Soil enzyme activity in a mediterranean forest after six years of drought

A 6-yr experiment in drought manipulation was conducted in a Quercus ilex L. Mediterranean forest to simulate the drought conditions projected for the coming decades. We investigated the effects of those drought conditions on soil urease, protease, and β-glucosidase activities and the changes in C and N stocks in soil, leaves, and leaf litter. Elimination of runoff and rainfall resulted in lower soil water content than in control soils in autumn, winter, and spring (27, 61, and 53%, respectively). In soils subjected to runoff plus partial rainfall elimination, urease activities were reduced by 25% in autumn, winter, and spring; soil protease activities by 33% in winter and spring; and β-ghicosidase by 25 to 30% in summer and spring. Drought reduced the C/N ratio of the leaf litter of the dominant species, Q. ilex, by 11%, indicating a decrease in N remobilization before leaf fall. We therefore did not observe an increase in the C/N concentration ratio in litter and soil as we had expected. Drought decreased N availability in spring, the growing season, by reducing soil NO3- concentration. The reduction in enzyme activities in the droughtaffected soils was mainly due to the prolonged decrease in water availability and, to a lesser extent, to current soil water availability, mainly in summer, and to changes in the nutritional quality of the enzyme substrate. The observed drop in soil enzyme activity can contribute to a decrease in the amount of N liberated and consequendy to a decline in the plant N capture, which was observed in some community species such as Arbutus unedo L. © Soil Science Society ot America, 5585 Guilford Rd., Madison WI 53711 USA. All rights reserved.