PS 30-115 - Microarthropods alter abundance of arbuscular mycorrhizal fungi in a perennial bioenergy crop mesocosm

Background/Question/Methods

Bioenergy crops form associations with arbuscular mycorrhizal fungi (AMF), which will enhance plant nutrition and productivity. Another appealing aspect of AMF association in perennial bioenergy crops is carbon storage, as the bioenergy crops transfer carbon belowground to their AMF mutualists. Recent work has advocated for placing this bioenergy crop-AMF relationship in a more complete ecological context, specifically by incorporating the effects of soil fauna. Soil fauna such as mites and springtails may directly modify the crop-AMF relationship by feeding on crop roots and fungal hyphae. Indirectly, soil fauna may alter patterns of nutrient availability through processing of soil organic matter and regulating microbial activity. In a greenhouse mesocosm experiment, we tested for effects of microarthropod communities from two bioenergy cropping systems—switchgrass (Panicum virgatum) and energy sorghum on AMF abundance. Specifically, we asked does microarthropod community presence and origin alter AMF abundance in soil? Switchgrass plants were grown from rhizomes in one of three experimental conditions: 1) microarthropod community from switchgrass soil, 2) microarthropod community from energy sorghum soil, and 3) a defaunated control soil. Switchgrass plants were grown for 5 months, after which we assessed AMF root colonization and the length of extraradical hyphae in the mesocosm soil.

Results/Conclusions

We found that the soil fauna treatments altered mycorrhizal abundance in the mesocosms. Specifically, extraradical hyphal length was 75% and 107% greater in switchgrass mesocosms and energy sorghum mesocosms, respectively, than control mesocosms without microarthropods. There was no significant difference in extraradical hyphal length between the switchgrass microarthropod and the energy sorghum microarthropod treatments. The increase in extraradical hyphal length suggests that microarthropods may be altering nutrient availability in soil, promoting AMF growth in the soil. While extraradical hyphal lengths in soil differed among the treatments, levels of root colonization were similar among the three treatments, with average root colonization values between 62.9% and 77.2%. Collectively, these results suggest that the presence of microarthropods does impact AMF abundance in the soil, but perhaps not the activity of AMF in the roots of their host plants. Our results highlight the possibility that microarthropods may promote AMF abundance in the soil of bioenergy cropping systems, with potential carbon accrual benefits. Future efforts should quantify the carbon storage benefit from microarthropod presence.