Modelling the seasonal water use and the carbon economy of kiwifruit (Actinidia deliciosa) vines

Abstract

Patterns of water use and carbon assimilation of kiwifruit vines (Actinidia deliciosa cv. Hayward) growing in an orchard environment were quantified to provide growers with tools to improve productivity. A mechanistic model to calculate vine water use and stomatal conductance was developed from climatic variables, determined over the growing season, including temperature, PFD and VPD, and the Penman-Monteith equation. The total leaf area was divided into fractions of sunlight and shaded fractions. From photosynthetic PFD-responses for both sunlight and shaded leaves, and light interception throughout the canopy, the carbon assimilation per vine was also calculated. Rates of leaf appearance as a function of temperature were determined in controlled environments. Total leaf area development over the growing season was then modelled using this temperature response, along with temperatures measured over the growing season. Predictions of changes in leaf area development, water use and carbon supply were compared from direct measurements of vine leaf area, sap flow, conductance, and gas exchange. Results of the model showed the calculated measurements of transpiration, stomatal conductance and photosynthesis were in close agreement with actual measurements. For a total leaf area of 35 m2, transpiration reached a maximum of 70 L d-1 while net carbon acquisition was maximal at 17 gC d-1 in midsummer. The estimated total carbon gain of 2200 g compares favourably with that for grapevines. Validation of the model enables confident predictions of water use and carbon availability in kiwifruit crops, aiding irrigation allocation and managing productivity of kiwifruit vines.