Mineral nutrients, photosynthetic pigments and storage carbohydrates in turions of 21 aquatic plant species
Abstract
Turions are vegetative, dormant overwintering storage organs produced by perennial aquatic plants in autumn. They are storage organs for non-structural carbohydrates and also mineral substances (N, P).
Contents of photosynthetic pigments (chlorophyll a and b, carotenoids), storage carbohydrates (starch and five free sugars) and of mineral nutrients (N, P) were estimated in mature autumnal turions of 21 aquatic species from three different ecological groups and eight families; carbohydrates were also measured in the turions of eight species after an overwintering outdoors or in a refrigerator for 4-5 months. The mean turion N and P content was slightly higher than that reported in leaves or shoots of submerged aquatic plants.
Assuming effective reutilization, >54% of the total N and >70% of the total P amount in mature turions could be theoretically allocated to newly sprouting shoots. The chlorophyll a+b contents in turions were the same to 2-6 times lower than those in adult leaves/shoots of submerged plants, but they ensure very high photosynthetic rates in sprouting turions.
Starch and free sugars (total non-structural carbohydrates, TNC) created the main reserve substances in mature turions with variable ratios in different species. In mature turions, only TNC was significantly different between the rooted/unrooted species after application of a phylogenetic correction; the variability of other biochemical parameters has rather a taxonomic background.
About 20% of the autumnal TNC content in turions declined over winter but the rest is available to support turion germination and sprouting. However, what is the minimal TNC pool remains unknown.