Nitrogen cycling and tree nutrition in boreal forests: interactions with understory vegetation and soil water availability

我们有一个贫穷的了解的交互作用的养分供应，供水，林下竞争的林下竞争，如加拿大蓝节草丰富，生长旺盛，N往往是最有限的养分在北方森林的林分生产力。在这项研究中，我将使用两个领域和温室为基础的方法来研究土壤氮动态，林下植物和树种之间的竞争，以及它们如何受到资源（N和水）的影响。目标是：1）调查林下植被和水分有效性如何相互作用影响土壤养分动态和树木营养; 2）探索土壤资源有效性之间的联系（或竞争）与树木生理生态过程（气孔导度、光合作用、稳定碳同位素分馏和植物氮吸收）; 3）研究竞争和资源可利用性对土壤微生物种群功能和多样性的影响;（4）进一步了解有机氮在加拿大牛筋草和白色云杉营养中的作用。我将研究净和总氮矿化率，净和总硝化率，异养硝化率，可溶性有机氮生产率，微生物固定氮，树木和林下物种的氮吸收，以及森林生态系统的净初级生产力。稳定的N和C同位素（15 N和13 C）技术，生态生理学（例如，气体交换）测量和矢量分析将被用来调查N竞争和资源限制的机制。将进行温室实验以检验加拿大蓝关节草可以吸收简单有机形式的N的假设。这项研究的结果将有助于我们更好地了解控制森林生产力的因素与竞争性林下植被出没的网站，设计森林经营策略，以适应不断变化的降水模式，并提供信息的森林生产力的上限在北方地区。这项研究将推动土壤-植物关系、资源限制、竞争和北方植被动态等生态学理论的发展。

We have a poor understanding of the interactive effects of nutrient availability, water supply, and understory competition on stand productivity in boreal forests where competitive understory species such as Canada bluejoint grass are abundant and grow vigorously and where N is often the most limiting nutrient. In this study, I will use both field- and greenhouse-based approaches to study soil N dynamics, competition between understory and tree species, and how they are affected by resource (N and water) additions. The objectives are: 1) to investigate how understory vegetation and water availability interact to affect soil nutrient dynamics and tree nutrition; 2) to explore the linkage between soil resource availability (or competition) and tree ecophysiological processes (stomatal conductance, photosynthesis, stable C isotope fractionation, and plant N uptake); 3) to study the effects of competition and resource availability on the function and diversity of soil microbial populations; and 4) to gain a better understanding of the role of organic N in Canada bulejoint grass and white spruce nutrition. I will study net and gross rates of N mineralization, net and gross rates of nitrification, rate of heterotrophic nitrification, rates of soluble organic N production, N immobilization by microbes, N uptake by both tree and understory species, and the net primary productivity of the forest ecosystem. The stable N and C isotope (15N and 13C) techniques, ecophysiological (e.g., gas exchange) measurements, and vector analysis will be used to investigate the mechanisms for N competition and resource limitations. A greenhouse experiment will be conducted to test the hypothesis that Canada bluejoint grass can take up simple organic forms of N. Results from this study will help us better understand the factors controlling forest productivity in sites infested with competitive understory vegetation, design forest management strategies to adopt to the changing precipitation patterns, and provide information on the upper limits of forest productivity in the boreal region. The proposed research will advance ecological theories in soil-plant relations, resource limitation, competition, and boreal vegetation dynamics.