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Soil microorganisms are critical to soil health and environmental functions; however, the dynamics of microbial communities and their response to soil variables following conversion of desert soils to oasis farmland have not been well documented. We used high‐throughput pyrosequencing to investigate the dynamics of soil microbial communities along an irrigated cultivation chronosequence (cultivated for 16, 33, 45 and 60 years) and in adjacent non‐cultivated soil in a desert‐oasis ecotone in northwestern China. Additionally, we explored which soil variables may be responsible for shifts in microbial communities. Generally, cultivation in desert soil increased microbial community abundance and diversity; however, bacterial abundance and diversity increased along the cultivation chronosequence, whereas fungal abundance and diversity initially increased and then decreased. Continuous crop cultivation also resulted in a shift in microbial community composition, notably with a decrease in nitrogen (N)‐fixing microbes (Proteobacteria and Cyanobacteria) and an increase in ammonia‐oxidizing (Nitrosomonadales) and nitrite‐oxidizing microbes (Nitrospirae). Redundancy analysis showed that soil organic carbon, total N, available N, available phosphorus and bulk density explained over 80% of the variation in both bacterial and fungal communities; this indicated the critical roles of nutrient supply and soil structure in shaping the composition and diversity of microbial communities during the conversion of native desert soils to irrigated croplands. Highlights: Cultivation in desert soil increased microbial community abundance and diversity.Cultivation decreased N‐fixing microbes.Cultivation increased ammonia‐oxidizing and nitrite‐oxidizing microbes.Soil structure and nutrient supply shaped the diversity of microbial communities. [ABSTRACT FROM AUTHOR]

Nitraria sibirica usually exists in a form of nebkhas, and has strong ecological adaptability. The plant species has distinctive function for wind prevention and sand fixation, and resistance drought and salt. However, the water condition is still a limiting factor for the plant survival and development. In order to understand the water use strategy of the plant in different desert habitats, we selected the N. sibirica growing in sandy desert habitat and gravel desert habitat to study the seaso-nal variation of plant water sources and response to precipitation at the edge of the oasis of Linze in the Hexi Corridor. We measured the oxygen stable isotope of the plant stem water and the different potential water sources (precipitation, soil water and ground water), and used the IsoSource model to calculate the proportion of water sources from the potential water. The results showed that there were significant seasonal variation characteristics of δ 18 O value and water source of stem water for the plant in the two habitats. In the sandy habitat, the plant used more ground water in the less precipitation seasons including spring and fall, and more than 50% of the water sources absorbed from ground water. However, under the condition of gravel habitat, the plant could not achieve the ground water level depth of 11.5 m, and its water source was controlled by precipitation, which had large seasonal variability. The water sources of N. sibirica had significant responses to the change of precipitation in the two desert habitats. Following the rapid decrease of soil water content after the precipitation events, the plant in the sandy habitat turned to use the abundant ground water as the main sources of water, while the plant in the gravel habitat only used the less water from precipita-tion infiltration to the deep soil. Therefore, different water use strategies of the plant in the two habitats were the main reason for the difference in growth characteristics, and it had a strong ability of self-adjustment and adaptation.