Grass variety selection of microbial community composition is associated with differences in soil CO2 emissions

Plant-soil interactions play an important role in regulating C cycling in soils, with their management representing a potential means to regulate CO2 emissions and storage of C as soil organic matter (SOM). Therefore, crop selection, explicitly targeting beneficial plant-soil interactions may be a tool for sustainable agriculture and to support the maintenance of soil health, particularly in grassland systems which are important known stores of C. However, there is a need to understand whether the selection of different grass species and varieties can control the rates and products of C cycling, and the extent to which this is driven by the interaction with below ground microbial communities. In this study we used controlled environment microcosms to determine the emission of CO2, mineralization of soil organic matter (SOM) and plant driven microbial community selection from soil planted with one of 10 different grasses, representing 2 varieties from 5 different grass species. Total CO2 emissions significantly varied between soil planted with different grasses, with species explaining 43 % of the variation in CO2 emissions and variety 10 %. SOM mineralization and the composition of the microbial community as characterised by 16SrRNA gene profiling was also found to vary between soils planted with different grasses. Root biomass was a significant predictor (r2 = 0.17, P < 0.005) of total CO2 emissions, but not soil organic matter mineralization, while microbial community composition was found to explain 9 % of CO2 emissions. These results suggest that there is the potential to mitigate the production of CO2 from grasslands through the selection of grass varieties that promote the immobilization of C rather than its emission as CO2 and that this is both a function of plant traits and the soil microbial community.