Physically protected carbon stocks under cocoa-based agroforestry systems in the Colombian Amazon
摘要
Rapid forest loss and pasture degradation in the Colombian Amazon reduce carbon sequestration and threaten ecosystem services, yet effects of cocoa‑based agroforestry systems (cAFS) on physical protection of soil carbon below 1 m remain poorly known. We quantified aggregate‑size distribution and associated organic carbon (OC) to 150 cm and compared four monospecific shade‑tree cAFS (Cariniana pyriformis—Abarco; Calycophyllum spruceanum—Capirón; Anacardium excelsum—Caracolí; Genipa americana—Huito) with forest and degraded pasture. Using a randomized block design (n = 9), trenches were sampled at 0–30, 30–60, 60–90, 90–120 and 120–150 cm; samples were fractionated (> 2000, 250–2000, 53–250, < 53 µm), OC measured by Walkley–Black and analyzed with linear mixed models. Macrofractions dominated at 0–30 cm (e.g., Abarco: 47.25% in 250–2000 µm, 37.51% > 2000 µm). Surface OC peaked in Abarco (16.81 g C kg−1) and Huito (15.72 g C kg−1) and declined with depth (Abarco 9.65 g C kg−1 at 120–150 cm). Macroaggregates (> 250 µm) contained ~ 60–70% of occluded C. Total SOC stocks to 150 cm were: forest 216.5, Abarco 212.5, Capirón 210.9, full‑sun cacao 198.3, pasture 193.4 Mg C ha−1. Results show cAFS—notably Abarco and Huito—increase SOC stocks and physical protection to 1.5 m versus degraded pasture; shade‑tree choice markedly influences soil C accumulation and stability, with implications for restoration and climate‑mitigation strategies in the Colombian Amazon.