HR: 1340h
AN: B43A-0247    [Abstracts]
TI: Long-term carbon accumulation in a cold desert: Role of shrub islands and soil moisture across a long chronosequence of shoreline dunes at Mono Lake, CA
AU: * Shuldman, M I
EM: mishuldman@berkeley.edu
AF: University of California, Davis, 1 Shields Ave, Davis, CA 95616 United States
AU: Aanderud, Z T
EM: ztaanderud@ucdavis.edu
AF: University of California, Davis, 1 Shields Ave, Davis, CA 95616 United States
AU: Richards, J H
EM: jhrichards@ucdavis.edu
AF: University of California, Davis, 1 Shields Ave, Davis, CA 95616 United States
AB: It is widely recognized that old growth forests store a significant amount of carbon (C); however, little attention has been paid to the role of ``old-growth'' deserts in sequestering C. Although productivity in deserts is low, slow decomposition rates could result in significant amounts of stored C, especially when considering that deserts comprise 30% of the global terrestrial landscape. Carbon stores in deserts may be more permanent than in ecosystems with higher precipitation where decomposition is rapid or in agricultural fields with no permanent stores of woody material. Current models do not take into account the complex non-linear relationships present in soil C dynamics. Examinations at multiple scales of decomposition processes, SOM formation, and C accumulation are needed to further our understanding of this dynamic biological interface.
Our research integrates a direct inventory of stored C (to 2 m soil depth) with a decomposition study of four litter types (roots, woody stems, woody roots, leaves) to determine if net C accumulation is due to slow decomposition rates. This study utilizes the spatial variation of shrub islands and interspace patches typical of deserts, while also incorporating variation at a landscape scale across a chronosequence of dune systems ranging from 48 to 1800-3000 years old. Our global hypothesis is that decomposition rates and C storage at our site are functions of spatiotemporal variation at the landscape scale and variation at the scale of shrub islands and interspace patches. Further, soil moisture variation at these scales is one primary factor governing C loss and SOC accumulation.
We found heterogeneity in soil moisture, EC, pH, and microbial biomass at both the scale of shrub islands and interspaces and the landscape scale. In 2004, using average water content of soil from 25-75 cm depth, shrub island soils were 17-33% drier than interspace soils, and shrub islands at the youngest site were 54% wetter than shrub islands at the oldest site. At the youngest site pH was 25% higher than the oldest site in interspaces (9.8, 7.9) and 12% higher in shrub islands (9.9, 8.8). Between 0-200cm, amounts of coarse (>2mm) and fine (<2mm) litter were generally larger at the two older sites than the two younger sites. In contrast to both coarse and fine litter, which decreased with depth along the chronosequence, the highest amounts of roots were found from 40-100cm. After one year, woody stems in buried litter bags lost from 9.1% (± 1.7) to 22.1% (± 1.2) of their mass. The highest percent loss occurred in shrub islands and interspaces at our 300-year-old site. Preliminary data show that over the same period of time woody roots lost from 14.8% (± 0.03) to 33.0% (± 0.02) of their mass. In contrast to the woody stems, both the highest (in interspaces) and lowest (in shrub islands) percent mass lost occurred at the youngest site.
Our initial data show that soil moisture alone does not correlate with decomposition rates at our site, but that other factors such as microsite, dune age, pH, and EC are relevant. Work on other parameters, including soil organic and inorganic carbon amounts in soil and decomposition parameters of four litter types, is continuing to provide an integrated analysis of the factors interacting across the two spatial scales to determine decomposition rates and C accumulation.
DE: 0428 Carbon cycling (4806)
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: Fall Meeting 2005