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.
