Productivity and Nutrient Cycling of Alaskan Tundra: Enhancement by Flowing Soil Water

Patterns of biomass, productivity, and nutrient cycling were compared between water—track and nontrack areas in Alaskan tussock tundra. Water tracks (channels of subsurface water drainage) sampled in Alaskan tundra were 2.4—fold more productive than adjacent nontrack areas due almost entirely to the 10—fold greater aboveground production of the sedge Eriophorum vaginatum L. in the track. Nitrogen and phosphorus cycled more rapidly in water tracks than in nontrack areas due to slightly warmer soil temperature, deeper thaw, higher soil phosphatase and protease activities, and more rapid nitrogen mineralization. The importance of E. vaginatum in stimulating productivity and nutrient cycling in the water track may result from its deep—rooting habit, which enabled it to exploit flowing subsurface water. Observed lateral subsurface soil water flow rates in the track (0.57 ± 0.09 cm/h) were 6 and 8 times as rapid as diffusion of phosphate and ammonium, respectively, in water and are of the right magnitude to explain the 10—fold enhancement of Eriophorum productivity in the track. Roots of E. vaginatum growing in the track had a high capacity to absorb ammonium and phosphate and thus could exploit nutrients brought to the root surface by flowing soil water. The low degree of mycorrhizal colonization of these roots makes E. vaginatum particularly sensitive to the rate of nutrient movement to the root surface. The enhanced productivity and' nutrient cycling in the water track compared with adjacent tundra probably reflect increased nutrient flux to the root surface caused by flowing water in the water track.