Table 2. The bivariate correlation between the alpha diversity of diazotrophic communities and soil factors.

Diversity index†	pH	TN‡	TC‡	C/N	NH4+-N	NO3−-N	AP‡	AK‡	TP‡	TK‡
OTU number	−0.163	−0.095	−0.245	−0.121	0.146	−0.020	−0.297	−0.063	−0.009	−0.048
Shannon	0.095	−0.329	0.167	0.517*§	0.006	0.356	−0.664**§	0.037	0.107	−0.146
Simpson	−0.099	0.292	−0.171	−0.478*	−0.032	−0.421	0.627**	−0.096	−0.111	0.161
Chao1	−0.088	0.253	0.072	−0.174	−0.170	−0.267	−0.013	0.065	0.187	0.117

Notes:

^†All indices are calculated based on the minimum number of 6,545 sequences per sample.

^‡TN, TC, TP, TK, AP and AK represent soil total nitrogen, total carbon, total phosphorus, total potassium, available phosphorus and available potassium, respectively.

^§* and ** represent significant correlation at P < 0.05 and P < 0.01 level, respectively.