西南亚高山针叶林自然与人工恢复及调控管理对土壤有机质积累与稳定性影响机制

The accumulation and stability of soil organic matter (SOM) are important ecological functions for evaluating the forest restoration and management practices. There are evidences that SOM continuously decreases with increasing stand year after spruce plantations established on the cutovers in the subalpine coniferous forests of southwestern China. However, few studies focus on reasons and mechanisms resulting in the decline of SOM during spruce plantation succession. This study will select a chronosequence of spruce plantations and secondary broad leaf forests to investigate the dynamics and stability of SOM, compared with primary forest. We also will implement forest management practices (e.g. litter manipulation and root removal, and the technique of thinning by simulating gap formation) to elaborate the mechanisms of stability of SOM. The technique of soil physical fraction combined with microbial community composition and enzyme activities, 13C nuclear magnetic resonance (13C NMR), continuous extraction with water-acid method, and long-term incubation of soil CO2, are used to explore the accumulating rate of SOM and carbon fractions under different forest restoration approaches with increasing stand years. Additionally, we arm to explore the stability of SOM from the perspectives of physical, chemical and biological protection, through experiments of litter manipulation and root removal, and tree structure adjustment by decreasing tree density with different gap size. Furthermore, we analyze the relationship of the chemical composition and function of SOM and soil fertilization. Based on the analysis above mentioned, measures and theories will be put forward for sustainable management of carbon sequestration in soil and control of non-commercial ecological plantation.

土壤有机质(SOM)积累与稳定性是森林恢复和管理的重要生态功能评价依据。我国西南林区采伐迹地人工造林恢复后，随着时间演替SOM持续下降，但其下降原因及机制一直缺乏系统研究。本研究选择系列年龄梯度，人工恢复云杉林和自然恢复阔叶林SOM为研究对象，原始林为参照，结合人工林原位凋落物调控(切根、凋落物添加与去除)和间伐调控(不同大小林窗式疏伐)野外长期试验平台，利用土壤物理组分分离技术，团聚体水平微生物群落组成与酶活性分析，水-酸化学提取与13C NMR技术以及长期培养试验，对不同森林恢复途径和调控管理下土壤SOM进行物理分馏、化学功能团和生物活性分析，试图揭示不同植被恢复途径下SOM库与其组分碳的动态特征、积累过程和稳定性等; 阐明森林恢复过程与调控管理对SOM的生物、物理与化学稳定性机制；分析SOM功能团组成变化与土壤肥力的关系，为我国西南生态公益人工林土壤持续固碳的管理与调控提供理论依据。

揭示不同恢复途径及调控措施对土壤有机碳（SOC）积累与稳定性的机制是森林恢复与持续经营的科学基础。本研究选择亚高山自然与人工恢复途径的系列林地，结合氮、磷养分添加和不同人工林树种恢复样地试验平台，测定土壤团聚体及相联结的碳组分、微生物群落组成和酶活性等指标，分析不同恢复途径及调控措施对土壤有机碳（SOC）积累与稳定性的机制，主要发现：.（1）土壤有机碳组分和贮量受恢复途径的影响，自然恢复方式明显高于人工恢复，恢复方式通过改变大团聚体与微团聚体比例和细根生物量，进而影响土壤有机碳贮量。同时，恢复方式和时间也改变了与团聚体相结合的碳浓度和贮量。.（2）亚高山森林土壤微生物生物量对恢复途径、团聚体大小和林龄的响应主要取决于微生物群的类群、土壤有机碳、总氮和pH值，林龄和团聚体大小明显影响了β-1,4-葡萄糖苷酶, N-乙酰氨基葡糖苷酶, 酸性磷酸酶和多酚氧化酶的活性，然而恢复方式对对酶活性的影响取决于具体的酶种类。.（3）通过N、P养分的持续4年添加，揭示了氮、磷养分添加对云杉人工林土壤组分及稳定性的影响机制。由于土壤多酚氧化酶受抑制，在N添加处理土壤C含量增加21%，然而，P单独添加和NP共同添加后，由于细根生物量的减少，导致土壤全C含量降低；施肥也影响了土壤团聚体C库。总之，N添加诱导的土壤C含量增加，主要在粘粉粒组分，受多酚氧化酶抑制所驱动，而P单独添加和NP共同添加处理下土壤C含量变化，发生在大团聚体中，主要与细根碳输入相联系。.（4）证实了细根在调节亚高山土壤微生物群落和功能中的重要性，强调了细根际和粗根际或非根际土壤微生物及活性的差异取决于植被类型，土壤有机碳和总氮是调控土壤微生物群落和酶活性的主要因子。.（5）项目这些发现突出了自然恢复在土壤碳积累和稳定性中的重要性，特别是“碳中和、碳达峰”背景下为森林生态系统土壤固碳提供了科技支撑。