Variation of Soil Amino Acid Pools and N-hydrolysis Potential in Arid Lands

Identification of the patterns through which potential rates of proteolysis and ammonification are affected by key edaphic and climatic factors offer a powerful avenue for elucidating the potential of nitrogen (N) cycle processes in arid terrestrial ecosystems. Here, we aimed to investigate how the tradeoff between soil properties and climatic factors govern amino acids and the nitrogen cycling enzyme traits in steppe biomes. We analysed changes in amino acid pools and protease and amidohydrolase activities along arid and semi-arid climate gradients over time. The biome edaphic factors (site) were found to have significant (p < 0.001) effects on all enzyme activities, while climatic factors (time) showed significant (p < 0.001) effects on protease, L-glutaminase, and L-asparaginase activities. Over the sites and times, the soil moisture (%) explained 20%-27% of the variation in protease, L-glutaminase, and L-asparaginase activities. Soil-free amino acid concentrations were observed to be significantly affected by site (p < 0.05). The aliphatic and polar amino acid pools, however, were the only soil-free amino acid pools that significantly varied with time (p < 0.05). Pools of aliphatic and polar amino acids were significantly negatively correlated with soil moisture (r = -0.55, p < 0.05). These results find that the soil N dynamics in arid ecosystems might dramatically depend dramatically on edaphic factors and plant litter properties, and changes in soil pH, electrical conductivity, clay content, total soil organic carbon and total soil and litter N maybe even more important than the soil moisture, although sensitivity to edaphic factors were found to vary with a pathway and time of sampling. Thus, the information on N pools and N-hydrolysis potential could be useful in linking climatic-soil factors with arid ecosystem N fluxes.