中国东北森林湿地碳源/汇及其对人为活动干扰响应研究

Wetland ecosystems on the earth are one of the most important carbon stocks in terrestrial soils, and are considered to play an important role in global carbon cycling,coping with and eliminating global climate change. However,some scientific questions have not been sovled so far. For example, firstly,there are substantial uncertainties concerning the carbon stock of wetlands at local, national, regional, and global scales, and its impacts on global carbon cycling.It is mainly because the carbon storage of wetlands varied considerably for the different climatic zones and was affected by vegetation type,landscape and hydrologic condition；secondly, natural wetlands not only may sequestrate CO2 from atmosphere,but also may emit methane to it. This may result in wetlands to be a sink or a source of atmospheric greenhouse gases (CO2 and CH4), and this question is not still better understood due to the lack of evidence comparing researches such as measuring CO2 sequestration and CH4 emission simultaneously；lastly, it is still unclear that how anthropogenic disturbances affect the transformation between C sink and C source of wetlands. Therefore, the aim of this study will foucus on these mainly existing scientific questions in wetlands researches. (1)The total carbon storage of natural wetlands will be estimated on the basis of measuring ecosystem carbon storage of seven types of typical natural wetlands in the forest region of Northeast China,so as to evaluate the long-term carbon sink function of these wetlands in this region. (2)The carbon sink or source function of seven types of natural wetlands,which dominated by forested wetlands in temperate region,will be evaluated quantitatively by means of the net C exchange between wetlands ecosystem and atomosphere through measuring the net primary productivity (carbon sequestration) and heterotrophic respiration carbon emission(CO2 and CH4) simultaneously. Furthermore, we could provide evidences for a better understanding of wetlands C sink or C source. (3)The effects of anthropogenic disturbance such as harvest (including selective harvest and clear harvest),draining for forestry on the wetlands C sink or C source also will be probed by using harveast,drainage controlling expariment methods and net ecosystem carbon exchange methods, so as to reveal the major mechanisms of disturbance influence on wetland carbon sinks, and provide scientific bases for managing the wetland carbon sinks in temperate forest region.

湿地生态系统是陆地上重要土壤碳库之一，在全球碳循环方面具有重要作用。然而，目前全球湿地碳储量仍未实现客观准确估算；湿地既能吸收大气中CO2，同时也排放CH4，因缺乏两者同步对比研究，使其碳源/汇问题尚难以定论；其碳源/汇功能对人为活动干扰如何响应目前仍不清楚。针对这些科学问题，本项目将依据气候、立地及植被分异规律，测定我国东北温带和寒温带7种典型山地天然沼泽湿地（草丛沼泽、灌丛沼泽及5种森林沼泽）的生态系统碳储量，结合各类型湿地分布面积，估算东北林区湿地碳储量，揭示其长期碳汇作用；将同步测定各类型天然湿地的净初级生产力（净固碳量）与土壤异养呼吸碳排放量，依据生态系统净碳收支，定量评价湿地碳源/汇作用，为深入了解湿地碳源/汇问题提供试验证据；将通过采伐、排水造林干扰控制试验及测定生态系统净碳交换量，揭示人为活动干扰对湿地碳源/汇功能转化的影响机制，以便为我国东北林区湿地碳汇管理提供科学依据。

湿地是陆地上重要土壤碳库之一，在全球碳循环方面具有重要作用。然而，目前全球湿地碳储量仍未实现客观准确估算；湿地既能吸收大气中CO2，同时也排放CH4，因缺乏两者同步对比研究，使其碳源/汇问题尚难以定论；其碳源/汇功能对人为活动干扰如何响应目前仍不清楚。. 针对上述科学问题，本项目以东北温带7种典型山地天然沼泽湿地（草丛沼泽-C、灌丛沼泽-G和5种森林沼泽）为对象，重点开展：1）东北温带天然沼泽生态系统碳源/汇；2）采伐干扰对森林沼泽湿地碳源/汇影响；排水造林对沼泽湿地碳源/汇影响；东北林区天然沼泽湿地碳储量总量估算及空间分异规律等研究工作。. (1)温带7种天然沼泽湿地类型的碳源/汇(-2.32~2.09 tC/hm2.a)作用不同，即草丛沼泽为碳的强汇，灌丛沼泽为碳的强源，而森林沼泽基本维持碳平衡。同步测定土壤碳排放(CO2和CH4)与植被碳固定2个碳循环关键过程，定量刻划其碳源/汇作用，有助于解决目前国内外有关湿地究竟是碳源还是碳汇争议问题。. (2)择伐对温带针叶林沼泽湿地碳源/汇功能影响并不显著(仅使其源强增加0.7倍-1.1倍或弱汇转化弱源)，而皆伐却使其转化为碳的强排放源或中等排放源(提高5.8-11.3倍，P<0.05)。故在温带森林沼泽湿地碳汇管理实践中要避免皆伐方式。在生态系统尺度上研究采伐干扰对森林沼泽碳源/汇影响较过往单一研究有所推进。. (3)排水造林前期落叶松人工林碳汇(0.72 t/hm2.a)显著低于草丛沼泽近2/3(2.08 t/hm2.a)，后期其碳汇(1.20 t/hm2.a)仍低于草丛沼泽约2/5。因此，排水造林干扰初期显著降低草丛沼泽湿地碳汇功能，而其碳汇功能的恢复至少需要30年以上时间，故应避免对温带沼泽湿地进行排水造林。. (4)温带长白山5种原始沼泽类型生态系统碳储量(408.42- 827.68 tC/hm2)沿过渡带环境梯度呈递减趋势的立地分异规律性及东北林区沼泽湿地碳储量(226.84- 827.68 tC/hm2)沿纬度梯度呈现递减(F)或先降后升(C和G)的气候分异规律性。且东北林区沼泽湿地碳储量总量估算值为16.29亿t(其中，大兴安岭(43.4%) >长白山(34.3%) >小兴安岭(22.3%)，且该估计值为东北地区泥炭总储量估计值3.81亿t的4.3倍。