hide
Free keywords:
atmospheric co2
decomposition
soil carbon
soil respiration
global carbon-cycle
terrestrial ecosystems
interior alaska
grassland
soils
co2 evolution
turnover
storage
biomass
climate
forest
Abstract:
We studied soil organic matter (SOM) dynamics in allophanic soils (Udands) along independent gradients of temperature (altitude) and land use (forest-pasture) on the island of Hawaii. Using an integrated C-13 Signal derived from land conversion along with measurements of soil respiration and soil carbon, we separated rapid, intermediate, and very slow turnover SOM pools, and estimated turnover times for the large intermediate pool. These estimates were compared to independent estimates using either bomb-derived soil C-14 or the Century soil organic matter model. All calculations based on a three-pool SOM structure yield rates of turnover that are 3 times slower than those produced by a single pool model. Accordingly, analyses of potential feedbacks between changes in climate, atmospheric CO2, and soil carbon should incorporate the heterogeneous nature of soil organic matter. We estimate that roughly three-quarters of the carbon in the top 20 cm of these soils has turnover times less than 30 yr Turnover times for intermediate SOM double with a 10 degrees C change in mean annual temperature, suggesting that recalcitrant pools of SOM may be as sensitive to changes in temperature as the smaller labile pools.
