Low soil water content during plant growth influences soil respiration and microbial biomass after plant removal and rewetting

Abstract

The aim of this experiment was to study the effect of previous water content in planted and unplanted soil on microbial biomass and nutrient availability after plant removal and rewetting. A silt loam was maintained 10-50% of water holding capacity (WHC) and planted with wheat or left unplanted. After four weeks, plants were removed and soils were kept at the same water content as in the pots (original) or rewetted to 50% WHC (rewet). Then, soil respiration was measured continuously for 20 days, available N and P and microbial biomass C, N and P were measured on days 5, 10 and 20. In original soil, cumulative respiration, MBC and MBN decreased with water content in planted soil and were higher in planted than unplanted soil only at 30-50% WHC. Available N was up to 3-fold higher in un-planted than planted soil at 30-50% WHC. Only in planted soil, available N increased with decreasing water content. Rewetting increased cumulative respiration and MBN only in soil that had been at 10-20% WHC. In rewet soil, the previous water content had no effect on cumulative respiration, MBC and MBN in unplanted soil. In planted soil, cumulative respiration, MBC and MBN remained lower in soil that was at 10% WHC previously compared to that at 50% WHC. It is concluded that the effect of low water content on soil microbes is exacerbated by reduced plant growth and the reduced C input, even if soils are rewet.