Soil microbial eco-physiology as affected by short-term variations in environmental conditions

Abstract

Short-term variations in abiotic and biotic environmental conditions modify microbial metabolism. These effects were studied in an arable soil during the oat straw decomposition. Cumulative CO 2 evolution was significantly higher when soil was subjected weekly to drying–rewetting cycles (DR) or had been initially fertilised with nitrogen (+N, as NH 4NO 3) in comparison to samples incubated at constant conditions (CC). The microbial metabolic quotient (respiration rate per unit microbial C) of DR and +N exceeded CC by approximately 100–150%, indicating that variable water availability and improved N availability induced a higher activity level of the microbial biomass. In addition, the metabolic-responsive microbial communities, calculated by the ratio of microbial C estimated by substrate-induced respiration to fumigation–extraction technique, increased from 1.0 to approximately 1.3 after 7 weeks for DR and +N, but remained essentially at 1.0 for CC and control. A high abundance of soil nematodes significantly affected respiration rate, metabolic-responsive biomass and metabolic quotient during the early stages of decomposition. We concluded that short-term variation in environmental conditions promoted decomposition processes by influencing the physiology of soil microorganisms and increasing the metabolic-responsive biomass. Such a stimulated microbial metabolism seems to be unspecific due to stressing environmental conditions. The role of the interacting fauna such as nematodes varied during decomposition.