Effects of Continuous Cropping on Growth and Photosynthetic Characteristics in Leaves of Flue-cured Tobacco in Northeast of China

In this paper, photosynthetic characteristics in leaves of flue-cured tobacco grown in the field of continuous cropping for one year and five year were investigated by measuring plant growth, chlorophyll content and photosynthesis. The results showed that continuous cropping decreased chlorophyll content and photosynthesis capacity, and reduced the tobacco growth and leaf yield. Although little influence on tobacco growth and photosynthesis capacity was observed in the field with one year continuous cropping, Chlorophyll content in leaves of flue-cured tobacco grown under 5-year continuous cropping reduced significantly, especially, chlorophyll A content, which restricted light capture, energy conversion and utilization in leaves of tobacco. The net photosynthetic rates, transpiration rate and stomatal conductance of tobacco leaves under 5-years continuous cropping decreased, but, intercellular carbon dioxide concentration changed little. The apparent quantum yield, light saturation point, photosynthetic rate saturated light, carbolyation efficiency, carbon dioxide saturation point and photosynthetic rate at saturated carbon dioxide in leaves of tobacco grown under continuous copping decreased, and carbon dioxide compensation point and light compensation points increased significantly under 5-years continuous cropping. It indicated that light use efficiency in leaves of tobacco grown in continuous cropping field was not only decreased significantly but also CO₂ assimilation, and photosynthesis decrease under 5-years continuous cropping was caused by stomatal factors and nonstomatal factors. It suggested that the decreases of photochemical and assimilation capacity in leaves of tobacco grown in continuous cropping field limited photosynthetic production to reduced leaf yield of tobacco.