Perennial ramie cropping sustainably increases C sequestration of subtropical upland soils

Abstract

Perennial cropping has been advocated to increase soil C sequestration, but its sustainability and mechanism remain poorly understood. A chronosequence (0, 5, 10, 15, 20-yr) of perennial ramie cropping was identified and used to study the mechanism of sustainable C sequestration of subtropical upland soils. Soil C sequestration rate averaged at 0.93 Mg ha−1 yr−1 within the 20-year chronosequence, with a maximum of 1.65 Mg ha−1 yr−1 during the 5–10th year. This was mainly attributed to the accumulation of organic C in top 50-cm soil, particularly 20–40 cm soil layer. Along the chronosequence, ramie cropping logarithmically increased annual organic input of residues and fine roots by 166%–534%, and surface soil total N, C/N ratios, and water-stability index by 5%–39%, and microbial catabolic diversity by 7%–19% (P < 0.05). Soil induced respiration rates of aromatic, amino acids, and saccharides were increased by 10%–98%, whereas those of carboxylic acids were reduced by 37%–91% (P < 0.05). Structural equation modeling indicated that the increasing organic input, particularly fine roots, drove the sustainable C sequestration in soil with perennial ramie cropping, through improving soil N nutrition and microbial catabolic functions. Therefore, perennial ramie cropping could be advocated as an alternative practice to accelerate the improvement and C sequestration of the subtropical upland soils.