G05_P04

Old-growth forest and adjacent prairie show contrasting soil carbon properties not linked to aboveground litter input and chemistry

McFarlane K¹,  Mambelli S², Porras R³, Wiedemeier D⁴, Schmidt M⁴, Dawson T², Torn M^2,3

¹Lawrence Livermore National Laboratory, Livermore, United States, ²University of California - Berkeley, Berkeley, United States, ³Lawrence Berkeley National Laboratory, Berkeley, United States, ⁴University of Zurich, Zurich, Switzerland

Old-growth coast redwood (Sequoia sempervirens) forests store more carbon in aboveground biomass per area than any ecosystem, in trees that are among the oldest, largest, and most productive plant species on earth.  Moreover, redwood litter contains high levels of aromatic compounds and is relatively resistant to decay. However, little is known about belowground carbon storage or turnover time in these forests.  We compared soil carbon storage, distribution, chemical composition, and age in an old-growth redwood forest and adjacent prairie with comparatively lower productivity and more decomposable litter. Contrary to what the relative litter quality would suggest, total soil carbon stocks to 110 cm depth were higher in prairie (350 Mg C ha-1) than in redwood (277 Mg C ha-1) even with the forest O-horizon included, although differences were limited to the top 50 cm. In addition, radiocarbon values reflected shorter turnover times for bulk soil and light density fractions in redwood than prairie throughout the sampled profile. Higher amounts of pyrogenic carbon and a higher degree of SOM stabilization, as indicated by light density fraction carbon molecular characterization with ¹³C-NMR spectroscopy, appear to be instrumental in explaining the larger soil carbon stocks and longer turnover times in prairie, while differences in fine-root carbon inputs likely contribute to comparatively shorter turnover times in redwood. We conclude that at these sites fire residues, root inputs, and soil properties influence soil carbon dynamics to a greater degree than the properties of aboveground litter.