Photochemical efficiency of tropical forage grasses submitted to water deficit

In this study, individuals of setariagrass (Setaria anceps Stapf.), limpograss (Hemarthria altissima [Poir] Stapf. & Hubbard), nilograss (Acroceras macrum Stapf.) and angola grass (Brachiaria purpurascens [Raddi] Henr.) were Submitted to moderate drought. The characteristics of chlorophyll a fluorescence (inicial fluorescence, F-0; maximum fluorescence, F-m; photochemistry efficiency, F-v/F-m photochemical quenching, qP; non-photochemical quenching, qN and relative electron transport rate, ETR) were investigated in an experiment carried Out in greenhouse, using plastic pots. The experimental treatments were allocated in a randomized complete blocks design, with three replications. The values of F. and F,,, decreased in all species after 10 days of drought, this effect being more evident in nilograss and setariagrass. The F-v/F-m values for nilograss and setariagrass decreased dramatically while that one for hemarthriagrass did not differ from the control. This results suggest a lower photochemical efficiency of photosynthesis in nilograss and setariagrass under water stress compared to hemarthriagrass and to the healthy plants. The highest values of qN were observed for hemarthriagraas and angolagrass. This showed that the increased capacity to dissipate the excessive energy to drive photosynthesis was satisfactory to maintain a low reduction state of the primary electron acceptor of the photosystem II (measured as qP). In general, ETR curves in response to increasing photosynthetic photon flux differed from control to stressed plants. especially for nilograss. In this species, a serious damage caused by water stress provoked a significant reduction to the efficiency of the electron transporters of PSII.