Effects of recurring droughts on microbial functioning in mountain grassland

Wien

2014

S. 9

Artikel aus einer ZeitschriftUnselbständiges Werk

200189767

Climate projections suggest increasing variability of precipitation inducing more frequent extreme drought periods also in many regions which are to date well water supplied. Water availability is a key factor for physical, physiological and biogeochemical processes and determines microbial activity and functioning in soils by affecting the osmotic potential, soil pore connectivity, substrate diffusion and eventually nutrient availability. Thus drought could directly affect microbial activity and functioning; however, effects of drought could persist and might enhance or decrease the susceptibility of microbial functioning during further drought periods. We therefore investigated effects of 1-5 recurring experimental extreme drought periods on microbial activity in mountain grassland soils in situ during the growing season by measuring a set of extracellular enzyme activities (EEA) targeting different substrates as a proxy for microbial functioning. Drought distinctly affected carbon (Cellobiohydrolase, CBH), nitrogen (Leucine amino peptidase, LAP) and phosphorus (Phosphatase, PHOS) substrate targeting, as well as oxidative potential EEA (phenoloxidase , POX), indicating a shift of microbial functioning. All EEA showed a strong temporal fluctuation. During drought simulation potential CBH activity was only marginally reduced compared to controls, while the extractable organic C content in soils increased. LAP, PHOS and POX, in contrast, decreased during drought, but the extractable organic N increased. This on the one hand proves a higher drought sensitivity of N- than C-acquiring enzymes, and on the other hand could indicate altered microbial physiology, activity, or hint towards an altered active microbial community composition. Nonetheless, under recurrent drought effects were similar and moreover, whenever EEA were altered during drought, they quickly recovered after drought. Overall, our data suggest that microbial functioning in mountain grassland appears to be sensitive to drought, but also highly resilient even after 5 years of recurring drought.