PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Setting bounds on belowground NPP: Evaluating three approaches in a bottomland hardwood forest.
Whitbeck, Julie*,1, 1 University of New Orleans, New Orleans, LA, USA
ABSTRACT- Because existing methods for assessing belowground net primary production (BNPP) have important limitations, my objective is to set upper and lower bounds on the fine root component of the carbon (C) budget by using three distinct approaches in parallel: the compartment flow method employing sequential coring with decomposition corrections, minirhizotron–based root demography, and the C–balance (or total belowground C allocation) method calculated from soil respiration and fine litterfall. In addition to bracketing BNPP, I evaluate points of agreement and difference among these widely used methods. This study is set in an old growth bottomland hardwood forest at the southernmost end of the Lower Mississippi Alluvial Valley. My research team sampled at three points along a hydrologic gradient in this forest, ranging from a rarely flooded natural levee "ridge" site to a regularly inundated (5–9 month hydroperiod) "swamp" site. Tree species richness and total basal area are similar at the three focal sites, and soils along the entire gradient are fine textured Sharkey clay. My multi-year dataset spans extremely dry through normally wet years. In contrast to many upland ecosystems, fine root growth in periodically flooded bottomland forests is at least as sensitive to changes in soil water content as to variation in temperature. My data indicate that fine root production and turnover in this ecosystem are limited by both low and high soil water content and are correlated with ambient temperature. While all three approaches captured these patterns, the carbon balance approach yielded the highest estimates of BNPP, while minirhizotron–based estimates were consistently low. Variation in BNPP estimates differs among approaches and is influenced by key environmental parameters.
Key words: belowground net primary production (BNPP), bottomland hardwood forest, fine root dynamics, carbon cycle