秦岭南坡林地土壤有机碳密度空间分异特征

【目的】研究陕西秦岭南坡林地土壤有机碳密度空间分异特征,为秦岭林区土壤有机碳科学管理提供理论依据。【方法】在陕西秦岭南坡不同林区(洋县长青、佛坪县龙草坪、太白县太白山、宁陕县宁东和宁陕县宁西)及立地条件(海拔、坡向、坡位和坡度)设置样地,通过调查、取样和测定,采用差异性检验分析不同立地因子对土壤有机碳密度(tC·hm^-2)的影响,并通过逐步回归分析量化各因子对土壤有机碳密度影响的相对重要性。【结果】秦岭南坡林地土壤有机碳密度均值为125.41tC·hm^-2(52.60~307.36tC·hm^-2),在0~10,10~30和30~60cm土层分别为59.04,41.65和24.73tC·hm^-2,分别占土壤有机碳总密度的47.07%,33.21%和19.72%;秦岭南坡不同林区土壤有机碳密度差异较大,表现为龙草坪(143.55tC·hm^-2)>宁东(138.37tC·hm^-2)>宁西(134.09tC·hm-2)>太白山(109.29tC·hm^-2)>长青(90.22tC·hm^-2);土壤有机碳密度随海拔升高先增后降,在海拔800~1200m最低(平均90.24tC·hm^-2),在海拔2000~2400m最大(平均166.43tC·hm^-2),当海拔高于2400m后下降(平均132.51tC·hm^-2);阴坡土壤有机碳密度(127.23tC·hm^-2)稍高于阳坡(123.25tC·hm^-2);土壤有机碳密度随坡度增大而降低,由147.52tC·hm^-2减至87.06tC·hm^-2;土壤有机碳密度在下坡位(166.36tC·hm^-2)大于中坡位(129.43tC·hm^-2)和上坡位(77.14tC·hm^-2)。【结论】秦岭南坡林地土壤有机碳密度存在显著的区域差异,并随海拔升高先升后降,在各海拔间和不同坡位间均差异显著(P<0.05)或极显著(P<0.01),但在阴坡与阳坡间无显著差异。逐步回归分析表明,坡位和海拔是影响土壤有机碳密度差异的主导立地因子。与我国其他主要林区相比,陕西秦岭南坡林地土壤有机碳密度处于较高水平,在我国森林土壤碳库中具有重要地位,应加强管理。

Spatial Variation of the Density of Soil Organic Carbon in Forest Land on the Southern Slope of Qinling Mountains

【Objective】 The patterns of spatial variation of the density of soil organic carbon (SOC) in forest land was studied on the southern slope of Qinling Mountains in Shaanxi Province,which provided a theoretical basis for the scientific management of SOC in Qinling Mountains.【Method】Sample plots were set up in different forest regions (Changqing of Yang County,Longcaoping of Foping County,Taibai Mountain of Taibai County,Ningdong of Ningshan County and Ningxi of Ningshan County) and different site conditions (elevation,slope aspect,slope position and slope) on the southern slope of the Qinling Mountains.Investigation,sampling and determination were carried out. Difference tests were used to analyze the effects of different site factors on SOC density (tC ·hm^-2 ).Stepwise regression analysis was employed to quantify the relative importance of each factor on the variation of SOC density.【Result】The average SOC density was 125.41 tC ·hm^-2 (52.60-307.36 tC ·hm^-2 )on the southern slope of Qinling Mountains,which were 59.04,41.65,and 24.73 tC ·hm^-2 in 0-10,10-30,and 30-60 cm soil layers respectively,accounting for 47.07%,33.21% and 19.72% of the total SOC density,respectively.The SOC density varied greatly among different regions on the southern slope of Qinling Mountains,showing Longcaoping of Foping County (143.55 tC ·hm ^-2 ),Ningdong of Ningshan County (138.37 tC ·hm^-2 ),Ningxi of Ningshan County (134.09 tC ·hm^-2 ),Taibai Mountain of Taibai County (109.25 tC ·hm^-2 ),and Changqing of Yang County (90.22 tC ·hm^-2 ).The SOC density firstly increased and then decreased with increasing altitude.The SOC density (90.24 tC ·hm -2 ) was the lowest at 800-1 200 m above sea level,and the SOC density (166.43 tC ·hm^-2 ) was the highest at the 2 000-2 400 m above sea level.When the altitude was higher than 2 400 m,the SOC density decreased,with an average of 132.51 tC ·hm^-2.The SOC density (127.23 tC ·hm^-2 ) of shady slope was slightly higher than that (123.25 tC ·hm^-2 ) of sunny slope.The SOC density decreased from 147.52 to 87.06 tC ·hm^-2 with the increase of slope.The SOC density in the down slope (166.36 tC ·hm -2 ) was higher than those in the middle (129.43 tC ·hm ^-2 ) and up-slope (77.14 tC ·hm^-2 ).【Conclusion】 The variations of SOC density among different forest regions were significant.The trend was increased first and then decreased with the increase of elevation.Significant differences ( P <0.05) or extremely significant differences ( P <0.01)of SOC density appeared in elevation ranges and different slope position.However,the difference of SOC density was not significant between shady slope and sunny slope.Stepwise regression analysis showed that the slope position and elevation were the dominant topographic factors that affect the SOC density.Compared with other forest areas in China,the SOC density in forest land on the southern slope of Qinling Mountains was at a higher level in the country.The SOC on the southern slope of Qinling Mountains plays an important role in the soil carbon pool of forest ecosystem in China and the management should be strengthened.