EFFECTS OF ELEVATED CARBON-DIOXIDE ON 3 MONTANE GRASS SPECIES .1. GROWTH AND DRY-MATTER PARTITIONING

Upland grasslands are a major component of natural vegetation within the UK. Such grasslands support slow growing relatively stable plant communities. The response of native montane grass species to elevated atmospheric carbon dioxide concentrations has received little attention to date. Of such studies, most have only focused on short-term (days to weeks) responses, often under favourable controlled environment conditions. In this study Agrostis capillaris L.(5), Festuca vivipara L. and Poa alpina L. were grown under semi-natural conditions in outdoor open-top chambers at either ambient (340 mu mol mol(-1)) or elevated (680 mu mol mol(-1)) concentrations of atmospheric carbon dioxide (CO2) for periods from 79 to 189 d, with a nutrient availability similar to that of montane Agrostis-Fescue grassland in Snowdonia, N. Wales. Whole plant dry weight was increased for A. capillaris and P. alpina, but decreased for F. vivipara, at elevated CO2. Major components of relative growth rate (RGR) contributing to this change at elevated CO2 were transient changes in specific leaf area (SLA) and leaf area ratio (LAR). Despite changes in growth rate at 680 mu mol mol(-1) CO2, partitioning of dry weight between shoot and root in plants of A. capillaris and P. alpina was unaltered. There was a significant decrease in shoot relative to root growth at elevated CO2 in F. vivipara which also showed marked discoloration of the leaves and increased senescence of the foliage.