Dark respiration and photosynthesis of dormant and sprouting turions of aquatic plants

Turions are overwintering, dormant organs, produced by aquatic plants. In spring, aerobic dark respiration (R(D)) and photosynthetic rates (P(N)) were measured as criteria of metabolic activity and photosynthetic capacity in dormant turions of 7 temperate aquatic plant species. These rates were also measured in old, original turion segments and in the newly formed shoots of sprouting turions. Two non-carnivorous rooting species (Caldesia parnassifolia, Hydrocharis morsus-ranae) and 5 carnivorous rootless species (Aldrovanda vesiculosa, Utricularia vulgaris, U. australis, U. stygia, U. bremii) were studied. R(D) values of dormant turions per unit fresh weight (range 1.1-5.4 mmol kg(FW)(-1) h(-1)) were significantly lower (1.9-13 times) for all species, except A. vesiculosa, than those for old segments of sprouting turions (range 5.2 -14 mmol kg(FW)(-1) h(-1)). However, R(D) and P(N) values of old and newly formed turion segments in U. australis and U. stygia were similar. P(N) values of dormant turions under optimum conditions were either very low or negative, while P(N) values of old segments of sprouting turions of all species except H. morsus-ranae were very high (18-94 mmol kg(FW)(-1) h(-1)). In a N-and P-free solution, turions of all species except A. vesiculosa formed distinct new organs after 6-20 days. In conclusion, the intensity of metabolism (both R(D) and P(N)) in sprouting turions reaches the level of adult shoots or leaves of the same species. Turions of aquatic plants also function as important storage organs for mineral nutrients (N, P, S and Mg) to ensure the growth of new organs.