Resorption of N, P and K from the floating and submerged leaves of the aquatic fern Salvinia natans

Abstract

Nutrient resorption from senescing leaves and shoots decreases the nutrient losses associated with biomass turnover and represents a significant component of mineral nutrient economy. In submerged aquatic plants, N and P resorption efficiencies (REN, REP) from senescing leaves or shoots are high (usually >40% in dry weight, DW), but K resorption efficiency (REK) is usually very low or zero. The free-floating aquatic fern Salvinia natans has a linear, modular shoot structure exhibiting steep growth and a physiological polarity, and consists of oval, floating, natant leaves with photosynthetic functions and thread-like submerged leaves which absorb nutrients. To obtain the basic mineral nutrient characteristics, REN, REP and REK were estimated in the senescent floating and submerged leaves of this species grown in an outdoor culture. The N content in all the leaves was in the range between 1.10-1.42% DW, P 0.33-0.57% DW and K between 4.03-6.20% DW, indicating a partial N growth limitation but a liberal P uptake. Contrary to expectations, the REN values in both types of leaves were relatively low (7-31%), those of REP even negative (-7 to -12%), while the REK values were relatively high (31-44%). These results are in contrast to much higher N and P resorption efficiencies reported in both submerged plants and the similar tropical species S. molesta. The REK values found in S. natans are in accordance with those reported in S. molesta, but are much higher than those in submerged plants. Thus, the submerged leaves (rhizophylls) of the Salvinia species do not behave in the same way as the leaves of higher submerged plants in terms of the K economy.