色季拉山西坡高海拔区土壤养分含量及化学计量特征

【目的】探究高寒生态系统土壤有机碳(SOC)、全氮(TN)、全磷(TP)、全钾(TK)含量及化学计量比的垂直分布特征。【方法】以西藏东南部色季拉山西坡海拔4 200~4 400 m区域为研究区,选择苔草高寒草甸(CAM)、嵩草沼泽化草甸(KSM)、林芝杜鹃灌丛(RTS)和雪山杜鹃灌丛(RAS)4种典型植被类型土壤为研究对象,分别采集0~10、10~20、20~40、40~60 cm层次土壤样品,测定SOC、TN、TP、TK含量。【结果】1)SOC、TN、TP含量随土层加深而下降,TK则呈升高趋势(KSM除外),空间变异系数(CV)分别为51.99%、55.52%、4.55%、18.58%,SOC、TN表聚特征明显,TP、TK垂直变化相对稳定。不同植被类型SOC、TN、TP、TK变化范围分别为53.41~338.72、2.89~15.02、0.57~1.00、5.59~18.22 g·kg-1,CV分别为95.58%、84.57%、26.03%、42.21%。2)土壤C∶P、N∶P随土层加深而降低(KSM除外),C∶N比呈升高趋势,垂直变异系数分别为37.40%、37.39%、12.81%,表明区域土壤TP相对稳定,SOC随土层加深的变化稍滞后于TN。不同植被类型土壤C∶N、C∶P、N∶P分别在13.85~28.16、73.34~553.13、4.26~29.15之间,CV分别达29.11%、108.85%、111.16%,即由植被类型不同造成的立地条件差异深刻影响着土壤C∶P、N∶P。3)研究区SOC、TN均值分别达139.65、6.74 g·kg-1,显著高于全国0~10 cm土壤平均水平(24.56、1.88 g·kg-1),TP均值为0.73 g·kg-1,略低于我国0~10 cm土壤水平(0.78 g·kg-1)。与全球0~10 cm森林土壤的C∶N(12.40)、C∶P(81.90)、N∶P(6.60)水平比较,4种植被类型的C∶N、C∶P均较高,N∶P较低(KSM除外),C∶N除RAS外均小于25,表明SOC易分解,KSM的C∶P大于200,表明其土壤P的有效性较低,同时KSM的N∶P高达29.15,可能存在P限制。4)相关性分析表明机械组成、容重是影响土壤化学计量比的主要内在因子,其中C∶P、N∶P主要与容重、黏粒、粉粒负相关(P <0.01),与砂粒正相关(P <0.01),C∶N则主要与pH值负相关(P <0.05),与容重、机械组成的相关性未达显著水平。【结论】研究结果可为高寒环境下不同植被类型土壤养分供应状况及循环研究提供理论支撑。

Characteristics of soil stoichiometric and nutrient contents in high altitude area on the west slope of Sejila mountains

【Objective】Probe the vertical distribution characteristics of soil organic carbon(SOC), total nitrogen(TN), total phosphorus(TP), total potassium(TK) and stoichiometry in the alpine ecosystem.【Method】Carex alpine meadow(CAM), Kobresia swamp meadow(KSM) and Rhododendron tanastylum shrub(RTS), Rhododendron aganniphum shrub(RAS) were selected as the research objects, which distributed in altitude of 4 200-4 400 m, in the west slope of Sejila mountains, southeast Tibet.Soil samples were taken at depth intervals of 0-10, 10-20, 20-40, 40-60 cm, the content of SOC, TN, TP, TK were measured.【Result】1) Content of SOC, TN and TP decrease with the soil deepens, TK is the opposite, except KSM, Coefficient of variation(CV)is 51.99%, 55.52%, 4.55%, 18.58%, respectively.SOC and TN have obvious surface aggregation characteristics while the vertical changes of TP and TK are relatively stable.The change ranges of SOC, TN, TP, and TK for different vegetation types are 53.41-338.72 g·kg-1, 2.89-15.02 g·kg-1, 0.57-1.00 g·kg-1, 5.59-18.22 g·kg-1, CV is 95.58%, 84.57%, 26.03%, 42.21%, respectively. 2) The ratios of C ∶ P and N ∶ P decrease with the deepening of soil layer, except KSM, and the ratios of C ∶ N is opposite, CV of C ∶ P, N ∶ P, C ∶ N is 37.40%, 37.39%, 12.81% in turn,it shows that the regional soil TP is relatively stable, and the change of SOC with soil layer lags slightly behind TN.The C ∶ N, C ∶ P, N ∶ P ratios of different vegetation types are between 13.85-28.16, 73.34-553.13, and 4.26-29.15.CV is 29.11%, 108.85%, 111.16% in turn, that is, differences in site conditions caused by different vegetation types profoundly affect the soil C ∶ P, N ∶ P ratios. 3) The average values of SOC and TN in this study area were 139.65 g·kg-1 and 6.74 g·kg-1, respectively, they were both significantly higher than the national average values at 0-10 cm(24.56 g·kg-1, 1.88 g·kg-1). The average values of TP is 0.73 g·kg-1, is slightly lower than national average values at 0-10 cm(0.78 g·kg-1).Compared with the global C∶N(12.40), C∶P(81.90), and N∶P(6.60) levels of forest soils at 0-10 cm, the C∶N ratio and C∶P ratio of the four vegetation types are higher, while N∶P ratio is lower, but except KSM. The C∶N ratio is less than 25 except for RAS, which indicates that the SOC is easily decomposed, and the C∶P ratio of KSM is greater than 200, which indicates that its soil P is less effective, at the same time, the N∶P ratio of KSM is as high as 29.15, and there may be P restrictions. 4) Correlation analysis shows that mechanical composition and bulk density are the main intrinsic factors affecting soil stoichiometry, among them, the C∶P and N∶P ratios are mainly negatively related to bulk density, clay particles and powder particles(P < 0.01), and positively correlated to sand particles(P < 0.01). C∶N ratio was mainly negatively correlated with pH(P < 0.05), and the correlation with bulk density and mechanical composition did not reached a significant level.【Conclusion】The research results can provide theoretical support for soil nutrient supply and cycle research in different vegetation types in alpine environment.