Effects of rewatering on soil fungi and soil enzymes in a spruce-beech forest after a 5-year experimental drought

The functioning of temperate forests may change dramatically in the future due to more extreme precipitation events. In contrast to drought effects, little is known about the reaction of soil fungi to rewatering. We studied soil fungal communities and soil enzymatic activities over a period of 3 months following rewatering after 5 years of experimental drought.

The most pronounced changes compared to the drought phase occurred early after rewatering in the beech root zone and were mainly attributed to litter decomposers. In the spruce zone, the relative abundance of ectomycorrhizal fungi (ECMf) was lower during the initial phase of response to rewatering but approached control levels after 3 months. The previous drought treatment was influencing the structure of the saprotrophic fungal community (SAPf) more than that of the ECMf community during rewatering. The composition of the SAPf community was associated with changes in nitrogen (mineral nitrogen: control 2.86, rewatering = 1.53), while that of the ECMf community was associated with the soil water content (control = 26%, and rewatering = 22%). Soil enzyme activities were positively correlated with the diversity and composition of SAPf communities, especially in previously drought-treated plots. In beech and mixed root zones, plant cell wall-degrading enzyme activities were elevated in rewatered plots compared with control plots, while in spruce, only cellobiohydrolase and β-glucosidase were elevated.

Structural changes within SAPf communities associated with nitrogen dynamics correlated with enzymatic activity in response to rewatering. A low responsiveness of fungal community composition in the mixed root zone suggests its buffering capacity against fluctuating soil moisture conditions.