Browsing by Author "Luo, Yu"

Abstract Plant‐ and microbially derived carbon (C) are the two major sources of soil organic matter (SOM), and their ratio impacts SOM composition, accumulation, stability, and turnover. The contributions of and the key factors defining the plant and microbial C in SOM along the soil profile are not well known. By leveraging nuclear magnetic resonance spectroscopy and biomarker analysis, we analyzed the plant and microbial C in three soil types using regional‐scale sampling and combined these results with a meta‐analysis. Topsoil (0–40 cm) was rich in carbohydrates and lignin (38%–50%), whereas subsoil (40–100 cm) contained more proteins and lipids (26%–60%). The proportion of plant C increases, while microbial C decreases with SOM content. The decrease rate of the ratio of the microbially derived C to plant‐derived C (C M:P ) with SOM content was 23%–30% faster in the topsoil than in the subsoil in the regional study and meta‐analysis. The topsoil had high potential to stabilize plant‐derived C through intensive microbial transformations and microbial necromass formation. Plant C input and mean annual soil temperature were the main factors defining C M:P in topsoil, whereas the fungi‐to‐bacteria ratio and clay content were the main factors influencing subsoil C M:P . Combining a regional study and meta‐analysis, we highlighted the contribution of plant litter to microbial necromass to organic matter up to 1‐m soil depth and elucidated the main factors regulating their long‐term preservation.

Abstract Manure‐based biochar is an effective amendment to increase both carbon sequestration and the fertility of degraded soils, whereas the responses of N 2 O emissions and microbial‐N cycling genes to its application and the underlying mechanisms are poorly understood. Here, four biochars were produced under two pyrolysis temperatures (300 and 700°C) and with two organic C extraction procedures (water and acetone extraction). The resulting biochars were either with relative enrichment or depletion in easily mineralizable carbon (EMC) compared with recalcitrant C. We added biochars, with urea and sodium nitrate, to a degraded red soil and incubated the amended soils at moisture levels of 60% and 130% field capacity. All the biochars decreased nitrification gene abundance, that is, amoA. Biochars with EMC had greater stimulatory effects on the abundance of denitrification genes (nirK, nirS, and nosZ) and N 2 O emission, regardless of moisture level and N form, compared with biochar without EMC. Biochar‐induced microbial activity, biochar aliphatics, and alkyl groups correlated positively with N 2 O emission and denitrification gene abundance. The water dissolved organic C of biochar facilitated the conversion of N 2 O to N 2 , whereas the acetone extractable C fraction postponed the completion of denitrification. In conclusion, the N 2 O emission and denitrification gene abundance increased with decreasing biochar aromaticity and increasing EMC content. Our study emphasizes that the EMC supply in manure‐based biochars also importantly mediates soil N 2 O emission and microbial N cycling genes, adding to current understanding of influencing factors such as biochar pH, porosity, N availability, and redox property.