Microbial Communities in Cogongrass (Imperata cylindrica (L.) Beauv.) Invaded Commercial Loblolly Pine (Pinus taeda L.) Stands

Abstract

The economy of the southeastern United States is heavily influenced by the forest products industry with a 103 billion dollar industrial output. A significant amount of this industry relies on production forestry to meet increased consumer demands on increasingly less area. To this end over 1 billion P. taeda seedlings are produced annually, comprising over 50 % of the dominant and co-dominant growing stock. Invasion represents a substantial threat to productivity through introduction of new primary and secondary pests as well as competitors for natural resources. Imperata cylindrica is an invasive C4, perennial grass species from Japan that was initially introduced into the southeastern United States in 1912. Imperata cylindrica produces rhizomonous mats that can directly compete with native vegetation and their microbial symbionts mechanically as well as indirectly through production of potentially allelopathic compounds. In addition I. cylindrica can alter natural nutrient cycles, fire regimes and water availability. In order to determine the extent to which I. cylindrica alters commercial P. taeda stands we conducted research to ascertain specific effects. We conducted measurements of percent colonization by ectomycorrhizal fungi in the top 60 cm of the soil profile as well as measurements of fine root abundance. We conducted vegetation sampling from which we applied multiple diversity indices. We measured organic carbon and nitrogen present in the microbial biomass, as well as several other key nutrients in the soil. Finally, we analyzed the effect of individual exudate components on several ectomycorrhizal fungi found in association with P. taeda to help determine what the mechanism of invasion was. We determined that some variations in mycorrhizal abundance and fine feeder roots were evident. Vegetation was significantly less diverse in invaded plots which we were able to attribute to I. cylindrica presence. Variations were present in microbial biomass as well as several other nutrients and no one compound in I. cylindrica exudate consistently resulted in reduced growth.