Soil moisture has both direct and indirect effects on carbon dioxide (CO 2) exchange in tundra vegetation. More detailed studies are required to explain the causes of discrepancy between activity and presence of high-affinity methanotrophs and its relation to the transit from ice-covered probably anoxic to ice-free oxic conditions. We put forward the hypothesis that aerobic methanotrophs were at very low abundance and diversity during glaciation probably due to anoxia at the ice-sediment interface and that colonization after deglaciation is not completed yet. In addition, the results of the diversity study show that the diversity of the methanotrophic community at the younger, recently deglaciated site P5 is poorer than the diversity of the community retrieved from the LIA moraine. This was indicated by successful amplification of partial pmoA genes, which code for a subunit of a key enzyme involved in methane oxidation. Methane consumption was not detected in younger samples, despite the presence of high-affinity methanotrophs in all samples. Soil variables revealed poor soil development, and incubation experiments showed methane consumption rates of 2.14 nmol CH 4 day −1 g soil −1 at 22 ☌ and 1.24 nmol CH 4 day −1 g soil −1 at 10 ☌ in the LIA terminal moraine. Soil samples from this chronosequence were examined in order to elucidate main soil variables, as well as the activity and community structure of methanotrophs, a group of microorganisms involved in regulation of atmospheric methane. The Mittivakkat Gletscher has receded since the end of the Little Ice Age (LIA about AD 1850) and has left behind a series of deposits of decreasing age concurrently with its recession. We report on a study from the Mittivakkat Gletscher forefield in Southeast Greenland with special focus on methanotrophy in relation to exposure time to the atmosphere. Consequently, glaciers retreat and ice-covered areas become exposed. Increasing global annual temperature leads to massive loss of ice cover worldwide. Given the current state of knowledge, we propose that future research directions focused on a spatial approach should specifically address cross-scale hypotheses using statistics and simulations designed for nested hierarchies these analyses will benefit from geographic extension of treeline research. In recent years, both lines of research have been motivated greatly by global climate change. However, treeline research today also includes a rich literature that seeks local, landscape-scale causes of treelines and reasons why treelines vary so widely in three-dimensional patterns from one location to the next, and this approach and some of its consequences are elaborated here. A continuing, fundamental emphasis has centered on seeking the general cause of mountain treelines, thus seeking an answer to the question, “What causes treeline?” with a primary emphasis on searching for ecophysiological mechanisms of low-temperature limitation for tree growth and regeneration. The questions treeline researchers have raised and continue to raise have undoubtedly directed the current state of knowledge. The purpose of this paper is to examine aspects of the epistemology of mountain treeline research-that is, to investigate how knowledge on treelines has been acquired and the changes in knowledge acquisition over time, through a review of fundamental questions and approaches. For over 100 years, mountain treelines have been the subject of varied research endeavors and remain a strong area of investigation.
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