Effects of Temperature and Substrate Quality on Element Mineralization in Six Arctic Soils

We compared the effects of temperature on rates of microbial respiration, N mineralization, nitrification, and P mineralization in soils from six arctic ecosystems located along a toposequence on Alaska's North Slope. Soils from these ecosystems were incubated aerobically in the laboratory for 13 wk and at temperatures representative of field values during a typical growing season. Rates of C and N mineralization were insensitive to temperature between 3° and 9°C but increased by factors of 2 or more between 9° and 15°. For both C and N, differences in mineralization rates among soils were greater than differences due to incubation temperature within single soils. This suggests that the quality of soil organic matter varies widely among these ecosystems and is more important than soil temperature differences in controlling rates of these processes in the field. Nitrification occurred in all soils, even at 3°, but there were large differences among soils in nitrification potentials. Overall differences in P mineralization between soils were small. Rates of P mineralization, however, decreased with increasing temperature in soils from some sites and increased with temperature in others. Carbon respired during the 13—wk incubations ranged between 1.5 and 8% of total soil organic C across soil types incubation temperatures. In contrast to the relatively high C mineralization rates in these soils, net N and P mineralization rates were very low and were likely due to high microbial demand for these nutrients. High microbial demand for mineral nutrients can severely limit plant N and P availability in arctic soils.