Drying and rewetting affect chemical speciation and bioavailability of soil phosphorus in a hyper-arid desert ecosystem

Climate change is expected to alter the frequency and intensity of drying-rewetting cycles, impacting water availability and consequently soil nutrient availability. However, the effects of these fluctuations on the chemical speciation and bioavailability of phosphorus (P) in soil remain uncertain, both in the presence of desert species and in their absence. We conducted a pot experiment involving bare soil (absence of plants) and two desert species (Alhagi sparsifolia and Calligonum mongolicum) to determine the short-term impacts of drought (no water supply), drying-rewetting 1 (D-RW1, high frequency of low water inputs), and drying-rewetting 2 (D-RW2, low frequency of high water inputs) on soil Hedley P pools, plant P concentration, and plant biomass accumulation. Results demonstrated that the presence of plants significantly increased soil labile P and organic P (Po) concentrations by 60%-150% and 1%-68%, respectively, compared to the absence of plants. Both D-RW1 and D-RW2 treatments significantly increased soil dissolved organic carbon concentration by 2%-35% relative to the drought treatment. Moreover, in the presence of A. sparsifolia, soil resin-extractable P and NaHCO3-extractable inorganic P (Pi) concentrations in the D-RW1 treatment significantly increased by 31% and 75%, respectively, when compared to the drought treatment, with the NaHCO3-and NaOH-extractable Po concentrations in the D-RW2 treatment rising by 14% and 32%, respectively. Furthermore, the D-RW2 treatment significantly increased leaf P concentration and plant biomass compared to the D-RW1 and drought treatments. Overall, compared to the drought treatment, frequent low-intensity drying-rewetting cycles enhanced soil Pi turnover, whereas infrequent high-intensity drying-rewetting cycles increased Po turnover and P bioavailability. These findings will inform better water management strategies for desertification restoration in hyper-arid desert ecosystems.