Paclobutrazol application in eucalypt clones promotes morphological changes without affecting the physiological characteristics

The aim of this study was to investigate the morphophysiology of young eucalypt clones in response to different water regimes and paclobutrazol (PBZ) concentrations applied to the soil. The experiment was conducted in a greenhouse environment at the Federal University of Acre, Rio Branco, Brazil. Commercial clones of Eucalyptus urophylla × E. camaldulensis hybrid were planted in 11 l pots using a randomised block design in four blocks arranged at a 5 × 3 factorial scheme. Five PBZ concentrations were applied through substrate — 0.0 (control), 1.0, 2.0, 4.0 and 8.0 mg plant−1 — and three water regimes were used (40%, 70% and 100% field capacity (FC)). Results indicated that PBZ promoted morphological changes in the investigated species without affecting its physiological features. Eucalypt clones recorded increased root dry mass and decreased shoot/root ratio (S:R) after the application of 8.0 mg plant−1 of PBZ. Treatment conducted with 100% FC may have contributed to the hypoxic condition of the roots, and the limited plant height and S:R ratio. The 70% FC water regime increased plant height, stem diameter, leaf area, dry mass accumulation and CO2 partial pressure, and plants subjected to 40% FC recorded higher carboxylation and water use efficiency.