The Effects of Topography and Nutrient Status on The Biomass, Vegetative Characteristics, and Gas Exchange of Two Deciduous Shrubs on An Arctic Tundra Slope

Abstract

The effect of topography and water drainage patterns on the nutrient status, aboveground biomass, vegetative characteristics, and leaf gas exchange of Betula nana and Salix pulchra were studied on an Alaska tussock tundra slope. To help evaluate whether any differences found were due to variation in nutrient availability or other factors that varied along the gradient, fertilizer-treated plots were used as a comparison. The highest nitrogen and phosphorus concentrations occurred in plants from water-drainage areas, indicating improved nutrient availability. Downslope movement and accumulation of these nutrients, on the other hand, appeared limited and localized. While aboveground biomass of the two shrubs was also consistently higher in drainage areas, it was not closely correlated with tissue nutrient levels, indicating that other factors besides nutrients are involved in controlling the biomass of these species along the gradient. The variation in vegetative characteristics suggests that S. pulchra may be more strongly limited by nutrient availability on the slope than B. nana. Net photosynthesis and leaf conductance were unaffected by nutrients both on the slope and in fertilized plots, but were depressed at the drier end of the moisture gradient on the slope during a midseason period of drought.