Microbial activity and biomass recover rapidly after leaching of saline soils

Abstract

The effect of salinity on microbial activity, biomass, and community structure has been studied extensively, but little is known about the effect of decreasing salinity without strong changes in soil water content as they may occur when irrigation water of lower salinity is used. An incubation experiment with three naturally saline soils [electrical conductivity of the saturated paste (ECe): 12, 32, and 41 dS m−1] was conducted, in which the EC was decreased to 8 ECe levels (from 6 to 32 dS m−1) by leaching with solutions of different NaCl concentrations. Finely ground pea straw was added at 20 g kg−1 as a nutrient source. The soils were incubated at optimal water content for 15 days, during which soil respiration was measured continuously. Microbial biomass C was determined on days 5, 10, and 15. Both cumulative respiration and microbial biomass C were negatively correlated with EC. At a given adjusted EC, irrespective of the original EC, cumulative respiration recovered to the same level as in the soils which had originally this lower EC. This was also the case for microbial biomass C except for the soil that had the highest original EC; there, microbial biomass C did not fully recover. The results suggest that even in very saline soils, activity and growth of a proportion of microbial community can rapidly increase when the EC is reduced and substrate is added. Thus, microbial activity and biomass are mainly a function of the final EC. However, while microbial activity (respiration) had completely recovered after 15 days, recovery of the microbial biomass may take longer when the original EC was high.