Effects of Simulated Climate Change on Soil Microbial Diversity and Plant-Microbe Association in Lake Superior Provincial Park, Canada

糖枫是北美落叶林中具有重要生态和经济意义的树种，可能会受到其北部边界附近气候变化的影响。在过去与冰川作用有关的气候变暖和变冷期间，北美的森林通过树木在整个大陆上向北和向南移动来跟踪气候。然而，对未来几百年人类引起的气候变化的预测表明，变暖的速度可能比过去18,000年树木物种所经历的要快得多-事实上，可能比过去200万年还要快。这种快速的气候变化可能会对许多物种的繁殖能力产生负面影响，并在目前发现的地区持续存在。就糖枫而言，气候影响可能包括生长速度的改变，生存率的变化，以及植物/土壤群落动态的变化，包括与土壤微生物伙伴的长期联系。本项目将在人工温度和降水控制实验下评估气候变化对糖枫幼苗土壤微生物群落的影响。它的目的是补充同一调查人员正在进行的一个项目，该项目正在研究糖枫幼苗的生长对位于加拿大苏必利尔湖上级省立公园的北方落叶林边界的温度和降水变化的反应。2008年5月建立了配备防雨结构和红外线加热灯的试验田。研究人员将在经历实验性气候变化的栖息地中解决两个广泛的问题：1）气候变化如何改变土壤微生物多样性和土壤微生物群落结构？2）在糖枫占优势的土壤微生物群落在气候变化与土壤呼吸之间的反馈中起着什么样的作用？微生物多样性将以三种方式进行评价：1）通过基于聚合酶链反应（PCR）的产物分析，2）通过微生物培养，3）通过磷脂脂肪酸（PLFA）分析。土壤微生物群落在土壤养分矿化和土壤有机质转化等地球化学过程中起着重要作用，但土壤微生物与植物群落组成/多样性之间的反馈机制尚不清楚。毫无疑问，在很长一段时间内，植物和微生物物种对气候变化的反应是通过范围变化来实现的，但如果森林生态学家希望模拟生物（地上和地下）对下一个世纪气候变化的反应，那么使用过去气候变化的类似物可能并不合适。因此，模拟更明显和快速的温度变化的实地实验可以提供建设性的结果，确定对温度和大气浓度变化的具体反应，模仿人为影响。充分理解和量化植物-土壤-大气连续体中碳循环的各个方面，对于确定森林土壤是否将成为大气碳的净汇或源至关重要。详细了解气候变化对土壤微生物的影响，可能是全球气候变化生态影响不断扩大的领域中的一个重要组成部分。此外，研究人员希望他们的结果将提供有关是否存在糖枫及其相关微生物可能无法生存的生态阈值的信息，以便森林管理者，土壤科学家，建模者和政策制定者可以开始监测环境，以寻找这些变化即将发生的迹象。由于糖枫是这些森林中的优势物种，它可能会在气候变化的情况下推动大部分生态变化。该项目将提供森林生态学和微生物学方法的研究和教育机会，以便调查气候变化对自然生态系统的影响。

Sugar maple, an ecologically and economically important species in the deciduous forests of North America, is likely to be affected by altered climates near its northen limit. During past warming and cooling espisodes associated with glaciation, the forests of North America have tracked climate by the trees shifting their ranges north and south across the continent. However, projections of human-induced climate change over the next several hundred years suggest that warming may be much faster than tree species have experienced in the past 18,000 years---in fact, probably faster than over the last two million years. This rapid rate of climate change may negatively impact many species' ability to reproduce and persist in regions where they are currently found. In the case of sugar maple, climate effects may include altered growth rates, changes in survivorship, and changes in the plant/soil community dynamics including long term associations with soil microbial partners. This project will evaluate the impact of climate change on soil microbial communities associated with sugar maple seedlings under an artificial temperature and precipitation manipulation experiment. It is designed to complement an ongoing project by the same investigators that is examining growth of sugar maple seedlings in response to temperature and precipitation change in the boreal-deciduous forest boundary located in Lake Superior Provincial Park, Canada. Experimental plots, outfitted with rain-exclusion structures and infrared heat lamps, were established in May 2008. The investigators will be addressing two broad questions in habitats undergoing experimental climate change: 1) how will climate change alter soil microbial diversity and soil microbe community structure?, and 2) what role does the soil microbe community play in the feedback between climate change and soil respiration where sugar maple is dominant? Microbial diversity will be evaluated in a three-fold manner: 1) via polymerase chain reaction (PCR)-based product analysis, 2) via cultivation of microbes, and 3) via phospholipid fatty acid (PLFA) analysis. Soil microbial communities play a key role in geochemical processes including nutrient mineralization and soil organic matter transformation, but feedbacks between soil microorganisms and plant community composition/diversity are largely unknown. There is no doubt that over long periods of time plant and microbial species respond to climate changes by range shifts, but using analogs from past climate change may not be appropriate if forest ecologists wish to model biotic (both above- and below-ground) response to climate change over the next century. Thus, field experiments that simulate the more pronounced and rapid temperature changes can provide constructive results identifying specific responses to alterations in temperature and atmospheric concentrations mimicking anthropogenic impacts. Fully understanding and quantifying aspects of the carbon cycle in the plant-soil-atmosphere continuum will be critical in determining whether forest soils will become net sinks or sources of atmospheric carbon. A detailed understanding of the largely unstudied impact of climate change on soil microbes may prove to be a vital component in the expanding field of ecological impacts of global climate change. Further, the investigators expect that their results will provide information on whether ecological thresholds exist beyond which sugar maple and their associated microorganisms may not survive, so that forest managers, soil scientists, modelers, and policy makers can begin to monitor the environment for indications that those changes are imminent. Because sugar maple is a dominant species in these forests it may drive much of the ecological change under modified climates. This project will provide both research and educational opportunities in approaches from forest ecology and microbiology that allow for the investigation of the impact of climate change on natural ecosystems.