Chlorophyll fluorescence and water content parameters are good biomarkers for selecting drought tolerant eucalyptus clones

Abstract

Fields of Eucalyptus throughout the world have faced ever more frequent events of water restriction, whilst the burgeoning demand has promoted the planting of crops in even drier sites. This study evaluated the ability of fast measurement variables (gas exchange, chlorophyll fluorescence, and water content) to determine the functional diversity of eucalyptus clones with differential tolerance to drought. For this, ten commercial eucalyptus clones were submitted to two treatments: control (90% of field capacity) and water deficit (50% of field capacity). After 40 days, the following parameters were measured: stem growth parameters, predawn water potential, relative water content, leaf succulence, and photosynthetic parameters. Based on the obtained data, three groups of plants were identified: (I) high stem growth and high tolerance clones; (II) high stem growth and low tolerance; and (III) low stem growth and low tolerance. The higher tolerance and stem growth of clones from group I involved the maintenance of cell water status and central physiological process (e.g. photosynthesis). Such clones, notwithstanding, did not present the highest carbon fixation rates. Even though the gas exchange parameters are easily and quickly obtained, they do not constitute a suitable tool for the selection of eucalyptus clones tolerant to drought. Conversely, parameters, such as chlorophyll a fluorescence, F0/Fm ratio, and relative water content, represented strong predictors to describe the behavior of the clones subjected to differential water regimes. These tools will facilitate early plant selection, which is important in tree improvement programs and sustainable eucalyptus forest management.