24 research outputs found
Photosynthesis, stomatal conductance and leaf water potential in crabwood (Carapa guianensis)
Leaf water potential is one of the most important factors affecting stomatal functioning. The aim of this study was to assess the effect of variation in diurnal irradiance and vapour pressure deficit on photosynthesis (A), stomatal conductance (g s) and leaf water potential (psi) in Carapa guianensis (Aubl.). Data were collected from 07:00 to 17:00 h. Photosynthetic rates reached a maximum (2.5 µmol m-2 s-1) at 10:00 h, thereafter declined to a minimum of 1 µmol m-2 s-1 at 16:00 h. Stomatal conductance oscillated during the day, from 0.04 mol m-2 s-1 (at midday) to 0.02.mol.m-2.s-1 at the end of the afternoon. Leaf water potential was higher early in the morning (-0.3 MPa) and lower (-0.75 MPa) at mid-afternoon (14:30 -15:00 h). After reaching a minimum, psi increased up to -0.64 MPa at sunset. Photosynthetic rates increased linearly as a function of g s (P < 0.01). Also there was a positive relationship between psi and g s (P< 0.01). Photosynthetic rates declined during the day after reaching a peak early in the morning, which makes clear that environmental factors that influence psi greatly affect carbon assimilation of C. guianensis.O potencial hÃdrico da folha é um dos fatores mais importantes que afetam o funcionamento dos estômatos. O objetivo deste trabalho foi avaliar o efeito da variação diurna na irradiância e déficit de pressão de vapor (DPV) na fotossÃntese (A), condutância estomática (g s) e potencial hÃdrico da folha (psi) em Carapa guianensis (Aubl.). Os dados foram coletados de 07:00 à s 17:00 h. A taxa fotossintética atingiu um valor máximo (2,5 µmol m-2 s-1) à s 10:00 h, depois declinou até atingir um mÃnimo de 1 µmolm-2 s-1 à s 16:00 h. A condutância estomática oscilou durante o dia, de 0,04 molm-2s-1 (ao meio dia) para 0,02 molm-2s- 1 no final da tarde. O potencial hÃdrico da folha foi máximo nas primeiras horas do dia (-0,3 MPa) e mÃnimo (-0,75 MPa) no meio da tarde (14:30 a 15:00 h). Após ter alcançado um mÃnimo, o psi aumentou até -0,64 MPa no fim da tarde. A taxa fotossintética aumentou linearmente em função do g s (P < 0,01). Também houve uma relação positiva entre psi e g s (P < 0,01). A taxa fotossintética declinou durante o dia após ter alcançado um pico no inÃcio da manhã, demonstrando que os fatores ambientais que afetam o psi têm efeito significativo na assimilação do carbono de C. guianensis
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