Kristen Howerton, The Effect Of Herbicides On Natural Rates Of Lignocellulose Degradation By Indigenous Soil Microflora
Faculty Chair: Dr. Henry Spratt
This is an ex situ mesocosm study that investigates the effects of four commonly used non-crop herbicides, Krenite®, Velpar®, Plateau®, and Roundup®, on the rates of uniformly 14C-labeled lignocellulose degradation in soil. Mineralization of small amounts of Quercus alba 14C-labeled lignocellulose, previously prepared in H.G. Spratt's laboratory, was then observed. Herbicide treated soil was twice transferred from the mesocosm apparatus to a microcosm apparatus. The amount of 14CO2 released from the 14C-lignocellulose was collected and quantified in order to establish rates of lignin and cellulose degradation for each treatment and then compared with the controls. Using t-tests, no significant differences in lignin degradation were observed for herbicide treated microcosms during the first incubation. During the second incubation, the Plateau treated microcosms stimulated lignin degradation (p=0.07). This indicates the possibility of a second microbial population using the Plateau as a food source and indirectly supplying lignin degrading microbes with nutrients, possibly nitrogen and phosphorous, to enhance degrading potential. In 14C-cellulose labeled microcosms, Krenite, Roundup, and Velpar stimulated microbial degradation during the first incubation (p=0.01, p=0.03, and p<0.01, respectively). This may indicate the possibility of an acute stimulatory effect on cellulose degrading microbes. During the second incubation, faster cellulose degradation was observed for Krenite (p=0.01) and Roundup (p<0.01). This indicates a longer-term microbial stimulation for these two treatments that is continued from the first incubation. Analyses that compared lignocellulose degradation rates of the first and second incubations, for all herbicide treatments, found significantly faster rates during the second incubation in every case. This indicates that exposure to the selected herbicides, at concentrations specified by label instructions, may have an effect on the rates of lignocellulose degradation in forest soil. More information is necessary to fully characterize the effects herbicides may have on the soil microbial community if herbicide application continues to grow in popularity as a forest management technique.