PARENT SESSION
Oral Session #54: Vegetation: Controls on NPP, Global Climate Change. Presiding: W. Oechel.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
How sensitive are fine root dynamics and BNPP to short and long-term changes in soil water content?
Whitbeck, Julie1, 1
ABSTRACT- Over the last century, blockage of sediment inputs, combined with ongoing subsidence, have led to an increased hydroperiod at lower elevations in the Barataria Basin in Southeastern Louisiana. Anticipating that variation in hydroperiod and soil water content across a forested landscape will significantly influence the depth distribution, temporal dynamics and production of fine roots, I present data contrasting the effects of persistent vs. short-term differences in soil water content. In general in this bottomland hardwood forest, fine root standing crop diminishes rapidly with increasing depth; over 50% of the fine root length in the top 0-50 cm resides in the top 10 cm. Standing stocks of live and dead roots increase with increasing soil water content along a subtle topographic gradient and belowground net primary productivity (BNPP) appears greater in areas with higher soil water content. Yet severe reductions in soil water content, brought about by prolonged drought, had greater impact on fine root stocks in usually-wet than in usually-drier soils. Linking these data with preliminary observations of fine root lifespan, we anticipate increases in BNPP in coastal forested wetlands where increasing relative sea level is leading to increased hydroperiod, but annual variation in BNPP may also increase due to the greater drought-sensitivity of root dynamics in wet soils.
KEY WORDS: roots, BNPP, hydroperiod, bottomland hardwood forest