CONTENT Vol. 2 - Humus.ru

15th IHSS Meeting- Vol. 2
Microbial Carbon Turnover and Dynamics from Biochemically Diverse
Microbial Groups in Temperate and Tropical Forest Soils
Heather M. Throckmorton a , Jeffrey A. Bird b , William R. Horwath a , Mary K. Firestone c
a Dept. Land, Air and Water Resources, UC, Davis, One Shields Ave., Davis, CA 95616,
United States; b School of Earth and Environmental Sciences, Queens College CUNY, 65-30
Kissena Blvd., Flushing, NY 11367, United States; c Dept. Environmental Policy and
Management, UC, Berkeley, 137 Mulford Hall #3114, Berkeley, CA 94720, United States.
E-mail: hthrockmorton@ucdavis.edu
1. Introduction
Microorganisms represent an important source of actively cycling carbon (C) in terrestrial
ecosystems, yet little is known of the relative importance of microbial biochemistry as a
factor influencing C stabilization across different microbial groups. This project utilized
uniformly 13 C-labeled, biochemically diverse, non-living microbial residues as substrates in a
reciprocal transplant experiment in Blodgett Forest (BF), a temperate forest in the Sierra
Nevada, and Luquillo Forest (LF), a tropical forest in Puerto Rico to examine the stability of
unique microbial biochemistries. These sites represent diverse ecosystems that are known to
support substantially different microbial communities, and provide an excellent opportunity to
look at the effects of climate, parent material, and microbial community on factors affecting
humification processes.
2. Materials and Methods
Temperate and tropical microorganisms from four biochemically contrasting groups (fungi,
actinomycetes, bacteria Ggram (+), and bacteria Ggram (-)) were isolated from BF and LF
and grown in 99-atom-percent 13 C media. Enriched microorganisms were autoclaved and
lyophilized lypholized and lysed microbial cells were added back to soil at both sites. Treated
soils were excavated at 5 time points over a span of 3 years at BF and 2 years at LF. Soils
were separated by ultrasonic/liquid density fractionation into light, aggregate-occluded, and
mineral-associated fractions. Whole soils and fractions were analyzed for total C and 13 C
using combustion gas chromatography-isotope ratio mass spectrometry (GC-IRMS). Soils
treated with temperate fungi were analyzed using Curie point pyrolysis- gas chromatographymass
spectrometry- isotope ratio mass spectrometry (Py-GC-MS-IRMS) to determine
compound-specific turnover.
3. Results and Discussion
Microbial C dynamics differed substantially between the two sites, with microbial C levels
stabilizing at 35% of input C after 12 months in BF, while in LF microbial C did not to begin
Vol. 2 Page - 19 -