Litter Chemistry Is a Main Driver of Inorganic Nitrogen in Disturbed Soils in the Arid Patagonian Monte

Abstract

Changes in plant cover and soil characteristics induced by grazing may affect litter quality and nitrogen (N) release under varying abiotic conditions. Our study was focused on the importance of litter chemistry as a main driver of inorganic N (ammonium-N: NH4 +-N and nitrate-N: NO3 −-N) release to soil. Both inorganic N forms are important components for N availability to plants and soil processes, and the long-term conservation of soil-N fertility. We analyzed the effect of secondary compounds and the C/N ratio in litter under varying soil water, and UV exposure on soil inorganic N (NH4 +-N and NO3 −-N) in Patagonian Monte degraded soils. We hypothesized that secondary compounds and C/N ratio in litter are main drivers of soil inorganic N under varying abiotic conditions. We conducted a microcosm experiment (13 months) using intact upper soil blocks from denuded soil areas. Surface soils were added with shrub (SL), and mixed grass and shrub (GSL) litter with high versus low secondary metabolites concentration and low vs. high C/N ratio, respectively. Microcosms were maintained under ambient and reduced UV exposure, and high and low soil water. We used microcosms without litter as controls. Monthly, we assessed NH4 +-N and NO3 −-N concentrations in upper and sub-superficial soils. Litter chemistry interacting with abiotic factors did not significantly influence soil NH4 +-N at any soil depth while litter chemistry was a main driver of NO3 −-N in upper soil. SL enhanced NO3 −-N in upper soil compared with GSL independently of abiotic factors. In upper soils without litter and in those with GSL, the highest NO3 −-N concentration occurred mostly under high soil water and exposition to UV. We concluded that litter chemistry was a main driver of soil N fertility in disturbed rangelands. Shrub litter may enhance N fertility (NO3 −-N) in degraded soils.