Mechanisms of abundance decline and potential responses to climate warming in C3 grass species

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(1)Although the perennial grass Dactylis glomerata L.has established dominant populations in Japan since the first introduction in the 1870s', its abundance shows a marked reduction in the southern part of Tohoku regions. In this study, mechanisms of abundance decline and potential responses to climate warming of the naturalized populations of D.glomerata.(2)Abundancs of naturalized populations of D.glomerata were measured in 43 sites of Tohoku and Kantoh regions and their relationships with climate factors were examined. There were highly positie correlation between abundance and maximum temperature in September, which suggests that abundance decline is closely related to duration of hot climate rather than by highest temperature of mid summer.(3)Photosynthetic efficiency of light response and dark response were measured by A-Ci curve during 26℃ to 40℃ at two degree intervals. The decline of Jmax, which represent the maximum efficiency of light reaction, showed a large decline with increasing temperature, but no deline was found for Jcmax, which is the maximum efficiency of dark reaction. These results show that decline of photosynthesis under heat stress is caused by decreased function of light harvesting or light transfer reactions.