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USE OF THE COMPOSITION AND STABLE CARBONIISOTOPE RATIO OF MICROBIAL FATTY ACIDS TO STUDY CARBON CYCLING
Citation:
Burke Jr., R A. USE OF THE COMPOSITION AND STABLE CARBONIISOTOPE RATIO OF MICROBIAL FATTY ACIDS TO STUDY CARBON CYCLING. Presented at Centro de Energia Nuclear na Agricultura (CENA), Sao Paulo, Brazil, September 16, 1999.
Description:
We use measurements of the concentration and stable carbon isotopic ratio (*13C) of individual microbial phospholipid fatty acids (PLFAs) in soils and sediments as indicators of live microbial biomass levels and microbial carbon source. For studies of soil organic matter (SOM) cycling, the PLFA *13C technique is easiest to apply in ecosystems that have undergone a vegetation change (e.g. from C3 to C4 photosynthetic pathway) at known times in the past. For example, in Hawaiian soils we found that conversion of forest to sugar cane cultivation resulted in >65% reduction in total soil PLFA content. In contrast, the total soil PLFA content in a pasture converted from forest long ago (~90 y) was not different from that of the forest soil. PLFA Delta 13C values strongly reflected the C3 vegetation in the forest sites (-36 to -27 l), and the C4 vegetation in the pasture site (-19 to -13 l). PLFA Delta 13C values from the sugar cane soils (~50 y and 90 y since conversion) were intermediate (-24 to -15 l), which suggests that either soil microbes have adapted to more recalcitrant, older C3 carbon or that physically-protected labile C3 carbon has been released for microbial use by the greater disturbance of sugar cane cultivation. Application of PLFA Delta13C measurements to forest-pasture chronosequence ecosystems should yield valuable information regarding carbon cycling rates by adding a time component to this stable isotope technique.