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.