Toward modeling of stomatal conductance under elevated ozone in forest trees

Hoshika, Yasutomo*; Watanabe, Makoto*; Katata, Genki; De Marco, A.*; Deushi, Makoto*; Carriero, G.*; Koike, Takayoshi*; Paoletti, E.*

Ozone (O) enters leaves via stomata and causes a damage to leaves of trees. Modeling of stomatal conductance (g) is considered as an essential factor to assess O impacts. In this presentation, our recent progress of research for the modeling of g under elevated O is summarized. First, we investigated g parameters of the Jarvis-type model for forest tree types throughout the world. The optimal temperature of g and g response to predawn water potential changed according to the growth conditions. Next, an optimization model of stomata including O effects was tested in free-air O exposure experiment on Siebold's beech in Japan. The optimal stomatal model explained O-induced stomatal closure in early summer. However, in late summer and autumn, the model did not explain the effects of O on g. This reflects the loss of closing response of stomata by O (stomatal sluggishness) such as under low light conditions. Finally, we examined the effects of O-induced stomatal sluggishness on carbon gain and transpiration of temperate deciduous forests in the Northern Hemisphere by combining a detailed multi-layer land surface model and a global atmospheric chemistry model. Our findings are consistent with previous experimental evidences, suggesting significant impairment of forest carbon and water balances attributed by O-induced stomatal sluggishness.