HR: 10:40h
AN: H52B-02    [Abstracts]
TI: Microbial community evolution across a granitic chronosequence, Santa Cruz, California
AU: * Moore, J
EM: joelmoore@psu.edu
AF: Dept. of Geosciences, Pennsyvlania State University, University Park, PA 16801, United States
AU: Macalady, J M
EM: jmacalad@geosc.psu.edu
AF: Dept. of Geosciences, Pennsyvlania State University, University Park, PA 16801, United States
AU: White, A F
EM: afwhite@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Schulz, M S
EM: mschulz@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Brantley, S L
EM: brantley@essc.psu.edu
AF: Dept. of Geosciences, Pennsyvlania State University, University Park, PA 16801, United States
AB: Ongoing research at a marine terrace chronosequence in Santa Cruz, CA includes quantification of biogeochemical and physical processes to better understand the evolution of soil development and the soil microbial community. The chronosequence, formed on granite-derived marine sediments, is located in a Mediterranean climate zone and is dominated by grassland vegetation. Two features of the chronosequence relevant to the soil microbial community are the progressive depletion of primary minerals--containing nutrients such as Ca, K, and P--with soil age, and the increase of the aboveground plant biomass from terrace 1 (65 ka) to terrace 2 (90 ka) with a subsequent decrease for terraces 3 (137 ka) and 5 (226 ka). This study investigated soil microbial community size and composition in both the surface soils (0-0.07 m) and in subsurface depth profiles (down to at least 2 meters) across the chronosequence. Trends in the surface concentrations of carbon and microbial biomass carbon (MBC) were similar to the aboveground plant biomass with an increase from terrace 1 to terrace 2 and then a slight decrease in terraces 3 and 5. Soil microbial community composition trends, measured by phospholipid fatty acids (PLFA), with soil age were somewhat different. Concentrations of the 18:2^9,12 lipid, a lipid derived from fungi as well as fine plant roots, declined with soil age. As expected from previously published studies of soil microbial communities with depth, concentrations of carbon, MBC, and PLFAs declined with increasing depth in the subsurface. Preliminary PLFA data indicated two main microbial community changes with depth. First, the 18:2^9,12 concentration decreased as a fraction of the total PLFA concentration, and second, branched chain lipids commonly associated with gram-positive bacteria increased as a fraction of the total PFLA concentration. The variation of soil carbon and the soil microbial community as a function of depth appeared to change with soil age. Shallow subsurface (0.2-1 m) carbon, MBC, and PLFA concentrations declined more rapidly relative to surface concentrations in the older terraces (3 and 5) than in terrace 2. Interestingly, the decline in the 18:2^9,12 lipid fraction was more pronounced in the younger terrace 2 soil than in the older terrace 3 and 5 soils. Results from this first study of soil microbiology across a long-term (declining ecosystem) grassland chronosequence differed from similar studies on forested long-term chronosequences. In particular, the 18:2^9,12 lipid declined as a fraction of the total PLFA pool in the surface soil with soil age, rather than increasing as was the case for the forested chronosequences. Additionally, this was the first study of subsurface soil microbiology across a long-term chronosequence. PLFA results indicated that variations in the soil microbial community with age were more significant in the subsurface than at the surface. These changes in the soil microbial community were likely connected to changes in the plant biomass. Plant biomass changes were, in turn, probably driven by the increased depletion of primary minerals and nutrients such as Ca or P with soil age across the chronosequence. At the Santa Cruz chronosequence, changes in soil chemistry due to chemical weathering appear to be driving changes in the ecology of the soil microbial community.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 1865 Soils (0486)
DE: 1886 Weathering (0790, 1625)
SC: Hydrology [H]
MN: 2007 Fall Meeting