Leaf assimilation, carbon translocation and root respiration in ‘Budagovski 9’ apple cuttings grown in low soil moisture condition.

The objective of the present study was to investigate the effect of moderately limited soil water supply on root C allocation and root respiration of non-bearing apple trees. Potted 1-year-old apple trees of ‘Budagovski 9’ grown in sand where water content was reduced (7 % w:w) were compared to plants grown in soil irrigated at field capacity (12 % w:w). Canopies were labelled with 13CO2 and excess 13C allocation within tree organs and evolution from the soil were monitored for 16 days after the labelling. The moderate reduction of soil water content induced a decrease in predawn leaf water potential and leaf gas exchange; however, root and above ground dry weight were not affected. Compared to well-watered control, trees growing in condition of moderately limited soil water supply fixed a lower amount of pulsed 13C. From day 1 to 16, 13C concentration decreased in leaf, increased in root and trunk, and was stable in herbaceous shoots, in both irrigation treatments, with no difference in the 13C partitioning. Root respiration rate of new fixed 13C was reduced by water limitation, was linearly related to the amount of excess 13C allocated into the roots, and became equal to zero by day 16.