Decomposition of Metrosideros polymorpha leaf litter along elevational gradients in Hawaii

We examined interactions between temperature, soil development, and decompo sition on three elevational gradients, the upper and lower ends of each bei ng situated on a common lava flow or ash deposit. We used the reciprocal tr ansplant technique to estimate decomposition rates of Metrosideros polymorp ha leaf litter during a three-year period at warm and cool ends of each gra dient. Litter quality was poorest early in soil development or where soils were most intensely leached and waterlogged. In situ litter decomposition w as slowest on the young 1855 flow (k = 0.26 and 0.14 at low and high elevat ion, respectively). The more fertile Laupahoehoe gradient also supported mo re rapid in situ decay at the warmer low elevation site (k = 0.90) than at high elevation (k = 0.51). The gradient with the most advanced soil develop ment showed no difference for in situ decay at low and high elevations (k = 0.88 and 0.99, respectively) probably due to low soil nutrient availabilit y at low elevation, which counteracted the effect of warmer temperature. Co mparisons of in situ, common litter, and common site experiments indicated that site factors influenced decomposition more than litter quality did. Th e effect of temperature, however, could be over-ridden by soil fertility or other site factors. Field gradient studies of this sort yield variable est imates of apparent Q(10), even under the best conditions, due to interactio ns among temperature, moisture, nutrient availability, decomposer communiti es and litter quality. Such interactions may be as likely to occur with cha nging climate as they are along elevational gradients.