Atividade fotossintética e crescimento inicial em espécies lenhosas do Bioma Cerrado: implicações para recuperação de áreas degradadas

Abstract

The cerrado is a large biome with a high geographical extension, originally occupying 2,000,000 km2, about 23% of the national territory. Even though it is considered a biodiversity hotspot, it is under threat. It is estimated that about 50% of the original territory of the Cerrado is destined for agriculture. In these areas there is the removal of the vegetation cover, implying microclimatic changes in the region, leading to the disappearance of species not tolerant to these conditions. Native plants that undergo this sudden change in environmental conditions are subject to stressful factors, such as photoinhibition, characterized by a reduction in photosynthetic rates due to the increase in light intensity. Many species of the Cerrado have a high plastic potential with ability of the individual to express a different phenotype according to environmental conditions. Light is one of the limiting conditions in the establishment, growth and survival of species of arboreal species in tropical forests, mainly in the juvenile phase. Therefore, knowing the responses of plants in contrasting light environments becomes important for carrying out management and reforestation practices. Therefore, this work aimed to evaluate the initial growth and photosynthetic potential in juvenile plants of Inga laurina (Fabaceae) and Lithraea molleoides (Anacardiaceae) both native to the Cerrado Biome under different light conditions. The objective of this work was 1) to investigate the existence and influence of photoinhibition, whether dynamic or chronic, in the growth process under contrasting light conditions and 2) to evaluate changes in the biomass distribution of the studied individuals and the photosynthetic activity in contrasting light environments. The experiment was conducted at the Federal University of Uberlândia. One hundred seedlings of each species, L. molleoides and I. laurina, were obtained by purchasing the forest nursery of the Brazilian Forestry Institute. Twenty-five individuals of each species were placed in the treatment in full sun, and 65 in the shade for 95 days. During the experimental period, daily courses of microclimatic variables were performed in sun and shade treatments, with quantification of PPFD, temperature, relative humidity and DPVatm. In addition, chlorophyll fluorescence measurements, chlorophyll index a, b, total and a/b ratio, gas exchange, photosynthetic assimilation light curves and growth measures, dry mass, biomass partition and relative growth rates and net assimilation rate were carried out. L. molleoides showed high capacity for photosynthetic adjustment, with higher values of fluorescence variables and chlorophyll index in the shade. The biggest a/b ratios, maximum CO2 assimilation rate, dry mass variables, root biomass partition, relative growth rate and liquid assimilation rate at full sun in L.molleoides. In the shade, L. molleoides obtained increases in the rates of Leaf Mass Ratio (LMF), Specific Leaf Area (SLA), Leaf Area Ratio (LAR). I. laurina showed a lower photosynthetic adjustment between the treatments evaluated. With higher values of fluorescence and chlorophyll indexes in shaded environment, and higher rate of maximum assimilation of CO2 in the shade. In addition, higher values of SLA and LAR were observed in the shade in I. laurina. For both species, photoinhibition occurred, being more accentuated in I. laurina in full sun. The studied species present different occupation and establishment strategies so that in its initial phase, L. molleoides tends to be a pioneer and I. laurina is more shade tolerant. L. molleoides is more suitable for restoring more open areas, while I. laurina for areas that have some level of shading.