CARBON AND WATER FLUXES IN VEGETATING 3-YEAR-OLD WALNUTS
The translocation pattern, already highly basipetal in summer, became even more so in fall; in the same time, the daily fluxes of recent photoassimilates incorporated into all biochemical fractions decreased sharply at the whole plant level, and the metabolic rate slowed down. However, not all organs changed their activity to a similar extent, particularly among the different components of the root system. In contrast to the C fluxes incorporated into plant dry matter, the fluxes allocated to respiration were only little affected.
In parallel, water fluxes were investigated, both at the day-and the infra-day level. An average of ca. 7 liters daily were transported through the transpiration stream for correctly irrigated trees. During a normal summer day, absorption lagged transpiration and dehydration leading to shrinkage. In the evening and night the situation reversed and plants rehydrated. The fine dynamics of sap flow and stem diameter allow a precise monitoring of the water status.
The effects of drought on both fluxes and their interaction are briefly discussed.