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.

受磷（P）限制的环境中的植物已经开发出各种策略，可从土壤中获取磷，并维持植物内的P稳态。我们分析了两年内极度贫磷的生态系统中年降水量形成对比的情况下，草绿孢子菌-根际微生物群使用的磷获取机制。我们确定了连续两年的丛枝菌根真菌（AMF）根和土壤定植，以及三种P相关的生态酶的活性。我们还确定了植物生物量，微生物生物量和土壤中C，N和P的浓度和比率，以评估土壤微生物群落和植物的养分稳态。拟南芥在干旱年份，受P限制的地点（Pozas Azules地点）在AMF共生中投入了更多的碳。另外，磷酸单酯酶的比活性在该位点更高，表明微生物群落投入更多的能量来产生该酶以从有机分子中释放出P。总而言之，我们的结果表明，AMF共生对拟南芥有很重要的作用，以应对高度贫营养的生态系统中磷和水的限制。