fungi increased with soil relative water content and maize growth. These results demonstrate that modest water supplementation, especially during maize's tasseling, postulation, and mature stages, enhances its growth and increases the relative abundances of bacterial and fungal communities in the soil.

With remarkable impacts of climate change and anthropogenic activities, the Horqin Sandy Land presents southward invading trend, which threatens the city development in southern water shortage cities. Therefore, to prevent the sandy land from southward invading and to protect the city water security, it is of great importance to reasonably explore the groundwater in southern Horqin Sandy Land. Based on the data of groundwater level, precipitation, temperature, population, etc. from 1997 to 2016 in Kangping County, this paper focused on evolution characteristics analysis and genesis analysis of the groundwater level in Kangping County. The results show a significant decrease of groundwater level from 2014 to 2016, with a substantial increase of population in 2015. The PCA (Principal Component Analysis) ordination showed that the groundwater level in the south, middle and north of Kangping county was positively related to each other. The groundwater level had a significantly negative correlation with population and temperature, while a remarkably positive correlation with precipitation. It is calculated that the annual extraction of groundwater by thermal power generation in Kangping County releases about 18,740 t of CO2. As population increases, the groundwater level will continue to decrease, the carbon emissions will increase as well. It is suggested to reduce thermal power generation pattern by developing the abundant local wind and solar energy resources, thus achieving the low-carbon development in water shortage cities.

As one of the ecological measures to control soil erosion and land degradation, the Returning Farmland to Forest Program (RFFP) has been implemented about 30 years in China. To date, the effectiveness of the RFFP is debated. Most studies have focused on the changes in landscape patterns at different scales, exploring the forest cover changes. However, few studies revealed the ecological effects especially the ecological stability, even less in alpine areas. Twelve sampling sites in the Huangshui River Basin were selected to test whether the RFFP improved the quality and stability of rhizosphere ecosystems. The sampling sites located in the RFFP zone, natural ecosystems (perennial grassland, perennial forest), and anthropogenic ecosystems (farmland, human activity zone), respectively. The results showed that the RFFP has improved the physicochemical properties of soil and plant, has increased the relevant abundance of nitrogen fixing bacteria and phosphate-solubilizing bacteria, and has high network stability than anthropogenic ecosystems, while still has certain distance with natural ecosystems. The RFFP definitely has positive impacts on improving the stability and diversity of the ecosystems in alpine areas. This study provides references for estimating the implementation effects of the RFFP from the ecological perspective, which could further guide the next round of the RFFP policy.

Over the past few decades, the Nu River watershed (NRW), which originates in the Qinghai–Tibet Plateau and covers an area of 113,414 km2, has experienced increased streamflow, temperatures, and precipitation along with cryospheric degradation. To determine the mechanism of increase of the observed streamflow composition, a distributed hydrological model (WEP-C) was developed to investigate the streamflow composition and its changes in the NRW from 1979 to 2019. During this period, glaciers, snowmelt, permafrost, groundwater, and precipitation accounted for 3.2%, 13.4%, 0.8%, 10.4%, and 72.2% of the NRW streamflow, respectively. The streamflow of the watershed increased at a rate of 1.36 mm/year. Among the contribution rates to the increase of streamflow, glaciers increased at a rate of 0.28 mm/year and snowmelt decreased at a rate of -0.53 mm/year. Additionally, permafrost meltwater, groundwater, and precipitation increased at a rate of 0.03 mm/year, 0.60 mm/year, and 0.98 mm/year, respectively. Thus, the present study provides an understanding of the composition and change of streamflow in the Qinghai–Tibet Plateau and similar watersheds, wherein the cryosphere plays an important part in the hydrological cycle.

Study region The Nagqu River Watershed in the Qinghai–Tibet Plateau. Study focus A computational unit is the basic spatial unit employed in distributed hydrological models (DHMs), which combines the spatiotemporal distributions of meteorological variables and physical parameters denoted within a region to reveal the characteristics affecting the water cycle of watersheds. However, the current methods developed for spatially divided regions into computational units fail to consider the physical meaning and impact of climate change in montane altitudinal zones (MAZs), which significantly affects alpine watersheds. This study proposes a method for assigning the computational units of alpine DHMs according to one-period MAZ that explicitly account for physical meaning and climate change. New hydrological insights for the region The benefits of the proposed altitudinal discretization method are verified by applying it to construct a DHM based on the water and energy transfer processes in large river basins (WEP-L) models. The results obtained using the WEP-L, SWAT model and the new regional division method (denoted as the WEP-C model) that applies the proposed altitudinal discretization method are compared. The results demonstrate that the simulation accuracy of the daily and monthly streamflows and daily soil moisture from the alpine watershed is improved by the use of the proposed altitudinal discretization method, which provide guidance for further DHM development and can be applied to other hydrological models.

Phosphorus (P) is well known as a vital nutrient required for plant growth and a critical factor often causing eutrophication in water bodies. However, few studies have focused on the effects of drought-flood abrupt alternation (DFAA), a new type of extreme climate event, on the transformation of P in farmland systems. In this study, we, therefore, focused on DFAA effects on available P (AP) in topsoil, soluble P (SP) and total P (TP) in surface runoff, as well as plant P contents and P uptake in summer maize farmland systems. Field control experiments (sheltered under a ventilated shed with an artificial rainfall device) were conducted to simulate two levels of DFAA (i.e., light drought-light flood and moderate drought-light flood) during parts of two summer maize growing seasons (i.e., seeding-jointing stage and tasseling-grain filling stage). Results showed that DFAA increased AP concentration in topsoil, which was probably induced by the accumulation of the phyla Proteobacteria and Actinobacteria under moderate drought and by an increase in phosphate-solubilizing bacteria (PSB), especially the genera Bacillus and Bradyrhizobium. In addition, broken soil aggregates and increasing soil porosity caused by DFAA could also cause an increase of AP in topsoil. Soluble P and TP in surface runoff showed a decreasing trend with moderate drought in DFAA. The higher AP increased the root P uptake, while P in stems and leaves could be transported to fruits under DFAA with moderate drought. The results could provide some references for the study of the effects and adaptation-strategies related to extreme climate events and their effects on P in farmland systems.

Understanding the response of runoff composition in the Qinghai-Tibet Plateau (QTP) is essential for the ecology and environment. However, precise measurements of runoff composition in the QTP, especially in remote areas with limited climatic records, are a challenge. In rivers and lakes, some plankton is highly sensitive to changes in runoff composition. Here, we demonstrated how plankton indicators could be used as an indicator of runoff composition in the QTP. The stable isotopes of runoff, precipitation, groundwater and snowmelt in 9 sampling sites were studies of the Nagqu River in the QTP. The multi-source mass balance model (IsoSource model) was used to calculate the range of runoff composition at each sampling site. We found that the change of plankton biodiversity was associated to the runoff composition, and groundwater ratio was negatively correlated with biodiversity, while precipitation ratio was positively correlated with biodiversity, but not with snowmelt. Therefore, plankton diversity is expected to be a simple indicator of runoff composition, which can be easily quantified in remote plateau areas.

Region: The Nagqu River Basin in the Qinghai-Tibet Plateau. Focus: Climate change and human activities have altered the type of land use in the Qinghai-Tibet Plateau (QTP), which has affected the variation laws of water resources. We calibrated and verified the Water and Energy Transfer Process for a Large basin model (WEP-L), and calculated the impacts of climate change and human activities on runoff change and separated the impact of land use. New hydrological insights: The Archimedean Copula function was used to diagnose the variance between precipitation and runoff. The contribution of climate change to the runoff in the Dasa and Jiayuqiao subbasin was 81.7% and 71.5%, of which the contribution of land use was 39.3% and 32.6%, respectively. Human activities contributing to the runoff in the Dasa and Jiayuqiao subbasins were 18.3% and 28.5%, of which the contribution of land use is 7.9% and 2.8%, respectively. Climate change has led to the melting of glaciers, permanent permafrost and the shift of the vertical distribution of vegetation, which is the main reason for the runoff variation in the NRB. This research provides a scientific basis for the rational protection and utilization of water resources, as well as soil and water conservation work. Keywords: Precipitation–runoff, Mutation diagnosis, Climate change, Human activities, Land use, Hetao area

River network coding is important for hydrological model on the aspects of water cycles simulation, water resources evaluation and extreme hydrological events forecast. However, the existing river network coding methods had several disadvantages, such as, the river network coding structure is too complex to understand, the river network topology is difficult to identify, the river network coding capacity is limited. To overcome the above-mentioned shortcomings, this paper proposed a new topological and hierarchical river coding method based on the river network created by the DEM (Digital Elevation Method) data and ArcGIS software. This method systematically defines the river levels based on the hydrology structure from outlet to source. The river directly flows into the watershed outlet is river L1, the branch of river L1 with a certain catchment area is river L2, the branch of L2 with a certain catchment area is river L3, and so on. Secondly, we proposed a flexible coding scheme that encode the river segments with pure digital numbers hierarchically. Taking the two-digits scheme for example, the L1 river segments are coded with a sequence number, such as [01], [02], [03], […]. The L2 river segments inherit the river code from the L1 stem river segment, add a serial of self-order numbers (01, 02, 03, ……) from the junction to the river source, and become [0101], [0102], [0103], […]. The process of coding the river segments at subsequent level is similar. Finally, this new coding method was programmed in Matlab software, and successfully examined in the Amazon River basin, the world's largest watershed, as a case study. The results show that the new method is competent for easily controlling the river level and river segment density, flexibly adjusting the code digital numbers to fit different basins with abundant or little rivers, easily plotting the topological relationship, automatically encoding by computer program and easily understood. In a word, this study is a useful attempt to create new river network coding method, and it also has positive significance to promote the hydrological simulation research.

Under the background of climate change, droughts have occurred widely and frequently in North China in recent years. Using tree-ring to study droughts has advantages such as accurate dating, strong continuity and high resolution. This paper uses the Chinese pine ring-width of Xiaowutai Mountain, China, to analyze the correlations between the ring-width and climatic factors. The results show that the standard and residual chronologies of Chinese pine have significant correlations between spring precipitation, 0 cm ground temperature in May, average relative humidity of April and May, hours of sunshine and percentage of sunshine in May, and Z index of spring. The Chinese pine ring-width is fundamentally affected by the precipitation of the study area. 0 cm ground temperature, average relative humidity and hours of sunshine all affect the ring-width by affecting the soil water content indirectly. The years when the Chinese pine ring-width index of Xiaowutai Mountain falls into 0–0.80 could indicate spring drought years. This paper has demonstrated the feasibility of applying tree-rings to study the spatial and temporal development of drought in the study area.