PARENT SESSION
Poster Session #42: Carbon Storage.
Thursday, August 9, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
145
Influence of N Availability on C Sequestration in Soils.
Bailey, Vanessa1, Smith, Jeffrey2, Bolton, Harvey1, 1 2
ABSTRACT- The carbon and nitrogen cycles in soil are intimately linked. The availability or lack of one drives the mineralization or immobilization of the other. Insufficient N in soil may result in the mineralization of soil organic matter (SOM) as SOM-N is "mined" by soil microorganisms. Excess N in soil may result in the mineralization of SOM-C by soil microorganisms. We hypothesize that soils from different ecosystems will have an optimal level of soil N that will enhance soil C sequestration. To test this, we incubated soils from four different ecosystems (tall grass prairie, desert, Douglas fir forest, no-till agroecosystem) for 12 weeks. Each soil received a pre-set amount of 14C-labelled glucose and varying amount of 15N-labelled N to provide a C:N ratio of 0, 100:1, 80:1, 40:1, and 20:1. The N and C in various soil pools was assayed at 1, 2, 4, 8, and 12 weeks. In addition to monitoring 14CO2 evolution weekly for the duration of the experiment, each sample was sequentially extracted with water, subjected to chloroform fumigation-extraction to measure soil microbial biomass, and then extracted with 0.5 M sodium hydroxide (humic fraction). Examination of the 14C enrichment of these fractions over the duration of the incubation indicates that while each soil stored a different amount of C in the humic fraction, this quantity did not differ greatly in response to the different N additions. Storage of C in this fraction reached a plateau after 8 weeks at ~1.9% of the applied 14C for the desert soil, ~2.5% for the agricultural soil, ~3.5% for the tall grass prairie soil, and ~1.8% for the Douglas fir forest soil.
KEY WORDS: C Sequestration, Soil C and N, Soil C cycling