Soil Microbes Compete Strongly with Plants for Soil Inorganic and Amino Acid Nitrogen in a Semiarid Grassland Exposed to Elevated CO2 and Warming

Authors

Janet Chen, University of Wyoming
Yolima Carrillo, University of Western Sydney
Elise Pendall, University of Western SydneyFollow
Feike A. Dijkstra, University of SydneyFollow
R. Dave Evans, USDA-ARS
Jack A. Morgan, Washington State University
David G. Williams, University of WyomingFollow

Date of this Version

2015

Citation

Ecosystems (2015) 18: 867–880

Comments

U.S. Government Work

Abstract

Free amino acids (FAAs) in soil are an important N source for plants, and abundances are predicted to shift under altered atmospheric conditions such as elevated CO₂. Composition, plant uptake capacity, and plant and microbial use of FAAs relative to inorganic N forms were investigated in a temperate semiarid grassland exposed to experimental warming and free-air CO₂ enrichment. FAA uptake by two dominant grassland plants, Bouteloua gracilis and Artemesia frigida, was determined in hydroponic culture. B. gracilis and microbial N preferences were then investigated in experimental field plots using isotopically labeled FAA and inorganic N sources. Alanine and phenylalanine concentrations were the highest in the field, and B. gracilis and A. frigida rapidly consumed these FAAs in hydroponic experiments. However, B. gracilis assimilated little isotopically labeled alanine, ammonium and nitrate in the field. Rather, soil microbes immobilized the majority of all three N forms. Elevated CO₂ and warming did not affect plant or microbial uptake. FAAs are not direct sources of N for B. gracilis, and soil microbes outcompete this grass for organic and inorganic N when N is at peak demand within temperate semiarid grasslands.