## 4 Discussion  
### Comparison in Phenological Points and Biomass of P. australis from Other Sites  
The biomass and phenological points of _P. australis_ from four additional sites were collected from the literature to compare with the results in the HWNR (Table 7). Compared with _P. australis_ from higher-latitude area (e.g., Nesyt fish pond, Czech Republic, and Loch of Balgavies, Scotland), the maximum AGB of _P. australis_ in the HWNR was larger, and its start dates of shoot growth and panicle formation were relatively later, which was consistent with the general pattern of latitudinal variation reported by [PERSON] et al. [59] and [PERSON] et al. [60] (Figure 7). However, significant variability can also be found between biomass of _P. australis_ in the HWNR and those in similar latitudes, such as Baiyangdian Lake (Hebei, China) [61] and Yeya Lake wetland (Beijing, China) [62], which indicated that biomass is also affected by other confounding local factors, such as nutrient level [63; 64], inundation depth, and hydroperiod (i.e., inundation frequency and duration) [65; 66]. This variability can be found in other latitudes as well, e.g., _P. australis_ in Loch of Balgavies, Scotland, and Vejerne Nature Reserve, Denmark--two sites with similar latitudes that also have significant differences in biomass [67; 68].  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{5}{c}{**Region**} \\ \cline{2-6}  & **AR** & **HWNR** & **NFP** & **LB** & **VNR** \\ \hline Latitude & 35\({}^{\circ}\)51\({}^{\prime}\) N & 40\({}^{\circ}\)06\({}^{\prime}\) N & 48\({}^{\circ}\)48\({}^{\prime}\) N & 56\({}^{\circ}\)65\({}^{\prime}\) N & 57\({}^{\circ}\)05\({}^{\prime}\) N \\ Primary shoot growth & 93 & 140 & 110 & 83 & 100 \\ start (J-day) & 213 & 225 & 196 & 213 & 232 \\ Panicle appearance (J-day) & 213 & 225 & 196 & 213 & 232 \\ Maximum & 230000 biomass & 3379.6 & 2930.1 & 2050 & 669 & 1145.6 \\ (g/m\({}^{2}\)) & & & & & \\ \hline \hline \end{tabular}  
* AR: Arakawa River in Saitama City, Japan [59]; LB: Loch of Balgavies, Scotland [67]; NFP: Nesyt fish pond, Czech Republic [69]; VNR: Vejerne Nature Reserve, Denmark [68].  
\end{table}
Table 7: The phenological and growth traits of _P. australis_ in various study sites from different latitudes.  
Figure 7: The maximum AGB of _P. australis_ in various sites from different latitudes.  
Figure 7 shows that the maximum AGB of _P. australis_ in the HWNR was considerably higher than that in Baiyangdian Lake (Hebei, China) [65; 61] and Yeya Lake wetland (Beijing, China) [62], which can be attributed to the influence of nutrients and inundation depth. [PERSON] et al. [70] studied the optimum inundation depth for _P. australis_ in different growing stages and found that a relatively low inundation depth (\(\leq\)0.10 m) can facilitate the germination and establishment of _P. australis_ at the early stage (from the end of April to May) and that higher inundation depth is more suitable at the rapid growth stage (from the end of June to the end of August). Due to the annual precipitation and evaporation pattern [28], a prominent seasonal variation trend with lower inundation depth in spring and higher inundation depth in summer was exhibited in the HWNR, which was consistent with the general requirement of suitable inundation depth for _P. australis_[70] and contributed to the relatively high biomass of _P. australis_ in the HWNR.  
In addition, previous studies have shown that higher nutrient concentration facilitates the growth of _P. australis_[71; 72]. Comparing the nutrient concentration between the HWNR and Yeya Lake wetland, the annual average values of total nitrogen and total phosphorus in the former (1.93 mg/L and 0.33 mg/L) were significantly higher than those in the latter (1.59 mg/L and 0.067 mg/L) [73], which can also lead to the higher maximum ABG of _P. australis_ in the HWNR.