Physiological mechanisms for the rapid growth of Pennisetum clandestinum in Mediterranean climates.
Kikuyugrass, Pennisetum clandestinum, is a C4 grass that has become an invasive weed in temperate climates. The ecophysiological mechanisms that have allowed it to become a successful weed in these locations were examined by comparing P. clandestinum and 2 other common turfgrass species, Festuca arundinacea (tall fescue cv. Mojave, a C3 cool-season grass), and Stenotaphrum secundatum (St. Augustinegrass, a C4 warm-season grass), grown in a warm or cool growth regime. Rates of photosynthesis were measured over a range of leaf temperatures as were the growth rate parameters of these species. At leaf temperatures between 25 and 40°C, P. clandestinum maintained the highest rates of photosynthesis in both temperature regimes. Under warm temperatures, this species rapidly increased biomass and leaf area to a greater extent than either of the other 2 grasses. Theoretical whole plant photosynthesis (mean leaf area × mean photosynthetic rate) was higher for P. clandestinum than for the other 2 species in both growth regimes and over most leaf temperatures. The results suggested that P. clandestinum is a successful weed in Mediterranean climates as a result of its capacity to photosynthesize over the full range of temperatures found in those climates, its rapid growth during warm weather, and its apparent tolerance to moderately cool temperatures.