Tieszen L.L.

Carbon Isotope Characterization of Vegetation and Soil Organic Matter in Subtropical Forests in Luquillo, Puerto Rico

Von Fischer J.C., Tieszen L.L., Carbon Isotope Characterization of Vegetation and Soil Organic Matter in Subtropical Forests in Luquillo, Puerto Rico. Biotropica Vol 27(2), 1995 pp 138-148.

Abstract: 
We examined natural abundances of "3C in vegetation and soil organic matter (SOM) of subtropical wet and rain forests to characterize the isotopic enrichment through decomposition that has been reported for temperate forests. Soil cores and vegetative samples from the decomposition continuum (leaves, new litter, old litter, wood, and roots) were taken from each of four forest types in the Luquillo Experimental Forest, Puerto Rico. SOM 613C was enriched 1.6%o relative to aboveground litter. We found no further enrichment within the soil profile. The carbon isotope ratios of vegetation varied among forests, ranging from -28.2%o in the Colorado forest to -26.9%o in the Palm forest. Isotope ratios of SOM differed between forests primarily in the top 20 cm where the Colorado forest was again most negative at -28.0%o, and the Palm forest was most positive at -26.5%o. The isotopic differences between forests are likely attributable to differences in light regimes due to canopy density variation, soil moisture regimes, and/or recycling of CO2. Our data suggest that recalcitrant SOM is not derived directly from plant lignin since plant lignin is even more "3C depleted than the bulk vegetation. We hypothesize that the anthropogenic isotopic depletion of atmospheric CO2 (ca 1.5%o in the last 150 years) accounts for some of the enrichment observed in the SOM relative to the more modern vegetation in this study and others. This study also supports other observations that under wet or anaerobic soil environments there is no isotopic enrichment during decomposition or with depth in the active profile.

carbon isotope characterization of vegetation and soil organic matter in subtropical forests in luquillo, puerto rico

Carbon Isotope Characterization of Vegetation and Soil Organic Matter in Subtropical Forests in Luquillo, Puerto Rico
Joseph C. von Fischer and Larry L. Tieszen
Biotropica
Vol. 27, No. 2 (Jun., 1995), pp. 138-148

Abstract: 
We examined natural abundances of 13C in vegetation and soil organic matter (SOM) of subtropical wet and rain forests to characterize the isotopic enrichment through decomposition that has been reported for temperate forests. Soil cores and vegetative samples from the decomposition continuum (leaves, new litter, old litter, wood, and roots) were taken from each of four forest types in the Luquillo Experimental Forest, Puerto Rico. SOM δ13C was enriched 1.6% relative to aboveground litter. We found no further enrichment within the soil profile. The carbon isotope ratios of vegetation varied among forests, ranging from -28.2% in the Colorado forest to -26.9% in the Palm forest. Isotope ratios of SOM differed between forests primarily in the top 20 cm where the Colorado forest was again most negative at -28.0%, and the Palm forest was most positive at -26.5%. The isotopic differences between forests are likely attributable to differences in light regimes due to canopy density variation, soil moisture regimes, and/or recycling of CO2. Our data suggest that recalcitrant SOM is not derived directly from plant lignin since plant lignin is even more 13C depleted than the bulk vegetation. We hypothesize that the anthropogenic isotopic depletion of atmospheric CO2 (ca 1.5% in the last 150 years) accounts for some of the enrichment observed in the SOM relative to the more modern vegetation in this study and others. This study also supports other observations that under wet or anaerobic soil environments there is no isotopic enrichment during decomposition or with depth in the active profile.
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