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一种重要的生态和经济树种，可能会受到其北部边界附近气候变化的影响。在过去与冰川作用相关的变暖和变冷时期，北美的森林通过在整个大陆上将树木的范围南北移动来跟踪气候。然而，对未来几百年人类导致的气候变化的预测表明，变暖的速度可能比过去18,000年来树木物种经历的速度快得多-事实上，可能比过去200万年更快。这种快速的气候变化可能会对许多物种在目前发现它们的地区繁殖和持续生存的能力产生负面影响。在糖枫的情况下，气候影响可能包括生长速度的改变，存活率的变化，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。本项目将通过人工调控温度和降水的实验，评估气候变化对糖枫幼苗相关土壤微生物群落的影响。这是为了补充同一研究人员正在进行的一个项目，该项目正在研究加拿大苏必利尔湖省级公园北部落叶森林边界的温度和降水变化对糖枫幼苗生长的影响。试验田于2008年5月建立，配备了防雨结构和红外加热灯。研究人员将在经历实验气候变化的生境中解决两个广泛的问题：1)气候变化将如何改变土壤微生物多样性和土壤微生物群落结构？2)土壤微生物群落在气候变化和以糖枫为主的土壤呼吸之间的反馈中发挥什么作用？微生物多样性将通过三种方式进行评估：1)通过基于聚合酶链式反应(PCR)的产品分析，2)通过微生物培养，以及3)通过磷脂脂肪酸(PLFA)分析。土壤微生物群落在包括养分矿化和土壤有机质转化在内的地球化学过程中起着关键作用，但土壤微生物和植物群落组成/多样性之间的反馈作用在很大程度上是未知的。毫无疑问，在很长一段时间内，植物和微生物物种通过范围变化来响应气候变化，但如果森林生态学家希望在下个世纪建立生物(地上和地下)对气候变化的反应模型，那么使用过去气候变化的类比可能是不合适的。因此，模拟更显著和更快速的温度变化的实地实验可以提供建设性的结果，以确定对温度和大气浓度变化的具体反应，以模拟人为影响。充分了解和量化植物-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碳源至关重要。详细了解气候变化对土壤微生物的影响在很大程度上没有被研究过，这可能是全球气候变化生态影响这一不断扩大的领域的重要组成部分。此外，研究人员预计，他们的结果将提供关于是否存在生态阈值的信息，超过这个阈值，糖枫及其相关微生物可能无法生存，以便森林管理者、土壤科学家、模型师和政策制定者可以开始监测环境，以寻找这些变化即将到来的迹象。由于糖枫是这些森林中的优势物种，在气候变化的情况下，它可能会推动大部分生态变化。该项目将在森林生态学和微生物学方法方面提供研究和教育机会，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.