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Climate change alters stoichiometry of phosphorus and nitrogen in a semiarid grassland

Dijkstra, F.A., E. Pendall, J.A. Morgan, D.M. Blumenthal, Y. Carrillo, D.R. LeCain, R.F. Follett, D.G. Williams. 2012. New Phytologist 196:807-815

Abstract

Nitrogen (N) and phosphorus (P) are essential nutrients for primary producers and decomposers in terrestrial ecosystems. Although climate change affects terrestrial N cycling with important feedbacks to plant productivity and carbon sequestration, the impacts of climate change on the relative availability of N with respect to P remain highly uncertain. In a semiarid grassland in Wyoming, USA, we studied the effects of atmospheric CO2 enrichment (to 600 ppmv) and warming (1.5/3.0 C above ambient temperature during the day/night) on plant, microbial and available soil pools of N and P. Elevated CO2 increased P availability to plants and microbes relative to that of N, whereas warming reduced P availability relative to N. Across years and treatments, plant N : P ratios varied between 5 and 18 and were inversely related to soil moisture. Our results indicate that soil moisture is important in controlling P supply from inorganic sources, causing reduced P relative to N availability during dry periods. Both wetter soil conditions under elevated CO2 and drier conditions with warming can further alter N : P. Although warming may alleviate N constraints under elevated CO2, warming and drought can exacerbate P constraints on plant growth and microbial activity in this semiarid grassland.

Key Words

elevated carbon dioxide; grasslands; homeostasis; N : P stoichiometry; nutrient availability; PHACE; soil moisture; temperature