The abiotic environment can dictate the relative costs and benefits of plant-arbuscular mycorrhizal fungi (AMF) symbioses. While the effects of varying light or soil nutrient conditions are well studied, outcomes of plant-AMF interactions along soil moisture gradients are not fully understood. It is predicted that mycorrhizal associations may become parasitic in extreme soil moisture conditions. Under low soil moisture stress, costs of maintaining a mycorrhizal symbiont may outweigh benefits for the host plant, whereas under high soil moisture stress, the host plant may not need the symbiont. In a factorial growth chamber study, we investigated the effects of a plant-arbuscular mycorrhizal fungus symbiosis along a soil moisture gradient on growth, cell wall chemistry, and root architecture of a biofuel crop, Panicum virgatum (switchgrass). Regardless of soil moisture conditions, we found an increase in the number of tillers, number of leaves, root biomass, and amount of cellulose and hemicellulose in response to root colonization by the arbuscular mycorrhizal fungus. The fungus also increased aboveground biomass and changed several root architectural traits, but only under low soil moisture conditions, indicating a reduction in benefits of the mycorrhizal association under high soil moisture. Results from this study indicate that an arbuscular mycorrhizal fungus can increase some key measures of plant growth and cell wall chemistry regardless of soil moisture conditions but is most beneficial in low soil moisture conditions.

非生物环境可以决定植物丛枝菌根真菌（AMF）共生的相对成本和收益。尽管已经很好地研究了变化的光照或土壤养分条件的影响，但尚未完全了解植物-AMF沿土壤水分梯度的相互作用结果。据预测，在极端土壤湿度条件下，菌根结合可能会寄生。在低土壤水分胁迫下，保持菌根共生体的成本可能超过寄主植物的利益，而在高土壤水分胁迫下，寄主植物可能不需要共生体。在一项析因生长室研究中，我们研究了土壤水分梯度下植物丛枝菌根真菌共生对生物燃料作物的生长，细胞壁化学和根系结构的影响，Panicum virgatum（柳枝switch）。无论土壤湿度条件如何，我们发现响应丛枝菌根真菌的根定殖，分ers数，叶片数，根生物量以及纤维素和半纤维素的数量都会增加。真菌还增加了地上生物量，并改变了一些根部建筑特征，但仅在土壤湿度较低的情况下，这表明在土壤湿度较高的情况下，菌根结合的益处降低。这项研究的结果表明，无论土壤湿度如何，丛枝菌根真菌均可提高植物生长和细胞壁化学的某些关键指标，但在土壤湿度低的条件下最有利。