季节冻融对若尔盖泥炭沼泽碳排放的影响机理

As a significant terrestrial carbon pool, peatlands play an important role in earth climate system with their carbon emission. The carbon emission from peatlands during freeze-thaw period accounts for a considerable but uncertain portion of the annual budget. The dramatic variations of both hydrological and thermal factors during this period are thought to be responsible for the variation of carbon emission. To date, our knowledge on the impact of freeze –thaw on carbon emission was limited in the northern region, there has not been any attempts at evaluating the effect of frozen-thaw on carbon emission from peatlands on the Tibetan Plateau, despite the distinct pattern of freeze-thaw in alpine region.. In the proposed program, the Zoige Peatland which is situated on the eastern Tibetan Plateau will be chosen to be studied. Based on in situ freeze-thaw process, various modes of freeze-thaw cycle will be applied in simulated experiments to different layer of peat sampled from the field. Under above-mentioned conditions, rate of carbon emission, Q10 of carbon emission, potential of methane production, mineralization rate, property of organic carbon, soil microbe community structure, soil enzyme activity, etc. will be examined, meanwhile, in situ carbon emission and associated processes will also be studied. Based on the results of those experiments, we aim to obtain a better understanding on the spatio-temporal pattern of freeze-thaw process and its effect on the carbon emission from peatlands on the Tibetan Plateau, and the underlying mechanism during different stages of freeze-thaw process will be studied as well.

泥炭沼泽是全球尺度上的重要碳库，其碳排放一直备受关注。季节冻融期间泥炭沼泽的碳排放占全年排放比重大，且呈现出极高的不确定性。季节冻融过程中泥炭水热条件的剧烈变化与泥炭沼泽碳排放相关过程关系密切。当前学术界对于泥炭沼泽在季节冻融影响下碳排放动态的有限认识均建立在高纬度低海拔地区，而青藏高原的季节冻融过程与高纬度低海拔地区相比具有较大差异。.本项目选取位于青藏高原东部的若尔盖泥炭沼泽为研究对象。基于野外条件下监测的季节冻融过程，通过室内模拟对不同泥炭层施加不同的冻融模式，进而对泥炭沼泽碳排放的相关过程进行动态监测与分析。同时，在野外原位条件下监测季节冻融期间泥炭沼泽的碳排放过程。通过综合分析上述实验结果，阐明高原泥炭沼泽的季节冻融节律，探讨季节冻融对高原泥炭沼泽碳排放的影响，揭示冻融影响泥炭沼泽碳排放的关键过程及机理，最终为青藏高原泥炭沼泽的碳评估提供基础数据和理论依据。

季节冻融期间泥炭沼泽的碳排放占全年排放比重大，且呈现出极高的不确定性。当前学术界对于泥炭沼泽在季节冻融影响下碳排放动态的有限认识均建立在高纬度低海拔地区，而青藏高原的季节冻融过程与高纬度低海拔地区相比具有较大差异。本项目监测和分析了野外条件下若尔盖泥炭沼泽在季节冻融不同时期的碳排放特征，估算并比较了各时期碳排放占泥炭沼泽全年总排放的比重；通过对泥炭样本进行不同模式的日冻融循环模拟实验，比较了土壤碳排放速率及其相关的土壤、微生物等指标的变化。对若尔盖高原泥炭沼泽的连续野外监测发现：季节冻融期间的CO2排放量约占全年排放量的68.4%，其中冻融期和融冻期虽然持续时间短，但是其排放量是生长季排放量的1.7倍；季节冻融期间的CH4排放量占全年的27.3%，冻融期和融冻期土壤物理结构的变化是影响甲烷排放的主要因素。实验室模拟结果显示：冻融循环初期促进了CO2和CH4的排放，整体上冻融循环对CO2排放呈现出抑制作用，而对CH4则呈现出促进作用；经冻融循环的泥炭更易受到植物根系分泌物添加的影响，产生激发效应进而促进CO2的排放。上述研究结果强调了青藏高原季节冻融期间泥炭沼泽碳排放的重要性，特别需要对日冻融循环剧烈发生的冻融期和融冻期进行关注，在机理方面应进一步探究不同冻融模式的效应及关联，以便更好解释碳排放在冻融循环过程中的变化。