Drying–rewetting effects on N cycling in grassland soils of varying microbial community composition and management intensity in south central Chile

Factors including site management, seasonal climate and the weather (notably soil drying–rewetting events, DREs) reportedly affect microbial soil communities and processes. However, little is known about the strength of effects of microbial community composition, and microbial interactions with other variables, on responses of N cycling processes to DREs. Therefore, we sampled soils at four grassland sites in south-central Chile with varying management intensities early and late in the dry season, subjected the samples to continuously wet conditions or DREs, and measured their nitrification rates (by 15N isotope dilution analysis) and potential urease and protease activities. Both sampling time and site management significantly affected viable phospholipid fatty acid (PLFA)-based biomass and community composition estimates. Nitrification at the intensively managed sites was mainly performed by rapidly cycling bacterial communities that were unable to maintain their functioning after DRE, but DRE-resistant heterotrophic nitrifying fungi at the least intensively managed site sustained nitrification after DREs. Season had no impact on nitrification responses to DRE as the microbial groups associated with PLFA biomarkers that varied strongly between sampling times were not involved in nitrification. PLFA biomarkers correlated with potential urease and protease activities varied between sampling times, and were characteristic of Gram-positive or non-specific bacteria. No significant interactive effect between season and laboratory water treatment on the enzyme activities was detected, due to similarities in physiological and functional responses of these bacterial groups to DREs. We conclude that site management may influence soil N cycling responses to DREs via changes in functional microbial groups with differing DRE susceptibility.

► Season and site management had a main effect on microbial community composition.
► Site management influences nitrification responses to dry–rewetting events.
► Lack of interaction between season and water treatment for potential enzyme activities.
► Relationship between microbial community composition and ecosystem functioning.