增温对我国东北典型针阔混交林土壤氮损失的影响

Human activities have caused an increase in air temperature at a global scale. It is predicted that air temperature will increase by 0.3 to 4.8 Celsius degrees by the end of this century across the world. However, it remains unclear on how ecosystems, particularly forest ecosystems respond to global warming. There are a few warming experiments with large warmed plots to explore ecosystem responses in the world. Furthermore, most warming studies paid much more attentions on carbon cycling than nitrogen cycling. In this proposed study, we will warm the soil of a typical temperate forest in northeastern China by 2 Celsius degrees above the control for three years. This forest is about 65 year old. Two treatments will be set up, with three replicate plots for each treatment. Each plot sizes 10 m by 10 m. The warmed plots will be heated by infrared lamps controlled automatically by a system. We will investigate the responses of nitrogen transformations (mineralization, nitrification, and denitrification), nitrogen losses via nitrogenous gases and leaching. The gas losses via NO and N2O will be monitored by a on-line automatic system. We will quantify the contribution of nitrification and denitrification to NO and N2O production by 15N labelling techniques, and will link the N transformation rates with the functional gene abundance of associated microbes. This study will be the first in situ warming experiment with large plots in temperate region of eastern Asia under the monsoon climate. The results will provide understanding for the soil N cycling in response to warming in the study region and will help reduce uncertainties in modelling and predicting the responses of temperate forest ecosystem to global warming.

人类活动已经导致了全球气温升高，预计全球到本世纪末平均气温上升0.3-4.8℃。生态系统，特别是森林，对全球变暖的响应及其生物学机制的认识仍然十分有限。目前全球森林生态系统尺度上的大面积原位增温实验不多，特别是东亚温带地区。另外，有关增温对生态系统的影响的研究主要关注碳循环，而对土壤氮循环及其损失对增温的响应研究非常有限。为此，本研究将以东北一典型的针阔混交林为研究对象（清原站），对土壤连续三年增温2℃，1）量化气态氮损失的形态和量、氮流失的形态和量对增温的响应；2）区分土壤硝化与反硝化作用对NO与N2O排放的贡献及其对增温的响应；3）建立土壤氮转化与相关微生物的功能基因丰度之间的关系，以揭示该区域森林土壤氮循环及其相关微生物对全球变暖的响应。研究结果将有利于加深温带森林土壤氮素循环对增温的响应的认识，为模拟和预测全球温带森林对全球变化的响应提供基础数据，减少模型预测的不确定性。

全球变暖已经是不争的事实。森林生态系统对全球变暖的响应及其生物学机制的认识仍然十分有限。本研究将以东北一典型的针阔混交林为研究对象，对土壤连续四年增温2℃，并采用多通道连续观测技术量化土壤NO和N2O排放。结果发现，1）连续观测数据显示，清原温带次生林生态系统土壤NO和N2O的年排放量分别为0.44±0.06 kg N ha-1 yr-1和0.85±0.16 kg N ha-1 yr-1。增温降低了土壤NO和N2O的排放，达24.8±4.8%。土壤NO排放主要受到土壤温度的调控，但是增温并不改变土壤NO的表观温度敏感性Q10。2）增温仅对有机层土壤硝态氮含量有促进作用，但不改变其他土层中铵态氮和硝态氮含量。增温也不影响土壤净氮矿化速率。3）增温对含氮气体排放的相关功能基因影响也不明显。4）土壤淋溶水中硝态氮和铵态氮的含量呈现明显的季节性和年际动态，生长季初期和末期的含量高于生长季中期的含量，硝态氮的含量明显高于铵态氮的含量，但是增温并没有改变这些特征。5）室内培养、结果发现，N2O和N2的Q10值在各站点之间的差异很小，N2O的Q10平均值为2.2（1.4-2.7），N2的Q10平均值为2.9（2.2-3.6），说明气候变暖会直接导致更多的硝酸盐消耗并以N2的形式转移。反硝化作用对N2O和N2释放占主导，其贡献率在各温度和各森林土壤之间差异也较大。6)原位水分梯度研究发现，土壤水分增加会促进土壤NO和N2O排放。本项目的实施为我国东北森林氮循环的机制性研究和培养国内年轻的生态学研究人员等多方面做出贡献。培养青年工作人员3名，研究生5名。资助发表SCI论文18篇，如New Phytologist等。