Response of Bog and Fen Plant Communities to Warming and Water-Table Manipulations

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 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...

Production and microtopography of bog bryophytes: response to warming and water-table manipulations

“…The experimental design consisted of all combinations of three water-table treatments and three infrared loading treatments randomly assigned to three replicate plots. Details of mesocosm construction, infrared loading and water-table treatments, and biotic and abiotic response to these treatments are provided by Bridgham et al (1999), Weltzin et al (2000), and Northern Peatlands Soil Warming Project (2001). A summary is provided below.…”

“…For each speciesspecific sample, we determined shoot density (no./dm 2 ). In addition, we established shoot mass/length relationships for individual shoots by clipping the top 1 cm for P. strictum, and 2 cm excluding the capitula for Sphagnum spp., drying them at 60°C, weighing them to the nearest milligram, and calculating shoot mass/shoot length ratios (Weltzin et al 2000).…”

“…Research was conducted within the context of a field-scale climate change experiment in northern Minnesota, USA. The overall objective of the experiment is to examine interactions among plant communities, the energy balance, carbon and nutrient cycling, and trace gas emissions in response to potential scenarios of climate change (Bridgham et al 1999;Weltzin et al 2000;Updegraff et al, in press;Northern Peatlands Soil Warming Project 2001).…”

Methane flux dynamics during mire succession

“…The variation in controlling factors can partly be connected with weather conditions. However, during mire succession, a directional change also takes place in factors such as microbial and plant community structure, biogeochemistry and hydrology (Matthews 1992; Klinger and Short 1996;Weltzin et al 2000;Merilä et al 2006). The directional changes in the controlling factors during the succession result in changes of ecosystem C dynamics Whiting 1994;Leppälä et al 2008).…”

Biodiversity in Wetlands

“…The likely impacts of the increased concentration of carbon dioxide, a rise in temperature and the increased variability in precipitation will have serious consequences for wetlands (Gitay et al 2001). The rise in temperature and increased winter precipitation in northern latitudes will alter both plant and animal communities (Weltzin et al 2000(Weltzin et al , 2001(Weltzin et al , 2003Graham 2003;Keller et al 2004). The seasonal migration patterns and routes of many wetland species will change considerably and their survival will be reduced to the extent of risk of extinction (Finlayson et al 2005;Reid et al 2005;Zalakevicius and Svazas 2005).…”