Differential Responses of Soil Phosphorus Availability to Variations in Repeated Drying–Rewetting Cycles Under Different Land-Use Types in the Semi-Arid Loess Plateau of China

Soil phosphorus (P) deficiency is an important factor limiting plant growth in the semi-arid Loess Plateau region in China. The topsoils in this area undergo repeated drying–rewetting (DRW) cycles, which can influence soil P availability, a process that may become more pronounced due to climate change. However, little is known about how soil P availability responds to DRW cycles under different land-use types. To investigate this issue, we conducted three 120-day soil culture experiments to investigate the direction and magnitude of soil available P and the responses of its influencing factors to repeated DRW cycles and their frequency and intensity under three typical land-use types (cropland, grassland, and shrubland) in Gansu Province, North-western China. The results showed that the available P concentration of cropland, grassland, and shrubland soils after repeated DRW cycles significantly decreased by 8.9%, 11.5%, and 14.2%, respectively, compared with a constant humidity control. With increasing intensity of the DRW cycles, the available P concentration of grassland and shrubland soils significantly increased by 14.3% and 15.5%, respectively, while in cropland soil P significantly decreased by 10.4%. Compared with low-frequency DRW cycles, high-frequency DRW cycles significantly reduced the available P concentration by 6.4% in grassland soil and increased it by 9.8% in shrubland soil but had no significant effect in cropland soil. Overall, the responses of soil P availability to repeated DRW cycles vary among different land-use types, and the magnitude of the soil P availability response to repeated DRW cycles depended strongly on soil microorganism biomass, phosphatase activity, and the initial soil properties, being more pronounced in grassland and shrubland soils than in cropland soils. It is therefore essential to consider land-use type when studying the effects of DRW on soil P cycling in semi-arid regions, especially in the context of climate change.