Abstract
In-depth understanding about the vertical distribution of soil organic carbon (SOC) density is crucial for carbon (C) accounting, C budgeting and designing appropriate C sequestration strategies. We examined the vertical distribution of SOC density under different land use/land cover (LULC) types, altitudinal zones and aspect directions in a montane ecosystem of Bhutan. Sampling sites were located using conditioned Latin hypercube sampling (cLHS) scheme. Soils were sampled based on genetic horizons. An equal-area spline function was fitted to interpolate the target values to predetermined depths. Linear mixed model was fitted followed by mean separation tests. The results show some significant effects of LULC, altitudinal zone and slope aspect on the vertical distribution of SOC density in the profiles. Based on the proportion of mean SOC density in the first 20 cm relative to the cumulative mean SOC density in the top meter, the SOC density under agricultural lands (34%) was more homogeneously distributed down the profiles than forests (39%), grasslands (59%) and shrublands (43%). Similarly, the SOC density under 3500–4000 m zone (35%) was more uniformly distributed compared to 3000–3500 m zone (43%) and 1769–2500 m and 2500–3000 m zones (41% each). Under different aspect directions, the north and east-facing slopes (38% each) had more uniform distribution of SOC density than south (40%) and west-facing slopes (49%).
Highlights
Soil, as the largest terrestrial carbon (C) sink, stores almost three times the amount of C in the vegetation and approximately double that in the atmosphere [1]
This study has shown some significant effects of LULC type, altitude zone and aspect direction on soil organic carbon (SOC) density and its vertical distribution in the soil profiles
Forests, 3500–4000 m zone and north-facing slopes stored the largest SOC density compared to other LULC types, altitudinal zones and aspect directions
Summary
As the largest terrestrial carbon (C) sink, stores almost three times the amount of C in the vegetation and approximately double that in the atmosphere [1]. The amount of stored soil organic carbon (SOC) is the net balance between C inputs from plant production and losses through decomposition and leaching [6]. Jobbàgy and Jackson [5] reported a strong relationship between vertical distribution of SOC and climate, vegetation and soil texture with an estimated 1502, 491 and 351 Pg·C for the first, second and third meter, respectively. Temperature, moisture (precipitation) and solar radiation are the most important factors influencing plant growth, litter production and SOC mineralization [11]. The sensitivity of SOC decomposition to temperature becomes decreasingly acute at higher than at lower temperatures [12]. This is critical for maintaining high SOC stocks in high-altitude areas, such as the Himalayas, in response to global warming
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