Drought-stress effects on physiology, growth and biomass production of rainfed and irrigated bell pepper plants in the Mediterranean region

Physiological characteristics, growth, and biomass production of rainfed an d irrigated bell pepper [Capsicum annuum L. var, anuum (Grossum Group) 'Qua drato d'Asti'] plants were measured in the semiarid conditions of a Mediter ranean summer to determine if drought stress effects are transient and do n ot affect plant growth and crop yield or are persistent and adversely affec t plant growth and crop yield, A low midday leaf water potential indicated the occurrence of transient drought stress episodes in rainfed plants durin g the first 2 months of the study. Later on, predawn water potential also i ncreased, indicating a persistent drought stress condition despite the occu rrence of some rainfall. Photosynthesis was reduced when stress conditions developed, but the reduction was transient and limited to the central part of the day during the first 2 months, As plants aged, however, the impact o f drought stress on photosynthesis was not relieved during the overnight re covery period. Stomatal conductance was reduced both during transient and p ermanent stress conditions while CO2 transfer conductance (i.e., conductanc e to CO2 inside the leaf) was only reduced when photosynthesis inhibition w as unrecoverable, However, chloroplast CO2 concentration was higher in rain fed than in irrigated leaves indicating that CO2 availability was not limit ing photosynthesis, Nonphotochemical quenching of fluorescence increased si gnificantly in rainfed leaves exposed to permanent stress indicating the li kely impairment of ATP synthesis. Transient inhibition of photosynthesis di d not significantly affect leaf area index and biomass production, but grow th was significantly reduced when photosynthesis was permanently inhibited, Fruit dry weight was even higher in rainfed plants compared to irrigated p lants until drought stress and photosynthesis reduction became permanent. I t is suggested that bell pepper growth without supplemental irrigation over the first part of the vegetative cycle does not impair plant growth and ma y even be useful to improve yield of early fruit.