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

Abstract

Boreal peatlands, which contain a large fraction of the world's soil organic carbon pool, may be significantly affected by changes in climate and land use, with attendant feedback to climate through changes in albedo, fluxes of energy or trace gases, and soil carbon storage. The response of peatlands to changing environmental conditions will probably be dictated in part by scale-dependent topographic heterogeneity, which is known to interact with hydrology, vegetation, nutrients, and emissions of trace gases. Because the bryophyte community can contribute the majority of aboveground production in bogs, we investigated how microscale topography affects the response of bryophyte species production and cover to warming (using overhead infrared lamps) and manipulations of water-table height within experimental mesocosms. We removed 27 intact peat monoliths (2.1-m surface area, 0.5-0.7 m depth) from a bog in northern Minnesota, USA, and subjected them to three warming and three water-table treatments in a fully crossed factorial design. Between 1994 and 1998, we determined annual production of the four dominant bryophyte taxa within three microtopographic zones (low, medium, and high relative to the water table). We also estimated species cover and calculated changes in topography and roughness of the bryophyte surface through time. Total production of all bryophytes, and production of the individual taxa Polytrichum strictum, Sphagnum magellanicum, and Sphagnum Section Acutifolia, were about 100% greater in low microtopographic zones than in high zones, and about 50% greater in low than in medium zones. Production of bryophytes increased along the gradient of increasing water-table heights, but in most years, total production of bryophytes was negatively correlated with height above the set water table only for the wettest water-table treatment. Although bryophyte production was unaffected by the warming treatments, the bryophyte surface flattened in proportion to the degree of warming. These results indicate that production of bryophytes is driven most strongly by the absolute and relative height of the bryophyte surface above the water table. Predicted changes in water-table height commensurate with changes in surface temperature may thus affect both production and superficial topography of bryophyte communities.

Response of Sphagnum species mixtures to increased temperature and nitrogen availability

“…This proved to be the case, including the small positive effect of high temperature on height increment of S. fuscum. Negative effects of increased temperature have been found in other studies too (Gerdol et al 2007;Weltzin et al 2001) but have usually been ascribed to desiccation. In our experiment desiccation could not have been the cause of the negative effect of temperature, because we saw no desiccated capitula.…”

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

“…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). Niche overlap among Sphagnum species along the water-table gradient has been shown to be rather wide (e.g., Nordbakken, 1996;Bragazza, 1997).…”

“…Once established, P. strictum is able to survive for long periods through vegetative production of new shoots, keeping pace with Sphagnum growth (Li and Vitt, 1995). Under favourable conditions for Sphagnum growth, however, competitive interactions cause a decline in P. strictum cover (Li and Vitt, 1995;Weltzin et al, 2001).…”

Carbon dioxide flux and net primary production of a boreal treed bog: Responses to warming and water-table-lowering simulations of climate change

“…The drier conditions may favour some species in peatland communities to yield more NPP than others, and, as a result, plant composition will shift, leading to changes in species dominance (Sternberg et al, 1999). In northern bogs, the balance could shift towards a shrub-or tree-dominated system (Weltzin et al, 2001;Lohila et al, 2011), which in combination with deeper water tables could lead to an increase in both soil (Ise et al, 2008) and plant respiration (Tarnocai et al, 2009). A shift in species dominance after drainage in a Swedish peatland accelerated soil respiration rates, ranging from 513 to 6516 g CO 2 m −2 d −1 (Von-Arnold et al, 2005).…”