Physiological characteristics of eucalypts in association with signal grass

The objective of this work was to evaluate the physiological characteristics of eucalypts growing alongside the signal grass species Urochloa brizantha and U. decumbens (weeds). The experiment was conducted in a controlled environment using randomised blocks with four replications. Three different treatments were studied: no weeds, addition of U. brizantha and addition of U. decumbens, with both weeds at a density of 50 plant m(-2). Physiological characteristics were evaluated at 18, 38 and 48 days after transplanting (DAT) and root collar diameter and height of the plants were measured at 2, 22, 34 and 44 DAT. The coexistence of eucalypts with these two species of signal grass did not modify the physiological variables of the eucalypts at 18 DAT and 38 DAT. However, at 48 DAT, the eucalypts in the two weed treatments showed reduced photosynthetic activity. When with U. decumbens, the eucalypts showed reduced transpiration, CO2 consumption, stomatal conductance and the ratio between internal carbon concentrations and atmospheric carbon concentrations. The root collar diameter was more sensitive to competition with weeds than was the total height of the plants. We conclude that both U. brizantha and U. decumbens have negative effects on physiological characteristics and growth parameters of the eucalypts at 48 DAT.