Response of black spruce (Piceamariana) ecosystems to soil temperature modification in interior Alaska

This paper reports results of a study designed to examine the control that soil temperature exerts on soil processes associated with nutrient flux, and in turn, on tree nutrition in interior Alaska black spruce ecosystems. Approximately 50 m 2 of forest floor in a 140-year-old black spruce ecosystem, which had developed on permafrost, was heated to 8-10 °C above ambient temperature. This perturbation amounted to approximately a 1589 degree-day seasonal heat sum (above 0 °C), 1026 degree-days above the control total of 563 degree-days. The forest floor, surface 5 cm of mineral soil, and soil solution were compared with those of an adjacent control plot to evaluate the change in nutrient content and decomposition rate of the forest floor. The nutritional response to soil heating of current black spruce foliage also was evaluated. Soil heating significantly increased decomposition of the forest floor, principally because of an increase in biomass loss of the O21 layer. The increased decomposition resulted in greater extractable N and P concentrations in the forest floor, higher N concentrations in the soil solution, and elevated spruce needle N, P, and K concentrations for the experimental period. These results are discussed in light of the importance of soil temperature and other state factors that mediate ecosystem function.