Litter as a regulator of N and C dynamics in macrophytic patches in Negev desert soils

In desert ecosystems, nutrient cycling activity is concentrated in brief periods of intense biological activity following wetting events. Release and uptake of N from litter and microbial biomass may be important regulators of N availability to plants and N loss to denitrification and NH₃ volatilization. Litter and microbial biomass dynamics may also be important to the maintenance of shrub-dominated patches of high fertility in desert ecosystems. We have measured soil C and N cycling processes (respiration, NH₄⁺ and NO₃^- dynamics, denitrification and microbial biomass C and N dynamics) in rewetted Negev desert soil treated with different size classes of desert plant litter in 30-day laboratory incubations. The results suggest that litter plays a strong role in conserving N following wetting events in Negev soils. Amounts of soil NH₄⁺ and NO₃^- and microbial biomass N were reduced in litter-amended treatments, suggesting that significant quantities of N were sequestered in litter, especially the largest size classes of litter. Denitrification was a significant sink for N, and was stimulated by the presence of litter, but was less important than immobilization of N in litter. Immobilization and release of N by litter may be especially important in the N cycle in desert ecosystems, moderating seasonal patterns of N availability and regulating patch interactions that facilitate the development of "islands of fertility" in these ecosystems.