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

Abstract

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-1 FW 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-1 FW 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-1 FW 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.

The Growth and Establishment of Floating Turions of Potamogeton crispus Are Not Favored by Summer Climate

“…a). These results were in agreement with previous studies that the R D were high during the turion sprouting process and may indicate the high metabolism in these turions .…”

“…4a). These results were in agreement with previous studies that the R D were high during the turion sprouting process and may indicate the high metabolism in these turions [4,36]. The SOD and POD activities of both floating and sinking turions were similar at the beginning of experiment, whereas these two enzymatic activities of floating turions increased significantly after 15 days of experiment ( Fig.…”

“…Turions are dormant organs of aquatic vascular plants, which become detached from parental plants at the end of a growing season . Turions are formed by specialized shoot apices, which usually are tough and sturdy organs . Previous studies concluded that the turions are formed as a response to stressful conditions (e.g., freezing temperature or nutrient limitation) .…”

“…For those turions in the innate dormancy state, presumably, a very low storage material is needed to ensure their maintenance function [3,4,13]. As turions cannot take up nutrients from the surrounding environment until new roots/shoots are formed, the main function of turions' storage could thus be supporting the growth of new roots/shoots [4,23,25,26]. Moreover, recent studies reported that red light pulses induce starch degradation in turions [13,[27][28][29], suggesting the sprouting and establishment of P. crispus turion could be also controlled by light condition.…”

Turion morphological responses to water nutrient concentrations and plant density in the submerged macrophyte Potamogeton crispus

“…Turions of P. crispus store large amounts of total nonstructural carbohydrates (30–70% dry weight) and mineral nutrients (TN and TP) 20 28 31 . As turions cannot take up nutrients from the surrounding environment until new roots/shoots are formed, the main function of turions' storage could thus be supporting the growth of new roots/shoots 32 33 34 35 . Previous studies have mainly focused on how environmental factors influence turion germination 27 , formation 20 and dispersal 29 .…”