Plant responses to climate and relationships with pasture persistence

Abstract

Relationships between climatic factors and persistence of grazed perennial ryegrass and white clover pastures in New Zealand are reviewed from an ecophysiological perspective. 'Persistence' is defined in terms of physical survival of plants of sown cultivars: the effects of climate on plant populations are considered. Substantial information is available on the population dynamics of perennial ryegrass and white clover in different climatic environments, particularly on the influence of drought on populations. Substantial, direct negative effects of drought on the density of perennial ryegrass tillers and white clover stolons have been recorded, though populations have generally recovered after release from drought conditions. Otherwise, the effects of climaterelated resource limitations on population size are more likely to be interactive, working in concert with other factors such as management, soil fertility and insect pest challenges to limit the capacity of homeostatic responses to restore the optimal (for long term survival) balance between above- and below-ground resources. The relative extent to which more recent cultivars of perennial ryegrass are able to tolerate multiple, simultaneous resource limitations compared to older cultivars (with different phenotype) is considered, but there is little direct evidence on this matter. Issues that should be considered in future pasture persistence research are identified and discussed. One of these concerns is the persistence of trait expression in cultivars bred for specific traits. More research on this topic is warranted, since molecular plant breeding techniques are strongly based on trait manipulation, and genotype x environment interactions can be expected in the spatially and temporally variable environment of grazed pastures. Keywords: drought, ecology, plant breeding, ryegrass, white clover