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

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. 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...

Effects of experimental warming and drought on biomass accumulation in a Mediterranean shrubland

“…5). Other studies have also described that the differential response of species and life-forms to treatments may cancel out a clear overall response (Harte and Shaw 1995;Weltzin et al 2000). The studied shrubland was a carbon sink throughout almost all the studied years.…”

A Decade of Plant Species Changes on a Mire in the Italian Alps: Vegetation-Controlled or Climate-Driven Mechanisms?

“…Peat accumulation can be claimed as responsible for the decline of Carex species, particularly on the relatively drier hand of the water-tale gradient (Table II). Accordingly, a rapid decline in sedge frequency has been reported after peatland drainage (Laine et al, 1995) or water-table manipulation in mesocosm experiments (Weltzin et al, 2000(Weltzin et al, , 2003. Anyway, the strong decrease of C. rostrata and C. limosa frequencies in the wettest end of the watertable gradient can not be explained by peat accumulation alone.…”

“…A second possible explanation stems from the significant correlation between Carex shoot density in 1992 and subsequent frequency decrease (Pearson's correlation = −0.80; P < 0.05), indicating a densityrelated factor. In this case, experimental manipulations have shown that Carex dynamic is negatively affected by litter deposition ("thatch" effect) after some years of increased biomass production, the latter enhanced by high precipitation amounts (Thormann and Bayley, 1997a, b;Weltzin et al, 2000Weltzin et al, , 2003. Indeed, when accumulation of litter reaches critical levels for reducing light penetration and/or peat temperature, sedge biomass decreases.…”

“…Biomass production by peatland mosses fluctuates widely from year to year, due to variations in precipitation and, to a lesser extent, air temperature (Backéus, 1988;Bayley, 1997a, 1997b;Weltzin et al, 2000;Sonesson et al, 2002). Depth to the water table, which is directly affected by fluctuations in precipitation, is a major environmental factor controlling bryophytes dynamics through its influence on tissue water content of poikilohidric mosses (Rydin, 1993;Weltzin et al, 2001).…”

Responses of tree fine roots to temperature

“…Roots grow faster at higher temperatures in annual crop plants (Kasper & Bland, 1992) and perennials (Larson, 1970 ;Wilcox & Ganmore-Neumann, 1975 ;Teskey & Hinkley, 1981 ;Bevington & Castle, 1985 ;Kuhns et al, 1985 ;Lieffers & Rothwell, 1986 ;McMichael & Burke, 1998 ;King et al, 1999 ;Weltzin et al, 2000). Many of these observations have come from controlled growth-chamber and glasshouse studies, but field experiments and observational studies report similar results.…”