滇东南典型常绿阔叶林土壤酶活性的海拔梯度特征

Variations of Soil Enzyme Activity in Typical Evergreen Broadleaved Forests Along Altitude Gradient in Southeast Yunnan

[目的]探究滇东南文山国家级自然保护区土壤酶活性沿海拔的变化规律,为理解“海拔-水热-植被-土壤”间相互耦合对土壤酶活性影响的过程与机制提供数据支撑。[方法]以不同海拔典型植被类型(亚热带季风常绿阔叶林、半湿润常绿阔叶林及湿性常绿阔叶林)为研究对象,研究不同森林类型土壤酶活性沿海拔及土层变化特征,采用前向选择法、蒙特卡洛检验与冗余分析,分析水热、植被及土壤理化性质沿海拔梯度变化对土壤酶活性的影响。[结果](1)土壤酶活性随海拔升高呈显著不同的变化规律(P<0.05),土壤过氧化氢酶、脲酶和蔗糖酶的活性呈增加趋势,而土壤酸性磷酸酶活性呈先下降后上升的趋势。随着土层深度增加,土壤酶活性均逐渐降低;(2)水热条件、植物多样性及土壤理化性质沿海拔梯度呈显著不同的变化规律。年均降水量随海拔升高呈增加趋势,植物多样性、年均气温和土壤温度呈下降趋势。随着海拔升高,土壤含水量、总有机碳、全氮、全钾、速效氮和速效钾含量呈上升趋势,土壤全磷和速效磷呈先下降后上升趋势,土壤容重和pH呈降低趋势;随着土层深度增加,土壤含水量、总有机碳、全氮、全磷、全钾、速效氮、速效磷和速效钾含量呈降低趋势,而土壤容重和pH呈上升趋势;(3)冗余分析表明,水热条件、植物及土壤理化性质与土壤酶活性有不同程度的相关性,其对土壤酶活性变化的重要性大小排序为:总有机碳>全氮>容重>速效钾>pH>含水量>速效氮>全钾>有效磷>全磷>Pielou指数>年均降水量>年均气温>土壤温度>Simpson指数>Margalef index指数>Shannon-Wiener指数。[结论]海拔梯度变化引起文山国家级自然保护区内水热条件、植物多样性及土壤理化性质的显著改变,进而调控森林土壤酶活性沿海拔及土层垂直分布的变化,其中,土壤含水量、pH、容重、总有机碳及氮、磷、钾均能较好地解释土壤酶活性的海拔梯度差异。

[Objective]To study the change of soil enzyme activities along altitude gradient in the Wenshan National Nature Reserve of Southeast Yunnan,and provide data for understanding the influencing process and mechanism of inter-connections among hydrothermal conditions,vegetations and soil physicochemical properties on soil enzyme activities.[Method]Three typical vegetation types(i.e.,subtropical monsoon evergreen broadleaved forest,sub-humid evergreen broadleaved forest,humid evergreen broadleaved forest)along altitude gradient were chosen to study the changes of soil enzyme activities of these forests along altitude gradient and soil layers.The methods of forward selection,Monte Carlo permutation test,and redundancy analysis were used to analyze the effects of hydrothermal,vegetations and soil properties on soil enzyme activities along altitude gradient.[Result](1)The soil enzyme activities varied with altitude gradient(P<0.05).The activities of soil catalase,urease,sucrase increased,while the activities of soil acid phosphatase increased at first and then decreased.The soil enzyme activities decreased along with soil profiles.(2)The hydrothermal conditions,plant diversity,and soil properties followed different change patterns along altitude gradient.With the increase of altitudes,the annual precipitation increased,but plant diversity,annual temperature,and soil temperature decreased;the values of soil moisture content,soil organic carbon,total nitrogen,total potassium,available nitrogen and potassium increased,the total phosphorus and available phosphorus decreased at first and then increased;the soil bulk density and pH decreased significantly.Along with the soil profiles,the soil moisture content,soil organic carbon,total nitrogen,total phosphorus and potassium,and available nitrogen,phosphorus,potassium decreased,while the soil bulk density and pH increased.(3)The changes of hydrothermal conditions,vegetations and soil properties along altitude gradient had different degree of correlations with soil enzyme activities.Their importance was ranked as soil organic carbon>total nitrogen>bulk density>available potassium>pH>moisture content>available nitrogen>total potassium>available phosphorus>total phosphorus>Pielou index>annual precipitation>annual temperature>soil temperature>Simpson index>Margalef index>Shannon-wiener index.[Conclusion]Altitude will significantly alter the distribution of hydrothermal conditions,plant diversity,and physicochemical properties in Wenshan National Nature Reserve.This thus regulates the alteration of soil enzyme activities along altitude gradient and the soil layers.Soil moisture content,pH,bulk density,organic carbon,nitrogen,phosphorus,and potassium can explain the changes of soil enzyme activities along the altitude gradient.