Cogongrass (Imperata cylindrica) reduces colonization of mycorrhizal fungi on loblolly pine (Pinus taeda) in commercial stands

Background/Question/Methods

Loblolly pine comprises over 50 percent of growing stock in commercial forests of the United States.  Imperata cylindrica, an invasive grass species native to Asia, has been shown to reduce tree vigor in Pinus taeda plantations.  This species produces allelopathic exudates that may influence community dynamics of P. taeda symbionts, like soil microbes, which have not been adequately quantified.  This interaction has the potential to negatively influence the forest products industry, which has an industrial output of $103 billion annually.  Root colonization by mycorrhizal fungi and soil microbial communities were sampled at an intensively managed site in Greene County, Mississippi, in I. cylindrica invaded (>50%) (n=3), I. cylindrica invaded (<50 %) (n=2) and non-invaded sites (n=3).

Results/Conclusions

Invaded plots had at least a 15 % reduction in abundance of ectomycorrhizal percent colonization of pine fine feeder roots in the top 40 cm of soil.  Abundance of pine fine feeder roots in the 21–40 cm and 41–60 cm layers of the soil profile was also reduced in I. cylindrica invaded plots.  Lower vegetative diversity was also observed in plots in which I. cylindrica was present, and these two variables were negatively correlated, which could have contributed to the reduced microbial diversity in I. cylindrica plots.  In addition, there were higher organic C:N ratios at sites in which I. cylindrica was present.  The variety of roles that these microorganisms undertake are vast and the loss of any functional group could negatively influence the health of a forest.  In order to determine the production and ecological ramifications of I. cylindrica we must measure the differences in biodiversity across an invasion gradient.  These differences observed in I. cylindrica plots may alter nutrient cycling, plant biodiversity and P. taeda growth, which will negatively affect industry paramount to the economy of the southeastern United States.