Within plant (xylem) and canopy conductance characteristics in bell pepper: influence of soil-moisture regimes

摘要

The effect of soil moisture (irrigation) regimes on water transport properties (xylem and canopy conductance) through the plant to the canopy (SPAC) was studied in bell pepper. Whole plant hydraulic conductance (K_T) was estimated by the evaporative flux method, canopy conductance (gc) was estimated from VPD and sap-flow parameters (heat-pulse probes), while cumulative sap flux (daily totals) were summed for the estimation of whole plant transpiration. Water use is affected by soil environment, plant architectural and xylem traits, and irrigation regimes alter the hydraulic conductivity through the plant to the canopy (SPAC). The estimated value of K_T confirmed increased hydraulic resistance under deficit water application, but greater water consumption in well irrigated pepper plants resulted from remarkably larger root and canopy conductances. Regardless of daytime decreases in sap velocity and leaf water potential, hydraulic conductance in the vascular system (Kr-1) were maintained, hence plant water stress did not attain level of cavitation threshold and disruption of water conducting system. The adjustment of the stomatal and crop water use to xylem hydraulic sufficiency and soil water status explains the influence of xylem water-transport capacity on stomatal response to soil drought. Hydraulic characteristics optimize water uptake from the soil, while within plant xylem-conductance properties limit canopy water use. Xylem hydraulic resistance responds to soil water status and does contribute to hydraulic non-isolation (coupling) of canopy from the water status of the soil and stem conduits, and adaptive advantage of stomatal behavior. Daytime trends of water uptake and use (sap flux, xylem and canopy conductance) as function of soil moisture status would be useful in modeling pepper crop water use.