Which Is More Sensitive to Water Stress for Irrigation Scheduling during the Maturation Stage: Grapevine Photosynthesis or Berry Size?

Abstract

To better understand the sensitivity of berry size and grapevine photosynthesis to water stress, and determine the soil water potential (psi) threshold for scheduling irrigation during the maturation stage, we simultaneously measured berry size with photographs, leaf net photosynthesis with a portable meter, and psi with tensiometers during the drying cycles for grapevines (Vitis vinifera L.). Our results showed that in berry development stage III (maturation), photosynthesis was more sensitive to water stress than berry size. When psi decreased beyond -13.2 +/- 0.82 kPa, photosynthesis, stomatal conductance, transpiration, and extrinsic (A(N)/E) and intrinsic (A(N)/g(s)) water use efficiency (WUE) decreased rapidly and did not recover thereafter. In contrast, the berry size remained close to unaffected by the decreasing psi until it reached a value of -16.2 +/- 0.77 kPa and, thereafter, the berry shrank significantly. In conclusion, we suggest that during the maturation stage of grapevines, for the potted mixture used in our experiments, irrigation should be triggered when the psi reaches a value of -13.2 +/- 0.82 kPa. Further, psi should be kept lower than -6.9 +/- 0.15 kPa after irrigation, because the highest values of intrinsic WUE (A(N)/g(s)) occurred when psi decreased from -6.9 +/- 0.15 to -14.6 +/- 0.7 kPa. In arid areas, the threshold psi should be considered as -16.2 +/- 0.77 kPa during maturation to achieve high-efficiency use of water resources and sustainable production of grapevines.