The impact of prolonged flood-irrigation on leaf gas exchange in mature pecans in an orchard setting

Woody perennials subjected to root oxygen-stress often respond with varying levels of reduced assimilation and leaf gas exchange. Yet in most of these studies, seedlings grown in pots were subjected to experimental conditions that rarely exist in nature for mature trees. To determine if flooding mature orchard-grown pecan (Carya illinoiensis (Wangh) K. Koch) results in a similar depressed photosynthetic rate (Pn), transpiration (E), and stomatal conductance (gs) as found in potted seedling studies, 27 year-old trees were continuously flooded for 35 days during which gas exchange measurements were compared with non-flooded controls. Flood-treated trees exhibited a continuous decline in Pn, gs, and E without any apparent recovery throughout the treatmentperiod, and progressively higher levels of intercellular CO2 (Ci). Flooded trees also exhibited widespread interveinal ‘bronzing’ in subtle blotchy patterns, sporadic adaxial interveinal scorching, and simultaneously put on a flush of new growth, not seen in the control trees. Mechanisms are considered relating a putative disruption in carbohydrate export to the reduced levels of photosynthesis