LAUSR

Abstract The growth-rate hypothesis (GRH) says that fast-growing organisms have relatively high P content and lower N:P ratios because they need more P-rich ribosomal RNA (rRNA) to fuel increased protein-synthesis. However, there is a lack of understanding for how environmental factors influence plant N:P stoichiometry, and it is unknown if the GRH applies to vascular plants in drylands. Here, we test the GRH in dryland plants by measuring biomass N:P ratios in Leymus chinensis, a perennial dryland grass commonly found in Inner Mongolia grasslands. We determined relative growth rates (RGR) and adaptation to changes in water, N, and P availability in substrate. Generally, adding water, N, and P to substrate stimulated growth. Increased water supply decreased plant N concentrations, but increased plant P concentrations. As expected by GRH, N:P ratios in plant biomass decreased as water supply and RGR increased. Biomass N:P ratios increased as N substrate addition and RGR increased, but decreased as P substrate addition and RGR increased. We conclude that plant N:P stoichiometry reflects substrate nutrient supply. Our results suggest that the GRH also applies to terrestrial dryland photoautotrophs, but is dependent upon resources.