Impact of Tree Inoculation by Leptographium terebrantis on Soil Microbial Communities in Commercial Loblolly Pine Stand

Abstract

A variety of abiotic and biotic stressors, including root-feeding bark beetles and pathogenic ophiostomatoid fungi, are associated with root disease of Pinus spp. Our research goal was to analyze if a tree inoculation by ophiostomatoid fungus, Leptographium terebrantis affects soil microbial biomass, new root growth, and ectomycorrhizal colonization of fine roots in a commercial loblolly pine stand in Eufaula, AL. The study design included three replicates of five treatment levels. We also examined soil physiochemical composition and foliar nutrients prior to the inoculation treatment. The treatment effect on microbial biomass and ectomycorrhizal colonization of fine roots were insignificant. Seasonal variation in microbial biomass and soil C/N ratio was evident, both before and after the inoculation treatment. Microbial biomass responds positively to soil moisture and soil organic matter. The treatment effect on new root growth was insignificant until December 2018. A difference in new root growth among treatments was observed in February 2019. In 2017 and 2018, new root growth was rapid in the spring and summer, while it declined in the fall. Maximum new roots during the two-year study period were observed at 28.3 and 35.4 cm depths. New root growth was not significant for the treatment and control pairs within the treatment plots. Ectomycorrhizal colonization varied by depth and was highest at the 20-30 cm soil depth. More acidic soil favored ectomycorrhizal colonization in our commercial loblolly pine stand. Total soil N, total S, available Mg, and pH were significantly different among treatments before inoculation. Excluding available Cu and Al, soil chemical properties were significantly different among depths. Except for foliar Mn, pre-inoculation foliar nutrients were not significantly different among treatments. Our study has allowed us to understand the response of soil biological properties to loblolly pine infection with L. terebrantis as well as the importance of soil moisture, soil organic matters and balanced soil pH for overall stand health.