Large-scale changes in climate may have unexpected effects on ecosystems, given the importance of climate as a control over almost all ecosystem attributes and internal feedbacks. Changes in plant community productivity or composition, for example, may alter ecosystem resource dynamics, trophic structures, or disturbance regimes, with subsequent positive or negative feedbacks on the plant community. At northern latitudes, where increases in temperature are expected to be greatest but where plant species diversity is relatively low, climatically mediated changes in species composition or abundance will likely have large ecosystem effects. In this study, we investigated effects of infrared loading and manipulations of water-table elevation on net primary productivity of plant species in bog and fen wetland mesocosms between 1994 and 1997.We removed 27 intact soil monoliths (2.1 m 2 surface area, 0.5-0.7 m depth) each from a bog and a fen in northern Minnesota to construct a large mesocosm facility that allows for direct manipulation of climatic variables in a replicated experimental design. The treatment design was a fully crossed factorial with three infrared-loading treatments, three water-table treatments, and two ecosystem types (bogs and fens), with three replicates of all treatment combinations. Overhead infrared lamps caused mean monthly soil temperatures to increase by 1.6-4.1ЊC at 15-cm depth during the growing season (May-October). In 1996, depths to water table averaged Ϫ11, Ϫ19, and Ϫ26 cm in the bog plots, and 0, Ϫ10, and Ϫ19 cm in the fen plots.Annual aboveground net primary production (ANPP) of bryophyte, forb, graminoid, and shrub life-forms was determined for the dominant species in the mesocosm plots based on speciesspecific canopy/biomass relationships. Belowground net primary production (BNPP) was estimated using root in-growth cores.Bog and fen communities differed in their response to infrared loading and water-table treatments because of the differential response of life-forms and species characteristic of each community. Along a gradient of increasing water-table elevation, production of bryophytes increased, and production of shrubs decreased in the bog community. Along a similar gradient in the fen community, production of graminoids and forbs increased. Along a gradient of increasing infrared loading in the bog, shrub production increased whereas graminoid production decreased. In the fen, graminoids were most productive at high infrared loading, and forbs were most productive at medium infrared loading. In the bog and fen, BNPP:ANPP ratios increased with warming and drying, indicating shifts in carbon allocation in response to climate change.Further, opposing responses of species and life-forms tended to cancel out the response of production at higher levels of organization, especially in the bog. For example, total net primary productivity in the bog did not differ between water-table treatments because BNPP was greatest in the dry treatment whereas ANPP was greatest in the wet treatmen...

Peatlands often have readily apparent gradients of plant species distributions, biogeochemistry, and hydrology across several spatial scales. Many inferences have been drawn about lhe colinearity of these gradients, and these assumptions have become ingrained in the terminology that describes and classifies peatlands. We review the literature and present some of our own data that show that many of these inferences are either wrong or correct only under a limited set of ecological conditions. We examine historical classification schemes of peatlands and, in this context, gradients of alkalinity, pH, nutrient availability for plant growth, nutrient mineralization, hydrology, and decomposition. We further suggest a strictly defined set of terms to describe separate gradients of hydrology, alkalinity, and nutrients that limit plant growth in peatlands. Specifically, we make the following suggestions concerning terminology. (1) The suffix "-trophic" should only be used when referring to nutrients that direcdy limit plant growth at natural availabilities (e.g., eutrophic and oligotrophic). (2) Terms such as circnmneutral, moderately acid. and very acidic (or alternatively strong, intermediate, and weak) should be used to describe the pH of peatlands. (3) Ombrogenous and geogenous (or limnogenous, topogenous, and soligenous) should be used to describe the hydrology of peatlands. (4) The terms bog and fen should be defined broadly based on water/soil chemistry and dominant plant species without accompanying assumptions regarding hydrology, topography, ontogeny, nutrient availability, or the presence or absence of nondominant indicator plant species. Better yet, the generic term peatland be used when possible to avoid confusion about conditions that may or may not be present at a particular site.

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. Large-scale changes in climate may have unexpected effects on ecosystems, given the importance of climate as a control over almost all ecosystem attributes and internal feedbacks. Changes in plant community productivity or composition, for example, may alter ecosystem resource dynamics, trophic structures, or disturbance regimes, with subsequent positive or negative feedbacks on the plant community. At northern latitudes, where increases in temperature are expected to be greatest but where plant species diversity is relatively low, climatically mediated changes in species composition or abundance will likely have large ecosystem effects. In this study, we investigated effects of infrared loading and manipulations of water-table elevation on net primary productivity of plant species in bog and fen wetland mesocosms between 1994 and 1997.We removed 27 intact soil monoliths (2.1 m2 surface area, 0.5-0.7 m depth) each from a bog and a fen in northern Minnesota to construct a large mesocosm facility that allows for direct manipulation of climatic variables in a replicated experimental design. The treatment design was a fully crossed factorial with three infrared-loading treatments, three water-table treatments, and two ecosystem types (bogs and fens), with three replicates of all treatment combinations. Overhead infrared lamps caused mean monthly soil temperatures to increase by 1.6-4.1?C at 15-cm depth during the growing season (May-October). In 1996, depths to water table averaged -11, -19, and -26 cm in the bog plots, and 0, -10, and -19 cm in the fen plots.Annual aboveground net primary production (ANPP) of bryophyte, forb, graminoid, and shrub life-forms was determined for the dominant species in the mesocosm plots based on speciesspecific canopy/biomass relationships. Belowground net primary production (BNPP) was estimated using root in-growth cores.Bog and fen communities differed in their response to infrared loading and water-table treatments because of the differential response of life-forms and species characteristic of each community. Along a gradient of increasing water-table elevation, production of bryophytes increased, and production of shrubs decreased in the bog community. Along a similar gradient in the fen community, production of graminoids and forbs increased. Along a gradient of increasing infrared loading in the bog, shrub production increased whereas graminoid production decreased. In the fen, graminoids were most productive at high infrared loading, and forbs were most productive at medium infrared loading. In the bog and fen, BNPP:ANPP ratio...

The idea that carnivorous plants capture insects to supply limiting nutrients is often conjectured but rarely tested with fertilization trials or the construction of nutrient budgets. Accordingly, Sarracenia pupurea plants were analyzed for nitrogen and phosphorus after a 4-month fertilization of the pitchers with nitrogen, phosphorus, micronutrients, combinations thereof, and insect material. Neither the number of leaves produced in the same season nor average leaf mass differed significantly between treatments. Nitrogen and phosphorus concentrations were significantly higher in those leaves that received the respective treatments. Plots of concentration versus content indicated that plants were nitrogen and phosphorus limited. A nutrient budget for nitrogen was determined by soil mineralization, insect removal from the pitchers, and rainwater analysis. This budget showed that nitrogen in captured insects is one-tenth the annual plant requirement. However, soil N mineralization is sometimes more than adequate to supply demands were it to be exploited.R&sum& : On accepte gCnCralement l'idte que les plantes carnivores capturent des insectes pour y trouver les nutriments qui limitent leur croissance, mais peu de donnCes viennent dlexpCriences de fertilisation ou de 1'6tablissement de bilans nutritifs. ConsCquemment, l'auteur a effectuC des analyses d'azote et de phosphore, 4 mois aprbs la fertilisation de sarracCnies avec de l'azote, du phosphore, des micronutrients et une combinaison de ces derniers en plus de tissus d'insectes. Ni le nombre de feuilles produites au cours de la mCme saison, ni le poids moyen des feuilles diffkrent significativement entre les traitements. Les teneurs en azote et en phosphore sont significativement plus ClevCes dans les feuilles qui ont r e y ces traitements, respectivement. Un graphique representant les concentrations versus le contenu indique que la croissance des plants Ctait limitCe par l'azote et le phosphore. Une bilan nutritif de l'azote i Ct C constituC en dCterminant la mineralisation Cdaphique, la rCcupCration des insectes dans les rCservoirs foliaires et l'analyse de l'eau de pluie. Ce budget montre que l'azote captC dans les insectes reprCsente un dixibme des besoins annuels de la plante. Cependant, l'azote provenant de la minkralisation est quelques fois plus que suffisant pour les besoins lorsqu'il est exploit&.