## 3 Results
They can also degrade apatite and aluminosilicate minerals in the soil [63]. These solubilized nutrients may then be utilized by plants. Thirteen out of twenty-six NFB isolates generated clear halos on the silicate plates (Table 1), demonstrating that they are also KSB. Among them, S18P02-2 and S18P12-1 are the two strongest potassium solubilizers which generated clear halos as large as 2.2 cm in diameter (Figure 1c). Tests using the Salkowski reagent showed that all NFB isolates secreted IAA (Figure 1d). They were classified into four categories based on their IAA production capacity (\(\mu\)g/mL) [64], including \"below 2\" (S18P11-1 [0.41] and S18P12-2 [1.97]), \"2-4\" \begin{table}
\begin{tabular}{c c c c c c} \hline
**Strain No.** & \begin{tabular}{c} **Nitrogenase** \\ **(nmol C\({}_{2}\)H\({}_{4}\)/mL/h)** \\ \end{tabular} & \begin{tabular}{c} **Inorganic P** \\ **(cm)** \\ \end{tabular} & \begin{tabular}{c} **Organic P** \\ **(cm)** \\ \end{tabular} & \
\begin{tabular}{c} **K** \\ **(cm)** \\ \end{tabular} &
\begin{tabular}{c} **IAA (\(\mu\)g/mL)** \\ \end{tabular} \\ \hline S18P01-1 & 73.89 & 0.00 & 0.00 & 0.00 & 3.956 \\ S18P01-2 & 73.89 & 0.70 & 0.00 & 1.70 & 2.442 \\ S18P02-1 & 10.67 & 0.00 & 0.00 & 0.00 & 2.975 \\ S18P02-2 & 71.85 & 0.00 & 2.80 & 2.20 & 3.480 \\ S18P02-3 & 62.27 & 1.30 & 0.00 & 0.00 & 2.961 \\ S18P03-1 & 73.89 & 0.00 & 0.00 & 2.10 & 2.370 \\ S18P03-2 & 67.06 & 0.00 & 0.00 & 0.00 & 4.259 \\ S18P04-1 & 77.36 & 0.00 & 0.00 & 0.00 & 5.067 \\ S18P04-2 & 68.38 & 0.00 & 0.00 & 0.00 & 2.168 \\ S18P04-3 & 70.77 & 1.10 & 0.00 & 1.70 & 3.076 \\ S18P05-1 & 85.02 & 0.00 & 0.00 & 1.70 & 2.615 \\ S18P05-2 & 79.87 & 2.00 & 4.00 & 2.00 & 7.100 \\ S18P06-1 & 60.24 & 1.20 & 0.00 & 2.10 & 2.240 \\ S18P06-2 & 79.63 & 0.00 & 0.00 & 0.00 & 2.283 \\ S18P06-3 & 74.01 & 0.00 & 0.00 & 0.00 & 3.740 \\ S18P07-1 & 77.96 & 1.50 & 0.00 & 0.00 & 5.485 \\ S18P07-2 & 0.00 & 0.00 & 0.00 & 0.00 & 2.600 \\ S18P07-3 & 77.48 & 0.00 & 0.00 & 1.60 & 2.038 \\ S18P08-1 & 78.32 & 0.00 & 0.00 & 2.00 & 3.769 \\ S18P08-2 & 89.45 & 1.50 & 0.00 & 0.00 & 4.721 \\ S18P08-3 & 79.15 & 1.30 & 2.80 & 1.80 & 5.399 \\ S18P09 & 74.01 & 0.00 & 0.00 & 0.00 & 2.903 \\ S18P10 & 77.24 & 0.00 & 0.00 & 0.00 & 2.658 \\ S18P11-1 & 54.37 & 1.70 & 0.00 & 2.00 & 0.408 \\ S18P11-2 & 72.09 & 0.70 & 0.00 & 2.20 & 2.081 \\ S18P12-1 & 85.86 & 1.10 & 0.00 & 2.10 & 2.370 \\ S18P12-2 & 75.92 & 0.00 & 0.00 & 0.00 & 1.966 \\ \hline \end{tabular}
\end{table} 
Table 1: Nitrogen fixation (nitrogenase), nutrient (phosphorus and potassium) solubilization, and IAA production activities of the 27 putative nitrogen-fixing bacterial (NFB) strains identified from pea embryos. Solubilization of inorganic and organic phosphorus (P) and potassium (K) is indicated by the diameters of halos produced on the respective nutrient plates. (18 isolates), \"4-6\" (5 isolates), and \"above 6\" (S18P05-2 [7.10]) (Table 1). Isolates with the highest (S18P05-2) and the lowest (S18P11-1) IAA production levels were isolated from FGPS and SPS, respectively. Quality Control of Bacterial 165 rDNA Sequencing Data and Operational Taxonomic Unit (OTU) Clustering  
A range of 23449 to 37104 (33793 on average) effective DNA sequencing reads were obtained from each replicate of the 20 pea embryo bacterial collections (two replicates per collection, 40 samples total) after removing low-quality sequences (Table S2). Most of these high-quality reads are 410-450 base pairs (bp) in lengths (Figure S1). A total of 4234 OTUs were obtained using 97% identity as the threshold for clustering high-quality effective reads (valid tags). Clustered OTUs per pea embryo sample varied from 271 (S18P02.1) to 690 (S18P01.1), with 396 OTUs being annotated on average.