Net photosynthetic rate performance of <em>Eucalyptus citriodora</em> Hook and <em>E. grandis</em> W. Hill in response to different levels of water and associated with <em>Brachiaria brizantha</em> Stapf

Abstract

The effects of Brachiaria brizantha (Poaceae) interference on the net photosynthetic rate (A) of Eucalyptus citriodora and E. grandis (Myrtaceae) seedlings cultivated in soils with three levels of water under greenhouse conditions are provided. Treatments were arranged in a factorial design, with four repetitions 2x3x4: two species of eucalyptus (E. citriodora and E. grandis), three levels of water (20, 23 and 26%), and four populations of B. brizantha (0, 1, 2 and 3 plants per vase). Water level in the vases was maintained constant until the evaluation of final experiment 70 days after transplant of seedlings. Moisture control was done by a microtensiometer and daily weighting of vases with three replenishments of evapotranspired water. Measurements were executed with an infrared gas analyser (IRGA). In spite of any water level in the soil, B. brizantha demonstrated its competitiveness for E. citriodora and E. grandis initial growing, by A reduction. Upper third part of leaves of E. citriodora or E. grandis seedlings presented higher A than mean and lower third section, independently of B. brizantha population and water level in the soil