MATTER ACCUMULATION AND PHOTOSYNTHETIC RESPONSES OF MACAW PALM TO CYCLICAL DROUGHT

RESPOSTAS FOTOSSINTÉTICAS E ACÚMULO DE MASSA EM PLANTAS JOVENS DE MACAÚBA SUBMETIDA AO DÉFICIT HÍDRICO CÍCLICO

ABSTRACT

The objective of this work was to evaluate the plant-water relations, photosynthetic parameters and growth of macaw (Acrocomia aculeata (Jacp.) Lodd. ex Mart.) plants, thus, ten plants were subjected to three successive drought and rehydration cycles and ten other plants were irrigated normally as control. The drought cycles consisted of a suspension of irrigation until the net CO2 assimilation rate (A) reach values lower than 5% of the control, and a rehydration until a plants recover at least 85% of A of the control plants. Reductions in A, stomatal conductance (g_s ) and transpiration (E), above 95%, were found with predawn leaf water potential (Ψ_pd) of -1.85 MPa. After rehydration, the g_s and E of plants with and without water stress was not different, however, A presented a significant difference. Leaf water potentials below -0.5 MPa reduced the intracellular and atmospheric CO2 ratio and increased water use efficiency, and values of -1.85 MPa, when both showed an increase and decrease, respectively. The reduction of A and g_s was linear and proportional to Ψ_pd. Total dry matter accumulation reduced by 50% in the plants subjected to drought. The cyclic water stress resulted in reduction of gas exchange and matter accumulation in macaw palm plants; a stomatal limitation of A occurred until Ψ_pd of -1.85 MPa, and then a non-stomatal limitation.

Keywords:
Acrocomia aculeata; Photosynthesis; Water use efficiency; Plant-water relations.