喀斯特不同土地利用方式和恢复模式对土壤酶活性C:N:P比值的影响

Effects of different land use and ecological restoration types on soil enzymatic C:N:P ratios in a karst ecosystem

关键词:  喀斯特生态系统, 土地利用, 土地恢复, 土壤酶活性, 酶活性生态化学计量

Key words:  karst ecosystem, land use, land restoration, soil enzyme activity, enzymatic stoichiometry

摘要:

为探究喀斯特地区不同土地利用方式和生态恢复模式对土壤酶活性及其碳(C):氮(N):磷(P)比值的影响,该文在广西环江县的中国科学院环江喀斯特生态系统观测研究站长期定位观测试验地选取了3种土地利用方式 [退化干扰地、牧草地和果树(枇杷)林地]和4种恢复模式(常绿乔木林、落叶乔木林、常绿落叶混交林和自然恢复林)作为研究对象,分析了4种土壤酶 [β-1,4-葡萄糖苷酶(βG)、β-1,4-N-乙酰葡萄糖苷酶(NAG)、亮氨酸氨基肽酶(LAP)和碱性磷酸酶(ALP)]的活性和C:N:P比值变化与土壤生态因子之间的关系。结果表明:(1)恢复模式土壤的4种酶活性均高于土地利用方式。在不同土地利用方式中,牧草地4种酶的活性、C:P和N:P比值高于其他两种土地利用方式; 在不同恢复模式中,落叶乔木林的βG和ALP酶活性显著高于自然恢复林和常绿乔木林,常绿乔木林的NAG酶活性显著高于其他3种恢复模式,而落叶乔木林的酶活性C:P比值和常绿落叶混交林的酶活性N:P比值均显著低于其他3种恢复模式。另外,酶活性计量比值矢量角度分析显示,所有土地利用和恢复模式受磷限制。(2)4种酶活性均与土壤有机碳(SOC)、铵态氮(NH⁺₄-N)和硝态氮(NO₃^--N)含量呈显著正相关,与全磷(TP)含量呈显著负相关; βG酶活性与速效磷(AP)含量呈显著正相关,ALP酶活性与全氮(TN)含量呈显著正相关。(3)冗余分析(RDA)显示,土壤TP、NH⁺₄-N、NO₃^--N和AP含量分别解释了土壤酶活性和C:N:P比值变化的38.3%、9.5%、9.3%和8.0%。综上认为,喀斯特不同土地利用和恢复模式中土壤磷限制普遍存在,意味着土地利用开发和恢复过程中磷的赋存和转化是土壤质量改善的重点。另外,牧草地、常绿落叶混交林和落叶乔木林相对于其他土地利用和恢复模式具有较高的土壤酶活性和C:P比值以及AP含量,表明牧草和落叶植物可能对喀斯特土地利用和生态恢复过程中土壤质量改善有积极作用。

Abstract:

To explore the effects of land use and ecological restoration types on soil enzyme activities and C:N:P ratios in the karst ecosystem, we selected three land use types [disturbed land, pasture grassland, and orchard forest(loquat)] and four restoration types(evergreen forest, deciduous forest, evergreen-deciduous mixed forest, and natural restoration forest), which are long-term positioning observation experimental plots of the Huanjiang Observation and Research Station for Karst Ecosystems, measured the activities of four soil enzymes [β-1,4-glucosidase(βG), β-1,4-N-acetylglucosaminidase(NAG), leucine aminopeptidase(LAP), and alkaline phosphatase(ALP)], and analyzed the relationships between activities levels and the C:N:P ratios and soil-associated physical and chemical factors. The results were as follows:(1)Enzyme activities were higher in the restoration types than in the three land use types. In addition, the activities of the four enzymes, enzymatic N:P, and enzymatic C:P of pasture grassland were higher than those in the other restoration types. The βG and ALP activities in the deciduous forest were significantly higher than those in the natural restoration and evergreen forest, and NAG activity in the evergreen forest was significantly higher than that in the other three restoration types. The enzymatic N:P ratios of the evergreen-deciduous mixed forests were significantly lower than those in the other restoration types, as was the enzymatic C:P ratio of the deciduous forest. In addition, vector analysis of the enzyme activity measurement ratio showed that all land use and restoration types were limited by P.(2)The activities of the four enzymes were positively correlated with soil organic C(SOC), ammonia N(NH⁺₄-N), and nitrate N(NO₃^--N), whereas negatively correlated with total P(TP). βG activity was positively correlated with available P(AP)and ALP activity was positively correlated with total N(TN).(3)Redundancy analysis(RDA)showed that the levels of TP, NH⁺₄-N, NO₃^--N, and AP explained 38.3%, 9.5%, 9.3%, and 8.0%, respectively, of the changes in soil enzyme activities and C:N:P ratios. Based on these results, the different land use and restoration types in karst areas are shown to generally exist under the limitation of soil P, which implies that the fixation and transformation of P should be the focus of soil quality improvement in the land use development and restoration process. Furthermore, soil enzyme activities, C:P ratios, and AP contents in pasture grassland, evergreen-deciduous mixed forest, and deciduous forest were higher than those in the other land use and restoration types. The result indicates that forage and deciduous plants are important for soil nutrient cycling and should be considered in the process of karst land use and restoration.