Oxidant-antioxidant balance and tolerance against oxidative stress in pioneer and non-pioneer tree species from the remaining Atlantic Forest.

Abstract

The extensive land occupation in Southeast Brazil has resulted in climatic disturbances and environmental contamination by air pollutants, threatening the Atlantic forest remnants that still exist in that region. Based on previous results, we assumed that pioneer tree species are potentially more tolerant against environmental oxidative stress than non-pioneer tree species from that Brazilian biome. We also assumed that reactive oxygen species (ROS) are accumulated in higher proportions in leaves of non-pioneer trees, resulting in changes in the oxidant-antioxidant balance and inmore severe oxidative damage at the cellular level than in the leaves of pioneer trees. We tested these hypotheses by establishing the relationship between oxidants (ROS), changes in key antioxidants (among enzymatic and non-enzymatic compounds) and in a lipid peroxidation derivative in their leaves, aswell as between ROS accumulation and oscillations in environmental stressors, thus permitting to discuss comparatively for the first time the oxidant-antioxidant balance and the tolerance capacity of tree species of the Atlantic Forest in SE Brazil.We confirmed that the non-pioneer tree species accumulated higher amounts of superoxide and hydrogen peroxide in palisade parenchyma and epidermis, showing a less effective antioxidant metabolism than the pioneer species. However, the non-pioneer species showed differing capacities to compensate the oxidative stress in both years of study, which appeared to be associated with the level of ROS accumulation, which was evidently higher in 2015 than in 2016. We also applied exploratory multivariate statistics, which revealed that the oscillations in these biochemical leaf responses in both functional groups coincided with the oscillations in both climatic conditions and air pollutants, seemingly showing that they had acclimated already carried out, including Bussotti (2008) that concluded that early successional species in Mediterranean forests have a lower tolerance against oxidative stress than late secondary species and Favaretto et al. (2011) that classified native tree species of the Atlantic Forest into two major functional groups based on their tolerance against solar radiation exposure. Brandão et al. (2017) assumed that pioneer species from disturbed remnants of the Atlantic Forest in São Paulo (Brazil) are potentially more tolerant against oxidative stress than non-pioneer species based on the levels of antioxidants. However, this hypothesis would be definitely confirmed only if the lower antioxidative capacity in nonpioneer trees occurred in parallel with increased levels of ROS in the leaves, resulting in loss of the oxidant-antioxidant equilibrium, severe oxidative damage at the cellular level and consequently decreased tolerance against oxidative stress. The present study brought a new contribution to this broader issue, permitting to discuss comparatively the oxidant-antioxidant balance and the tolerance capacity of pioneer and non-pioneer tree species of Atlantic Forest remnants affected by multiple environmental stressors in SE Brazil.We achieved this goal by establishing the relationship between oxidants (ROS), changes in key antioxidants (among enzymatic and non-enzymatic compounds) and in a lipid peroxidation derivative in their leaves, as well as between ROS accumulation and oscillations in environmental stressors.