Phosphorus Cycling in Alaskan Coastal Tundra: A Hypothesis for the Regulation of Nutrient Cycling

The bulk of all phosphorus which circulates through the Barrow wet meadow tundra occurs in dead soil organic matter and has a residence time of 220 yr. In contrast, the soil solution phosphorus pool has a residence time of 10 h and must be replenished 200 times in the course of the growing season. Since atmospheric and weathering inputs of phosphorus to the Barrow tundra are negligible, decomposition of organic matter is the major avenue by which the soil solution phosphorus is replenished. Plant and animal biomass is largely belowground and is associated with the decomposition process or with extraction of phosphorus and other nutrients from soil. Forty percent of the annual transfer of phosphorus to the soil soluble P pool occurs within 10 d of snowmelt. Evidence is presented indicating that decomposition is the bottleneck in the Barrow phosphorus cycle. We hypothesize that phosphorus released by microorganisms during their periodic population crashes accounts for most of the phosphorus return to the available phosphorus pool and that decomposition rate at Barrow is limited by the rate at which these microbial populations recover. This rate of return to the available phosphorus pool in turn determines the rate of phosphorus uptake by vascular plants.