Arid Regions Of China Research Articles

Suitable Scale of an Oasis in Different Scenarios in an Arid Region of China: A Case Study of the Ejina Oasis

The main objective of this work is to calculate the suitable scale of the Ejina Oasis in different scenarios (high-, normal-, and low-flow years), assess the stability of the Ejina Oasis, and, finally, accurately determine if an artificial oasis area and total oasis area need to be reduced or increased. Using the water balance method, we calculated the suitable scale of the artificial Ejina Oasis as 767.80, 624.00, and 451.33 km2 in high-, normal-, and low-flow years, respectively. By utilizing the water-heat balance method combined with an assessment of the present stability of the Ejina Oasis, the results showed that in high-flow years, the suitable scale of the Ejina Oasis is 1174–1762 km2, and the stability index of the current oasis is 0.55. In normal-flow years, the suitable scale of the Ejina Oasis is found to be 915–1373 km2, and the stability index of the current oasis is 0.43. In low-flow years, the suitable scale of the Ejina Oasis is 590–885 km2, and the stability index of the current oasis decreases to 0.27. In order to further improve the stability of oases, it remains necessary to control the scale of oases to cope with water resource shortages that result from water resource instability under climate change. The present study’s findings will enable optimal water-use planning decisions that take social, economic, and ecological issues into account, and provide the foundation for optimal decision-making for regional administrative departments to effectively coordinate regional economic development, farmland protection, environmental protection, and water resource protection.

Physiological evaluation of nitrogen use efficiency of different apple cultivars under various nitrogen and water supply conditions

Nitrogen (N) deficiency is a common problem for apple (Malus×domestica) production in arid regions of China. However, N utilization efficiency (NUE) of different apple cultivars grown under low N conditions in arid regions has not been evaluated. In this study, NUE was assessed for one-year-old seedlings of six apple cultivars, Golden Delicious, Qinguan, Jonagold, Honeycrisp, Fuji and Pink Lady, grafted onto Malus hupehensis Rehd. rootstocks. Four treatments were used, including control water with control N (CWCN), limited water with control N (LWCN), control water with low N (CWLN) and limited water with low N (LWLN). Our results showed that growth indices such as biomass, plant height and stem diameter, and photosynthetic rate of all cultivars decreased in the order CWCN>CWLN>LWCN>LWLN. When subjected to LWLN treatment, Qinguan showed better growth and photosynthetic characters than other tested cultivars. Additionally, Qinguan and Pink Lady had higher NUE, while Honeycrisp and Jonagold had lower NUE, based on the determination of biomass, photosynthetic parameters, chlorophyll content, the maximal photochemical efficiency of PSII (Fv/Fm), 15N and N contents.

Do Ecosystem Service Value Increase and Environmental Quality Improve due to Large–Scale Ecological Water Conveyance in an Arid Region of China?

With the rapid development of the economy and the intensification of human activities, ecological systems have been degraded, especially in arid areas. The lower reaches of the Tarim River represent a typical arid area in China. Since 2000, the Chinese government has been heavily investing in the protection and restoration of the natural ecological environment of the lower reaches of the Tarim River. In this study, we aimed to resolve two key scientific issues: (1) reveal the changing characteristics of land-use in the region and identify the changes in ecosystem service value caused by these land-use changes and (2) evaluate whether the environmental quality has improved or worsened. The objective of this study is to verify whether the ecological water conveyance project promotes an increase in the ecosystem service value, with an improvement in the ecological environment, to thereby provide references for the evaluated effects of ecological water conveyance for the management of water resources. In this way, economic development can support environmental protection. Thus, the economy can be sustainably developed. Hence, based on the remote sensing data of land-use in 1990, 2000, 2010, and 2016, with the value coefficients proposed by Constanza in 1997 and changing characteristics in the land-use, the ecological service value, and environmental conditions from 1990 to 2016 were analysed. According to our results, from 1990 to 2016, the ecosystem service value has increased substantially, indicating that the benefits of ecological water conveyance were significant. The environmental condition index increased by 21.14%, showing that the ecological environment has improved. However, the environmental quality remained low. In the future, we should formulate plans for reasonable land-use that control the replacement of woodlands and grasslands with farmlands and construction. The results of this study provide a scientific basis and practical guide for restoring inland river ecosystems in arid regions.

Stoichiometry of leaf carbon, nitrogen, and phosphorus along a geographic, climatic, and soil gradients in temperate desert of Hexi Corridor, northwest China

Abstract Aims Understanding the regional pattern of leaf stoichiometry and its contributing variables are of importance for predicting plant responses to global change and modelling the productivity and nutrient fluxes of ecosystems. In this study, we investigated leaf stoichiometry of plants that sampled from Hexi Corridor, a typical arid region in China, and tried to explore the contribution variables on leaf stoichiometry along the geographic, climatic, and soil gradients. Methods In August 2012, 70 sites in Hexi Corridor were investigated. Plant leaves and soils from five equivalent plots within each site were sampled. C, N, and P contents of leaf and soil were measured. Important findings Compared with leaf N and P contents in regional and global scales, leaf N content in Hexi Corridor was close to them with the value of 20.19 mg g-1, while leaf P content was lower than them with the value of 1.34 mg g-1. Overall, leaf N:P value in Hexi Corridor was 15.70. Individually, leaf N:P values of shrubs and herbs were 16.81 and 14.80, respectively. Scaling exponents for leaf N vs. P of overall and shrubs in Hexi Corridor were 1.29, higher than the scaling exponent of herbs (1.08). Leaf stoichiometry of shrubs and herbs did not show significant latitudinal and longitudinal patterns, meanwhile, it has no significant correlation with mean annual precipitation (MAP), mean annual temperature (MAT), and soil elements. However, only leaf stoichiometry of herbs has significant correlation with altitude and aridity degree. These results indicate that plants in Hexi Corridor are possibly co-limited by N and P, while shrubs are mainly limited by soil P and herbs are limited by soil N. Scaling relationship reveals that leaf N vs. P of herbs is isometric. With increasing altitude, the quadratic regression for leaf C and N contents and the linear regression for leaf P content of herbs reflect the difference responses of the three elements on the variation of MAT along the altitude and it could be explained by plant physiology hypothesis and biogeochemical hypotheses. With decreasing aridity, leaf N and N:P of herbs increased significantly, inferring that herbs growth would be limited by P increasingly and strengthening the increasing nitrogen availability with increasing precipitation. In conclusion, different altitude and aridity patterns for leaf stoichiometry of herbs and shrubs reveal the plastic survive strategies of different xerophytes in Hexi Corridor. Moreover, leaf stoichiometry of herbs in Hexi Corridor could be as indicator of the changing environment that caused by aridity.

Interactions of high-rate nitrate reduction and heavy metal mitigation in iron-carbon-based constructed wetlands for purifying contaminated groundwater

Groundwater, as the most important drinking water source in arid regions of China, has been polluted seriously by accumulated nitrate and heavy metals. An economic alternative with capacity of simultaneous mitigation of nitrate and heavy metals is urgently needed. This study explored the incorporation of iron scraps and biochar into constructed wetlands (CWs) for enhancing purification performance and investigated interactions of effective nitrate reduction and heavy metals mitigation. The results showed that nitrate reduction performance could reach 87% in iron and carbon-based (Fe–C) CWs through Fe–C micro-electrolysis process, with lower nitrous oxide (N2O) emission (4.6–11.75 μg m−2 h−1) due to the complete denitrification process. Moreover, efficient heavy metals mitigation of 75–97% total chromium (Cr) and total lead (Pb) was obtained from Fe–C systems. However, the occurrence of heavy metals (Cr and Pb) in the influent posed an adverse impact on nitrate removal with the reduction rate of 19–43%. Biochemical characteristics of wetland plants indicated that the plants also suffered from the stress which induced from heavy metals. Overall, although the addition of iron and biochar in CWs enhanced nitrate and heavy metals removal in low carbon groundwater, further investigation is still needed to reveal the complex relationships between the removal of nitrate and heavy metals in CWs.

Insights into non-symbiotic plant growth promotion bacteria associated with nodules of Sphaerophysa salsula growing in northwestern China.

In addition to rhizobia, other non-symbiotic endophytic bacteria also have been simultaneously isolated from the same root nodules. The existence of non-symbiotic endophytic bacteria in leguminous root nodules is a universal phenomenon. The vast majority of studies have detected endophytic bacteria in other plant tissues. In contrast, little systemic observation has been made on the non-symbiotic endophytic bacteria within leguminous root nodules. The present investigation was carried out to isolate plant growth-promoting endophytic non-symbiotic bacteria from indigenous leguminous Sphaerophysa salsula and their influence on plant growth. A total of 65 endophytic root nodule-associated bacteria were isolated from indigenous legume S. salsula growing in the northwestern arid regions of China. When combining our previous work with the current study, sequence analysis of the nifH gene revealed that the strain belonging to non-nodulating Bacillus pumilus Qtx-10 had genes similar to those of Rhizobium leguminosarum Qtx-10-1. The results indicated that horizontal gene transfer could have occurred between rhizobia and non-symbiotic endophyties. Under pot culture conditions, out of the 20 representative endophytic isolates, 15 with plant growth-promoting traits, such as IAA production, ACC deaminase, phosphate solubilization, chitinase, siderophore, and fungal inhibition activity showed plant growth-promoting activity with respect to various plant parameters such as chlorophyll content, fresh weight of plant, shoot length, nodule number per plant and average nodule weight per plant when co-inoculated with rhizobial bioinoculant Mesorhizobium sp. Zw-19 under N-free culture conditions. Among them, Bacillus pumilus Qtx-10 and Streptomyces bottropensis Gt-10 were excellent plant growth-promoting bacteria, which enhanced the seeding fresh weight by 87.5% and the shoot length by 89.4%, respectively. The number of nodules grew more than 31.89% under field conditions. Our findings indicate the frequent presence of these non-symbiotic endophytic bacteria within root nodules, and that they help to improve nodulation and nitrogen fixation in legume plants through synergistic interactions with rhizobia.

Carbon fluxes across alpine, oasis, and desert ecosystems in northwestern China: The importance of water availability

Dryland regions cover >40% of the Earth's land surface, making these ecosystems the largest biome in the world. Ecosystems in these areas play an important role in determining the interannual variability of the global terrestrial carbon sink. Examining carbon fluxes of various types of dryland ecosystems and their responses to climatic variability is essential for improving projections of the carbon cycle in these regions. In this study, we made use of observations from a regional flux tower observation network in a typical arid endorheic basin, the Heihe river basin (HRB). As a representative area of both the arid region of China and the entire region of central Asia, the HRB includes the main ecosystems in arid regions. We compared the spatial variations of carbon fluxes of five terrestrial ecosystems (i.e., grassland, cropland, desert, wetland, and forest ecosystems) and explored the responses of ecosystem carbon fluxes to climatic factors across different ecosystems. We found that our region exhibits a carbon sink ranging from 85.9 to 508.7 gC/m2/yr for different ecosystems, and the water availability is critical to the spatial variability of carbon fluxes in arid regions. Carbon fluxes across all sites exhibited weak correlations with temperature and precipitation. Marked differences in precipitation effects were observed between the sites within oases and those outside of oases. Irrigation and groundwater recharge were of great importance to the variations in carbon fluxes for the sites within oases. Evapotranspiration (ET) exhibited strong relationships with carbon fluxes, indicating that ET was a better metric of soil water availability than was precipitation in driving the spatial variability of carbon fluxes in arid regions. This study has implications for better understanding the carbon budget of terrestrial ecosystems and informing ecological management in dryland regions.

Influence of soil moisture and plant roots on the soil infiltration capacity at different stages in arid grasslands of China

The accurate measurement of soil infiltration rates is a challenging task in hydrological studies, as they are governed by complex interactions between the plant and soil components. To explore the effects of plant roots and soil moisture (SM) on infiltration process, an automatic measurement system based on a point source device was used to determine infiltration rates at different cultivated grasslands (leguminous, gramineous and mixed) in an arid region of China. The results showed that SM and plant roots significantly affected the infiltration process at different stages in the three grasslands. The soil infiltration rates were negatively correlated to SM, but a positive correlation was observed with the below-ground biomass (BGB). SM was the main factor influencing the infiltration rates in the initial stage of infiltration, whereas both SM and BGB determined the steady-state infiltration rates. The influence of the combined effects of SM and plant roots decreased over infiltration time. The decreased rate of determining coefficient showed that SM was more influent than plant roots. These results may contribute to interpret the observed higher soil infiltration capacity in the leguminous grasslands than in the gramineous and the mixed grasslands, and were conducive to better understand the effects of plant and soil properties on infiltration processes in arid areas.

The effects of runoff on Hydrochemistry in the Qilian Mountains: a case study of Xiying River Basin

With the increase of water consumption and deterioration of water quality in the arid region of China, attention has been raised on issues such as the selection of water sources, water resources protection and water source protection. Based on the surface water samples of Xiying River Basin in the upper reaches of Shiyang River from June 2015 to May 2016, the sampling period is once a month for 1 year. At the same time, combined with the same-day runoff and precipitation data of Nine Ridges Hydrological Station at Xiying River outlet, the influence of runoff process on Hydrochemistry in Xiying River upstream was analyzed using Piper triangle diagram, Gibbs diagram and PCA. The results show that: (1) The surface water is generally weak alkaline, mainly enriched with Ca2+ and $${\text{HCO}}_{3}^{ - }$$ , and the water type is generally Ca–HCO3. (2) The seasonal variation of inorganic ion concentration is very obvious. Ion concentration is high in winter and spring, but low in summer and autumn. (3) Because erosion and transport of rock weathering by runoff process are the main source of runoff ion, the ion concentration in watershed water varies significantly in space, gradually enriched with altitude from high to low, especially Ca2+, $${\text{HCO}}_{3}^{ - }$$ . (4) Ion concentration is positively correlated with precipitation and negatively correlated with runoff in the same period.

Does Climate Change or Human Activity Lead to the Degradation in the Grassland Ecosystem in a Mountain-Basin System in an Arid Region of China?

In mountain-basin systems in the arid region, grasslands are sensitive to the impacts of climate change and human activities. In this study, we aimed to resolve two key scientific issues: (1) distinguish and explain the laws of grassland ecosystem deterioration in a mountain-basin system and identify the key factors related; and (2) evaluate whether damaged grasslands ecosystem have the potential for natural revegetation. Hence, by combining spatial analysis with statistical methods, we studied the trends of the deterioration of the grassland ecosystem and its spatial characteristics in Kulusitai, a mountain-basin system in the arid region of Northwest China. According to our results, vegetation coverage and productivity exhibited significant decreasing trends, while the temperature vegetation drought index (TVDI) exhibited a significant increasing trend. Drainage of groundwater, because of increase in irrigation for the expanded irrigated area around Kulusitai, and climate warming were the critical triggers that leaded to the soil drought. Soil drought and overgrazing, resulting from the impact of human activities, were the main factors responsible for the deterioration of the grassland ecosystems. However, limiting the number of livestock to a reasonable scale and reducing the irrigated area may help to increase the soil moisture, thus promoting the germination of soil seed banks and facilitating the normal growth of grassland vegetation. Furthermore, based on analysis of the phenology of the grassland vegetation, the reasonable period for harvesting and storage is from July 29 to August 5. The results of this study provide a scientific basis and practical guide for restoring mountain-basin grassland systems in arid regions.

Responses of soil organic and inorganic carbon vary at different soil depths after long‐term agricultural cultivation in Northwest China

AbstractWhether the dryland to cropland conversation in arid regions could lead to a decrease in soil carbon (C) and land degradation remains unclear. In this study, we investigated the vertical patterns of soil C change with different lengths of land use history in the arid regions of China and explored the controls and mechanisms of these changes. One native desert grassland and six croplands with similar management but different cultivation times (i.e., 1, 3, 5, 15, 30, and 50 years) and were selected in Xinjiang, Northwest China. We measured both soil organic and inorganic C concentrations and soil properties (e.g., total nitrogen [N], NO3−‐N, NH4+‐N, pH, and electrical conductivity) with a 20‐cm depth interval down to 2 m in all croplands. The results showed that soil organic carbon (SOC) stocks increased with cultivation year for the topsoils (0–120 cm), which could be a result of higher plant C inputs and decreased soil pH in cropland than in the native desert. Soil pH explained the largest variation (45%) of SOC concentration. Soil inorganic C (SIC) stocks decreased with cultivation year in topsoils layers (0–40 cm) but increased in deep soil layers (120–200 cm), resulting in the net increment of SIC to the depth of 200 cm. This pattern might be caused by changes in soil pH in the cropland. Overall, this study demonstrated that, instead of reducing soil C, proper management of the desert ecosystem can enhance soil C sequestration in the arid regions.

Contributions of climate change to the terrestrial carbon stock of the arid region of China: A multi-dataset analysis

Dryland ecosystems have been threatened in recent decades by rapid climate change. However, the effects of climate change and rising CO2 levels on the terrestrial carbon stock of the arid region of China remain unclear. In this study, we used three climate reanalysis datasets to drive an arid ecosystem model (AEM), which we used to assess uncertainties in spatial climate datasets. All simulations suggest that the arid region of China acted as a carbon sink (0.20–0.34 Pg C) from 1980 to 2014. However, we found large uncertainties in the spatial pattern of carbon stocks during this period, especially in northern Xinjiang and western Inner Mongolia. These uncertainties are related to changes in precipitation. To reduce the uncertainty of carbon stock assessment results in the arid region of China, efforts should be implemented to improve the reliability of climate data in northern Xinjiang and western Inner Mongolia. Specifically, China's policy makers should pay close attention to climate change and ecosystem health in southwestern Xinjiang. According to our study, this area experienced significant decreases in precipitation and increases in temperature from 1980 to 2014. The severe ecosystem degradation that occurred will very likely continue into the future. In addition, the Climate Forecast System Reanalysis (CFSR) dataset may overestimate ecosystem carbon sinks as this dataset overestimates the increase in precipitation in the arid region of China. Therefore, it is advisable to be cautious when using the CFSR dataset in ecological studies in northern Eurasian dryland areas.

Does animal manure application improve soil aggregation? Insights from nine long-term fertilization experiments

Manure application is widely recognized as a method of improving soil structure and soil fertility due to additional organic matter and nutrient inputs. However, the salinity of animal manure may have a detrimental effect on soil aggregation. The objective of this study was to determine the effects of long-term animal manure application on soil aggregation, binding agents (soil organic carbon, SOC and glomalin-related soil protein, GRSP), and dispersing agents (e.g., Na+) and their relationships based on nine long-term fertilization experiments (12 to 39 yr) across China. The two red soil experiments (Qiyang, QY and Jinxian, JX) and one paddy soil experiment in Jinxian (JX-P) were conducted in southern China (precipitation above 1200 mm yr−1), whereas the other six experiments were established in semi-humid or arid regions in China with precipitation in the range of 500–900 mm yr−1. Each experiment included three treatments as follows: no fertilization (Control), inorganic fertilizer (NP or NPK), and a combination of inorganic fertilizer and animal manure (NPM or NPKM). Long-term animal manure application not only significantly increased the biological binding agents (i.e., SOC and GRSP) in the nine experiments but also considerably increased the dispersing agents (i.e., exchangeable Na+) (P < 0.05), except for the paddy soil experiment. Consequently, soil aggregate stability increased after animal manure application in three experimental sites in southern China but not in the experimental sites in northern China. Aggregate stability had a positive relationship with SOC and GRSP in the experimental sites in southern China (P < 0.01) but a negative relationship with exchangeable Na+ in the experimental sites in northern China (P < 0.05). The Na+ accumulation in soils was negatively related to mean annual precipitation (P < 0.001). Our study demonstrates that the long-term application of animal manure may degrade soil structure via the Na+ accumulation.

Exploring Drivers of Nitrate Contamination of Drinking Water in an Arid Region of China

Nitrate contamination of groundwater is increasingly becoming a global concern due to its potential risks for human health. Fertilizer overuse is often thought to be the cause and a reduction in fertilizer use considered the most effective way of reducing contamination. The present study, however, presents the case of Zhangye City, Gansu Province, China, in which the nitrate contamination of underground sources of drinking water resulted from a combination of fertilizer overuse and a mismatch between the geological structure of farmland and the crop type cultivated upon it. In addition, a market-induced driver was identified for its role in accelerating the contamination process. This new evidence emphasizes that environmental pollution is often driven by multiple factors of great complexity, demonstrating that causes of environmental problems should be addressed and analyzed with a cross-sectoral perspective. Furthermore, this case revealed that Chinese cabbages cultivated in a drought-stressed region contained very high nitrate concentrations that exceeded Acceptable Daily Intake level, whereas tomatoes and cucumbers from the same region were shown to contain nitrate levels within the safe range. These findings are useful for developing a new policy framework for environmentally sound agricultural planning.

Similarities and improvements of GPM IMERG upon TRMM 3B42 precipitation product under complex topographic and climatic conditions over Hexi region, Northeastern Tibetan Plateau

Building upon the success of TRMM launched in 1997, NASA and JAXA successfully deployed the Global Precipitation Measurement (GPM) mission on February 28, 2014. GPM started to release the new-generation global precipitation products Integrated Multi-satellite Retrievals for GPM (IMERG) since April 2014. Critical data validation over diverse topographic and climatic regions could effectively help users and algorithm developers maximize the accuracy, strengths and weaknesses of the new product. To this end, this study comprehensively evaluated and compared this newly released precipitation product (IMERG V05B) and its predecessor TRMM 3B42V7 based upon the ground-based observations under complex topographic and climatic conditions over the Hexi Region in the northwest arid region of China. The evaluation was conducted at daily, monthly, seasonal and annual scales from April 2014 to September 2017. Results indicated that: (1) compared to ground-based observations, both IMERG and 3B42V7 showed good performance with slightly overestimation (with RB values of 4.58% and 2.27%, respectively) at basin scale. While at the point-to-pixel scale, both products showed overestimation in low-elevation regions and underestimation in high-altitude mountainous areas; (2) on multiple temporal and spatial scales, IMERG correlated better with ground-based observations than 3B42V7, whereas its bias were larger than 3B42V7; (3) both IMERG and 3B42V7 showed better performance in warm seasons (summer and autumn) than in cold seasons (spring and winter); (4) Compared to 3B42V7, IMERG represented both larger hit rate (POD) and false alarm ratio (FAR), but similar correct detection rate (CSI); (5) IMERG showed poorer detection capabilities in light precipitation events (0–2 mm/day), while represented a certain advantage in detecting moderate (5–10 mm/day) and heavy (>25 mm/day) rain events. Most of precipitation estimates over Hexi region are unreliable on daily and monthly time scales. Results suggest that IMERG do not show significant improvement compared to its predecessor 3B42V7, and performed even worse in estimating precipitation amounts. Further data bias-correction is needed before IMERG can be used for climatic and hydrologic research in the Hexi region.

Inter-Regional Coordination to Improve Equality in the Agricultural Virtual Water Trade

Sustainable agriculture in China is threatened by rapid socioeconomic development, urbanization, and climate change. In addition, the distribution of freshwater resources between regions is highly unequal, and water shortages are common in arid regions. The virtual water trade can help to ease water shortages in arid areas by utilizing the comparative advantage of water resources in other areas. However, sometimes the patterns of the virtual water trade do not fit the distribution of water resources and, in these instances, inter-regional coordination would help to improve the level of equality in the virtual water trade. We combined the concept of the Gini coefficient with a multi-objective optimization model to investigate the inter-regional coordination of the virtual water trade in an arid region of China. Agricultural data from different regions of Gansu Province in 2014 were used to explore methods of improving the equality of virtual water flow patterns in the agricultural sector. Three constraints (a crop supply constraint, an irrigation water constraint, and an economic benefit constraint) were set up to investigate the relationship between different challenges and the effects of inter-regional coordination. Our results validated the use of the proposed method in Gansu Province and indicated that it could be applied to other arid regions. Variations in crop supply, irrigation water, and economic benefits were found among the different constraint scenarios, illustrating the trade-offs between water-saving and agricultural objectives. Our results also showed the balance between various factors, including the equality of the virtual water patterns, water-saving measures, and economic benefits. These results support the effectiveness of inter-regional coordination and indicate that the improvement in equality and the adjustment cost should be balanced. Our findings will help to guide the planning of local crop acreages to achieve the best virtual water balance model between regions.

Effects of mulching biodegradable films under drip irrigation on soil hydrothermal conditions and cotton (Gossypium hirsutum L.) yield

Biodegradable mulches are advocated as an alternative to plastic mulches. Here, we carried out an experiment in Xinjiang, an arid region in China, to demonstrate the effects of mulching biodegradable films under drip irrigation on soil conditions and cotton (Gossypium hirsutum L.) yield in 2015 (with less precipitation) and 2016 (with more precipitation). Plastic mulch made from polyethylene (PE) and four types of biodegradable mulch were compared, namely, BD1 to BD4, with different levels of thickness and induction periods. Our results indicated that PE mulch was the most efficient in soil water and heat conservation. Biodegradable mulches performed similarly in warming the soil in both years, which increased topsoil (5–20 cm depth) temperature than no mulching in the cropping season by 0.66 °C and 0.61 °C in 2015 and 2016, respectively. The effect of mulching on increasing soil water storage was stronger in the wet year. The increased soil water storage (0–100 cm depth) by biodegradable mulches than no mulching was 113 mm and 194 mm in 2015 and 2016, respectively. Earlier onset of the phenological events of cotton growth was similar between PE mulch and biodegradable mulches. Mulching shortened the number of days from sowing to cotton maturity by 4 days and 10 days in 2015 and 2016, respectively. Compared with no mulching, biodegradable mulches achieved better performance in enhancing cotton yield and water use efficiency (WUE) in the dry year (916 kg ha−1; 1.85 kg ha−1 mm−1) than in the wet year (568 kg ha−1; 1.22 kg ha−1 mm−1). Although PE mulch resulted in the highest yield, there was no significant difference in WUE between PE mulch and BD1 or BD2. Therefore, some of the commercially available biodegradable mulches can be used as a competitive alternative to plastic mulch to enhance crop yield and control soil pollution.

Spatiotemporal Variation of Snowfall to Precipitation Ratio and Its Implication on Water Resources by a Regional Climate Model over Xinjiang, China

Snow contributes one of the main water sources to runoff in the arid region of China. A clear understanding of the spatiotemporal variation of snowfall is not only required for climate change assessment, but also plays a critical role in water resources management. However, in-situ observations or gridded datasets hardly meet the requirement and cannot provide precise spatiotemporal details on snowfall across the region. This study attempted to apply the Weather Research and Forecasting (WRF) model to clarify the spatiotemporal variation of snowfall and the ratio of snowfall to total precipitation over Xinjiang in China during the 1979–2015 period. The results showed that the snowfall increased in the southern edge of the Tarim Basin, the Ili Valley, and the Altay Mountains, but decreased in the Tianshan Mountains and the Kunlun Mountains. The snowfall/precipitation (S/P) ratio revealed the opposite trends in low-elevation regions and mountains in the study area. The S/P ratio rose in the Tarim Basin and the Junggar Basin, but declined in the Altay Mountains, the Tianshan Mountains, and the west edge of the Junggar Basin. The study area comprises two major rivers in the middle of the Tianshan Mountains. Both the runoff magnitude increase and earlier occurrence of snowmelt recharge in runoff identified for the 1980s were compared with the 2000s level in decreasing S/P ratio regions.

Comparative study of the airborne microbial communities and their functional composition in fine particulate matter (PM2.5) under non-extreme and extreme PM2.5 conditions

Asian dust (AD) events increase environmental pollution and have a detrimental effect on human health. Particulate matter with an aerodynamic diameter <2.5 μm (PM2.5) and containing airborne microorganisms increases during AD events due to the transportation of dust by wind from several arid regions in China. This study analyzed the bacterial and fungal communities associated with average daily PM2.5 concentrations less than (on non-event day: ND) and exceeding (on event day: ED) the air quality standard (36 μg PM2.5 m-3) set by the Korean government. The taxon compositions and functional genes of airborne microorganisms were assessed using shotgun metagenomics sequencing and metagenome rapid annotation using subsystem technology (MG-RAST) analysis. MG-RAST is an open source web application, serving as a platform that automatically analyzes uploaded metagenomes. During ND, 51% of total bacteria sequences consisted of those from Proteobacteria, which were closely related to nitrogen-fixing bacterial species. A high percentage of functional genes consisted of those genes related to nitrogen metabolism, suggesting that the airborne microorganisms are associated with environmental nitrogen cycles. During ED, 57% of total bacteria sequences consisted of those from Bacteroidetes, accompanied by high relative abundance of sequences from pathogenic species of Bacillus and Staphylococcus. Fungal sequences were mainly composed of those from the phyla Ascomycota and Basidiomycota, which include spore-forming species transported frequently by wind. The abundance of Ascomycota sequences was higher in ED (81%) than in ND (22%) samples, and mainly included those from the plant pathogens Phaeosphaeria and Pyrenophora. These findings indicated that microbial composition shifted from ND to ED samples, even at the phylum level. This switch was likely due to the sources of dust particles, with those during ED being primarily from arid regions in Mongolia and industrial regions in China. Additional studies are required to further understand the diversification of airborne microbial communities in downwind areas.

Modeling the distribution of Populus euphratica in the Heihe River Basin, an inland river basin in an arid region of China

Populus euphratica is a dominant tree species in riparian Tugai forests and forms a natural barrier that maintains the stability of local oases in arid inland river basins. Despite being critical information for local environmental protection and recovery, establishing the specific spatial distribution of P. euphratica has rarely been attempted via precise and reliable species distribution models in such areas. In this research, the potential geographic distribution of P. euphratica in the Heihe River Basin was simulated with MaxEnt software based on species occurrence data and 29 environmental variables. The result showed that in the Heihe River Basin, 820 km2 of land primarily distributed along the banks of the lower reaches of the river is a suitable habitat for P. euphratica . We built other MaxEnt models based on different environmental variables and another eight models employing different mathematical algorithms based on the same 29 environmental variables to demonstrate the superiority of this method. MaxEnt based on 29 environmental variables performed the best among these models, as it precisely described the essential characteristics of the distribution of P. euphratica forest land. This study verified that MaxEnt can serve as an effective tool for species distribution in extremely arid regions with sufficient and reliable environmental variables. The results suggest that there may be a larger area of P. euphratica forest distribution in the study area and that ecological conservation and management of P. euphratica should prioritize suitable habitat. This research provides valuable insights for the conservation and management of degraded P. euphratica riparian forests.