Antioxidant metabolism of Panicum maximum and Stylosanthes capitata under climate change

Abstract

Drought and heat stresses are considered the main climatic factors damaging the plant growth. In addition, according to Intergovernmental Panel on Climate Change (IPCC), the effect of combined drought and heat stresses will also be exacerbated in the next years, resulting in crop yield and economic losses. In spite of the consequences of the drought and heat combinations, the investigations to reduce its detrimental effects are scarce, particularly under climate change conditions. In this sense, we carried out two experiments in field conditions to determine the plant antioxidant responses to drought (wS), elevated temperature (+2 °C above air temperature) (eT) and combined drought and elevated temperature stresses. We used Panicum maximum during the first experiment and Stylosanthes capitata during the second one. In order to increase the temperature, we used the Temperature Free-Air Controlled Enhancement (T-FACE) facility. Samplings of P. maximum were taken 13, 19 and 37 days after the treatments have begun in the first experiment; meanwhile, the samplings of S. capitata were taken 17, 24 and 46 days in the second experiment. In both experiment, the samplings were taken at 6:00 am and 12:00 pm. The following combined stresses displayed an increase of chlorophyll and carotenoid contents in P. maximum (particularly at 19 days after the treatments have begun). Furthermore, the occurrence of precipitation after the second sampling reflecting induced the decreased in MDA and carbonyl contents, such as observed in wS treatment at 6:00 am in the third sampling. In relation to antioxidant enzymatic responses, the combination of drought and heat stresses enhanced SOD and APX activities, whilst quantum efficiency (PSII) and quantum yield of non-regulated energy dissipation in PSII (Y(NO)) were not affected by stresses. By the other way, the combination of drought and elevated temperature decreased the chlorophyll content in S. capitata at 6:00 am, nevertheless, we noticed an increase in photosynthetic pigments at 12 pm. MDA and H2O2 contents were also increased by simultaneous stresses such as exhibited by third sampling, at 6:00 am. In addition, combined stresses caused detrimental effect on antioxidant enzymatic responses (SOD, CAT and GR) at 46 days. SOD, GR and GSH have a crucial role to counteract the overproduction of MDA and H2O2 contents. In conclusion, P. maximum exhibited moderate response to combined stresses related to the good performance of its enzymatic antioxidant defence; whereas, S. capitata was severely affected by combined stresses.