冰灾后南岭常绿阔叶林碳汇功能及相关过程的变化

The carbon sequestration function of forest ecosystems and related processes exploration have remained as the frontier researches in global change ecology. The rational understanding of this issue needs to pay accurate estimation of varying carbon sequestration capability and carbon fixation processes of forests damaged by increasing climate extremes. Such study is getting increasingly important in the further with enhancing impacts of climate change. In this project, the typical natural evergreen broadleaved forests at Nanling Mountains which were severely damaged by the 2008 Chinese icestorm, were chosen to study the scientific issue: how the forest structure changes and how it impacts the carbon-fixing processes and carbon sequestration function. Based on the long-term located researches on this site and combined with controled experiments of forest canopy damage simulation, the growth dynamics, carbon input onto and release from forest floor, changes of carbon pool both in vegetation and soil, and the carbon allocation etc will be studied in the damaged forests during their recovering periods. Two scientific hypothesises will be confirmed. The first is that the heavily damaged forests will decrease the devotion of photosynthetic products and other nutrition resources to stem growth, but allocate more to the increment of undergrowth and the branch/foliage/root biomass; and the second is that the violent fluctuation of non-inert carbon pool and the gradually accumulation of inert carbon pool in soil after the forest damaged will appear. The achievements of this project will provide scientific basis for a more accurate evaluation of the impacts of ice storm disturbance on the cabon sequestration function of forest ecosystems, and for the prediction of changes in the carbon-fixing capability in the recovering periods of damaged forests, and for the decision-making of reasonable measurements to promote the healthy recovery of damaged forests.

森林生态系统碳汇功能及相关过程是全球变化生态学的前沿研究领域，合理解读这一问题需要准确评估日益频发的极端气候事件导致森林受损所带来的森林固碳过程及碳汇功能变化，这在气候变化影响不断增强的未来尤为重要。本项目拟在南岭山地选择2008年华南冰灾严重损害的典型天然常绿阔叶林，结合长期定位研究与模拟林冠受损的控制实验，针对受损森林恢复过程中的森林结构变化如何影响固碳过程及碳汇功能这一科学问题，开展受损森林生长动态、林地碳输入和排放、植被和土壤碳库动态及分配规律等过程与机理研究；论证两个科学假说：一是严重受损森林会减少光合产物等资源分配于树干生长，但集中分配在林下植被生长和受损林木的枝、叶、根生产；二是森林受损后土壤非惰性碳剧烈波动和惰性碳逐渐积累。此项目成果可为准确评估冰雪灾害干扰对森林固碳功能的影响、预测森林灾后恢复过程中固碳能力变化和制定合理的受损森林健康恢复促进措施等提供科学数据。

本项目在南岭山地选择2008年华南冰灾严重损害的典型天然常绿阔叶林，结合长期定位研究与模拟林冠受损的控制实验，针对受损森林恢复过程中的森林结构变化如何影响固碳过程及碳汇功能这一科学问题，采用13C同位素示踪法标记植物叶片后野外原位培养，同时结合土壤微生物高通量测序法，研究了冰灾产生的新鲜植物残体的分解过程和对土壤碳的激发效应以及其微生物机制，研究结果表明“非正常凋落物”能促发土壤碳的3段式激发效应，即强烈的负激发—缓和负激发—正激发；不同阶段的碳激发现象有不同的主导机制，其中以放线菌门（Actinobacteria）为代表的细菌对碳激发效应作出了重要贡献；“非正常凋落物”中超过77%的碳是以二氧化碳的形式释放。通过在冰灾受损森林不同恢复阶段开展生物量实测构建了常绿阔叶林冰灾受损后不同恢复阶段的生物量模型，同时发现了受损树木的枝叶存在超补偿生长现象。通过对冰灾受损杉木生物量的实测发现，杉木树冠受损后生物量在不同器官的分配发生了变化，根系和枝叶生物量占比提高而树干生物量占比降低。通过生态系统模型研究了冰灾对针叶林和针阔叶混交林生产力的影响，结果表明，冰灾后针叶林生产力恢复延迟，杉木可以继续在针阔叶混交林中占据主导地位，针阔叶混交林比针叶林对冰灾和择伐的抵抗力和恢复力更强。通过对冰灾受损森林群落的持续监测发现，冰灾后林冠层恢复时间为3年，地上生物量累积速度恢复时间为3-4年，凋落物输入量的恢复时间为4年。冰灾增加了土壤碳库的季节波动幅度，但对土壤碳库的影响主要集中在表层快速周转部分，对土壤稳定碳库影响较小。此项目成果可为准确评估冰雪灾害干扰对森林固碳功能的影响、预测森林灾后恢复过程中固碳能力变化和制定合理的受损森林健康恢复促进措施等提供科学数据。

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