Contributed by Katarzyna Marcisz
How do testate amoeba communities respond to fire? How does burning affect this group of microorganisms and the environment where they occur in exceptionally high abundance – Sphagnum peatlands?
Answering these questions is crucial, as fire has a significant impact on peatland ecosystems. Peatlands are an important carbon pool, containing 1/3 of the global soil carbon (Parish et al., 2008). It has been shown that even a moderate drop in water table influences vegetation composition in peatlands and disturbs carbon accumulation (Kettridge et al., 2015). Peatlands experiencing drying are also more often ignited, and the frequency of fire and the extent of peat fires often increases (Turetsky et al., 2015). Peat fires can be deceptive: peat often burns by smouldering combustion that can persist for long periods of time rather than by more visible large fires as in the case of forests. The consequence is nevertheless that this burning affects the peat carbon stock.
The relationships between testate amoebae and fire are still quite a mystery. In studies from North America, Clifford and Booth (2013) and Clifford and Booth (2015) revealed peaks in microscopic charcoal accumulation rates that corresponded to drought periods as reconstructed with the use of a testate amoeba-based transfer function. However, these charcoal peaks were likely primarily derived from regional, upland fires rather than fire on the peatlands themselves. The effects of peatland fires on testate amoeba communities, and the response of individual species, have not been adequately examined. For example, Trigonopyxis arcula was suggested to be a possible fire indicator by Warner (1990) and Turner et al. (2014), and Hyalosphenia subflava was correlated with fire in the work by Turner and Swindles (2012). However, Turner et al. (2014) later suggested it should rather not be regarded as a reliable local fire indicator.
Recently the relationships between individual testate amoeba species and fire were examined in a study by Marcisz et al. (2015), which was conducted within the RE-FIRE Sciex project (http://www.swissuniversities.ch/en/topics/sciex) and CLIMPEAT project (www.climpeat.pl), in northern Poland at a beautiful Linje mire (Fig. 1).
The analyses revealed that the peatland was wet before the onset of the Little Ice Age (ca. AD 1300-1850), when a rapid drop in water table occurred. Drying was also correlated with human migrations in the region, and with changing agricultural practices. Anthropogenic fires preceded hydrological changes on the mire; the response of the mire recorded as hydrological changes towards drier conditions was delayed in relation to the surrounding fire-related vegetation changes.
Individual testate amoeba species were correlated with macroscopic charcoal particles recorded in the peat profile (Fig. 2). Testate amoebae indirectly responded to vegetation removal in the catchment driven by fire. While all the wet indicator species were negatively correlated with fire activity, most of the dry indicators (as well as Arcella discoides) were positively correlated. Although no explicit local fire indicator was found, from all the testate amoeba species Nebela tincta s.l. had the highest positive correlation recorded (Fig. 3)…..
Additional work is needed to better quantify the relationships between testate amoebae, hydrological change, and fire, and experimental work is needed to assess the causes of these relationships. Such work may provide insight into the underlying processes controlling microbial community responses to fire and hydrological change. However, fire activity likely affects peatland microbial food webs, both directly (combustion of surface Sphagnum and peat layers) and indirectly (surrounding vegetation and surface run-off changes).
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