Root herbivory alters soil microbial processes and carbon cycling

Root herbivory has the capacity to alter multiple ecosystem services in urban grass systems; it causes substantial reductions in plant productivity, and also forces new inputs of organic matter into the soil carbon pool. In this study, we quantify the impact of root herbivory on soil microbial activity and organic matter dynamics.

Third instar larvae of the European chafer (Rhizotrogus majalis) were introduced to aeroponic microcosms containing tall fescue, (Festuca arundinacea) and allowed to feed for 8 days.  Larval and plant biomass loss due to herbivory were measured. Larval frass was also collected daily from microcosms and added to frass-free soils at typical field densities (0.1% of frass to soil in dried weight). Half of the frass was heated (80 ^oC) and frozen (- 80 ^oC) to reduce microbial activity before adding to the soil. Soils were incubated at approximately 20°C for 20 days.  Over the course of the incubation, microbial respiration rates and extracellular enzyme activities were measured on soils with and without frass addition.   

Preliminary results from the soil incubation experiment indicate that frass amendments stimulated soil microbial activity. However, amendment of frass with reduced microbial activity did not alter microbial respiration. Our results suggest that root herbivory has the potential to impact belowground microbial processes and soil carbon cycling, and that microbes inhabiting insect frass modify the activity of the free-living soil microbial community.