Daily dynamics of photosynthetic characteristics of oriental tobacco under different soil moisture conditions during vigorous growing stage

Pot experiments of oriental tobacco plants were carried out to investigate effect of soil moisture on photosynthetic characteristics by using portable Li-6400 photosynthesis system during vigorous growing stage.Correlation analysis was conducted between environment factors and tobacco leaf characteristics,such as net photosynthesis rate and transpiration rate under different soil moisture levels.Results showed that(1) daily dynamics of Pn in oriental tobacco leaves under different soil moisture levels were all in the form of double peaks curves.Increase of soil moisture stress resulted in decline of peak value of Pn and midday depression intensified.(2) daily dynamics curves of Pn,Tr,Ci and Gs of oriental tobacco leaves showed significant differences under different soil moisture levels.(3) midday depression in oriental tobacco leaves may be controlled by both stomatal and non-stomatal factors.When soil moisture decline,non-stomatal is the main control factor.Correlation analysis indicated that Gs was key to Pn under three different treatments while air temperature under 65%-75% soil moisture and photosynthetic active radiation under 50%-60% and 35%-45% soil moisture levels were important to Tr.Maintaining relative soil moisture within 50%-60% may contribute to high levels of Pn and WUE.