Effects of fertilization and vegetation control on microbial biomass carbon and dehydrogenase activity in a juvenile loblolly pine plantation

Abstract

To characterize the influences of fertilization and understory vegetation suppression on microbial biomass and activity in a juvenile loblolly pine plantation, we measured microbial biomass C (Cmic) and dehydrogenase activity in soil monthly in response to (1) untreated control (CONT), (2) understory suppression with glyphosate (BC), (3) pine removal (NP), (4) pine removal with understory suppression (NPBC), (5) urea + diammonium phosphate with understory suppression (UDBC), and (5) slow-release urea with understory suppression (CUFBC). Cmic and dehydrogenase activity were significantly decreased relative to the CONT treatment by the NP, NPBC, UDBC, and CUFBC treatments. These reductions likely indicate a dependence of soil microbes on labile C sources derived from living vegetation. Fertilization + brush control decreased Cmic and dehydrogenase activity to a greater extent than brush control alone, suggesting that the availability of labile C sources was adversely affected by fertilization. Short-term reductions in C mic were correlated with increases in soil NO3-. Results of this study demonstrate that, in this young, intensively managed pine plantation, labile C substrates from vegetation may be a predominant determinant of soil N availability through its influence on microbial biomass and activity. Copyright © 2005 by the Society of American Foresters.