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31 May 2024, Volume 16 Issue 5 Previous Issue   
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Research article
Landscape ecological risk assessment and its driving factors in the Weihe River basin, China
CHANG Sen, WEI Yaqi, DAI Zhenzhong, XU Wen, WANG Xing, DUAN Jiajia, ZOU Liang, ZHAO Guorong, REN Xiaoying, FENG Yongzhong
Journal of Arid Land. 2024, 16 (5): 603-614.   DOI: 10.1007/s40333-024-0013-3
Abstract ( 12 )   HTML ( 2 )     PDF (1295KB) ( 13 )  

Weihe River basin is of great significance to analyze the changes of land use pattern and landscape ecological risk and to improve the ecological basis of regional development. Based on land use data of the Weihe River basin in 2000, 2010, and 2020, with the support of Aeronautical Reconnaissance Coverage Geographic Information System (ArcGIS), GeoDa, and other technologies, this study analyzed the spatial-temporal characteristics and driving factors of land use pattern and landscape ecological risk. Results showed that land use structure of the Weihe River basin has changed significantly, with the decrease of cropland and the increase of forest land and construction land. In the past 20 a, cropland has decreased by 7347.70 km2, and cropland was mainly converted into forest land, grassland, and construction land. The fragmentation and dispersion of ecological landscape pattern in the Weihe River basin were improved, and land use pattern became more concentrated. Meanwhile, landscape ecological risk of the Weihe River basin has been improved. Severe landscape ecological risk area decreased by 19,177.87 km2, high landscape ecological risk area decreased by 3904.35 km2, and moderate and low landscape ecological risk areas continued to increase. It is worth noting that landscape ecological risks in the upper reaches of the Weihe River basin are still relatively serious, especially in the contiguous areas of high ecological risk, such as Tianshui, Pingliang, Dingxi areas and some areas of Ningxia Hui Autonomous Region. Landscape ecological risk showed obvious spatial dependence, and high ecological risk area was concentrated. Among the driving factors, population density, precipitation, normalized difference vegetation index (NDVI), and their interactions are the most important factors affecting the landscape ecological risk of the Weihe River basin. The findings significantly contribute to our understanding of the ecological dynamics in the Weihe River basin, providing crucial insights for sustainable management in the region.

Grassland-type ecosystem stability in China differs under the influence of drought and wet events
CAO Wenyu, BAI Jianjun, YU Leshan
Journal of Arid Land. 2024, 16 (5): 615-631.   DOI: 10.1007/s40333-024-0098-8
Abstract ( 36 )   HTML ( 1 )     PDF (1811KB) ( 9 )  

Ecological stability is a core issue in ecological research and holds significant implications for humanity. The increased frequency and intensity of drought and wet climate events resulting from climate change pose a major threat to global ecological stability. Variations in stability among different ecosystems have been confirmed, but it remains unclear whether there are differences in stability within the same terrestrial vegetation ecosystem under the influence of climate events in different directions and intensities. China's grassland ecosystem includes most grassland types and is a good choice for studying this issue. This study used the Standardized Precipitation Evapotranspiration Index-12 (SPEI-12) to identify the directions and intensities of different types of climate events, and based on Normalized Difference Vegetation Index (NDVI), calculated the resistance and resilience of different grassland types for 30 consecutive years from 1990 to 2019 (resistance and resilience are important indicators to measure stability). Based on a traditional regression model, standardized methods were integrated to analyze the impacts of the intensity and duration of drought and wet events on vegetation stability. The results showed that meadow steppe exhibited the highest stability, while alpine steppe and desert steppe had the lowest overall stability. The stability of typical steppe, alpine meadow, temperate meadow was at an intermediate level. Regarding the impact of the duration and intensity of climate events on vegetation ecosystem stability for the same grassland type, the resilience of desert steppe during drought was mainly affected by the duration. In contrast, the impact of intensity was not significant. However, alpine steppe was mainly affected by intensity in wet environments, and duration had no significant impact. Our conclusions can provide decision support for the future grassland ecosystem governance.

Grain size and surface micro-texture characteristics and their paleoenvironmental significance of Holocene sediment in southern margin of the Gurbantunggut Desert, China
MA Yunqiang, LI Zhizhong, TAN Dianjia, ZOU Xiaojun, TAO Tonglian
Journal of Arid Land. 2024, 16 (5): 632-653.   DOI: 10.1007/s40333-024-0015-1
Abstract ( 14 )   HTML ( 4 )     PDF (3824KB) ( 5 )  

The southern margin of the Gurbantunggut Desert, China, is characterized by alternating layers of aeolian and alluvial deposits. Investigating the characteristics of arenaceous sediment in this area is of significant importance for understanding the interactive processes of wind and water forces, as well as the provenance of sediment. However, there are relatively few investigations on the characteristics of such sediment at present. In this study, we researched three aeolian-alluvial interactive stratigraphic profiles and different types of surface sediment on the desert-oasis transitional zone of southern margin of the Gurbantunggut Desert. Based on the optically stimulated luminescence (OSL) dating of aeolian sand and analyses of quartz sand grain size and surface micro-texture, we explored the aeolian-alluvial environmental change at southern margin of the desert in Holocene, as well as the provenance of sediment. The results indicated that the grain size characteristics of different types of sediment in the stratigraphic profiles were similar to those of modern dune sand, interdune sand, muddy desert surface soil, and riverbed sand. Their frequency curves were unimodal or bimodal, and cumulative probability curves were two-segment or three-segment, mainly composed of suspension load and saltation load. The quartz sand in the sediment at southern margin of the desert had undergone alternating transformation of various exogenic forces, with short transportation distance and time, and sedimentary environment was relatively humid. In Holocene, southern margin of the desert primarily featured braided river deposits, and during intermittent period of river activity, there were also aeolian deposits such as sand sheet deposits, stabilized dune deposits, and mobile dune deposits. The provenance for Holocene alluvial deposits at southern margin of the desert remains relatively constant, with the debris of the Tianshan Mountains being the primary provenance. Aeolian sand is mainly near-source recharge, which is formed by in situ deposition of fluvial or lacustrine materials in southern margin of the desert transported by wind erosion, and its provenance was still the weathered debris of the Tianshan Mountains. In addition, the sand in interior of the desert may be transported by northwest wind in desert-scale, thus affecting the development of dunes in southern margin of the desert. The results of this study provide a reference for understanding the composition and provenance changes of desert sand in the context of global climate change.

Near-surface wind field characteristics of the desert-oasis transition zone in Dunhuang, China
PAN Jiapeng, ZHANG Kecun, AN Zhishan, ZHANG Yu
Journal of Arid Land. 2024, 16 (5): 654-667.   DOI: 10.1007/s40333-024-0056-5
Abstract ( 8 )   HTML ( 1 )     PDF (1104KB) ( 2 )  

The desert-oasis transition zone (DOTZ) serves as a buffer area between the desert and oasis. Understanding its wind field characteristics is of great significance for the prevention and control of aeolian disasters in the oasis. In this study, we used meteorological data during 2013-2019 from the portable meteorological stations at five sites (site A on the edge of the oasis, sites B, C, and D in the DOTZ, and site O in the desert) in Dunhuang, China to analyze the near-surface wind field characteristics and their causes, as well as to reveal the key role of the DOTZ in oasis protection. The results showed that the mean wind speed, frequency of sand-driving wind, and directional variability of wind decreased from west to east within the DOTZ, and wind speed was significantly affected by air temperature. The terrain influenced the prevailing winds in the region, mainly from northeast and southwest. Only some areas adjacent to the oasis were controlled by southeasterly wind. This indicated that the near-surface wind field characteristics of the DOTZ were caused by the combined effects of local terrain and surface hydrothermal difference. At site D, the annual drift potential (DP) was 24.95 vector units (VU), indicating a low wind energy environment, and the resultant drift direction (RDD) showed obvious seasonal differences. Additionally, the DOTZ played an important buffering role between the desert and oasis. Compared with the desert, the mean wind speed in the oasis decreased by 64.98%, and the prevailing wind direction was more concentrated. The results of this study will be useful in interpreting the aeolian activity of the DOTZ in Dunhuang.

Utilizing sediment grain size characteristics to assess the effectiveness of clay-sand barriers in reducing aeolian erosion in Minqin desert area, China
SONG Dacheng, ZHAO Wenzhi, LI Guangyu, WEI Lemin, WANG Lide, YANG Jingyi, WU Hao, MA Quanlin
Journal of Arid Land. 2024, 16 (5): 668-684.   DOI: 10.1007/s40333-024-0075-2
Abstract ( 9 )   HTML ( 1 )     PDF (1375KB) ( 6 )  

The clay-sand barriers in Minqin desert area, China, represent a pioneering windbreak and sand fixation project with a venerable history of 60 a. However, studies on evaluating the long-term effectiveness of clay-sand barriers against aeolian erosion, particularly from the perspective of surface sediment grain size, are limited and thus insufficient to ascertain the protective impact of these barriers on regional aeolian activities. This study focused on the surface sediments (topsoil of 0-3 cm depth) of clay-sand barriers in Minqin desert area to explain their erosion resistance from the perspective of surface sediment grain size. In March 2023, six clay-sand barrier sampling plots with clay-sand barriers of different deployment durations (1, 5, 10, 20, 40, and 60 a) were selected as experimental plots, and one control sampling plot was set in an adjacent mobile sandy area without sand barriers. Surface sediment samples were collected from the topsoil of each sampling plot in the study area in April 2023 and sediment grain size characteristics were analyzed. Results indicated a predominance of fine and medium sands in the surface sediments of the study area. The deployment of clay-sand barriers cultivated a fine quality in grain size composition of the regional surface sediments, increasing the average contents of very fine sand, silt, and clay by 30.82%, 417.38%, and 381.52%, respectively. This trend became markedly pronounced a decade after the deployment of clay-sand barriers. The effectiveness of clay-sand barriers in erosion resistance was manifested through reduced wind velocity, the interception of sand flow, and the promotion of fine surface sediment particles. Coarser particles such as medium, coarse, and very coarse sands predominantly accumulated on the external side of the barriers, while finer particles such as fine and very fine sands concentrated in the upwind (northwest) region of the barriers. By contrast, the contents of finest particles such as silt and clay were higher in the downwind (southeast) region of the sampling plots. For the study area, the deployment of clay-sand barriers remains one of the most cost-effective engineering solutions for aeolian erosion control, with sediment grain size parameters serving as quantitative indicators for the assessment of these barriers in combating desertification. The results of this study provide a theoretical foundation for the construction of windbreak and sand fixation systems and the optimization of artificial sand control projects in arid desert areas.

Environmental dynamics of nitrogen and phosphorus release from river sediments of arid areas
SU Wenhao, WU Chengcheng, Sun Xuanxuan, LEI Rongrong, LEI Li, WANG Ling, ZHU Xinping
Journal of Arid Land. 2024, 16 (5): 685-698.   DOI: 10.1007/s40333-024-0099-7
Abstract ( 4 )   HTML ( 1 )     PDF (823KB) ( 4 )  

Human activities lead to the accumulation of a large amount of nitrogen and phosphorus in sediments in rivers. Simultaneously, nitrogen and phosphorus can be affected by environment and re-enter the upper water body, causing secondary pollution of the river water. In this study, laboratory simulation experiments were conducted initially to investigate the release of nitrogen and phosphorus from river sediments in Urumqi City and the surrounding areas in Xinjiang Uygur Autonomous Region of China and determine the factors that influence their release. The results of this study showed significant short-term differences in nitrogen and phosphorus release characteristics from sediments at different sampling points. The proposed secondary kinetics model (i.e., pseudo-second-order kinetics model) better fitted the release process of sediment nitrogen and phosphorus. The release of nitrogen and phosphorus from sediments is a complex process driven by multiple factors, therefore, we tested the influence of three factors (pH, temperature, and disturbance intensity) on the release of nitrogen and phosphorus from sediments in this study. The most amount of nitrate nitrogen (NO3--N) was released under neutral conditions, while the most significant release of ammonia nitrogen (NH4+-N) occurred under acidic and alkaline conditions. The release of nitrite nitrogen (NO2--N) was less affected by pH. The dissolved total phosphorus (DTP) released significantly in the alkaline water environment, while the release of dissolved organic phosphorus (DOP) was more significant in acidic water. The release amount of soluble reactive phosphorus (SRP) increased with an increase in pH. The sediments released nitrogen and phosphorus at higher temperatures, particularly NH4+-N, NO3--N, and SRP. The highest amount of DOP was released at 15.0°C. An increase in disturbance intensity exacerbated the release of nitrogen and phosphorus from sediments. NH4+-N, DTP, and SRP levels increased linearly with the intensity of disturbance, while NO3--N and NO2--N were more stable. This study provides valuable information for protecting and restoring the water environment in arid areas and has significant practical reference value.

Host plant traits play a crucial role in shaping the composition of epiphytic microbiota in the arid desert, Northwest China
Journal of Arid Land. 2024, 16 (5): 699-724.   DOI: 10.1007/s40333-024-0014-2
Abstract ( 6 )   HTML ( 1 )     PDF (6847KB) ( 6 )  

Phyllosphere microorganisms are a crucial component of environmental microorganisms, highly influenced by host characteristics, and play a significant role in plant health and productivity. Nonetheless, the impact of host characteristics on shaping phyllosphere microbial communities of plants with different life forms remains ambiguous. Utilizing high-throughput sequencing technology, this study analyzed the diversity and community composition of phyllosphere epiphytic microorganisms (e.g., bacteria and fungi) of various plant life forms in the hinterland of the Gurbantunggut Desert, Northwest China. Functional annotation of prokaryotic taxa (FAPROTAX) and fungi function guild (FUNGuild) were employed to assess the ecological functions of microorganisms and to investigate the role of stochastic and deterministic processes in shaping phyllosphere microbial communities. Result showed a diverse array of phyllosphere epiphytic microorganisms in the desert plants, with Proteobacteria, Cyanobacteria, and Actinobacteriota dominating bacterial community, while Ascomycota and Basidiomycota were prevalent in fungal community. Comparison across different plant life forms highlighted distinct microbial communities, indicating strong filtering effects by plant characteristics. FAPROTAX prediction identified intracellular parasites (accounting for 27.44% of bacterial community abundance), chemoheterotrophy (10.12%), and phototrophy (17.41%) as the main functions of epiphytic bacteria on leaves of different life form plants. FUNGuild prediction indicated that phyllosphere epiphytic fungi primarily served as Saprotrophs (81.77%), Pathotrophs (17.41%), and Symbiotrophs (0.82%). Co-occurrence network analysis demonstrated a predominance of positive correlations among different microbial taxa. Raup-Crick dissimilarity index analysis revealed that deterministic processes predominantly influenced phyllosphere bacterial and fungal community assembly. Variance partitioning analysis and random forest modeling suggested that plant leaf functional traits significantly impacted both bacterial and fungal community composition, with fungal community composition showing a closer association with leaf nutrients and physiology compared with bacterial community composition. The distinct responses of bacterial and fungal communities to plant traits were attributed to the differing properties of bacteria and fungi, such as bacteria having higher potential dispersal rates and broader ecological niches than fungi. Overall, the results indicate that phyllosphere bacterial and fungal communities undergo similar community assembly processes, with fungi being more influenced by plant characteristics than bacteria. These findings offer novel insights into the ecology of phyllosphere microbial communities of desert plants.

Effects of desert plant communities on soil enzyme activities and soil organic carbon in the proluvial fan in the eastern foothills of the Helan Mountain in Ningxia, China
SHEN Aihong, SHI Yun, MI Wenbao, YUE Shaoli, SHE Jie, ZHANG Fenghong, GUO Rui, HE Hongyuan, WU Tao, LI Hongxia, ZHAO Na
Journal of Arid Land. 2024, 16 (5): 725-737.   DOI: 10.1007/s40333-024-0076-1
Abstract ( 4 )   HTML ( 1 )     PDF (1225KB) ( 2 )  

It is of great significance to study the effects of desert plants on soil enzyme activities and soil organic carbon (SOC) for maintaining the stability of the desert ecosystem. In this study, we studied the responses of soil enzyme activities and SOC fractions (particulate organic carbon (POC) and mineral-associated organic carbon (MAOC)) to five typical desert plant communities (Convolvulus tragacanthoides, Ephedra rhytidosperma, Stipa breviflora, Stipa tianschanica var. gobica, and Salsola laricifolia communities) in the proluvial fan in the eastern foothills of the Helan Mountain in Ningxia Hui Autonomous Region, China. We recorded the plant community information mainly including the plant coverage and herb and shrub species, and obtained the aboveground biomass and plant species diversity through sample surveys in late July 2023. Soil samples were also collected at depths of 0-10 cm (topsoil) and 10-20 cm (subsoil) to determine the soil physicochemical properties and enzyme activities. The results showed that the plant coverage and aboveground biomass of S. laricifolia community were significantly higher than those of C. tragacanthoides, S. breviflora, and S. tianschanica var. gobica communities (P<0.05). Soil enzyme activities varied among different plant communities. In the topsoil, the enzyme activities of alkaline phosphatase (ALP) and β-1,4-glucosidas (βG) were significantly higher in E. rhytidosperma and S. tianschanica var. gobica communities than in other plant communities (P<0.05). The topsoil had higher POC and MAOC contents than the subsoil. Specifically, the content of POC in the topsoil was 18.17%-42.73% higher than that in the subsoil. The structural equation model (SEM) indicated that plant species diversity, soil pH, and soil water content (SWC) were the main factors influencing POC and MAOC. The soil pH inhibited the formation of POC and promoted the formation of MAOC. Conversely, SWC stimulated POC production and hindered MAOC formation. Our study aimed to gain insight into the effects of desert plant communities on soil enzyme activities and SOC fractions, as well as the drivers of SOC fractions in the proluvial fan in the eastern foothills of the Helan Mountain and other desert ecosystems.