Nitrogen mineralization rates of the soils incubated under different temperatures from different elevations along an environmental gradient on Yakushima Island

摘要

Soil nitrogen (N) mineralization is the product of the soil biochemical properties and temperature. It is known that in situ soil N mineralization monotonously decreases with increasing elevation along a mountain slope reflecting decreasing air temperature. However, inherent soil biochemical properties (quality of organic matter and soil microbe profile) may also affect the decreasing soil N mineralization. We analyzed how temperature and inherent soil organic matter quality affect soil N mineralization rates using the elevation gradient of Yakushima with a "common-site" approach with multiple incubation temperatures. We collected topsoils from seven forests at seven different elevations along 170-1,550 m a.s.l and incubated them under each of four temperatures at 15, 20, 25 and 30 degrees C for 10 days in the lab. We also measured soil microbial biomass and heterotrophic soil respiration rates. Net soil N mineralization rates incubated at 15, 25 and 30 degrees C decreased significantly linearly with increasing elevation of the origin of the soil samples at the same temperature and the intercepts of the regression lines were similar among incubation temperatures 15, 20 and 25 degrees C. These results indicated that in situ net N mineralization rates are regulated primarily by quality of soil organic matter in our sites. Soil phenolics/N ratios increased with increasing elevation reflecting the vegetation shift along elevation and significantly negatively correlated to net soil N mineralization rates incubated at 15 degrees C. We conclude that elevationally differentiated vegetation and associated inherent soil properties exert strong influences on net soil N mineralization rates on Yakushima Island.