Soil aggregation regulates distributions of carbon, microbial community and enzyme activities after 23-year manure amendment

Manure amendment affects soil organic carbon (SOC) sequestration, microbial biomass and activity, and aggregate formation. However, how soil aggregation regulates SOC sequestration and microbial activity after manuring has received less attention. We studied the distribution of SOC, microbial community composition and activity in four aggregate classes (>2, 1–2, 0.25–1, and <0.25mm) using field moisture sieving of soil from a 23-year manure addition field experiment under a rice–barley rotation. Long-term manuring increased the portion of large macroaggregates (>2mm) by 2.4% (p <0.05), and reduced the portion of microaggregates (<0.25mm, including sand and silt) by 5.9% (p <0.05) compared with soil without manure (control). Manuring increased SOC and total nitrogen contents of the large macroaggregates by 9.1% and 7.1%, respectively, but not of the microaggregates. Also, manuring increased the phospholipid fatty acids (PLFAs) contents of bacteria, fungi, arbuscular mycorrhizal fungi, and total microbes of the macroaggregates (>2, 1–2, and 0.25–1mm) but not of the microaggregates. The fungal/bacterial PLFA ratio remained unchanged in all aggregates. Manuring increased β-glucosidase and chitinase activities in two macroaggregate classes (>2, and 1–2mm), but not in the microaggregates. In conclusion, SOC, microbial biomasses and enzyme activities in the macroaggregates are more sensitive to manuring than in the microaggregates. Soil aggregation regulates the distributions of SOC and microbial parameters after 23-year manure amendment.