Different reutilization of mineral nutrients in senescent leaves of aquatic and terrestrial carnivorous Utricularia species

• Dark respiration polarity was measured in leaves and traps of aquatic Utricularia reflexa.
• Reutilization of N and P but not K was found in old leaves and traps of U. reflexa.
• The same reutilization pattern was found in the rootless aquatic Ceratophyllum submersum.
• Efficient N, P and K reutilization was found in old leaves of five terrestrial Utricularia species.
• The absence of K reutilization in shoots of aquatic plants is discussed.

Nutrient reutilization (recycling) from senescent tissues in aquatic and terrestrial plants is important especially in nutrient-poor environments. The hypothesis was verified that N and P are reutilized efficiently from senescent shoots in both aquatic and terrestrial plants, while K is reutilized only in terrestrial plants. The efficiency of N, P and K reutilization in old traps and shoot segments in the submerged carnivorous plant Utricularia reflexa and the leaves of non-carnivorous Ceratophyllum submersum was compared with that in the leaves of five terrestrial Utricularia species. Oxygen-based dark respiration rates of U. reflexa traps, measured as a criterion of physiological activity, exhibited a marked polarity, while a weak respiration polarity of leaves was not significant. No distinct polarity of trap and shoot N contents were found in U. reflexa shoots. When the correction factor of 0.71 was applied to compensate for the assumed dry weight (DW) decrease in old traps and leaf nodes, the mean reutilization efficiency for N was 19% in traps and 37% in leaf nodes and for P, 67% in traps and 52% in leaf nodes. However, in spite of the correction factor, the K reutilization efficiency in both types of organs was negative. In Ceratophyllum leaves, the corrected N, P and K reutilization efficiencies were similar to U. reflexa leaves. In five terrestrial Utricularia species, the N, P and K contents in adult leaves always significantly (usually at p < 0.01) exceeded that in senescent leaves. The following corrected reutilization efficiencies were found: 35–82% for N, 56–84% for P and 48–91% for K. These efficiencies are comparable with those in the aquatic species only for N and P, but are quite different for K. It may be concluded that reutilization of K (unlike N and P) in leafy shoots generally occurs only in terrestrial and not in aquatic plants. The lack of K reutilization in aquatic plants might be due to the direct K+ uptake from the water column.