Morphophysiological Responses to Drought in Ochroma pyramidale (Cav. ex Lam.) Urb. (Balsa) Seedlings from Contrasting Precipitation Regimes

Climate change is intensifying drought frequency and severity, posing increasing challenges for tropical forest species whose growth and survival depend on water availability. Ochroma pyramidale (Cav. ex Lam.) Urb. (balsa) is a fast-growing pioneer tree that plays important ecological roles, and it is valued for its lightweight timber, yet little is known about its drought tolerance or intraspecific variation among populations. This study evaluated the morphophysiological responses of O. pyramidale seedlings from three provenances spanning a rainfall gradient (850–6275 mm year−1) under controlled soil moisture levels. The experiment followed a completely randomized factorial design with two factors, provenance (high-, medium-, and low-rainfall origins) and soil moisture (100%, 50%, and 20% field capacity), with six replications per treatment (n = 54 total plants). Drought significantly affected growth, water status, and physiological variables. Seedlings maintained high relative water content and photosynthetic pigment concentration under moderate stress (50% field capacity) but showed marked declines at 20% field capacity. Soluble sugar accumulation increased with drought intensity, suggesting osmotic adjustment, while root proliferation was enhanced under moderate stress (50% FC), evidenced by significantly higher Total Root Length (TRL) and Number of Branch Points (NBP). Provenance effects were weak, with only the number of leaves differing significantly among provenances. These results demonstrate that O. pyramidale tolerates moderate drought through physiological adjustment and root plasticity, supporting its use in reforestation and restoration initiatives in water-limited tropical environments.