Document: CHR-3-30-18

Stand respiration and carbon balance in mid-rotation loblolly pine plantations in response to enhanced soil resource availability.

MAIER, C.A.* ¹, T.J.ALBAUGH ² and H.L.ALLEN ²

USDA Forest Service, Triangle Park, NC USA ¹
North Carolina State University, Raleigh, NC USA ²

Abstract:
Pine forests in the southeastern United States are some of the most intensively managed forests in the world and may be an important resource for sequestering atmospheric carbon (C). However, while intensive management (e.g. fertilization) increases productivity, the effect on stand C balance and loss via respiration is still unclear. In this study, we developed C budgets for 11 year-old loblolly pine plantations during the fourth year of a fertilization experiment to determine how autotrophic respiration (R_A), soil CO₂ evolution, and net ecosystem production (NEP) respond to changes in soil resource availability. C budgets were based on component analysis, i.e. biomass production and specific respiration (maintenance and growth) of individual tissues (foliage, branch, stem, fine and coarse roots) and soil CO₂ evolution. In the non-fertilized treatments, total net primary production (NPP) was 5.6 Mg C ha^-1 yr^-1 compared to 10.4 Mg C ha^-1 yr^-1 in fertilized treatments. Total R_A was 10.1 and 16.5 Mg C ha^-1 yr^-1 in non-fertilized and fertilized treatments, respectively. Belowground root respiration accounted for 63% of total R_A in non-fertilized stands, but only 53% of R_A in fertilized stands. Fertilization had no effect on soil CO₂ evolution. Annual C loss from the soil averaged 14 Mg C ha^-1 yr^-1 and contributed 79% (unfertilized) and 65% (fertilized) of ecosystem respiration (soil CO₂ evolution + aboveground R_A). NEP, calculated as the difference between NPP and soil CO₂ evolution minus belowground R_A (NEP=NPP- (soil CO₂ evolution-belowground R_A)), was 1.8 Mg C ha^-1 yr^-1 in non-fertilized stands and 4.7 Mg C ha^-1 yr^-1 in fertilized stands indicating that non-fertilized stands were functioning as slight C sources to the atmosphere while fertilized stands were strong C sinks. These results suggest that manipulating site resources may be an attractive management tool to increase the rate of C sequestration in forest ecosystems.

Keywords: respiration, soil CO₂ evolution, net ecosystem production, carbon sequestration, loblolly pine

This abstract is being presented at: 3:30 PM in session:
Oral Session #50: Plant Gas Exchange.