No abstract

No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 169.230.243.252 on Sun, Abstract.Because plant litter decomposition is directly mediated by extracellular enzymes (ectoenzymes), analyses of the dynamics of their activity may clarify the mechanisms that link decomposition rates to substrate quality and nutrient availability. We investigated this possibility by placing arrays of white birch sticks at eight upland, riparian, and lotic sites on a forested watershed in northern New York. For 3 yr, samples were analyzed for mass loss, protein, total Kjeldahl nitrogen (TKN), and total phosphorus (TP) accumulation, and the activity of 11 classes of extracellular enzymes involved in C, N, and P cycling. The relationship between lignocellulase activity and mass loss did not differ among sites. TKN and TP immobilization exhibited some spatial variation; rates of accumulation per 1% loss of initial mass, estimated from linear regressions, ranged from 2.2 to 4.4 pg/g OM for TP and from 43 to 139 pg/g OM for TKN, with maximum concentrations reached at -80% mass loss. The relationship between the activities of acid phosphatase (AcPase) and Nacetylglucosaminidase (NAGase), enzymes involved in the acquisition of P and N from organic sources, and mass loss displayed even greater variation among sites; the slopes of linear regressions relating mass loss and temporally integrated activity ranged from 0.019 to 0.135 activity-months per mass loss point and 0.107 to 0.775 activity-months per mass loss point, respectively, suggesting that edaphic rather than substrate quality factors were regulating activity. The extent of N limitation at each site was inferred by plotting TKN accumulation, defined as the slope of the linear regression TKN concentration vs. mass loss, in relation to NAGase activity accumulation, defined as the slope of the linear regression cumulative NAGase activity-months vs. mass loss. P limitation at each site was similarly assessed from an analogous plot of TP accumulation in relation to AcPase activity accumulation. Low N or P accumulation in conjunction with high acquisition activity was taken as an indication of nutrient limitation while the converse indicated surfeit. The diagrams suggested that decomposition at the upland hemlock and lotic sites, which displayed intermediate rates of OM loss (zero order k = 0.29 g/mo and 0.23 g/mo, respectively), was primarily N limited, while the riparian sites, which had the lowest rates of OM loss (k = 0.14 g/mo), appeared to be P limited. Relative to the others, OM loss at the upland deciduous sites (k = 0.38 g/mo) was not limited by either N or P. The concordance of field observations with predictions based on ectoenzyme regulation mechanisms suggest that enz...

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.

No abstract