Changes in 16S rRNA bacterial community structures after C and N additions – comparison of organic farmed and conventionally farmed soils

Misato TODA1, Yoshitaka UCHIDA2

1 Graduate School of Agriculture, Hokkaido University, Kita9 Nishi9 Kita-ku, Sapporo, Hokkaido, 0608589, Japan. www.uchidalab.com, [email protected]

2 Research Faculty of Agriculture, Hokkaido University, Kita9 Nishi9 Kita-ku, Sapporo, Hokkaido, 0608589, Japan.

Abstract

The use of legumes has received heightened interest as an alternative to chemical fertilizers in recent years. It adds not only nitrogen (N) but also carbon (C) to soils thus it might influence the soil microbial community structures. Considering that microorganisms play a key role in N dynamics, it is important to understand the relationship between the soil microbial structure and soil N dynamics, in relation to the use of legumes. Thus, we aimed to evaluate the relationship between the long-term legume application and soil microbial community structures. Also we aimed to investigate the relationship between the microbial communities and the soils’ N immobilization potential, because N immobilization by microbes often competes with plants in terms of N availability in soils. We compared a soil with the history of the use of green manure (hairy vetch, HV) and a soil with the history of the use of N chemical fertilizer (CF). First, we investigated the microbial communities using a colony counting method and a 16S rRNA gene analysis. Then we conducted an incubation experiment where we added C and N source into soils and measured N immobilization potentials. Bacterial community structures were analyzed to investigate the interaction between N immobilization potentials and bacterial community structures. Our results showed that there was a significant difference in microbial community structures for the two soils before the addition of C and N. However, no significant difference was detected on N immobilization potential during the incubation. Moreover, the difference between the bacterial community structures in the two soils became smaller as the incubation progressed, within 14 days. According to these results, it is indicated that microbial community structures were clearly influenced by the use of hairy vetch but with added C and N, the community structure differences due to the use of hairy vetch might disappear.