Data from: Spatial variability in soil organic carbon in a tropical montane landscape: associations between soil organic carbon and land use, soil properties, vegetation, and topography vary across plot to landscape scales

Presently, the lack of data on soil organic carbon (SOC) stocks in relation to land-use types and biophysical characteristics prevents reliable estimates of ecosystem carbon stocks in montane landscapes of mainland SE Asia. Our study, conducted in a 10 000 ha landscape in Xishuangbanna, SW China, aimed at assessing the spatial variability in SOC concentrations and stocks, as well as the relationships of SOC with land-use types, soil properties, vegetation characteristics and topographical attributes at three spatial scales: (1) land-use types within a landscape (10 000 ha), (2) sampling plots (1 ha) nested within land-use types (plot distances ranging between 0.5 and 12 km), and (3) subplots (10 m radius) nested within sampling plots. We sampled 27 one-hectare plots – 10 plots in mature forests, 11 plots in regenerating or highly disturbed forests, and 6 plots in open land including tea plantations and grasslands. We used a sampling design with a hierarchical structure. The landscape was first classified according to land-use types. Within each land-use type, sampling plots were randomly selected, and within each plot we sampled within nine subplots. SOC concentrations and stocks did not differ significantly across the four land-use types. However, within the open-land category, SOC concentrations and stocks in grasslands were higher than in tea plantations (P < 0.01 for 0–0.15 m, P = 0.05 for 0.15–0.30 m, P = 0.06 for 0–0.9 m depth). The SOC stocks to a depth of 0.9 m were 177.6 ± 19.6 (SE) Mg C ha−1 in tea plantations, 199.5 ± 14.8 Mg C ha−1 in regenerating or highly disturbed forests, 228.6 ± 19.7 Mg C ha−1 in mature forests, and 236.2 ± 13.7 Mg C ha−1 in grasslands. In this montane landscape, variability within plots accounted for more than 50 % of the overall variance in SOC stocks to a depth of 0.9 m and the topsoil SOC concentrations. The relationships of SOC concentrations and stocks with land-use types, soil properties, vegetation characteristics, and topographical attributes varied across spatial scales. Variability in SOC within plots was determined by litter layer carbon stocks (P < 0.01 for 0–0.15 m and P = 0.03 for 0.15–0.30 and 0–0.9 m depth) and slope (P ≤ 0.01 for 0–0.15, 0.15–0.30, and 0–0.9 m depth) in open land, and by litter layer carbon stocks (P < 0.001 for 0–0.15, 0.15–0.30 and 0–0.9 m depth) and tree basal area (P < 0.001 for 0–0.15 m and P = 0.01 for 0–0.9 m depth) in forests. Variability in SOC among plots in open land was related to the differences in SOC concentrations and stocks between grasslands and tea plantations. In forests, the variability in SOC among plots was associated with elevation (P < 0.01 for 0–0.15 m and P = 0.09 for 0–0.9 m depth). The scale-dependent relationships between SOC and its controlling factors demonstrate that studies that aim to investigate the land-use effects on SOC need an appropriate sampling design reflecting the controlling factors of SOC so that land-use effects will not be masked by the variability between and within sampling plots.

目前，针对土壤有机碳（soil organic carbon, SOC）储量与土地利用类型及生物物理特征相关关系的数据缺失，阻碍了东南亚大陆山地景观生态系统碳储量的可靠估算。本研究在中国西南西双版纳一片10000公顷的景观区域内开展，旨在评估SOC浓度与储量的空间变异特征，以及在三个空间尺度下SOC与土地利用类型、土壤属性、植被特征和地形因子的相关关系：（1）景观尺度内的土地利用类型（10000公顷），（2）嵌套于土地利用类型中的1公顷样地（样地间距介于0.5至12千米），（3）嵌套于样地内的半径10米副样地。本研究共布设27个1公顷样地，其中成熟林10个、次生或重度干扰林11个、包括茶园与草地在内的裸地6个。采样采用分层结构设计：首先依据土地利用类型对研究区进行分类，随后在每类土地利用类型中随机布设样地，每个样地内再设置9个副样地开展采样。研究结果显示，四类土地利用类型间的SOC浓度与储量无显著差异。但在裸地类别中，草地的SOC浓度与储量显著高于茶园（0–0.15米土层：P<0.01；0.15–0.30米土层：P=0.05；0–0.9米土层：P=0.06）。0.9米深度内的SOC储量分别为：茶园177.6±19.6（标准误，SE）Mg C·ha⁻¹，次生/重度干扰林199.5±14.8 Mg C·ha⁻¹，成熟林228.6±19.7 Mg C·ha⁻¹，草地236.2±13.7 Mg C·ha⁻¹。在该山地景观中，样地内的变异占0.9米深度SOC储量及表层SOC浓度总变异的50%以上。SOC浓度与储量同土地利用类型、土壤属性、植被特征及地形因子的相关关系随空间尺度发生变化。裸地样地内的SOC变异主要受枯落层碳储量（0–0.15米土层：P<0.01；0.15–0.30米、0–0.9米土层：P=0.03）与坡度（0–0.15米、0.15–0.30米、0–0.9米土层：P≤0.01）调控；而林地表样地内的SOC变异则主要受枯落层碳储量（0–0.15米、0.15–0.30米、0–0.9米土层：P<0.001）与树木胸高断面积（0–0.15米土层：P<0.001；0–0.9米土层：P=0.01）调控。裸地样地间的SOC变异与草地和茶园间的SOC浓度及储量差异相关。林地表样地间的SOC变异则与海拔相关（0–0.15米土层：P<0.01；0–0.9米土层：P=0.09）。SOC与其调控因子间的尺度依赖关系表明，若要探究土地利用对SOC的影响，需采用能够反映SOC调控机制的合理采样设计，以避免采样样地间及样地内的变异掩盖土地利用的真实效应。