# Ammonia-Oxidizing Bacterial Communities in Tilapia Pond Systems and the Influencing Factors
## 3 Results
### Richness, Diversity of Ammonia-Oxidizing Bacteria and Influencing Factors  
Species richness is generally defined as the number of different species, while species diversity is formed from species richness by further classifying the species by some attribute, such as abundance, size, or ecological role. In the present study, the Ace index and the Shannon index were used to define the ammonia-oxidizing bacterial species richness and diversity, respectively. The results showed that they were all affected by monthly variations. The richness of the ammonia-oxidizing bacteria was significantly higher in the later stage of the cultivation cycle (September and October) (Figure 3A), and the diversity (Figure 3B) of the ammonia-oxidizing bacteria was higher in May and September and lower in July and October. Meanwhile, between the three different ponds, only the Ace index value, rather than the Shannon index value, and the abundance of the ammonia-oxidizing bacterial community appeared to be significantly different. In the sediment samples, the ammonia-oxidizing bacterial species richness (Figure 3C) could not be affected by neither the monthly variances nor pond differences. Meanwhile, the ammonia-oxidizing bacterial species' diversity (Figure 3D) was the exact opposite, as it could be affected by both monthly variances and pond differences. It showed the highest value in July, followed by May; the order of the values from high to low was pond 2 > pond 1 > pond 3. The number of reads and OTUs and the values of the Ace and Shannon indices of each sample are listed in Table S1 (water) and Table S2 (sediment).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sources** & **Parameters** & **Nitrosospira** & **Nitrosococcus** & **Nitrosomonas** & **Ace** & **Shannon** \\ \hline \multirow{4}{*}{water} & TP & \(-\)0.246 & \(-\)0.562 * & 0.730 * & \(-\)0.071 & 0.078 \\  & TN & 0.011 & 0.266 & \(-\)0.229 & \(-\)0.092 & \(-\)0.157 \\  & Ammonia & \(-\)0.085 & \(-\)0.445 * & 0.527 * & 0.122 & \(-\)0.087 \\  & Nitrite & \(-\)0.393 * & 0.658 * & \(-\)0.576 * & 0.012 & \(-\)0.330 * \\  & Sulfate & \(-\)0.142 & 0.502 * & \(-\)0.391 & 0.334 * & \(-\)0.460 * \\  & Nitrate & \(-\)0.427 * & 0.029 & 0.139 & 0.151 & 0.561 * \\ \hline \multirow{4}{*}{sediment} & TOC & \(-\)0.232 & 0.048 & 0.097 & \(-\)0.189 & 0.012 \\  & pH & 0.339 * & \(-\)0.561 * & 0.369 * & 0.287 & 0.285 \\  & DO & \(-\)0.158 & 0.503 * & \(-\)0.305 & 0.043 & \(-\)0.003 \\  & SD & \(-\)0.023 & \(-\)0.009 & 0.085 & 0.018 & \(-\)0.353 * \\  & FC & 0.265 & \(-\)0.016 & \(-\)0.154 & \(-\)0.056 & 0.000 \\  & STD & \(-\)0.275 & 0.180 & 0.239 & 0.033 & \(-\)0.206 \\  & STP & \(-\)0.118 & 0.363 * & \(-\)0.459 * & 0.064 & \(-\)0.129 \\  & STN & \(-\)0.547 * & 0.531 * & \(-\)0.407 * & \(-\)0.164 & \(-\)0.309 \\  & OM & \(-\)0.255 & 0.474 * & \(-\)0.665 * & 0.123 & \(-\)0.327 \\ \hline \multirow{4}{*}{
\begin{tabular}{c} * Represents \(p<0.05\). \\ \end{tabular} } & STD & 0.524 * & \(-\)0.436 & 0.072 & \(-\)0.043 & \(-\)0.400 * \\  & FC & \(-\)0.694 * & 0.851 * & \(-\)0.193 & 0.115 & 0.048 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Spearman correlation analysis on compositions, richness, and diversity of ammonia-oxidizing bacterial communities and physio–chemical parameters.  
Correlation analyses were also performed between the Ace index values, the Shannon index values, and the physio-chemical parameters (Table 1). The results show that both richness and diversity could not be significantly affected by the three parameters (total phosphorus, total nitrogen, and organic matter) in sediments. Meanwhile, in water, the Ace index appeared to have significantly positive correlations with sulphate (\(p<0.05\)), and the Shannon index appeared to have significantly positive correlations with nitrate as well as significantly negative correlations with nitrite, sulphate, and SD.  
Correlation analyses also showed that the diversity of ammonia-oxidizing bacteria in the surface sediments of tilapia ponds was negatively related to STD (Table 1).