Mycorrhization rates of two grasses following alterations in moisture inputs in a southern mixed grass prairie

Arbuscular mycorrhizal fungi (AMF) are plant root symbionts that often improve plant nutrient and water relations in exchange for photosynthetic carbon. During times of stress; however, plants may divert resources away from the AMF, eventually causing a reduction in mycorrhization rates. In short and mixed grass regions, where inter-annual precipitation varies widely, water availability may be the most influential limiting factor for plant growth and nutrient uptake. It may also impact plant relationships with AMF, further influencing nutrient, water, and carbon relations. To investigate the effect of precipitation rates on AMF relations, we manipulated moisture inputs in a southern mixed grass prairie and quantified mycorrhization rates of two common grasses: Bouteloua hirsuta and Schizachyrium scoparium. A multivariate analysis of variance confirmed differences in mycorrhization rates between years and differences between species responses within years; however, precipitation treatment was not a significant factor in the model. Trends in means pointed to a general reduction in mycorrhization with increasing precipitation, especially for the finer rooted B. hirsute, but these trends were not significant. Independent variables (growing season phosphate, nitrate and ammonium mineralization, volumetric soil moisture) did not meaningfully correlate to mycorrhization rates of either species. Our results indicate that absolute precipitation and nutrient availability do not alone act upon mycorrhization rates. Our results further support the idea that broad generalization regarding plant-AMF relationships and responses to abiotic forces must be supported by long-term datasets; plant-AMF relationships appear to be too vulnerable to inter-annual variability to make conclusions based on short-term datasets. (C) 2012 Elsevier B.V. All rights reserved.