HR: 0800h
AN: B11A-1015    [Abstracts]
TI: Biological N Fixation Rates in a Tropical Dry Forest Ecosystem
AU: * Santiago, L S
EM: santiago@berkeley.edu
AF: Center for Stable Isotope Biogeochemistry, University of California 3060 VLSB, Berkeley, CA 94720-3140 United States
AU: Dawson, T E
EM: tdawson@berkeley.edu
AF: Center for Stable Isotope Biogeochemistry, University of California 3060 VLSB, Berkeley, CA 94720-3140 United States
AB: Because tropical legumes are usually the dominant family in forests of the Neotropics and Africa, they represent the greatest potential terrestrial cover of N-fixing species globally. Tropical dry forests therefore may have the greatest rates of biological N-fixation of any ecosystem type. Our objective was to determine the number of legume species that fix N along a successional gradient (10, 20, and 30 years) using a combination of nodule excavation, nodule incubations, and N isotopic composition of foliage. We also quantified non-symbiotic N-fixation by free-living fixers in litter and soil. We found that 21 out of 23 legume species were nodulated. Calculations of percent N from fixation, based on N isotopic composition, ranged from 1-78 percent for individual species. At the stand level, estimates of symbiotic N-fixation was 13.9, 23.1, and 27.8 kg N/ha/yr in 10, 20, and 30 year old forest, respectively. Total non-symbiotic N-fixation, based on acetylne reduction incubations of leaf litter, fine woody debris and surface soil, was 7.5 kg N/ha/yr during the dry season and 17.1 kg N/ha/yr during the wet season. Total ecosystem estimates were 38.5, 47.7, and 52.4 kg N/ha/yr in 10, 20, and 30 year old forest, respectively. Overall, we found that non-symbiotic N-fixation was a greater proportion of total biological N-fixation than has been reported in other tropical dry forests and savanas, but our total biological N-fixation values were similar.
UR: http://ib.berkeley.edu/labs/dawson/research_mexico.php
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: Fall Meeting 2005