Enzymatic indicators reveal drought sensitivity of the deadwood-soil system in temperate forests.

Drought can disrupt biogeochemical functioning in forest ecosystems by limiting microbial activity and extracellular enzyme production. We investigated the effects of simulated moisture deficit on the activity of five enzymes involved in C, N and P acquisition in a deadwood-soil system: β-glucosidase (BG), β-D-cellobiosidase (CB), β-xylosidase (XYL), N-acetyl-β-D-glucosaminidase (NAG) and phosphatase (PH). Deadwood of six temperate tree species (broadleaf and conifer) was exposed to drought and control conditions over two years (2023-2024), and enzyme activities were measured seasonally in both deadwood and the underlying soil. Drought conditions led to a pronounced reduction in the activity of all analyzed enzymes in deadwood, frequently exceeding 50% compared to control treatments, which indicates strong moisture limitation of microbial processes during wood decomposition. Enzymatic activity in soil beneath deadwood also decreased, although the smaller absolute changes observed in soil are likely related to lower initial activity levels rather than increased resistance to drought. The extent of decline varied among enzymes and wood species, with β-glucosidase and β-xylosidase showing differences of approximately 30-40% between treatments in soil, and with some species (e.g. beech and spruce) exhibiting weaker responses to drought. Enzyme activity in both substrates followed a consistent seasonal pattern, with maxima in summer and minima in winter. The increasing divergence between control and drought treatments in the second-year highlights cumulative effects of prolonged water limitation. The results demonstrate that extracellular enzyme activity is highly sensitive to moisture availability and that deadwood and underlying soil respond differently to drought. This provides mechanistic insight into how drought may alter microbial functioning and decomposition dynamics at the deadwood-soil interface in forest ecosystems. General Linear Models, correlation analysis and PCA consistently indicated moisture as a major factor associated with enzymatic variation, whereas temperature showed no significant relationships with enzyme activities. Reduced enzyme activity under drought suggests a limitation of microbial decomposition processes and nutrient acquisition, particularly for carbon-, nitrogen- and phosphorus-related pathways, potentially constraining microbial metabolism and slowing organic matter turnover at the deadwood-soil interface.