Effects of climate, disturbance and nitrogen fertilization on the carbon balance of forests in western canada

北温带和北方森林是生物量和土壤碳(C)的大型储存库，对全球光合作用总量做出了重要贡献。重要的是要更好地了解这些碳库对气候变化的响应，研究近年来干扰增加的影响，并制定提高其碳汇强度的管理措施。本研究将在寒带、亚寒带和西海岸温带林分进行。我们的目标是：(1)研究气候变率对生态系统净生产力（NEP）、生态系统总光合作用(P)和生态系统呼吸(R)的影响；(2)量化环境因子、物候和P对R和土壤呼吸（Rs）的影响；(3)异养成分和根际成分之间Rs的分配；(4)评估氮肥对西海岸不同年龄道格拉斯冷杉林分C平衡和N2O排放的影响。(5)确定山松甲虫（MPB）侵袭对亚北方黑松成熟林分碳平衡和水分平衡的影响。我们将使用涡动相关（EC）方法测量冠层上的二氧化碳、水蒸气和感热通量。除了使用常规方法在P和R之间划分NEP之外，我们还将使用可调谐二极管激光吸收光谱对13CO2同位素通量进行EC和腔室测量。异养呼吸将使用改良的沟畦根系排除技术进行测量，并用于估算净初级生产力。土壤N2O排放将使用静态室的注射器采样来测量。从两个黑松林分的年NEP测量结果可以推断出MPB侵袭的时间效应。这项研究将提高我们对森林在全球气候系统和碳平衡中的作用的理解。量化施肥和MPB攻击的影响将有助于为加拿大制定增加其森林碳固存的战略。这项工作将为验证C循环模型提供有价值的数据，并为2名硕士和3名博士研究生，3名博士后和4名技术人员提供良好的培训。

Northern temperate and boreal forests are large reservoirs of biomass and soil carbon (C), and make a major contribution to gross global photosynthesis. It is important to better understand the response of these C pools to climate change, to study the impact of increased disturbance in recent years, and to develop management practices that will enhance their C sink strength. This research will be conducted in boreal, sub-boreal and West Coast temperate forest stands. Our objectives are to (1) study the impact of climatic variability on net ecosystem productivity (NEP), gross ecosystem photosynthesis (P) and ecosystem respiration (R), (2) quantify the effects of environmental factors, phenology and P on R and soil respiration (Rs), (3) partition Rs between its heterotrophic and rhizospheric components, (4) assess the effect of nitrogen fertilization on the C balance and N2O emissions in different-aged West Coast Douglas-fir stands, and (5) determine the impact of mountain pine beetle (MPB) attack on the C and water balances of mature sub-boreal lodgepole pine stands.   We will measure above-canopy CO2, water vapour and sensible heat fluxes using the eddy covariance (EC) approach. In addition to using conventional methods to partition NEP between P and R, we will use EC and chamber measurements of 13CO2 isotope fluxes with tunable diode laser absorption spectroscopy. Heterotrophic respiration will be measured using a modified trenched-plot root-exclusion technique and used to estimate net primary productivity. Soil N2O emissions will be measured using syringe sampling of static chambers. Temporal effects of MPB attack will be inferred from annual NEP measurements in two lodgepole pine stands at early and late stages of attack.   This research will improve our understanding of the role of forests in the global climate system and C balance. Quantification of the effects of fertilization and MPB attack will help develop a strategy for Canada to increase C sequestration in its forests. This work will provide valuable data to validate C cycling models and sound training of two M.Sc. and three Ph.D. students, three postdoctoral fellows and four technicians.