Leaf level gas exchange is modulated by the effects of mycorrhizae on aboveground production and soil moisture in a prairie restoration experiment

Complex interactions between community production and resource availability can modulate plant physiological responses that in turn serve as feedbacks for future production. Our objective herein was to investigate leaf-level responses of dominant plant species, established as part of a 4.5 ha experimental prairie restoration, to resource availability modulated by mycorrhizal fungi (MF) abundance; as these parameters likely affect restored community assembly. Light-saturated net photosynthetic rates (A_max) of newly mature leaves were measured over 2 years from the 10 most common species growing in 250 m² plots (n=24) with ambient or reduced levels of MF (chlorothalonil fungicide reduced MF root colonization by 35% across years). Complex interactions among leaf physiology, abundance of MF, aboveground production and soil moisture were found. A_max was reduced on average 32% across species in reduced MF compared to ambient MF plots in 2005, however in 2006 the reduction was only 11%. Similar reductions in leaf conductance to water vapor often explained the A_max response. Plots with reduced vs. ambient MF had lower aboveground production and higher soil water content, especially in 2006. The greater availability of water in reduced MF plots, due to lower evapotranspirational water loss of less productive plots, appeared to ameliorate the reduction in gas exchange of plants during the dry year of 2006. Pending nutrient analyses may reveal the role of tissue nutrient concentrations in these interactions. Changes in soil moisture brought about by vegetation will be important to consider as we investigate the multiple controls on community establishment in restoration efforts.