Hydraulic characteristics and water relations of net house-grown bell pepper as affected by irrigation regimes in a Mediterranean climate

Abstract

Trends in hydraulic architecture and water relation parameters of bell pepper ( Capiscum annuum, L.) as affected by fertigated drip irrigation regimes (well-watered and water-stressed conditions) in a Mediterranean climate were investigated. The aim were to evaluate the coupling of xylem conductance and stomatal conductance, the regulation of water use of bell pepper by xylem hydraulics and whether the functionality of xylem hydraulic conductance changes under different fertigation regimes. Fertigation (simultaneous application of irrigation water and fertilizers) consisted of daily fertigation rates of 1.2, 1.0 and 0.7 PET delivered using 8, 2 and 0.4 l/h drippers. Emitter discharge rates determine amount of time required to deliver a known quantity of water and hence soil water availability per unit time. Hydraulic conductance was monitored by the evaporative flux (EF) method from the slope of the water potential difference (Δ ψ) versus transpiration flux ( Q) using the Ohm's law analogy. Water potential gradient was estimated as the difference between pre-dawn and midday leaf water potential. Day time courses of leaf (lwp) and stem (swp) water potentials and stomatal conductance ( g s) were monitored at pre-dawn, 1000, 1200 and 1400 h. Values of midday stomatal conductance and leaf water potentials, water uptake rates (sap flow) and hydraulic conductance through the plant to the canopy (soil–plant–atmosphere (SPAC)) were affected by irrigation regimes. Plant water potential (pre-dawn and midday) ranged from 0.95 to −0.41 MPa for well-watered and water-stressed pepper. Plant hydraulic conductance ranged from 6.57 × 10 −01 to 2.27 × 10 −03 (g s −1 MPa −1) for well-watered and water-stressed plants. The estimated value of whole plant hydraulic conductance ( K T) confirmed increased hydraulic and stomatal resistance under deficit irrigation condition while well-watered pepper plants had greater water uptake rate and remarkably higher within plant (hydraulic) and stomatal conductance. The components of the resistance elements in the SPAC changed as a function of irrigation regimes (root zone water status). Hydraulic characteristics optimize water uptake from the soil, the stomatal respond to changes in leaf water status and the leaf system and sapwood area adjust as necessary to maximize water uptake and avoid loss of hydraulic contact with the soil. The hydraulic non-isolation of the shoot processes to root zone conditions are important attributes of bell pepper grown under variable irrigation regimes.