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Objective This study investigates the effects and mechanisms of biochar application on the accumulation of total soil organic carbon （SOC） and key organic carbon fractions such as microbial necromass carbon （MNC） in paddy soils. Methods A field experiment was conducted to analyze the changes in SOC fractions， such as MNC and enzyme activities， five years after a one-time application of maize straw biochar at rates of 20 t/hm2 （M20）， 30 t/hm2 （M30）， and 40 t/hm2 （M40）. Results Compared with the control （no biochar application）， biochar treatments increased the contents of SOC， particulate organic carbon （POC）， and mineral-associated organic carbon （MAOC） by 19.4%-45.0%， 36.3%-65.3%， and 13.4%-47.2%， respectively， whereas dissolved organic carbon （DOC） and microbial biomass carbon （MBC） decreased by 9.8%v29.2%， and 19.5%-29.1%， respectively. Biochar treatments had no significant effects on the contents of biomarkers such as mannosamine， glucosamine， muramic acid， and galactosamine， nor on fungal necromass carbon （FNC） and bacterial necromass carbon （BNC）. However， biochar treatments significantly reduced the contribution rates of FNC， BNC， and MNC to SOC by 16.6%-32.4%， 16.7%-27.2%， and 17.0%-30.8%， respectively. The M30 treatment significantly decreased the activities of polyphenol oxidase （PHOX）， peroxidase （PERO）， α-glucosidase （AG）， β-D-cellobiohydrolase （CB）， and β-xylosidase （XYL） by 19.8%， 24.7%， 32.7%， 34.2%， and 33.7%， respectively. Correlation analysis indicated that the contribution rate of MNC to SOC was significantly negatively correlated with pH， POC， and MAOC， and positively correlated with MBC and some hydrolytic enzyme activities. Random forest model prediction showed that MAOC and pH were the main driving factors determining the contribution of MNC to SOC. Conclusion Biochar application enhances the accumulation and stability of SOC mainly by promoting the accumulation of POC and MAOC rather than MNC. The results provide a theoretical reference for improving soil carbon sequestration in paddy soils through biochar application.
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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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