Poster: Ecophysiology
Abs #
53: Leaf senescence under different carbon and nitrogen availability
Photosynthetic activity and nitrogen content in the leaf start to decrease around at full leaf expansion. This process is referred to leaf senescence. Leaves senesce faster in plants grown under high light with low nutrient supply. Carbohydrates accumulate in mature leaves under nitrogen deficiency. Using sunflower (Helianthus anuuss) plants, it was suggested that leaf senescence was regulated by sugar level in the leaf (Ono and Watanabe 1997). In Phaseolus vulgaris plants grown under moderate light (330 mmol m-2 s-1, 12h light/12h dark) with nutrient supply, shading new leaves suppressed both the accumulation of carbohydrates and the decrease in photosynthetic activity in the first leaves. When plants were grown without nutrient supply, accumulation of carbohydrates was marked and photosynthetic activity decreased regardless of shading new leaves (Ono et al. 2001). Phaseolus vulgaris plants were also grown under the higher light (450 mmol m-2 s-1) and the longer photoperiod (14h light/ 10h dark). Plants grew rapidly with nutrient supply. Shading new leaves suppressed their growth, but they grew larger than those without nutrient supply. Photosynthetic activity of the first leaves decreased as in plants without shading. Under the higher light intensity, both carbon and nitrogen are available, therefore, sink strength would be strong. Under the higher light without nutrient supply, the nutrient deficiency would be severe. It will be discussed whether the regulation of leaf senescence by carbohydrate level is effective or not under these conditions.
