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Biochar serves as an excellent carrier for non-symbiotic nitrogen (N)-fixing bacteria, enhancing their microbial activity and functions. However, the coupling mechanism between non-symbiotic N-fixing bacteria and biochar remains unclear. Objective To explore the effects of different biochar materials on the colonization pattern and N fixation efficiency of non-symbiotic N-fixing bacteria. Methods Non-symbiotic N-fixing bacteria were inoculated onto biochar samples derived from maize straw and wood chips, the particle sizes of which were >2.00 mm, 0.25-2.00 mm, and <0.25 mm. We compared the porosity and specific surface area of different biochar samples. Throughout the incubation period, the dynamic changes in nitrogenase activity and the number of N-fixing bacteria, pH, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) were monitored. Results N-fixing bacteria exhibited more uniform colonization and higher N fixation activity on straw biochar than on woody biochar, especially in the 0.25-2.00 mm group. The straw biochar with the particle size of 0.25-2.00 mm and inoculated with strains showed increases of 82.33%-160.55% and 231.46%-356.08% in the average MBC content and nitrogenase activity, respectively, compared with woody biochar. Moreover, significantly higher content of DOC and DON were maintained in all straw biochar groups, which provided a richer pool of available nutrients for microbial growth. The correlation heatmap indicated that pH significantly affected bacterial colonization and nitrogenase activity. Furthermore, nitrogenase activity showed strong positive correlations with DOC and MBC (P<0.001), which suggested that a carbon-rich environment was a key factor for the growth and N fixation of N-fixing bacteria. Conclusion Straw biochar with the particle size of 0.25-2.00 mm serves as an optimal carrier for non-symbiotic N-fixing bacteria. It provides a favorable microenvironment for the N fixation and some other functions of the bacteria.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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