太行山区侧柏人工林土壤有机碳固存与周转机理研究

Afforestation has been proposed as an effective method for reducing the atmospheric CO2 concentration and increasing the ability to sequester carbon in soil. However, at home and abroad, we still have less understanding on: 1) the effect of litter-fall of artificial forests on soil total carbon; 2) the contribution ability of root-drived carbon to soil organic carbon (SOC) pool; 3) physical protection mechanism and the mineralization characteristics of SOC, etc., during afforestation recovery process. .This project intends to choose the representative artificial forests (Platycladus orientalis) with 6 kinds of forest ages (2a、8a、18a、28a、38a and 48a) in the South of Taihang Mountain as the research objects. Long-term field situ observation technology and laboratory controlling experiments will be combined to research mechanisms of SOC sequestration and turnover. We intend to determine the influence of forest age on litter-fall biomass and SOC turnover amount, as well as the distribution of SOC fractions in soil profile. Further, the response of SOC mineralization rate to litter addition and forest ages will be investigated. In order to explore the contribution of carbon rhizodeposition to SOC accumulation, a potted experiment with different density ratios of Platycladus orientalis seedlings will be conducted. 13C pulse-labelling method will be used to compare the distribution characteristics of labelled and unlabeledδ13C value in the soil and plant fractions. We aim to comprehensively reveal the mechanisms of SOC sequestration and turnover under the s forest ages, i.e. from organic carbon input (litter-fall and rhizodeposition), turnover of organic carbon in the soil (stabilization and distribution), and soil carbon output (SOC mineralization). Finally, we hope to provide more scientific information for building the theoretical system of soil carbon cycle in artificial forest ecosystem.

人工造林能有效增加土壤有机碳（SOC）固存、减缓全球变暖。但是，国内外对造林恢复过程中人工林凋落物对土壤碳含量的影响、根源型有机碳对SOC贡献率大小、SOC的物理保护机制和矿化特征等均尚存在很大的不确定性。本课题拟以6种林龄（2a、8a、18a、28a、38a和48a）侧柏人工林为研究对象，利用野外长期定位与培养试验相结合的方法，探明不同林龄凋落物年有机碳归还量和SOC在不同土层及不同土壤粒级中的分布特征，揭示SOC矿化速率对凋落物输入与种植年限的响应机理。其次，本课题拟采用13C脉冲标记法，对不同密度配比的侧柏盆栽苗木进行标记，对比标记前后土壤及植物体不同有机碳组分中δ13C的丰度变化，推测侧柏根际碳沉积对SOC积累的贡献率。旨在从SOC输入→SOC在土壤组分中的周转→SOC输出，全方面探讨不同林龄对SOC固存和周转的影响机理，以丰富人工林生态系统土壤碳循环的理论体系。

本项目基于中国森林生态系统定位研究网络（CFERN）黄河小浪底森林生态系统定位研究站，以5种林龄侧柏人工林为研究对象，开展了长期枯落物归还干预下土壤有机碳（SOC）在不同季节和土层的时空分布特征，并对枯落物干预两年后的土壤采用室内培养方法分析了土壤温室气体排放特征、土壤微生物生物量碳、氮及活性碳氮周转特征；采用13C脉冲标记法对不同密度配比的侧柏盆栽苗木进行标记，对比分析了δ13C在植物茎叶、根与土壤分配特征。结果表明5种林龄侧柏人工林下土壤溶解性有机质含量（DOC与DON)、土壤蔗糖酶与脲酶活性均呈明显的季节变化（P < 0.05），且有相似的趋势，均在夏季达到峰值；土壤DOC、DON含量及土壤蔗糖酶与脲酶活性总体上随土层加深而降低，呈表层富集的现象。林龄、枯落物处理均显著影响土壤累积CO2和N2O排放及CH4吸收，随着侧柏林龄的增加，CO2排放量呈先升高后减弱趋势，尤其是表层土壤表现最为突出；有枯落物平均土壤CO2和N2O累积生产量均显著高于去除凋落物处理（P < 0.05）；有无枯落物归还处理下平均土壤CO2和N2O累积生产量及土壤微生物代谢熵（qCO2）均随土层的加深而降低。根际碳沉积与植物生物量及茎叶的碳丰度显著相关，并受种植密度和根系生理指标的影响。侧柏δ13C光合碳在根系中所占比例为35.06%－38.03%，土壤中仅占0.01%－0.02%。总体而言，随着侧柏林龄的增加，土壤有机碳含量呈先增加后降低的趋势，枯落物归还有利于增加土壤活性碳含量并提高碳周转速率，表层土壤微生物活性较强，有机碳的周转速率快。