Topographic Patterns of above- and Belowground Production and Nitrogen Cycling in Alpine Tundra

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.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract.Topography controls snowpack accumulation and hence growing-season length, soil water availability, and the distribution of plant communities in the Colorado Front Range alpine. Nutrient cycles in such an environment are likely to be regulated by interactions between topographically determined climate and plant species composition. We investigated variation in plant and soil components of internal N cycling across topographic gradients of dry, moist, and wet alpine tundra meadows at Niwot Ridge, Colorado. We expected that plant production and N cycling would increase from. dry to wet alpine tundra meadows, but we hypothesized that variation in N turnover would span a proportionately greater range than productivity, because of feedbacks between plants and soil microbial processes that determine N availability. Plant production of foliage and roots increased over topographic sequences from 280 g.m-2.yr--l in dry meadows to 600 gm-2 yr-I in wet meadows and was significantly correlated to soil moisture. Contrary to our expectation, plant N uptake for production increased to a lesser degree, from 3.9 g N-m-2 yr-' in dry meadows to 6.8 g N.m-2 yr-' in wet meadows. In all communities, the belowground component accounted for the majority of biomass, among communities. These results indicate that the topographic soil moisture gradient is in fundamental control of the patterns of N turnover among communities and that differences in plant species do not appear to be as important.

Contrasting patterns of soil N-cycling in model ecosystems of Fennoscandian boreal forests

“…Many studies on gross N turnover in high-latitude forest and tundra ecosystems have shown that NH 4 + production seldom exceeds gross N consumption (all processes consuming NH 4 + ) (e.g., Davidson et al 1992;Fisk et al 1998;Fisk and Fahey 2001;Perakis and Hedin 2001;Carmosini et al 2002;Booth et al 2005). This was also found here in the DS and SH, but not in the TH forest type.…”

“…The parallel sub-sample, t 24 , was placed in O 2 -permeable polyethylene bags (Eno 1960) and incubated in the field under the mor-layer in the forest type, from which the soil was sampled, for 24 h before extraction. Short-term net N mineralization after 24 h (Stark and Hart 1997), was calculated as the difference in the sum of NH 4 + and NO 3 À between the t 24 and the t 0 extracts, (Fisk et al 1998). Long-term net N mineralization and net nitrification rates were determined in soil equivalent to 25 g d.m.…”

The unexpected versatility of plants: organic nitrogen use and availability in terrestrial ecosystems

“…Mayer et al (1995) found that amino acids released from sediment after incubation with proteases were depleted in methionine, and concluded that microbial coat proteins were an important source. Soil microbial biomass N typically turns over several times a year (Davidson et al 1992;Fisk et al 1998), and produces a labile N pool that is rapidly degraded (Marumoto et al 1982;van Veen et al 1987;Groffman et al 1993;Mengel 1996). Maximum soluble protein concentrations and/or protease activities are often observed immediately after a peak and decline in microbial biomass Nannipieri et al 1979;Asmar et al 1994;Lipson et al 1999b).…”

“…However, potential protease rates are usually several orders of magnitude higher then net N mineralization rates, even allowing for the fact that these protease rates were often measured with unlimiting substrate and at high temperatures (Alef et al 1988;Chapin et al 1988;Smith et al 1989;Asmar et al 1994;Watanabe and Hayano 1995;Yamagata and Ae 1999). Two studies in the Colorado alpine that measured rates of proteolysis of native substrate only, without protein amendments, and adjusted the rates for field temperature estimated amino acid fluxes of 42-109 µg N g -1 soil year -1 (Raab et al 1999;Lipson et al 2001), values which are slightly greater than estimates of gross N mineralization rates for the ecosystem (Fisk et al 1998), and much greater than net N mineralization (Fisk and Schmidt 1995). Published rates of soil protease activity using a variety of techniques and incubation temperatures usually range from 0.1 to 4 µmol g -1 soil h -1 amino acid released (Chapin et al 1988;Smith et al 1989;Asmar et al 1994;Yamagata and Ae 1999).…”

Nutrient and carbon relations in subalpine dwarf shrubs after neighbour removal or fertilization in northern Italy

“…Indeed the productivity of cold ecosystems has long been known to be limited by brevity of the growing season (Billings and Mooney 1968;Körner 1999) and reduced soil nutrient availability Havström et al 1993;Parsons et al 1994;Press et al 1998). Plant growth in cold ecosystems may also be influenced by soil moisture, especially in alpine regions where sharp differences in soil water availability are associated with micro-topography (Gerdol and Smiraglia 1990;Fisk et al 1998).…”