Title of
Journal：
Fundamental and Applied Limnology
Paper
Code：
Volume：
159
Number：
2
Page：
129-142
Others：
Classification：
Source：
Abstract：
The role of total ammoniacal nitrogen (TAN, [NH4-+NH3]) in the growth of submerged macrophytes in shallow eutrophication-prone lakes remains controversial. Contrasting responses of different submerged species to TAN have been reported in recent studies, with various explanatory factors proposed, e.g., different TAN uptake ability leading to carbon-nitrogen imbalance and different growth forms of submerged species resulting in different shading from phytoplankton and periphyton. However, it is well known that Of can affect the proportion of free ammonia (NH3) in TAN, which may be a primary cause of its phytotoxicity to submerged macrophytes, especially for species that produce a higher pH on the adaxial side of their leaves (i.e., polar leaf photosynthesis or leaf polarity). In this study, we hypothesised that leaf polarity in submerged macrophytes could interact with the toxicity of TAN. Three experiments were conducted to analyse the correlations between the toxic effects of TAN on submerged macrophytes and leaf polarity. We grouped macrophytes into three classes: i.e., strict free CO2 users (FC) and bicarbonate users with no leaf polarity (BIC) and with leaf polarity (LP). Experiment I (colour reaction microcosm study) showed that pH on the adaxial side of broad-leaved Potamogeton lucens and Potamogeton wrightii quickly increased to > 8.3 within 10 min. In Experiment II (TAN uptake microcosm study), the daily TAN uptake rate of 13 submerged macrophytes did not differ among the three macrophyte classes but was higher under high bicarbonate conditions. Experiment III (phytotoxicity microcosm study) showed strong species-specific responses to high TAN levels, but non-significant differences among the three macrophyte classes following NH4(+) exposure. Changes in the leaf chlorophyll fluorescence parameter, Yield, showed marginally different slopes between BIC and LP species when considering different responses to TAN treatments (with or without high bicarbonate concentrations). In summary, the polarity of submerged leaves can induce a higher pH in the phyllosphere but may only play a minor role in TAN phytotoxicity.
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