The stability of soil organic carbon across topographies in a tropical rainforest

Abstract

Mechanisms of soil organic carbon (SOC) stability are still unclear in forest ecosystems. In order to unveil the influences of topography on the SOC stability, a 60ha dynamic plot of a tropical montane rainforest was selected in Jianfengling, in Hainan Island, China and soil was sampled from 60 quadrats. The chemical fractions of the SOC were detected with 13C CPMAS/NMR and path analyses explore the mechanisms of SOC stability in different topographies. The chemical fractions of the SOC comprised alkyl carbon > O-alkyl carbon > carboxyl carbon > aromatic carbon. The decomposition index (DI) values were greater than 1 in the different topographies, with an average DI value was 1.29, which indicated that the SOC in the study area was stable. Flat and top areas (together named RF) had more favorable nutrients and silt contents compared with steep and slight steep areas (together named RS). The influencing factors of SOC stability varied across the topographies, where SOC, soil moisture (SM) and ammoniacal nitrogen (NH4+-N, AN) were the main influencing factors in the RF, while SM and AN were the main factors in the RS. Greater SOC and AN strengthened the SOC stability, while higher soil moisture lowered SOC stability. The inertia index was higher in the RS than the RF areas, indicating that local topography significantly affects SOC content and SOC stability by changing soil environmental factors. Topography cannot be neglected in considering SOC stability and future C budgets.

Variations and influencing factors of soil organic carbon during the tropical forest succession from plantation to secondary and old–growth forest

“…For deep soils (20-40 cm and 40-60 cm), the input of SOC is mainly from the leaching of surface SOC and a few roots. Since the soil clay proportions were higher in the study area (Jiang et al, 2021), there was less leaching of surface SOC to the deep soil. In addition, this study found a significant negative correlation between bulk density (BD) and SOC (Figure 2), which indicates that the high soil BD is also not conducive for the leaching of surface SOC to deep soil layers.…”

Preventive remediation methods minimize soil pollution

“…The stable liquid is expressed as a BOD/COD ratio close to 0.1 where each parameter has a concentration of less than 100 mg/L. The definition of stable quality [25], [26] is the insignificant change in BOD concentration due to the small BOD concentration. Between the two classes is a class of substances that can be decomposed by microbes or called biodegradable.…”