Contrasting effects of increase in water and nutrients availability on soil respiration and soil nitric and nitrous oxide emissions in desert.

Soil microbial processes in drylands are limited by multiple abiotic factors, the most important being water and macronutrients (nitrogen (N) and phosphorus (P)). Understanding of relative importance of different abiotic factors for soil microbial processes is important because drylands are important regulators of global carbon (C) cycle and there is close connection between water, N, and C cycles. To assess how soil activity is affected by removing multiple nutrient limitations and manipulating water availability we conducted a short-term, multifactorial field experiment. We manipulated water, N, and P availability by application of the nutrients and water in the field. We evaluated how soil respiration, nitrous oxide, and nitric oxide emissions responded to increasing water, N and P availability individually and interactively in the Negev Desert. We hypothesized that neither water nor nutrient addition alone will enhance the activity of desert soils. On the other hand, removing multiple limitations will accelerate soil nutrient cycling. Further we hypothesized that acceleration of soil nutrient cycling will be reflected in high soil emissions of N₂O, NO, and CO₂ as proxies for the N cycle and respiration, respectively. We found that increasing water availability in desert soils significantly accelerated soil respiration rates but not the N cycle. Nitrogen availability affected soil NO production but not soil respiration. Soil emissions of N₂O were unaffected by neither water nor nutrients additions. Phosphorus additions had no effect on soil microbial activity either alone or synergistically together with N and water.