Ecofisiologia em mudas de acariquara (minquartia guianensis aubl.) e mogno (swietenia macrophylla king.) aclimatadas à campos abertos

Abstract

The objective of this research was to study the ecophysiological behavior of saplings of acariquara (Minquartia guianensis Aubl.) and mahogany (Swietenia macrophylla King.) during acclimation to full sunlight. The experiment was conducted at the Campus V-8 of the National Institute for Research in the Amazon (INPA) in Manaus, between June and December of 2008. The acclimation periods (TS) were: 0 (T0, control, kept under shade, at 0.40 mol m-2 day-1), 30 (T30), 60 (T60), 90 (T90), 120 (T120), 150 (T150) and 180 days (T180). At each acclimation treatment, five saplings (replicates) per species were used. At the end of acclimation treatments were measured: the Fv/Fm ratio, photosynthetic rates (A), stomatal conductance (gs), maximum carboxilation rate of Rubisco (Vcmax), maximum rate of electron transport (Jmax), transpiration (E), leaf water potential (Ψf), height, diameter, number of leaves, specific leaf area (AFE), and chlorophyll and carotenoid contents. Gas exchange rates were measured with a photosynthesis meter (Li-6400, Li-Cor, USA). In acariquara, transfer to full sunlight immediately caused severe photoinhibition, which in some cases evolved to leaf photooxidation and premature leaf abscission. In this species, little production of new leaves during the experiment was observed. On the contrary, mahogany showed abundant production of leaves (and little leaf abscission) and absence of leaf photooxidation. The sudden plant exposure to full sunlight caused severe reduction in the Fv/Fm ratio, which was more pronounced in acariquara. However, at the end of the acclimation period, saplings of both species showed almost full recovery again photoinhibition, with Fv/Fm values close to those observed in control plants. Thus, in the last three months of the acclimation period to full sunlight, Vcmax was 12.9 μmol m-2 s-1 for acariquara and 20.4 μmol m-2 s-1 for mahogany, while the potential photosynthesis (Apot) for the same period, was 8.2 μmol m-2 s-1 for acariquara and 10.2 μmol m-2 s-1 for mahogany. There was no effect of the acclimation process on Ψf. Finally, the higher photosynthetic rate observed in mahogany also coincided with higher growth rates in this species, which grew about three times faster (growth in diameter of 0.9 mm month-1) than acariquara (0.25 mm month-1).