In order to quantify the effects of thinning on photosynthetic parameters and associated change in leaf nitrogen (N) contents, half of the trees in a 10-year-old Chamaecyparis obtusa (Sieb. et Zucc.) Endl. stand (36° 3'N, 140°7'E) were removed, giving a final density of 1 500 trees ha-1, in May 2004. Photosynthetic photon flux density (PPFD) and leaf N and carbon (C) contents in the lower (L), middle (M), and upper (U) crowns were monitored one, three, and five months after thinning in both the thinned stand and a non-thinned control stand. In addition, leaves' photosynthetic responses to CO2 concentration were simultaneously measured in situ to estimate the maximum rates of carboxylation (Vcmax) and electron transport (Jmax). Thinning increased PPFD in the L and M crowns but not in the U crown. Vcmax in both the L and M crowns of the thinned stand increased significantly in comparison with the same crown position of the control stand in the three and five months following thinning. In addition, the thinned stand exhibited an increase in N partitioned to ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) in the L and M crowns relative to the control stand three and five months after thinning, indicating that N had been redistributed within the photosynthetic machinery. Thinning did not affect N per unit area at any of the crown positions, but significantly increased the content of N as a fraction of the total leaf dry mass in the L and M crowns three and five months after thinning. This was a consequence of a decrease in leaf dry mass due to rapid shoot growth. Thus thinning did not cause a redistribution of N between leaves. Thinning improved irradiance in the L and M crowns of C. obtusa, leading to photosynthetic acclimation. Photosynthetic acclimation in the first year mainly occurred via redistribution of N within but not between leaves. and Q. Han, M. Araki, Y. Chiba.
The responses to root oxygen deficiency conceming the photosynthesis, saccharide contents and minerál uptake háve been investigated in Carex species, which were different in their anoxia-tolerance. The net rate of photosynthesis (Fn) anoxia- sensitive C. extensa was not affected by root anaerobiosis. Despite short-term effects of root anaerobiosis on values in the anoxia-tolerant species C. remota and C. pseudocyperus, root oxygen supply did not influence P^, when the plants were allowed to acclimate. The saccharide contents of the anoxia-tolerant species were almost not affected by prolonged anaerobiosis. 40 days of root oxygen deficiency led to significant changes in the shoot saccharide composition of C. extensa: contents of glucose and fructose were increased 4-fold and sucrose content was significantly decreased. In the roots no sucrose could be detected, but the starch content was increased, and the glucose and fructose contents did not change when compared with aerobic conditions. Under anaerobic conditions, minerál uptake of the anoxia- sensitive species decreased by 50 %, while the minerál uptake of the anoxia-tolerant species was significantly increased or did not change at all, in comparison with the aerobic conditions. The growth reduction of C. extensa under anaerobic conditions was therefore primarily due to inability to také up an adequate amount of nutrients.