Spatial and temporal responses of ammonia-oxidizing bacteria and archaea to organic amendments in rice-wheat rotation system

To determine the effects of organic amendment on communities of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in rice-wheat rotation ecosystem, a long-term plot experiment with 5 treatments was conducted, and the temporal dynamics (10 growth stages) and spatial distribution (0-100 cm) of AOB and AOA abundance were determined using qPCR. The five treatments were as follows: no fertilizer control (CK), regular fertilization (RT), straw returning (SR), straw biochar returning (SB) and organic-chemical mixed fertilization (MF). The results showed the following. 1) Organic addition did not affect the temporal dynamics of AOB abundance but altered those of AOA abundance. Relative to RT, SR and MF significantly lowered AOB population sizes across the 10 sampling time points by 34.49% and 16.42%, respectively, whereas no significant differences in total AOA population size were observed among the 4 fertilization regimes. 2) Compared with the other treatments, treatments involving organic addition had higher total AOB abundance in the 0-100 cm soil layer. However, SB was the only treatment with organic addition that had a significantly higher total AOA abundance than RT (by 24.91%). 3) Under organic addition, the potential nitrification rate (PNR) was still highly correlated with AOB abundance (P < 0.01) but not AOA abundance.