Effects of Long-Term and Short-Term Droughts on the Hydrolytic Enzymes in Haplic Luvisol

The transformation of organic matter in the soil is largely determined by hydrolytic enzymes. Under the conditions of climate change, understanding the mechanisms of microbial response is of particular importance for predicting the carbon cycle. Until now, the effect of drought duration and frequency on soil hydrolytic enzymes has been little studied. A multifactorial field manipulation experiment was carried out, simulating in the presence of plants and without them: two short-term droughts, a long-term drought, and an optimal level of soil moisture. The maximum reaction rate V max , Michaelis constant K m , and catalytic efficiency K a of five groups of enzymes involved in the carbon cycle (cellobiase, glucosidase, xylanase), phosphorus (phosphatase), and nitrogen (chitinase) were determined. In phosphatases, glucosidases, and xylanases, V max decreased during short-term drought. During prolonged drought, the V max value of phosphatases, cellobiohydrolases, and xylanases decreased and increased in chitinases, while remaining unchanged in glucosidases. Both long-term and short-term droughts led to an increase in K m and a decrease in catalytic efficiency ( K a ) for almost all enzymes. Short-term droughts were not a “weakened version” of a long-term drought, but had their own specifics—a decrease in K m of glucosidases, which led to an increase in K a . Long-term drought was characterized by an increase in V max of chitinases and spatial variability of V max of phosphatases and glucosidases. The influence of the presence of plants was secondary and manifested itself only during short droughts. The reversibility of the effect of drought on V max , K m , and K a decreased in the series first short-term drought > second short-term drought > long-term drought due to an increase in the total duration of the stress impact.