Long-term effects of site preparation and fertilization on total soil CO2 efflux and heterotrophic respiration in a 33-year-old Pinus taeda L. plantation on the wet flats of the Virginia Lower Coastal Plain.

摘要

Total soil CO2 efflux on the soil surface (FS) is the dominant respiratory flux in forest ecosystems. Therefore, minor changes in FS would impact net ecosystem productivity (NEP) and thus, short- and long-term carbon sequestration. Intensive site management (i.e., site preparation, competition control, fertilization amendments) affects FS by influencing resource availability and site productivity. We evaluated the long-term (rotation-age) effects of site preparation and fertilizer application on FS and heterotrophic respiration (RH) in a 33-year-old loblolly pine (Pinus taeda) plantation located in the wet flats on the Lower Coastal Plain of Virginia, USA. The study was established by the USDA Forest Service and Union Camp Corporation in 1968. Fertilizer was applied at stand age 9. We utilized an existing long-term study that consisted of a randomized complete block design split by fertilizer treatments which were replicated 3 times. Each of the 3 site preparation treatments (chopped, windrow-bedded and ditched) were split by 4 fertilizer treatments: (1) no nutrient additions (control); (2) 84 kg P ha-1 (P); (3) 112 kg N ha-1 and 84 kg P ha-1 (NP); and (4) 112 kg N ha-1, 84 kg P ha-1, and 2240 kg lime ha-1 (NPL). Total soil CO2 efflux and heterotrophic respiration were measured in July 2004 in 2 locations using an infrared gas analyzer with a dynamic closed cuvette chamber. We found decreased FS (P<0.05) in bedded and ditching treatments relative to the control 33 years after the treatment, and increased FS (P<0.05) 24 years later between NPL and P treatments. Our results indicate that silvicultural treatments can exert long lasting impacts on FS in intensively managed loblolly pine stands. Differences in FS among treatments were correlated with treatment differences in total stand biomass measured in a previous study. High within-treatment variation in RH masked potential differences in soil microbial biomass and activity for the treatment examined..