GRAFTING FOR IMPROVING NET PHOTOSYNTHESIS OF COFFEA ARABICA IN FIELD IN SOUTHEAST OF BRAZIL

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Abstract
SUMMARY: Leaf gas exchange and leaf water potential (Ψleaf) were measured seasonally on non-grafted and grafted Coffea arabica on Coffea canephora in the field to investigate whether grafting would be able to protect the carbon balance against the rise of in vapour pressure deficit (VPD) and air temperature (Tair) under future climate change. The net maximum photosynthetic rate obtained from the net photosynthesis (PN) curve as a function of photosynthetic photon flux density (PPFD) in wet and dry periods was used to estimate the integrated potential diurnal net CO2 assimilation (IPPN) around midday. The difference between IPPN and the integrated values of PN during diurnal courses (IPN) was measured to test grafting as suitable practice for minimizing midday depression of PN. Higher values of PN in grafted plants around midday showed that grafting was important even when environmental conditions were favourable in field conditions. Reduced susceptibility of grafted plants to midday depression was revealed by lower values of Ψleaf associated with higher values of PN and leaf transpiration (E) on sunny days in summer and spring, and by higher values of stomatal conductance (gs) around midday in autumn, winter and spring. The differences of E, gs, PN and Ψleaf between non-grafted and grafted plants were higher in dry periods in winter and spring. In addition, the ratio IPN/IPPN in grafted was double that in non-grafted plants around midday in sunny summer and in spring. Indeed, PN and gs of non-grafted plants showed higher dependence on VPD than grafted ones. The lower susceptibility of grafted plants to water stress demonstrated the graft efficiency for increasing positive components of leaf carbon balance of C. arabica in the field, especially under high VPD in projected future climate conditions.

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