Abstract
Paddy soils represent the largest anthropogenic wetlands on earth. Soil drying and rewetting that occurs annually inflict significant stress on soil microbial activities in paddy soils. An incubation experiment of 60 years of paddy soil was conducted to simulate the conditions of paddy fields (25 °C and 75% air humidity) during a 16-day incubation time. The effect of drying-rewetting [DRW, with 4 levels: (1) constant soil moisture (CSM), (2) one-stage drought stress (DRW1), (3) two-stage drought stress (DRW2), and (4) three-stage drought stress (DRW3)] and how it evolves over 0, 4, 8. 12, and 16 days after incubation on the concentration of available phosphorus (AP), microbial biomass P (MBP) and microbial biomass C (MBC), and respiration rate (RES) was determined using repeated measures analysis (RMA). The results revealed that an increase in the number of drying-rewetting increases MBC and RES. Compared to CSM, frequent drying and rewetting caused an increase in RES, MBC and MBP by 88%, 38%, and 11%, respectively. Drying-rewetting increased microbial biomass C (MBC) and P (MBP) by 24-38% and 11-54%, respectively, during 8-16 days of incubation. Increasing the number of DRW cycles reduced AP concentration (except in DRW1). The decrease in available phosphorus is due to the increase in the intensity of immobilization under these conditions. Positive correlations were also observed between AP and MBP (r = 0.52), and between RES and MBC (r = 0.91). In general, the frequency of moisture in the paddy soil is favorable for increasing microbial activity.