Coupling of Physical Protection and Molecular Composition Drives Carbon Sequestration Divergence in Soils Planted With Different Tea Varieties

ABSTRACT

Tea plantations represent significant carbon (C) sinks in agricultural landscapes, yet how variety‐specific organic inputs are associated with the molecular composition and stability of soil organic carbon (SOC) within aggregate hierarchies remains unclear. Here, we examined soils from 15‐year‐old plantations of four tea varieties, including Chuancha No. 3 (CC3), Chuanmu No. 217 (CM217), Chuannong Huangyazao (CN), and Camellia sinensis “ Fuding Dabaicha ” (FD), in subtropical China. Soil samples were collected from topsoil (0–20 cm) and subsoil (20–40 cm) layers and fractionated into macro‐ (> 2 mm), large meso‐ (2–1 mm), meso‐ (1–0.25 mm), and microaggregates (< 0.25 mm). Solid‐state ¹³ C cross‐polarization magic‐angle spinning nuclear magnetic resonance spectroscopy was used to characterize aggregate‐associated SOC molecular composition. Aggregate‐associated SOC composition and carbon sequestration capacity differed significantly among tea varieties and soil layers. Across both topsoil (0–20 cm) and subsoil (20–40 cm), FD soils exhibited the highest SOC stocks, followed by CN, CM217, and CC3, indicating enhanced carbon sequestration potential under FD cultivation. The greater SOC accumulation in FD soils was accompanied by distinct molecular signatures, characterized by higher proportions of alkyl C and aromatic C and lower proportions of O‐alkyl C within aggregate fractions. FD soils also exhibited greater hydrophobicity, aromaticity, and humification indices, particularly in macroaggregates and microaggregates. Stability indices were positively correlated with alkyl C, aromatic C, and humification indices, suggesting that the enrichment of chemically resistant carbon components coupled with aggregate‐scale physical protection contributed to enhanced SOC stabilization. Our findings indicate that tea variety selection and management practices favoring stable aggregate formation may help enhance long‐term soil C sequestration.