Does the responses of Vallisneria natans (Lour.) Hara to high nitrogen loading differ between the summer high-growth season and the low-growth season?

Higher Tolerance of Canopy-Forming Potamogeton crispus Than Rosette-Forming Vallisneria natans to High Nitrogen Concentration as Evidenced From Experiments in 10 Ponds With Contrasting Nitrogen Levels

“…The mean air and water temperatures were 28.0 and 29.1°C in Yu et al (2017) and 22.2 and 23.7°C in this study. Light intensity was 40998 and 38776 lux in this experiment and Yu et al (2017), respectively. Mean Secchi depth (SD) in Yu et al (2017) and this study were similar, being 52.1 and 51.9 cm, respectively.…”

“…The monthly rainfall during the experiments was 125.7 mm in Yu et al (2017) and 214.7 mm in this study (Supplementary Table 1). The mean air and water temperatures were 28.0 and 29.1°C in Yu et al (2017) and 22.2 and 23.7°C in this study. Light intensity was 40998 and 38776 lux in this experiment and Yu et al (2017), respectively.…”

“…For example, toxic effects tend to play a key role in acute tests, while shading effects of algae are important in chronic tests (Cao et al, 2004; Nimptsch and Pflugmacher, 2007; Olsen et al, 2015; Zhao et al, 2016). In a long-term pond experiment carried out by Yu et al (2015, 2017), shading by phytoplankton was identified as the main cause of declining growth for plants of Vallisneria natans , and high N-induced toxic stress seemed to have negative effects in both the growing season (summer and autumn) and the low-growth season (winter); however, active growth in the growing season enabled V. natans to partly overcome the stress.…”

“…The aim of this study was to explore the effects of high N concentrations on the growth of canopy-forming submersed macrophytes and compare their tolerance to high N with that of the rosette-forming species V. natans reported in Yu et al (2017), which showed that leaf length and dry mass of V. natans in summer declined with increasing ammonium (NH 4 ) concentrations. P. crispus, a typical canopy-forming and cosmopolitan species (Jackson and Kalff, 1993; Hudon et al, 2000), was selected and the experiment was performed 1 year before that of Yu et al (2017). The two experiments were undertaken in the same pond system.…”

Reply to Cao et al.'s comment on “Does the responses of Vallisneria natans (Lour.) Hara to high nitrogen loading differ between the summer high-growth season and the low-growth season? Science of the Total Environment 601–602 (2017) 1513–1521”

“…We agree. In Yu et al (2017) NH 3 and NH 4 + were commonly expressed as total ammonium. When the concentration of un-ionized NH 3 in our experiments was calculated according to the widely used method by Wood (1993) and Emerson et al (1975), NH 3 shows a significant increase along the treatment gradient (r = 0.94, n = 9, p b 0.001 in growing season; r = 0.99, n = 9, p b 0.001 in low-growth season) being much higher in the growing season (medians between 0.10 and 6.04 mg L ).…”