The effects of perennial grasses grown in interspecific and intraspecific combinations on the growth of their arbuscular mycorrhizal symbionts

Background/Question/Methods

Low-input high-diversity mixtures of perennial grasses possibly yield sustainable bioenergy. Research is being conducted to examine the “feasibility of feedstock production” from these grasses along a gradient of ecotypic species diversity at the Argonne National Laboratory. Although controversial, studies have identified a positive relationship between plant species diversity and productivity in various ecosystems, including grasslands. It is also known that the kinds of grasses proposed for use as biofuels feedstock offer the potential for sequestering carbon via significant inputs of their root systems and assoicated mycorrhizal fungi. In this study, we examine the influence that unfertilized Panicum virgatum commonly known as switchgrass has on extramatrical growth of arbuscular mycorrhizal fungi (AMF). We also examine whether the ecotypes of Panicum virgatum, select for specific microbial communities. Lowland ecotype Kanlow, and the upland ecotypes of Cave-in-Rockand Southlow were used in the study.  We also utilized a mixture of three ecotypes. The allocation of AMF was determined using marker fatty acid analysis to quantify AMF in the soil of various ecotypes. ANOVA and Principal Component Analysis were used to analyze data. We expected the community composition to be driven by the ecotype and the extramatrical growth to be controlled by host factors.

Results/Conclusions

Preliminary analysis on the unfertilized P. virgatum ecotypes indicate that the type of cultivar or the mixture of ecotype have no effect on extramatrical hyphae density of AMF (P=0.17). Characteristics such as plant height, or plant productivity did not show a significant variation in the unfertilized cultivars. However, ordination results indicate that higher soil carbon content was associated with Southlow and Cave-in-Rock than Mixture and Kanlow cultivars. Ordination results also indicated that each ecotype harbored a specific community of AMF. A greater abundance of Gigaspora spp as measured with fatty acid marker 20:1w9 was observed in association with up-slope Southlow and an abundance of Glomus spp bearing marker 16:1w5 was found in mid-slope Southlow cultivar. Our results indicate that P. virgatum ecotypes harbor host specific and landscape position specific AMF communities, but that AMF extrametrical hyphae density does not correlate with host factors such as root biomass.