Caracterização fisiológica e bioquímica de cedro australiano sob ciclos de déficit hídrico

Abstract

Australian cedar is a tropical and subtropical forestry species that has been planted in regions of the Brazilian cerrado that are subjected to water deficit. It has great capacity for reforestation allowing investigation of exposure to successive drought cycles, aiming for planting in locations with little water availability. This study aimed to evaluate and characterize physiological and biochemical mechanisms of different Australian cedar clones, when subjected to multiple water deficit cycles, compared to plants with a single stress event, both after rehydration. The experiment was carried out in a greenhouse with seedlings from the commercial clones BV 1110, BV 1210 and BV 1321. These clones were separated into groups classified as plants with continuous irrigation - CDH0, submitted to one water deficit event - CDH1 and three water deficit events - CDH3, all followed by rehydration. The clone performance, under these conditions, was evaluated by different physiological and biochemical traits. The performed analysis determined leaf water potential (Ψwfoliar), gas exchange (net photosynthetic rate - A, stomatal conductance - gS and transpiration - E), biometry (total height - H, main root length- CR, stem diameter at the base level - D, number of total leaves - NF, number of total leaflets - NFl, total leaf area - AF, dry mass of leaflets, stem and root, specific root length and root water percentage), chlorophyll fluorescence a, photosynthetic pigment content, carbohydrates (starch, sucrose, total soluble sugars, reducing sugars), proteins, amino acids, proline, enzyme activity of the antioxidant metabolism (superoxide dismutase - SOD, catalase - CAT and peroxidase ascorbate - APX) and content of hydrogen peroxide (H2O2) and lipid peroxidation (MDA). Under drought, the BV 1110 clone showed higher CR, but the stress was not enough to reduce its metabolism. Proline was an indicator of stress due to its high content in the groups CDH1 and CDH3 under water deficit, as well as H2O2. Among the antioxidant enzymes, SOD was the one active in leaves and roots. The BV 1210 clone had reduced number of leaves, leaflets and chlorophyll fluorescence a under DH, but they were restored after rehydration. The content of proline and H2O2 was reduced in the CDH3 group under DH. CAT was the most active enzyme in the leaves of this clone under water stress. The BV 1321 clone had the lowest CR, water potential and reduction in NF and NFl in the CDH3 group. The photosynthetic machinery was altered by drought and recovered after rehydration. Carbohydrates consumption was detected in the leaves and roots. H2O2 was also reduced in the CDH3 group under DH. APX was the active enzyme in the CDH1 plant group under DH. Thus, the BV 1110 clone proved to be resistant to the imposed water deficit by not changing its characteristics of growth and development. The BV 1210 and BV 1321 clones performed metabolic adjustments (non-standard) that allowed them to exhibit different responses in the CDH1 and CDH3 groups. The parameters used to characterize the Australian cedar clones proved to be satisfactory to consider the BV 1210 clone resilient to the imposed water deficit.