Species/defoliation/drought interactions on tuft survival and tiller and phytomass production in four sourveld grass species in KwaZulu-Natal, South Africa

Abstract

Productivity and mortality of grass plants following drought may be controlled by interactions between defoliation and severity of the drought. Prudent grassland management might mitigate deleterious changes in species composition in multispecies grasslands. This study, conducted in a horticultural tunnel, explored the interactions of drought duration, and the period of uninterrupted postdrought growth before defoliation, on phytomass, tiller production and mortality of Aristida junciformis, Eragrostis curvula, Hyparrhenia hirta and Themeda triandra. Pretreatment tiller production was highest for Aristida and Eragrostis, followed by Hyparrhenia and then Themeda. Mortality was positively related to tuft size and drought duration. Tiller mortality was controlled by a species × drought interaction and the covariate tuft-size. All species lost tillers following a 28-day drought, with the highest loss in Eragrostis and lowest in Themeda. Phytomass production was positively related to recovery, and inversely related to drought duration. Species-specific differences in production were apparent only in the no-drought treatment, where Hyparrhenia produced more phytomass than Themeda and Eragrostis. Aristida had the lowest phytomass production and showed little plasticity across drought treatments. Results indicated that postdrought rest is important for phytomass production, and that species may exhibit a tradeoff between productivity and survival.