DIRECT EFFECTS OF INCREASING CARBON-DIOXIDE ON PASTURE PLANTS AND COMMUNITIES

The atmospheric carbon dioxide (CO2) level is rising and is expected to double during the next century. This paper reviews information on the responses of pasture species and communities to elevated CO2. Data for some further non-arable species are included where relevant. The effect of CO2 on yield and on morphological and physiological characteristics are considered together with aspects of particular relevance to pasture, for example, herbivory, plant community relationships, and experimental methods for the exposure of pasture to elevated CO2. At the plant level, physiological responses to CO2 include enhanced net photosynthesis and reduced stomatal conductance; morphological changes include greater leaf areas, shoot production, and root: shoot ratios. Little is known about community responses or about plant-herbivore dynamics at elevated CO2. Changes in herbage quality, tissue turnover, and botanical composition may be expected but confirmation of these responses will only be possible when data are available from long-term studies of grazed pasture at elevated CO2.