The biogeochemistry of phosphorus across an alpine topographic/snow gradient

Phosphorus (P) availability has generally been assumed to be the limiting or co-limiting factor for plant growth in alpine environments. To test this assumption, the biogeochemistry of phosphorus (P) along an alpine topographic/snow gradient located on Niwot Ridge, Colorado Front Range was studied in the context of P limitation for plant growth. We measured the various P pools using a selective extraction procedure, determined sorption parameters, and quantified P availability indices. The topographic/snow gradient at Niwot Ridge is divided by the aspect and slope position in relation to the dominant westerly winds into leeward-sloping, windward-sloping and generally level sites. Our study found that the snow-melting gradient along the alpine transect greatly affected the antecedent soil moisture, which in turn, controlled the spatial pattern of the major soil attributes such as texture, OC, weathering index, bulk density, non-labile and labile P pools and P availability. The level sites exhibited the highest concentration of organically bound P (1056±75 mg/kg), labile P (315±32 mg/kg), and P in soil solutions corrected for soil adsorption capacity (field condition, 4.9±4.1 mg/l and saturated paste, 8.0±7.5 mg/l). Results of correlation analysis between the various P pools and aboveground biomass of different plant groups suggests that a high level of available P provides a growing advantage to only certain alpine plants and is not a good indicator of the spatial distribution of total aboveground biomass.