Castanea sativa burr growth in its final stages

The daily growth pattern and vascular flows of Castanea sativa Mill. (‘Marrone di Castel del Rio’) burrs, were monitored during a sensitive burr growing phenological stage (nut filling), through plant-based sensors (fruit gauges) connected to a wireless data-logger system. Environmental parameters were also recorded by a weather station placed in the middle of the orchard. The daily burr growth pattern was generally characterized by a rapid shrinkage in the early afternoon, corresponding to the highest vapour pressure deficit (VPD), followed by nocturnal swelling until the early morning. Daily burr net growth was positively influenced by high air relative humidity (RH) values and precipitation events while negatively affected by VPD. Vascular flows confirm that the daily shrinkage was due to high burr water losses by transpiration. The xylem was fully active and able to replenish the amount of water lost during the day by the transpiration process. Phloem inflow was the major component for the net daily burr growth. These observations, coupled to the increase in nut dry mass content typical of this stage, suggest a passive model of burr phloem unloading, able to persist at high levels of RH, likely energized by the high burr epidermal transpiration. This study aimed both to establish the influence of environmental conditions on daily burr growth and to identify the vascular flow model supporting burr growth during a period of strong demand by the nut. Knowing and monitoring, in real-time, the burr daily growth, could be promising for the adoption of smart and sustainable practices for chestnut orchard management, especially in areas characterized by water shortages.