Some physiological properties of Cryptomeria japonica leaves from Kanto, Japan: potential factors causing tree decline

Japanese cedar (Cryptomeria japonica D. Don) has been declining in urban ar eas of Japan. We examined if the decline was associated with physiological deterioration of leaves and resulting water stress. Leaves from three locat ions (severe decline, slight decline, and healthy) were analyzed for minimu m transpiration rates (MT), amounts of epicuticular wax (EW), contact angle s (CA), fractions of unhealthy stomata (US), cuticular thickness, and leach ing of elements (LE). Anthropogenic elements (e.g., antimony (Sb)) in aeros ols on the leaves were also analyzed by neutron activation analysis. MT, US , and amounts of Sb were 2, 15, and 10 times greater, respectively, at the severe decline location compared with the healthy location. LE was also gre ater at the severe decline location than at the slight decline and healthy locations. In contrast, CA was greatest at the healthy location and least a t the severe decline location. MT correlated with the values obtained from a linear trinomial function that included EW, CA, and US as variables (r = 0.872, P < 0.01), and US correlated with amounts of Sb in aerosols (r = 0.9 39, P < 0.01). Therefore, it is likely that the deterioration of epicuticul ar wax and stomatal unhealthiness resulting mainly from clogging with aeros ols, in combination with environmental aridification, have placed C. japoni ca under chronic and sometimes fatal water stress, causing tree decline.