Abstract
To evaluate the effects of hydric stress on CO2 and H2O exchange, five-month-old Tabebuia aurea seedlings cultivated in planting bags were subjected to hydric stress by suppressing irrigation for 21 days. After 14 days without irrigation, the rates of transpiration, stomatal conductance and net photosynthesis in leaves were zero, while the hydric potential of leaves reached -2.4 MPa. After this point, daily irrigation was resumed, and the values of the measured variables recovered to initial levels after 96 hours (transpiration rate from 3.2 to 3.5 mmol m-2 s-1; stomatal conductance rate from 0.32 to 0.35 mol m-2 s-1 and photosynthesis rate from 8.0 to 9.8 µmol m-2 s-1). Likewise, hydric potential values were similar to those at the beginning of the experiment (-0.6 MPa). These results demonstrate that T. aurea has mechanisms to tolerate a period of hydric deficit, which may be considered ecologically relevant.
Highlights
Environmental studies of woody tree species under conditions of hydric stress are of fundamental importance because the degree of stress tolerance varies by species, plant age and duration of stress
Water is the most common limiting factor for plant development (KRAMER; BOYER, 1995), and water deficit affects stomatal opening, which leads to a reduction in photosynthetic capacity and plant growth rates
Hydric stress affects plant development by reducing photosynthesis rates and by limiting the chloroplast CO2 fixation capacity. This reduction in photosynthesis is related to stomatal closing, causing a decrease in the partial CO2 pressure and thereby limiting transpiration, which is an important mechanism to avoid water loss and dehydration under conditions of stress (KRAMER; BOYER, 1995; LARCHER, 2004)
Summary
Environmental studies of woody tree species under conditions of hydric stress are of fundamental importance because the degree of stress tolerance varies by species, plant age and duration of stress. This reduction in photosynthesis is related to stomatal closing, causing a decrease in the partial CO2 pressure and thereby limiting transpiration, which is an important mechanism to avoid water loss and dehydration under conditions of stress (KRAMER; BOYER, 1995; LARCHER, 2004). According to Larcher (2004), mesophytic plants from tropical forests with water potentials between -1.5 and -4.0 MPa can reach photosynthesis rates of zero, indicating that T. aurea exhibits mesophytic plant characteristics in response to hydric stress.
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