Photosynthetic responses of Eucalyptus seedlings submitted to chemical and mechanical stimulus

Respostas fotossintéticas em mudas de eucalipto submetidas a estímulo químico e mecânico

Abstract

This work aimed to investigate the photosynthetic responses of Eucalyptus urophylla x Eucalyptus grandis hybrids 1528 submitted to the application of jasmonic acid (JA) and stem bending. The experiment was conducted in a shade house using a completely randomized design with five replicates of 20 seedlings, with the following treatments: T1: control, T2: 8.0 µmol of JA and T3: 40 stem bending. The net assimilation rate of CO₂ (A), stomatal conductance (gs), internal CO₂ concentration (Ci), leaf transpiration rate (E), water use efficiency (WUE), intrinsic efficiency of use of Water (iWUE) and carboxylation efficiency (Fc) were measured with an IRGA. The dose of JA applied to the seedlings was insufficient to alter the photosynthetic responses in relation to the control treatment. Mechanical stimuli induced by stem bending in eucalyptus hybrid 1528 seedlings promoted an increase in the maximum photosynthetic capacity and maximum assimilation of CO₂, but the seedlings presented a reduction in the efficiency of the water use, that is, lower photosynthetic efficiency when compared to the seedlings submitted to other treatments. Seedlings of eucalyptus hybrid 1528 submitted to mechanical stimuli and jasmonic acid show greater respiration under low flow levels of photosynthetically active photons.

Keywords:
Jasmonic acid; Stem bending; Quality of seedlings; Clone 1528