Effect of different soil water potential on leaf transpiration and on stomatal conductance in poinsettia

Abstract

Euphorbia pulcherrima Wild.'Lilo' was grown in containers in 60% peat, 30% perlite and 10% clay (v/v) mixture, with different irrigation treatments based on soil water potential. Plants were watered at two levels of drought stress: -50kPa or wilting. The treatments were applied at different stages of plant development for a month or soil was brought to the moisture stress only twice. Additionally, some plants were watered at -50 kPa during the entire cultivation period while the control plants were watered at -5kPa. Plants were also kept at maximum possible moisture level (watering at -0,5kPa) or close to it (-1.OkPa) through the entire growing period. Soil water potential was measured with tensiometer. Drought stress applied during entire cultivation period or during the flushing stage caused significant reduction in transpiration and conductance of leaves. Stress applied during bract coloration stage had not as great effect on the stomatal conductance and transpiration of leaves as the similar stress applied during the flushing stage. High soil moisture increased stomatal conductance and transpiration rate, respectively by 130% and 52% (flushing stage), and 72% and 150% (bract coloration stage) at maximum, compared to the control.