Indian Journal of Science and Technology

Abstract

Climate change may affect ecosystems worldwide, but can be aggravated in arid environments, leading to decreased rainfall and a consequent increase in air temperature. Objective: The present investigation aimed to study the behavior of a native plant, adapted to seasonal dry conditions, when faced with different conditions in two years: one extremely dry and the other with rains within the expected range. Methods/Analysis: To study the effects of the seasonal water deficiency, we collected all data in two consecutive years: 2012 and 2013. Results: In both years, we obtained data in May (rainy season) and August (dry season). The predawn water potential ( Ψw) ranged from -5.6 to -4.2 MPa in 2012 and from-2.16 to -2.98 MPa in 2013. These patterns show that even in the rainy season of the dry year, the plants were subjected to a very high water deficit when compared to the wet year; this was due to the sparse rains of 2012, the driest year of the preceding decade in the study area. All gas exchange and carbon uptake tended to zero in 2012; however, all the parameters recovered when the rains returned in 2013. Considering the entire data set, the water use efficiency (WUE) data presented a positive and significant correlation with all the photosynthetic parameters. However, when we excluded the 2012 data, the WUE was negatively correlated with transpiration (E ), stomatal conductance ( gs ) and leaf temperature ( Tleaf ). One average, the potential photosynthesis (PN-pot), maximum carboxylation velocity of Rubisco ( Vc-max ) and the maximum electron transport rate ( Jmax ) values were on average 62%, 50% and 63% lower in the dry season than in rainy season in 2013. Discussion/Conclusions: We argue that the increase of intercellular carbon caused the increase in photosynthesis to its limitation point of photosynthesis by Jmax . Below the collimation point, the photosynthetic rates were limited by Vc-max . Thus, the prolongation of the dry season could have potential impacts on the electron transport rate and on Rubisco carboxylation efficiency, taking into account the current concentrations of atmospheric carbon dioxide. During a prolonged drought, the reduced Ψw , osmotic adjustment and efficient antioxidative system appear to be the main strategies that C. pyramidale uses to avoid fatal plant dehydration, maintaining basal rates of net photosynthesis. However, with the intensification of climate changes expected for the study area, the species may no longer be a symbol of the ecosystem but rather a symbol of environmental degradation.

Keywords: World Climatic Change, Electron Transport Rate, Carbon Uptake, Gas Exchange, Reactive Oxygen Species, Water Scarcity