南岭山地土壤有机碳及组分海拔梯度变化特征

  目的  为了解我国亚热带山地土壤有机碳及组分海拔梯度变化规律及影响因素。  方法  以南岭国家级自然保护区不同海拔（400? ~ 1650?m）山地土壤为研究对象，调查了土壤有机碳及组分在不同土层深度的分布及密度特征，分析了土壤理化因子的影响。  结果  （1）总有机碳、易氧化碳、颗粒有机碳、惰性有机碳含量在相对较高海拔土壤中的含量整体更高，并在针阔混交林土壤中出现最大值，而水溶性有机碳含量则在低海拔的沟谷常绿阔叶林土壤中最高。（2）有机碳及组分含量随土层深度的增加呈明显下降趋势，随海拔变化幅度最大的组分为水溶性有机碳，随深度变化幅度最大的为颗粒有机碳，不同组分占总有机碳的比例在不同海拔和深度上的变化规律有所差异。（3）南岭山地土壤有机碳密度范围为8.81 ~ 26.59?kg m?2，整体略高于与其位置相近的山地土壤，有机碳及组分密度随海拔变化趋势与各自在土壤中的含量分布规律较为类似。（4）pH、黏粒含量、全氮与有机碳及组分含量的相关性较好，RDA分析结果表明全氮、全磷与土壤含水率对有机碳及组分变化的解释量占比较高。  结论  南岭山地土壤有机碳及组分具有明显的海拔梯度变化特征，土壤理化性质是影响有机碳及组分分布的重要因素。

Variation Characteristics of Organic Carbon and Fractions in Soils along the Altitude Gradient in Nanling Mountains

  Objective  Mountainous soil carbon (C) pool is an important component of terrestrial C pool, which plays a key role in adjusting C cycle of ecosystem and mitigating global climate change. Altitude gradient is a governing factor in influencing the content and property of mountainous soil C. Exploring the distribution characteristics of organic C and fractions in mountainous soil of different altitude gradients is of great significance for reasonably estimating the soil organic C pool and predicting its sensitivity to climate change. This study aims to investigate the variation characteristics of organic C and fractions in soils along the altitude gradient of subtropical mountainous and the related influencing factors.  Method  Gully evergreen broad-leaved forest (< 800 m), montane evergreen broad-leaved forest (800-1200 m), theropencedrymion (1200-1500 m), alpine meadow and montane elfin (> 1500 m) at different altitude gradients and depths (0-10, 10-20, 20-40, 40-60, and 60-100 cm) in Nanling national natural reserve were selected as the study objects, the distribution and density characteristics of soil organic C and various fractions (Water-dissolved soil organic C, WSOC; readily oxidizable carbon, ROC; particle organic carbon, POC, recalcitrant carbon, RC) were examined, as well as soil physicochemical properties including pH, mechanical composition, soil moisture content and nutrient indicators (total nitrogen, total phosphorus and total potassium).  Result  The results showed that: (1) the soils in Nanling mountains were extremely acidic or strongly acidic, and the pH values were relatively higher in the soil of montane evergreen broad-leaved forest. Sand was the predominant fraction of the mechanism composition and the proportion of clay particles decreased gradually with the increase of altitude. The contents of total nitrogen and total phosphorus in alpine meadow and montane elfin soils were significantly higher than those in the soils at other altitudes, while the content of total potassium increased first and then decreased with the increasing of altitude; (2) the content of SOC, ROC, POC and RC was relatively higher at high altitudes and the maximum values appeared in the soil of gully evergreen broad-leaved forest with low altitude, while the maximum values of WSOC appeared in the soil of gully evergreen broad-leaved forest with relatively low altitude. The content of soil organic C and fractions decreased obviously with the increase of depth. Among the various soil C fractions, WSOC varied the most with altitude, while POC varied the most with depth. The variation regularity of the proportions of different organic C fractions in total organic C were also different to some extent; (3) the soil organic C density of Nanling mountains varied in the range of 8.81-26.59 kg m?2, which was slightly higher than that of the nearby mountains overall. The variation tendency of different organic C fractions with altitude and depth was similar to that of total organic C; (4) pH, clay content, total nitrogen showed good relevance with soil organic C and fractions. The RDA results showed that TN, TP and soil moisture content had high proportions in explaining the variation of oil organic C and fractions.  Conclusion  There existed obvious difference in the organic C and fraction content of soils at different altitudes in Nanling mountains. Soil property is an important aspect influencing the distribution characteristics of organic C, while other environmental factors should also be considered in the future study.