Response of Soil Respiration and Microbial Biomass to Drying and Rewetting Is Greater in Planted than in Unplanted Soil

Purpose Determine the response of soil respiration and microbial biomass in planted and unplanted soil to drying and rewetting stress. Methods Barley was grown at high density in a loamy sand at 75% of water holding capacity to obtain planted soil. For unplanted soil, pots without plants were kept in the same conditions. After 4 weeks, soil from planted (brushed off the roots) and unplanted pots were used for the subsequent incubation experiment. For drying and rewetting (DRW), the soil was dried for 7 days immediately after collection of the soil. On day 8, the soil was rewet quickly to 75% of water holding capacity and kept moist until day 14. For the constantly moist treatment (CM), the soil was kept at 75% of WHC for 2 weeks. Results In CM, respiration rates were higher in planted than unplanted soil, but microbial biomass C (MBC) did not differ between planting treatments. In DRW, respiration rates rapidly decreased in the dry period, irrespective of planting treatment. The flush of respiration after rewetting was 50% greater in planted than unplanted soil. Only in planted soil, MBC doubled after rewetting (from day 7 to 9), but then halved again to day 14. Conclusion Previous planting increases organic C supply to microbes which increases the respiration flush after rewetting and microbial growth.