Fertilization makes strong associations between organic carbon composition and microbial properties in paddy soil.

Fertilization changes the soil organic carbon (SOC) composition, affecting the carbon cycle of paddy soil. Understanding the mechanisms of physical fraction and chemical composition of SOC responding to fertilization can help regulate the nutrient release and carbon sequestration. However, it is unclear whether these changes in SOC composition to fertilization are consistent and how these are regulated by biotic and abiotic properties. Therefore, a positioning experiment in a rice field was conducted with a total of nine treatments. Chemical fertilizers (0, 337.5, and 675 kg ha-1; C0, C50, and C100, respectively) and fungal residue (0, 10,000, and 20,000 kg ha-1; F0, F50, and F100, respectively) were applied to evaluated (i) changes in the physical fraction and chemical composition of SOC, (ii) changes in soil properties, microbial biomass and community, and (iii) establish relationships among soil properties, microbial community, microbial biomass, and SOC composition. Our results showed that the application of fungal residue exhibited more significant effects on SOC physical fractions than those with the chemical fertilizers. Furthermore, the chemical composition of SOC was more respond to the application of chemical fertilizers than fungal residue. The partial least squares path model indicated that soil properties mainly affected the mineral-associated organic carbon (MAOC) by microbial biomass. In addition, bacterial diversity played an important role in improving the accumulation of MAOC. The SOC chemical composition was mediated by fungal community composition and bacterial diversity. In conclusion, fungal residue application affected SOC physical fraction by increasing soil properties, microbial biomass, and bacterial diversity. Chemical fertilizers application mainly mediated the chemical composition of SOC by altering fungal community composition and decreasing bacterial diversity.

[Effects of Combined Application of Fungal Residue and Chemical Fertilizer on Soil Microbial Community Composition and Diversity in Paddy Soil].

Fungal residue is a unique abundant organic material undervalued in agricultural production. The application of chemical fertilizer combined with fungal residue can not only improve soil quality but also regulate the microbial community. However, it is unclear whether the response of soil bacteria and fungi to the combined application of fungal residue and chemical fertilizer is consistent. Therefore, a long-term positioning experiment in a rice field was conducted with a total of nine treatments. Chemical fertilizer (C) and fungal residue (F) were applied at 0, 50%, and 100% to evaluate 1 the change in soil fertility properties and microbial community structure and 2 the main driving factors of soil microbial diversity and species composition. The results showed that soil total nitrogen (TN) was highest after treatment C0F100 (55.56% higher than in the control), and the carbon to nitrogen ratio (C/N), total phosphorus (TP), dissolved organic carbon (DOC), and available phosphorus (AP) contents were highest after treatment with C100F100(26.18%, 26.46%, 17.13%, and 279.54% higher than in the control, respectively). The amounts of soil organic carbon (SOC), available nitrogen (AN), available potassium (AK), and pH were highest after treatment with C50F100 (85.57%, 41.61%, 29.33%, and 4.62% higher than in the control, respectively). Following the application of fungal residue with chemical fertilizer, there were significant changes in the α-diversity of bacteria and fungi in each treatment. Compared with that of the control (C0F0), different long-term applications of fungal residue with chemical fertilizer did not significantly change soil bacterial ß-diversity but resulted in significant differences in fungal ß-diversity, and the relative abundance of soil fungal Ascomycota and Sordariomycetes significantly decreased after the application of C50F100. The random forest prediction model indicated that AP and C/N were the main driving factors of bacterial and fungal α-diversity, respectively, and AN, pH, SOC, and DOC were the main driving factors of bacterial ß-diversity, whereas AP and DOC were the main driving factors of fungal ß-diversity. Correlation analysis suggested that the relative abundance of soil fungal Ascomycota and Sordariomycetes had a significantly negative correlation with SOC, TN, TP, AN, AP, AK, and C/N. PERMANOVA showed that variation in soil fertility properties, dominant species of soil bacteria at the phylum and class level, and dominant species of soil fungi at the phylum and class level were all best explained by fungal residue (46.35%, 18.47%, and 41.57%, respectively), and variation in bacterial diversity was best explained by fungal residue (23.84%) and to a lesser extent by the interaction between fungal residue and chemical fertilizer (9.90%). In contrast, the variation in fungal diversity was best explained by the interaction between fungal residue and chemical fertilizer (35.00%) and to a lesser extent by fungal residue (10.42%). In conclusion, the application of fungal residue has more advantages than chemical fertilizer in influencing soil fertility properties and microbial community structure changes.

Effect of the combined application of fungal residue and chemical fertilizers on the mineralization of soil organic carbon in paddy fields.

Improving soil quality, reducing waste, and mitigating climate change require an understanding of the balance between soil organic carbon (SOC) accumulation and depletion after the application of different quantities of fungal residue and chemical fertilizers. We evaluated the mineralized carbon (MC) content and mineralization rate (MR) after nine applications of chemical fertilizers (C) and fungal residue (F) in paddy fields, at rates of 0, 50, and 100%. A double exponential model was used to calculate the potential rates of MC and SOC turnover. The combined application of fungal residue and chemical fertilizers led to significantly higher MC and MR, by 24.97-100.05 and 24.36-98.07%, respectively, during 57 days of incubation than that of the control. The MC and MR values were highest with the C50F100 treatment. Simulations with the double exponential model showed that both the active SOC pools (C1) and potential SOC mineralization flux C1 + C2 were highest with C50F100, and the MR constants, k1 and k2, were highest with C100F100. The potential SOC MR [(C1 + C2) / SOC] was highest with C50F100. The application of fungal residue and chemical fertilizers to paddy fields effectively alleviated soil acidification caused by chemical fertilizers and increased the nutrient content, MC, MR, C1, and C1 + C2 of soils. However, the over-use of fungal residue or chemical fertilizers produces the reverse effects. Therefore, appropriate quantities of chemical fertilizers and fungal residue need to be applied to enhance the carbon sequestration capacity of soils while improving the MC and MR.