Abstract:

Higher maximum photosynthetic rate, apparent photosynthetic quantum yield and the efficiency of light energy conversion were observed in leaves of saplings of W. septentrionalis and T. lotungensis at full as comparison with that at 40% or 20% daylight. As light intensity decreased from full to 40%, apparent photosynthetic quantum yield and the efficiency of light energy conversion declined by 13.1% and 6.3% for W. septentrionalis, respectively and by 23.8% and 33.4% for T. lotungensis, respectively. Similar maximum carboxylation rates of Rubisco (Vcmax) were found in leaves of W. septentrionalis grown at full and 40%. However, maximum rate of photosynthetic electron transport decreased by 14.1% in decreasing light level from full to 40%. Decreasing ratio between Jmax and Vcmax was also observed. It means that response of Jmax to decreasing light intensity was more sensitive than that of Vcmax. The relative values were 7.7% and 31.7% for Vcmax respectively, and 9.7% and 42% for Jmax respectively, in T. lotungensis, as light intensity decreased from full to 40% and 20%. The partitioning coefficient for leaf nitrogen in Rubisco　(PR)　and the fraction of leaf nitrogen in thylakoid lightharvesting components　(PL) were almost the same in W. septentrionalis with decreasing from full to 40%. And the partitioning coefficient for leaf nitrogen in bioenergetics　(PB) decreased by 20.4% with decreasing light intensity. Whereas, in T. lotungensis, PR and PB were declined significantly. With decreasing light intensity. The results may suggest that W. septentrionalis would be a sun plant for which an open site would be considered the most optimizing environment for trans plantation and the shade-tolerant plant of T. lotungensis which adapts to a more shade environment.