Trees store non-structural carbohydrates (NSC) obtained through photosynthesis to withstand periods when carbon consumption exceeds gain. Carbon starvation hypothesis has been proposed as the physiological mechanism of death in trees with NSC depleted below survival threshold, usually due to severely reduced photosynthesis.
We examined the NSC pool in trees affected by Japanese oak wilt disease and its role in survival. This disease causes xylem dysfunction in Quercus serrata resulting in wilting during summer. Soluble sugar and starch content were measured in roots and stemwood sample from ten mature Q. serrata between April and December. Foliar characteristics including leaf δ¹³C were measured to understand individual conditions.
Increase in total NSC from April to July was the most pronounced seasonal pattern in most trees, likely owing to recovery from NSC loss through spring foliation. Two wilted trees showed significantly heavier leaf δ¹³C suggesting stomatal closure, but wood samples did not show any sign of NSC depletion and carbon starvation. Comparing surviving trees showed a negative correlation between leaf δ¹³C and proportion of starch in the total NSC pool in July. Although carbon starvation was not observed, there are indication that trees may reduce the proportion of starch in NSC to combat stresses.