Trocas gasosas e grau de tolerância ao estresse hídrico induzido em plantas jovens de Tabebuia aurea (paratudo) submetidas a alagamento

‘Paratudo’, Tabebuia aurea, is a common Brazilian tree from ‘Pantanal de Miranda’, Mato Grosso do Sul state, Brazil, an area with seasonal floodplain. To evaluate the gas exchange of Tabebuia aurea under flooding stress, groups of eight-month-old plants were grown in soil covered by a 2 to 3 cm layer of water and a control group. Stomatal conductance, transpiration and photosynthetic rates were measured during the experiment (115 days), with an infrared portable analyzer. The values of stomatal conductance of the control group and stress plants at the beginning of the experiment were 0.22 mol m-2 s-1 and reached 0.02 mol m-2 s-1 at the end of this event. The initial photosynthesis rate was 8.0 μmol m-2 s-1 and, by the 108th day, it had reached zero. When the photosynthesis rate reached zero, the rigid plastic container was dried and the rate analyzed (8 days). The values obtained for plants in drained soil were: stomatal conductance = 0.21 mol m-2 s-1 and photosynthesis rate = 8.0 μmol m-2 s-1, indicating a recovery response, returning to initial values. Flooded soil reduced photosynthesis and stomatal conductance, and it affected the shoot growth, leading to the symptoms resulting from flooding stress, such as hypertrophy of the lenticels. However, the species has a tolerance to the flooding process, indicating adaptability to areas under seasonal water stress.