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 t he UK. Such grasslands support slow growing relatively stable plant co mmunities. The response of native montane grass species to elevated at mospheric carbon dioxide concentrations has received little attention to date. Of such studies, most have only focused on short-term (days t o weeks) responses, often under favourable controlled environment cond itions. In this study Agrostis capillaris L.(5), Festuca vivipara L. a nd Poa alpina L. were grown under semi-natural conditions in outdoor o pen-top chambers at either ambient (340 mu mol mol(-1)) or elevated (6 80 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. Whol e plant dry weight was increased for A. capillaris and P. alpina, but decreased for F. vivipara, at elevated CO2. Major components of relati ve 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, partition ing of dry weight between shoot and root in plants of A. capillaris an d P. alpina was unaltered. There was a significant decrease in shoot r elative to root growth at elevated CO2 in F. vivipara which also showe d marked discoloration of the leaves and increased senescence of the f oliage.