Effect of tree microenvironment on sweet cherry fruit transpiration, xylem, and phloem flows

This study provides an overview of how shading covers can affect air vapor pressure deficit (VPD) and sweet cherry water status, and it fruit absolute growth rate (AGR), and its xylem (X), phloem (P), and transpiration (T) flows. The experiment was carried out from April to June 2024 on a 14-year-old sweet cherry orchard, variety ‘Sweet Saretta’ grafted on ‘Gisela 6’. These trees were cultivated under: (i) direct sunlight conditions, and (ii) a 20 % shading black net. During the experiment, environmental conditions, such as air temperature (Ta) and relative humidity (RH), were monitored, and from this data the VPD was calculated. Tree water status was assessed by measuring at 9:00 h stomatal conductance (gs), and net photosynthesis (Pn) and at 12:00 h stem water potential (Ψstem). During the experiment, the fruit equatorial diameter was measured at regular time intervals during the season. At the same time, fruit daily diameter variations were monitored precisely every 30 min at 33, 38, and 43 days after full bloom, corresponding with the early and late stage II, and with the early stage III of fruit growth. From these data, the 30-minute fruit AGR, X, P, and T flows were estimated, and their daily contribution was calculated. In addition, fruit X, P, and T flows were correlated with VPD at different fruit growth stages. During the experiment, VPD was reduced on average by 19 % under the net. At the same time, trees cultivated under a net showed less negative values of Ψstem and higher values of gs and Pn. Differences between treatments were also observed in the 30-minute and daily contributions of fruit AGR, X, P, and T flows. Results showed that cropping condition slightly affected the relationship between VPD and fruit T, X, and P flow. In conclusion, under netting, the lower air VPD had some positive effects on tree water status and seasonal fruit growth. These conditions mainly minimized the daily contribution of fruit T, X, and P flows, except in the case of P flow at stage III, and did not significantly affect the correlation between these flows and the VPD.