THE INFLUENCE OF PLANT-DENSITY ON THE RESPONSES OF SINAPIS-ALBA TO CO2 AND WINDSPEED

Plants in nature live in populations of variable density, a characteri stic which may influence individual plant responses to the environment . We investigated how the responses of Sinapis alba plants to differen t wind speeds and CO2 concentrations could be modified by plant densit y. In our wind-density experiment the expectation that mechanical and physiological effects of wind will be ameliorated by growing in high d ensity, as a result of positive plant interactions, was realised. Alth ough individual plants were smaller at higher densities, the effect of increasing windspeed was much less than at lower plant densities. A s imilar reduced sensitivity of individual plant growth under high densi ties was also observed under CO2 enrichment. When measured as a popula tion or stand response, there was no effect of density on the CO2 resp onses, with all stands showing very similar increases in total biomass with CO2 enrichment. In the wind speed experiment, total biomass per stand increased significantly with density, although there was no effe ct of density on the wind speed response. Specific leaf area decreased with increasing wind speed and this response was significantly affect ed by the density at which the plants grew.