IMMEDIATE EFFECT OF WETTING EVENT ON MICROBIAL BIOMASS AND CARBOHYDRATE PRODUCTION-MEDIATED AGGREGATION IN DESERT SOIL

The interrelationship between microbial processes and soil physical structure following rapid wetting of dry soil was studied in a field experiment in the Negev desert. Short-term influence of four different amounts of water, 0, 5, 1 0 and 20 mm, applied in a single event, on microbial biomass, C-mineralization, degree of macroaggregation ( > 0.3 mm) and aggregate stability was measured after 1 and 4 days. Immediately after wetting the amount of microbial biomass significantly increased coinciding with a decrease in C-mineralization rate; however, on the 4th day the biomass and the C-mineralization tended to stabilize again at the initial level of the non-irrigated control. Wetting of dry soil reduced the amount of carbohydrates within 4 days, regardless of water quantity added. More macroaggregates were formed in the wetted plots, probably due to physical attachment upon wetting cycle, but their stability was reduced compared to nonwetted aggregates. Carbohydrates were significantly correlated with aggregate stability, while microbial biomass and C-mineralization were not. Wetting of desert dry soil has triggered a rapid response in microbial activity-induced structure stability, and it was mostly dominated by the event itself, regardless of water quantity applied.