The functional role of Equisetum in nutrient cycling and maintaining the primary productivity of an Alaskan shrub wetland.

摘要

Access to sufficient supplies of available nutrients is important in maintaining the primary productivity of ecosystems. Although Equisetum has been considered a minor component of shrub wetland ecosystems, this study indicates that it plays an important functional role in phosphorus and potentially nitrogen cycling in the Myrica-Salix community of Alaska's Copper River Delta (60{dollar}spcirc{dollar}26-28'N, 145{dollar}spcirc{dollar}18-20'W). To identify plant function in the Myrica-Salix community, conditions for plant growth, plant productivity, phytomass distribution, and the storage and flux of nutrients in phytomass were examined, highlighting individualistic use of resources by the five plant groups that comprise the community: Equisetum spp., Carex spp., other herbaceous species, Myrica gale, and Salix spy.; The ability of plants to regulate ecosystem biogeochemistry and facilitate change to the environment appeared particularly important because conditions for plant growth were generally poor. Soils consisted of relatively unweathered glacial sediments overlain by a 13-33 cm organic mat, and were cold (averaging 9-11{dollar}spcirc{dollar}C over the growing season), low in total N and P (1.3-10.0 mg N g{dollar}sp{lcub}-1{rcub},{dollar} 1.0-1.1 mg P g{dollar}sp{lcub}-1{rcub}),{dollar} and generally saturated to within 10 cm of the surface. Plants in the community tolerated or avoided resource stress through spatial and temporal niche partitioning, allocation of non-limiting resources, and conservation of nutrients, and thus were able to maintain a high productivity for their climate and latitude (current-year shoot productivity 336 (16) g m{dollar}sp{lcub}-2{rcub}).{dollar}; Equisetum appeared to contribute to community productivity by acting as a P pump, supporting {dollar}rm Nsb2{dollar}-fixing microorganisms, and producing high quality litter that decomposed rapidly. Unlike other species in the community, Equisetum was able to absorb P primarily from available pools in the C horizon due to its deep rooting habit. P accumulated in Equisetum tissues in concentrations 1.5-3.8x greater than in tissues of other community members, so that while Equisetum represented only 5% of the biomass in the community, it had 16% of the P in the community. Nitrogenase activities associated with washed and unwashed excised roots of Equisetum (0.90 and 1.15 {dollar}mu{dollar}mol {dollar}rm Csb2Hsb4{dollar} g root{dollar}rmsp{lcub}-1{rcub} hrsp{lcub}-1{rcub}){dollar} suggest that Equisetum may acquire some N from the soil atmosphere. Equisetum litter decreased in mass faster than the litter of any other plant group, contributing as much as 52, 39, and 73% of the P, K and Ca inputs to O horizon nutrient pools from litter over a two year period. As a result of this ability to accumulate and cycle nutrients, it is recommended that managers consider potential effects on Equisetum in managing community vegetation.