The contribution of microorganisms to soil organic carbon stock under 1 fertilization varies among aggregate size classes 2

The contribution of microorganisms to soil organic carbon stock under 1 fertilization varies among aggregate size classes 2 Jinjing Lu, Shengping Li, Guopeng Liang, Xueping Wu, Qiang Zhang, Chunhua Gao, 3 Jianhua Li, Dongsheng Jin, Fengjun Zheng, Mengni Zhang, Ahmed Ali Abdelrhman, Aurore 4 Degré 5 Agricultural Environment and Resources Institute, Shanxi Agricultural University, Taiyuan 030031, PR 6

7 0.96%, 0.17% and 0.74% in cattle manure, respectively. All of the fertilizers and OM were applied 126 with conventional tillage (plowing once each year at a depth of 20 cm) after harvesting. Seeding was 127 done at the end of April without any tillage and harvesting at the beginning of October, with twice 128 weeding during growth seasons every year.
8 then shook and centrifuged. The supernatants were diluted with deionized water (1:250) and detected 148 by a UV spectrophotometer at 565 nm. Microbial biomass carbon (MBC) content was measured using 149 the fumigation-incubation method 43 . In detail, four aliquots offreeze-dried soil samples (25 g each 150 aliquot) were prepared, two aliquots being fumigated with ethanol-free CHCl3 for 24 h in the dark at 151 room temperature, while the other two was kept untreated ascontrol. Then, these samples were mixed 152 into 100 mL of 0.5 mol L -1 K2SO4 solution, respectively, and shaken for 30 min at 200 r min -1 . The 153 supernatants were diluted with deionized water and then detected by a total organic C (TOC) analyzer.

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Analysis of enzyme activity. In this study, the four soil enzymes activities of β-Glucosidase (BG),

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They were generally calculated as follow: 10 where H′, D and M were Shannon-Wiener, Simpson and Margalef indexes, respectively; pi was the 192 percentage of the peak area of i-th FAME to the total area in each sample; S was the total number of 193 FAME in each sample; and N was the amount of total microbial PLFA.

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Statistically, all data were carried out by SAS 9.4 in Windows 10.

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As showed in Table 1, significant (p < 0.05) interactive effects between fertilization and aggregate 237 size were observed in all indices of microbial diversity. The three indices were affected significantly by 238 fertilization almost in 0.25-1 mm and 2-5 mm (p < 0.05; Table 2), but not in micro-aggregates. Unlike

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CK and NP treatments, these three indices had no significant difference among variably sized

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All of the four soil enzymes activities varied with fertilization and aggregate size (p < 244 0.05; Table 1). In Fig. 6, the four soil enzymes activities were higher under NPM and NPS than under  14 biomass is associated with the soil aggregate size and nature of the OM 54 . Notably, the amount of fungi 279 was higher only in micro-aggregates under NPS and NPM than under CK, which indicates that fungi 280 within macro-aggregate are was more sensitive to environmental perturbation than in micro-aggregates 281 because of the vulnerability of microenvironment in macro-aggregate 55 . Especially, the amount of AM 282 was slightly higher in NPS than in NPM, due to the high decomposition ability of AM in cellulose 56 .

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This can also explain why lower F/B was found in macro-aggregates (> 0.25 mm) than in 284 micro-aggregates (< 0.25 mm) under the application of organic and inorganic fertilizers. Therefore, the 285 results supported that OM incorporation can build a more suitable environment for microbial surviving.

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Our results indicated that there were no significant influences of fertilization on H′, M and D

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indices (Table 1). Among the aggregate sizes, significant differences in microbial diversity were

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It has been documented that microorganisms and enzymes affect C cycling 13,18 . As Table 1 showed, 304 almost all soil microbial community and enzyme indices were associated with aggregate size.

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Meanwhile, it has subsequently been confirmed in the

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In > 0.25 mm aggregates, the PCA analysis divided the indices that have a significant (p < 0.05) 324 impact on SOC into three groups, and Venn models revealed that fungi-related factors were more 325 important than microbial diversity and enzyme activities in affecting the SOC stock in 326 macro-aggregates (Fig. 7). This is largely due to the structural heterogeneity of the macro-aggregate

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Microbial biomass and ratios of the phospholipid acid biomarkers and microbial diversity in different 679 sized aggregates.