CR 18:105-112 (2001)  -  doi:10.3354/cr018105

Climate impacts on pioneer saltmarsh plants

Alan J. Gray*, Rebecca J. Mogg

Centre for Ecology & Hydrology, Winfrith Technology Centre, Dorchester, Dorset DT2 8ZD, United Kingdom

ABSTRACT: The 2 grass species that dominate the lower zones of North European saltmarshes utilise different photosynthetic pathways. Puccinellia maritima, a C3 species, occurs at higher elevations than Spartina anglica, a C4 species, which is a relatively recent invader and appears not to form extensive swards in latitudes north of ~54°N because of the limiting effect of low early-season temperatures and the greater competitive ability of Puccinellia. We investigate the differential responses of the 2 grasses to rising temperatures and CO2 concentrations in the light of earlier work that predicts increases in their primary production, assuming a 3°C rise in temperature and a doubling of atmospheric CO2. Predictions of their responses to climate change are made using evidence from present day competitive interactions in relation to marsh elevation and latitude, and from a competition experiment in which the 2 species were grown under ambient and elevated temperature (+3°C) and ambient and enriched CO2 (+340 ppm) in all factorial combinations. Puccinellia biomass was significantly increased, as expected, by CO2 enrichment and, probably from increasing early-season growth, by elevated temperature; the effect appeared additive, with the highest yield at the +3°C +340 ppm treatment. Spartina growth increased as predicted in response to elevated temperature, but also unexpectedly in high CO2 treatment, possibly through increased efficiency in water-use. Competition was largely asymmetric in favour of Puccinellia, affecting Spartina height and shoot weight, with intraspecific effects on tiller production and total biomass; Spartina mainly responded to both treatments and competition by increased below-ground growth. These results are compared with other, single-factor, experiments and suggest that, depending critically on some other aspects of climate change such as rising relative sea level and nutrient dynamics, Spartina is likely to extend its range northwards as CO2 and temperatures rise, but Puccinellia will continue to replace it in the succession, and probably at lower marsh elevations than at present.

KEY WORDS: Spartina anglica · Puccinellia maritima · C4 and C3 photosynthesis · Elevational niche · Competition · Elevated temperature and CO2 enrichment · Saltmarsh range extension

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