兴安落叶松生态系统CO_(2)浓度及其δ^(13)C动态对环境因子的响应

CO_(2)Concentration and theδ^(13)C Dynamics in Larix gmelinii Ecosystem in Response to Environmental Factors

【目的】探明环境因子对兴安落叶松原始林生态系统CO_(2)浓度及其δ^(13)C动态的影响,深入理解生态系统的碳交换过程,为模拟和预测全球变化与生态系统之间的互馈机制以及科学评估寒温带森林生态系统碳汇能力提供参考。【方法】采用离轴积分腔输出光谱技术对兴安落叶松生态系统不同物候期、不同高度的CO_(2)浓度及其δ^(13)C进行连续高频观测,并分析环境因子与CO_(2)浓度变化的关系。【结果】1)兴安落叶松生态系统不同高度的CO_(2)浓度在生长季和日尺度上均呈单峰变化,峰值分别出现在展叶期(522.34μmol·mol^(-1))和凌晨(782.81μmol·mol^(-1)),谷值分别出现在落叶期(406.07μmol·mol^(-1))和中午(379.72μmol·mol^(-1));δ^(13)C变化趋势与CO_(2)浓度相反;2)CO_(2)浓度随垂直高度升高而减小,δ^(13)C随垂直高度升高而增大;不同高度的CO_(2)浓度及其δ^(13)C具有明显成层现象,夜间大气稳定性增加(理查逊数Ri≥0.083)会加剧冠层内外的差异;3)在0.5h尺度上,影响昼夜各高度CO_(2)浓度变化的主要因子为空气温度(T_(a))(0.714<PC<1.288);在日尺度上,决定生长季不同高度CO_(2)浓度变化的主要因子为土壤5cm温度(T_(s)5)(0.473<PC<0.718)。【结论】兴安落叶松生态系统不同高度的δ^(13)C与CO_(2)浓度呈极显著负相关,夜间大气稳定性增加会加剧二者的成层现象。土壤因子对兴安落叶松生态系统不同物候期、不同高度CO_(2)浓度变化的影响程度高于气象因子,土壤温度对其的影响程度大于土壤水分。研究区地处全球气候变化敏感区域,冻土是该区森林植被不可或缺的环境因素,全球变暖将通过直接的温度效应以及间接改变土壤理化性质和生物过程对兴安落叶松生态系统的碳交换过程产生显著影响。

【Objective】This study aims to explore the influence mechanism of environmental factors on the CO_(2) concentration and δ^(13)C dynamics in Larix gmelinii ecosystem,which would help to deeply understand the process and mechanism of carbon exchange in ecosystems,so as to provide reference for simulating and predicting the mutual feedback mechanism between global change and ecosystems,as well as for scientific assessment of carbon sink capacity of cold temperate forest ecosystems.【Method】The off-axis integral cavity output spectroscopy was used to perform continuous high-frequency observations to the CO_(2) concentration and δ^(13)C value at different heights in different phenological periods of L.gmelinii ecosystem,and thereby analyze the relationship between environmental factors and CO_(2) concentration.【Result】1)The CO_(2) concentration at different heights of L.gmelinii ecosystem showed a single peak variation in the growth season and daily scale.The peak value appeared in the leaf spreading period(522.34μmol·mol^(-1))and at night(782.81μmol·mol^(-1)),respectively.The valley value appeared in the leaf falling period(406.07μmol·mol^(-1))and at noon(379.72μmol·mol^(-1)),respectively.The δ^(13)C variation was opposite to CO_(2) concentration.2)The CO_(2) concentration decreased with the increase of vertical height,whileδ^(13)C increased with the increase of vertical height.The CO_(2) concentration andδ^(13)C at different heights had obvious stratification.The increase of atmospheric stability at night(Ri≥0.083)increased the difference inside and outside the canopy.3)On the 0.5 h scale,air temperature(T_(a))was the main factor affecting the variation of CO_(2) concentration at different heights in day and night(0.714<PC<1.288).On a daily scale,soil temperature(T_(s)5)in 5 cm depth layer was the main factor determining the variation of CO_(2) concentration at different heights in the growing season(0.473<PC<0.718).【Conclusion】There is a very significant negative correlation between δ^(13)C and CO_(2)concentration at different heights of L.gmelinii ecosystem.The increase of atmospheric stability at night aggravates their layering phenomenon.The influence level of soil factors on the variation of CO_(2) concentration at different heights in different phenological periods of L.gmelinii ecosystem is greater than that of meteorological factors.The soil temperature has greater influence on the variation of CO_(2) concentration than the soil water.The study area is located in a sensitive area to global climate change.Frozen soil is an indispensable environmental factor for forest vegetation in this area.Global warming will have a significant impact on the carbon exchange process of L.gmelinii ecosystem through direct temperature effect and indirect changes in soil physical and chemical properties and biological processes.