Nitrogen budget of a shortgrass prairie ecosystem

Abstract

A N budget is presented for a shortgrass prairie ecosystem. The grassland was ungrazed by domestic herbivores. The quantities of N in various plant, animal, microorganism, and soil components of the ecosystem are estimated for the date when aboveground living biomass was at its maximum for the growing season of 1973. Annual transfers of N between the various compartments were also estimated.Of the total N, 99.5% was in organic forms. The relatively inert heteropolycondensate fraction of the organic matter in the soils contained 88.8% of the N. Living organisms contained 4.2% and dead but recognizable organisms or part thereof contained 6.5% of the total N. Belowground animals contained more than 10 times as much N as abovegroud animals, but combined, animals contained less than 0.1% of the total in the system. Living plant material contained 2.5% of the total N. Seventy-two percent of the living plant N was below ground. Microorganisms contained 1.4% of the total N.Total N uptake by plants from soil solution was 2.9 g·m·yr. Aerial portions of plants were allocated 1.9 N·m·yr although apparently 26% of this amount came from internally recycled sources. The heteropolycondensate fraction of the soil contributed 0.7 g N·m·yr to mineral forms, but these components of the system were assumed to be in steady state; thus an equal amount of mineral N was allocated back to the source. Mineralization of N from plant residues was sufficient to account for all of the N taken up by plants from soil solution. Soil animals immobilized about 0.4 g N·m·yr while the amount shunted to aboveground animals was trivial.

The biogeochemistry of a north-temperate grassland with native ungulates: Nitrogen dynamics in Yellowstone National Park

“…Much attention has been devoted to the biogeochemical cycles of North American grasslands (e.g. Woodmansee et al 1978, Risser & Patton 1982, Schimel et al 1985b, including studies of nitrogen cycling on prairie dog (Cynomys Zudovicianus) colonies grazed by bison (Bison bison) in mixed-grass steppe (Holland & Detling 1990, Holland et al 1992. However, little is known about nutrient dynamics of temperate grassland ecosystems supporting large herds of free-roaming ungulates.…”

CO2ENHANCES PRODUCTIVITY, ALTERS SPECIES COMPOSITION, AND REDUCES DIGESTIBILITY OF SHORTGRASS STEPPE VEGETATION

“…A second objective was to determine whether growth under elevated CO 2 would alter forage digestibility of codominant species, as it had in the tallgrass prairie where lower forage N concentration was cited as a contributive factor (Owensby et al 1996a). Since N is cycled tightly in the shortgrass steppe, with much of it tied up in microbial biomass (Woodmansee et al 1978), we hypothesized that forage quality would decline in the shortgrass steppe under elevated CO 2 due to the inability of those soils to provide additional N to keep pace with CO 2 -induced growth responses , and would be reflected in reductions in in vitro dry-matter digestibility for all species. We also hypothesized that the decline in forage quality would be similar across species, based on the assumption of similar species production responses to CO 2 enrichment.…”

Nitrogen cycling of atmosphere-plant-soil system in the typical Calamagrostis angustifolia wetland in the Sanjiang Plain, Northeast China

“…In general, the content of inorganic N in wetland soil is much lower, and it is often the most limited nutrient which directly affects the productivity of wetland ecosystem (Mistch and Gosselin, 2000). At present, the studies related to N cycling in wetland were widely reported by researches (Woodmansee et al, 1978;Hayes, 1985;Yoneyamad et al, 1993;Middelburg and Joop, 1998), some researchers also adopted 15 N technique to study the movement, transformation and fate of N (McKinney et al, 2001;Nordbakken et al, 2003;Ulrike et al, 2004). In general, these researches Project supported by the Knowledge Innovation Foundation of Chinese Academy of Sciences (KZCX2-YW-309, KZCX3-SW-332) and the National Natural Science Foundation of China (No.…”