HR: 1340h
AN: B13B-1183    [Abstracts]
TI: Utilization of Soil C and N by Microbial Groups in the Presence of Living Roots
AU: * Bird, J
EM: jbird@qc.cuny.edu
AF: Queens College, CUNY, School of Earth and Environmental Science D-216 Science Bldg. 65-30 Kissena Blvd. Queens College, CUNY, Flushing, NY 11367, United States
AU: Herman, D
EM: skyhawk@nature.berkeley.edu
AF: UC Berkeley, Dept. of Environmental Science, Policy, and Management 137 Mulford Hall, #3114 UC Berkeley, Berkeley, CA 95616-3114, United States
AU: Firestone, M
EM: mkfstone@nature.berkeley.edu
AF: UC Berkeley, Dept. of Environmental Science, Policy, and Management 137 Mulford Hall, #3114 UC Berkeley, Berkeley, CA 95616-3114, United States
AB: The effects of living plant roots and N on belowground C dynamics were examined in a CA annual grassland soil (Haploxeralf) during a 2-y greenhouse study. The fate of ¹³C-labeled plant roots ( Avena barbata L.) and soil were followed under planted and unplanted conditions; and with and without N addition (20 kg N ha^-1 season^-1). The treatments were applied during 2 growing seasons and each growing season was followed by a dry, fallow period (~ 150-d long). Living roots increased the turnover rate and loss of belowground ¹³ C during and after 2 seasons compared with unplanted soils. After 2 seasons, planted soils had 21% less belowground ¹³C present than in unplanted soils. However, total soil C increased in planted soils by 4.6% compared to unplanted after 2 seasons. N additions decreased belowground ¹³C turnover during the first treatment season in both planted and unplanted soils, however no effect of N on soil C was observed thereafter. Planted soils had larger microbial biomass and the community structure differed compared with unplanted soils. Planted soils had higher proportions of gram (-) bacteria, while unplanted soils had higher proportions of gram (+) bacteria, actinomycetes, and fungi. New root and exudate C supplied from living roots increased the turnover of microbial assimilated ¹³C compared with unplanted for all microbial groups. This greater turnover of belowground ¹³C was especially significant for gram (-) bacteria, which were stimulated in the planted soil. In contrast, the activity among microbial groups in unplanted soils was similar to that prior to the initiation of the treatments and soil wet-up. Our findings suggest that A. barbata roots increased soil C levels over time because root and exudate C inputs are significant, however that C increase will be moderated by an overall faster C mineralization rate of belowground C. Increased N deposition may slow soil C losses, however, they appear minor and temporary at the rates applied and for the plant-soil system studied.
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0469 Nitrogen cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting