Cooperation between Sporobolus airoides and associated arbuscular mycorrhizal fungi for phosphorus acquisition under drought conditions in an oligotrophic desert ecosystem

Plants from phosphorus (P) limited environments have developed various strategies for acquiring P from the soil, and for maintaining P homeostasis within the plant. We analyzed the mechanisms of phosphorus acquisition used by the grass Sporobolus airoides-rhizosphere microbiota during two years with contrasting annual rainfall in an extreme P-oligotrophic ecosystem. We determined arbuscular mycorrhizal fungi (AMF) root and soil colonization, and the activity of three P-related eco-enzymes over two consecutive years. We also determined C, N, and P concentrations and ratios in plant biomass, microbial biomass and soil for assessing nutrient homeostasis of soil microbial community and plants. S. airoides invested more carbon in the AMF symbiosis in the drought year in the site more limited by P (Pozas Azules site). Additionally, the specific activity of phosphomonoesterases was higher in this site, suggesting that the microbial community invests more energy to produce this enzyme to release P from organic molecules. In conclusion, our results show evidence of the importance of AMF symbiosis for S. airoides to cope with P and water limitations in a highly oligotrophic ecosystem.