THE EFFECT OF NITROGEN-FERTILIZATION ON THE PHENOLOGY OF ROOTS IN A BARRIER-ISLAND SAND DUNE COMMUNITY

Little work has been done on the phenology of root growth and senescen ce largely due to methodological difficulties. The application of mini rhizotron technology has enabled the tracking of individual roots thro ugh an entire growing season. As a result, direct measures of mortalit y, root growth, and an analysis of cohorts can be obtained. This study examined the belowground response of vegetation in a nutrient limited system to nitrogen addition. Small plots on a 36 year old dune on Hog Island, a barrier island in the Virginia Coast Reserve Long Term Ecol ogical Research Site, were fertilized with nitrogen. Minirhizotron tub es were installed in each fertilized and control plot. Each tube was s ampled monthly for nine months, March through October of 1992. Root le ngth density increased throughout the growing season with the greatest root length density in the top 20 cm of the soil profile. The fertili zed plots had greater root length densities (14.1 mm cm(-2)) than the unfertilized plots (2.9 mm cm(-2)). There was no significant depth x t reatment interaction. Root mortality did not significantly change with fertilization. The largest loss of roots for a cohort occurred within the first month. The dune grassland community did not respond to fert ilization with large changes in root distribution or increases in mort ality in this study.