杉木人工林和天然次生林林龄对土壤酶活性的影响

Effects of stand ages on soil enzyme activities in Chinese fir plantations and natural secondary forests

森林类型和林龄是影响土壤酶活性的重要生物因子,但人工林和天然次生林两种森林恢复模式对土壤酶活性随林龄的变化规律及其影响机制还不明确。本研究以亚热带杉木人工林和天然次生林(5、8、21、27和40年生)为对象,探究与土壤碳、氮和磷循环相关的4种土壤酶[纤维素水解酶(CBH)、β⁃葡萄糖苷酶(βG)、酸性磷酸酶(AP)和乙酰氨基⁃葡萄糖苷酶(NAG)]活性对林龄的响应特征。结果表明:土壤酶活性在不同林型中呈现不同的变化趋势。杉木人工林土壤AP、βG和CBH活性显著高于天然次生林,而土壤NAG活性无显著差异。对于杉木人工林,随着林龄的增加,土壤AP活性呈降低趋势,5年生林分AP活性显著高于其他林龄阶段62.3%以上;土壤NAG和CBH活性呈先降低后增加趋势,土壤βG活性呈波动变化。对于天然次生林,随着林龄的增加,土壤NAG活性呈波动变化,8年生和27年生林分显著高于其他林龄阶段14.9%以上;土壤βG和CBH活性呈先增加后降低趋势,而土壤AP活性无显著差异。逐步回归分析表明,影响杉木人工林和天然次生林土壤酶活性的最优模型中,土壤预测因子解释了其变异的34%以上。综上,杉木人工林随着林龄的增加其土壤肥力有退化的风险,天然次生林则更有利于维持森林生态系统土壤肥力。

Forest type and stand age are important biological factors affecting soil enzyme activities.However,the changes in soil enzyme activities across stand ages and underlying mechanisms under the two forest restoration strate⁃gies of plantations and natural secondary forests remain elusive.In this study,we investigated the variations of four soil enzyme activities including cello⁃biohydrolase(CBH),β⁃1,4⁃glucosidase(βG),acid phosphatase(AP)andβ⁃1,4⁃N⁃acetylglucosaminidase(NAG),which were closely associated with soil carbon,nitrogen,and phosphorus cycling,across Cunninghamia lanceolata plantations and natural secondary forests(5,8,21,27 and 40 years old).The results showed that soil enzyme activities showed different patterns across different forest types.The acti⁃vities of AP,βG and CBH in the C.lanceolata plantations were significantly higher than those in the natural secon⁃dary forests,and there was no significant difference in the NAG activity.In the plantations,AP activity showed a decreasing tendency with the increasing stand ages,with the AP activity in the 5⁃year⁃old plantations significantly higher than other stand ages by more than 62.3%.The activities of NAG and CBH decreased first and then increased,andβG enzyme activity fluctuated with the increasing stand age.In the natural secondary forests,NAG enzyme activity fluctuated with the increasing stand age,with that in the 8⁃year⁃old and 27⁃year⁃old stand ages being significantly higher than the other stand ages by more than 14.9%.βG and CBH enzyme activities increased first and then decreased,and no significant difference was observed in the AP activity.Results of the stepwise regression analyses showed that soil predictors explained more than 34%of the variation in the best⁃fitting models predicting soil enzyme activities in the C.lanceolata plantations and natural secondary forests.In conclusion,there would be a risk of soil fertility degradation C.lanceolata plantations with the increasing stand age,while natural secondary forests were more conducive to maintaining soil fertility.