Variation in 13C abundance in Respiration Among Ecosystem Components: Implications for Flux Partitioning

Contrary to the longstanding notion of isotopic equilibrium among ecosystem respiration components, we found significant variation in the carbon isotope ratio of CO2 respired from leaves, stems, roots and soil microorganisms in five contrasting ecosystems along a climate gradient in California (redwood forest, chaparral, grassland, oak savanna, ponderosa pine plantation). The largest differences were observed between leaf and microbial respiration (5.84 per mil +/- 1.58 per mil; mean +/- SD) with the signature of ecosystem respiration always lying between that of leaves and microbes (leaves < ecosystem < microbes). Based on these differences, we determined that ecosystem respiration comprised an average of 25% microbial and 75% plant respired CO2 (+/- 10%). Further study is underway to determine the underlying cause of these isotopic differences.