Abstract
It has been reported that the δ13C of C3 plants changes with various environmentalstresses. In order to obtain baseline data for the assessment of environmental stresses in declining Japanese cedar (Cryptomeria japonica) in the Kanto Plain, Japan, I comparedthe δ13C variations with the height of needle position in the crown between declining and healthy trees. The results showed higher δ13C ratio in needles (1-year-old) from the upper crown of declining trees than that of healthy trees. There was no significant difference in the nutrient levels of needles and in the SO2 and 03 levels between the declining and healthy sites studied. Thus, nutrient levels and air pollution stress probably had little or no effect on the δ13C of needles. On the other hand, the atmo spheric water vapor saturation deficit was higher in declining areas, and Japanese cedar has the relatively low water stress tolerance. In addition, the vertical changes of δ13C in the crown were negatively correlated with those of twig volume (defined as an average volume of 1-year-old twigs at each position) probably caused by the reductionin leaf enlargement due to water stress. These results suggest that the δ13C of needles from the upper crown of declining trees is strongly affected by stomatal closure relatedto water stress.
