Effects of Nitrogen Fertility on Water Potential of Irrigated Cotton
Cotton (Gossypium hirsutum L.) grown in controlled environments responds to N deficiency with decreased hydraulic conductance and midday leaf water potential (Ψw). Experiments were initiated to determine whether N deficiency similarly affects plant water relations in the field. Cotton was grown for 4 yr with adequate N or a mild N deficiency. Nitrogen fertility had little effect on Ψw (determined with a pressure chamber) early in the season, but beginning in midseason the Ψw of N-deficient plants was 0.2 to 0.4 MPa higher than that of the fertilized plants. This difference was seen both before N had affected leaf area, and after canopy closure had occurred at both N levels. Stomatal conductances and transpiration rates of recently matured sunlit leaves (determined by steady-state porometry) remained unaffected by N. This evidence indicates that N deficiency increased plant hydraulic conductance in the field, contrary to its effect in controlled environments. However, in regressions of transpiration rate on leaf Ψw from dawn to midday, N had no consistent effects on the slopes (a putative measure of hydraulic conductance). These discrepancies have not been resolved. Nonetheless, N deficiency clearly does not decrease hydraulic conductance of cotton in the field in Arizona as it does in controlled environments.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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