Phosphorus addition enhances loss of nitrogen in a phosphorus-poor soil

摘要

Plants and microbes have limited stoichiometric flexibility to take up and store nitrogen (N) and phosphorus (P). Variation in the relative availability of N and P to plants and microbes may therefore affect how strongly N and P are held in terrestrial ecosystems with important implications for net primary productivity and carbon sequestration. We hypothesized that an increase in P availability in a P-poor soil would increase N uptake by plants and microbes thereby reducing N loss. We grew mixtures of the C3 grass Phalaris aquatica L. and the legume Medicago sativa L. in mesocosms with soils low in P availability and then used a novel technique by adding a N-15 tracer with and without 1 g P m(-2) to soil with different moisture and available N conditions, and measured the N-15 recovery after 48 h in microbes, plants and soil. In contrast to our hypothesis, we found that P addition reduced N-15 in microbes without water stress by 80% and also reduced total N-15 recovery, particularly without water stress. Water stress in combination with N addition further showed low total N-15 recovery, possibly because of reduced plant uptake thereby leaving more N-15 in the soil available for nitrification and denitrification. Our results suggest that P addition can result in large gaseous N loss in P-poor soils, most likely by directly stimulating nitrification and denitrification. (c) 2015 Elsevier Ltd. All rights reserved.