Evaluating the use of dominant microbial consumers (testate amoebae) as indicators of blanket peatland restoration
Introduction
Peatlands represent globally important habitats and carbon stores which are under threat from human activity and climate change (Holden et al., 2004, Charman et al., 2013, Swindles et al., 2015a). They store approximately one third of global soil carbon, whilst covering only approximately 3% of the land and freshwater surface (Holden, 2005). However, human activity has degraded peatlands through drainage and harvesting of peat in many parts of the world including NW Europe, North America, Russia and SE Asia (e.g., Baldock et al., 1984, Holden et al., 2004, Hooijer et al., 2010, Hooijer et al., 2012). This has led to recent efforts to re-wet peatlands in order to restore active peat-forming plant communities and promote carbon sequestration (e.g., Ramchunder et al., 2009, Parry et al., 2014).
Blanket peatlands are found in hyperoceanic regions such as those of northern Europe, Alaska, Newfoundland, Tasmania, New Zealand, South America and Eastern Russia (Gallego-Sala and Prentice, 2012, Parry et al., 2014). There has been much research interest in blanket peatlands as it has been suggested they are at risk of progressive erosion and vegetation change as a result of climate change (Gallego-Sala et al., 2010, Li et al., 2016). In the UK, large areas of blanket peatland have become degraded from the effects of atmospheric pollution (Smart et al., 2010), peat extraction (Cruickshank et al., 1995), artificial drainage (Holden et al., 2006), grazing (Ellis and Tallis, 2001), prescribed burning and wildfire (Davies et al., 2010), afforestation (Wellock et al., 2011), and the construction of buildings and access tracks (Holden, 2005). Since the 1940s, many upland blanket peatlands in the UK have been drained through the excavation of ditches which aimed to lower water-table levels and increase land productivity (Holden et al., 2006). The excavation of ditches in blanket peatlands has driven a series of ecosystem-level changes to biodiversity, hydrology, and carbon sequestration, and in some locations has increased the flux of dissolved organic carbon (DOC) to water courses (Holden et al., 2006, Mitchell and McDonald, 1995, Ramchunder et al., 2012, Parry et al., 2014). To reduce the impacts of such management practices, ditch blocking with dams is now a commonplace restoration technique. The blocking of ditches is thought to lead to shallower water tables in peatlands, which can have positive effects on ecological diversity and carbon sequestration (e.g., Beadle et al., 2015). However, the timescales involved for any effects to become apparent after re-wetting are poorly understood, and the effects may be subtle (e.g., within the boundaries of natural variability). As large-scale field experiments are unlikely to exceed two-five years duration due to the availability of financial resources, bioindicators can be used to detect small changes that may not be apparent in hydrological or biogeochemical data (i.e., instrument-based monitoring).
There have been several studies examining the effects of peatland restoration on different groups of organisms including beetles, rotifers, microcrustaceans and macroinvertebrates (Van Duinen et al., 2003, Van Duinen et al., 2006, Watts et al., 2008, Więcek et al., 2013, Beadle et al., 2015). Testate amoebae are a polyphyletic group of amoeboid protists characterised by the presence of a shell (test), and represent an important component of the soil microbial community. Testate amoebae are dominant microbial consumers in peatlands, representing 5–30% of the total microbial biomass, and can have a major influence on the ecological functioning of peatland ecosystems through nutrient cycling (Gilbert et al., 1998, Mitchell et al., 2003, Jassey et al., 2014). They have also been shown to be sensitive hydrological indicators in peatlands (Charman and Warner, 1992, Tolonen et al., 1994, Swindles et al., 2009, Swindles et al., 2015b, Turner and Swindles, 2012). The response of testate amoebae to peatland restoration has been investigated previously based on analysis of cores of peat accumulated post-restoration (Buttler et al., 1996, Jauhiainen, 2002, Davis and Wilkinson, 2004, Valentine et al., 2013). There have also been some experimental studies examining the response of testate amoebae to hydrological change (e.g., Marcisz et al., 2014a, Marcisz et al., 2014b). However, to date, there have not been any studies on blanket peatlands, and, critically, no time-series investigations of changes in surface testate amoebae before and after management intervention have been carried out relative to control systems. Here we investigate the responses of surface testate amoeba communities to restoration treatments in a UK upland blanket peatland (Migneint, North Wales). We examine changes in community composition, ecology, diversity and use these data to examine their potential as bioindicators of peatland restoration.
We tested the following three hypotheses: [H1] Ditch blocking drives a change in testate amoebae at the community-level. [H2] Key wet-indicator taxa (e.g., wet indicators from the genera Arcella and Archerella) increase in response to restoration. [H3] An increase in the diversity of testate amoebae is observed following restoration reflecting the greater variety of habitats.
Section snippets
Field site
The study was undertaken in part of the Migneint in North Wales (Fig. 1) close to Ffynnon Eidda (52°58′06.35″ N, 3°50′28.67″ W). Under the UK National Vegetation Classification (NVC) (Rodwell, 1991), the peatland is a mix of M19 Calluna vulgaris – Eriophorum vaginatum, and M18 Erica tetralix – Sphagnum papillosum blanket bog. The Migneint has been damaged by drainage, burning, over-grazing and, to a lesser extent, afforestation. Maps compiled by Natural Resource Wales from aerial photography
Results
In total, fifty one testate amoeba taxa were identified from 31,158 individuals (Fig. 3a, Fig. 3b, Fig. 3c). The most commonly occurring testate amoeba taxa at the site include Nebela tincta, Corythion-Trinema type, Euglypha ciliata type, Assulina muscorum and Cryptodifflugia oviformis. The taxa with maximum occurrences include C. oviformis, N. tincta, Corythion-Trinema type, Nebela militaris and Nebela flabellulum (Fig. 3a, Fig. 3b, Fig. 3c). The Shannon diversity of the communities varies
Discussion
Our analysis suggests that although there is high variability between sampling points, we can accept all three hypotheses based on multivariate statistical analysis, the appearance of wet indicators, and changes in community diversity: [H1] Ditch blocking drives a change in testate amoebae at the community-level. Accept: there are clear changes at the community-level at least partly driven by peatland restoration as illustrated by the NMDS, ANOSIM and PERMANOVA results (see Fig. 5, section 3). [H2] Key
Conclusions
We examined the responses of dominant microbial consumers (testate amoebae) to restoration treatments in a UK blanket peatland. We found that both time and treatment had a statistically-significant effect on community composition; however, the testate amoebae communities across the entire site have responded to changing weather conditions over the test period which partially obscures the effect of management. Despite considerable variability in the response of testate amoebae communities to
Acknowledgements
We thank the National Trust for access to the site. The field trials and the hydrological data collected from them were part of a project funded by the UK Government's Department for Environment Food and Rural Affairs (Defra). Further details of the project – SP1202: Investigation of peatland restoration (grip blocking) techniques to achieve best outcomes for methane and greenhouse gas emissions/balance – may be found at: http://goo.gl/MOEV7M.
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2022, Quaternary InternationalCitation Excerpt :Four categories of test construction of testate amoebae (idiosomes, idiosomes + organic, protein, and xenosomes) were distinguished, as described by Mitchell et al. (2007b). High-water table indicators of testate amoebae (Archerella flavum, Hyalosphenia papilio, Cyclopyxis arcelloides type, and Amphitrema wrightianum) (Diaconu et al., 2016; Mazei and Tsyganov, 2006; Swindles et al., 2016), dry indicators (Assulina muscorum, Corythion dubium, and Cryptodifflugia oviformis) (Marcisz et al., 2015; Mazei and Chernyshov, 2011; Warner and Chmielewski, 1992), and an indicator of hydrological instability - Arcella discoides (Lamentowicz et al., 2009; Lamentowicz and Mitchell, 2005a; Łuców et al., 2020; Sullivan and Booth, 2011) were marked on the diagrams. Moreover, the average percentages of testate amoebae determined in the modern samples from hummocks and hollows are summarized in two pie charts.
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2020, GeodermaCitation Excerpt :However, human activities such as agricultural drainage, peat cutting and climate change can lead to widespread peatland drying (Holden et al., 2011; Hooijer et al., 2012; Mpamah et al., 2017). TA have been considered as useful bio-indicators in peatlands and numerous studies have investigated their ecology, biogeography (e.g., Mitchell et al., 2008a,b; Lamentowicz et al., 2013; Payne et al., 2016; Mazei et al., 2017; Qin et al., 2017), and drainage effects on TA in peatlands (Warner and Chmielewski, 1992; Jauhiainen, 2002; Talbot et al., 2010; Chen et al., 2014; Marcisz et al., 2015; Swindles et al., 2016; Koenig et al., 2017). Changes in TA communities and corresponding protozoic Si pools might represent another example for the loss of Si due to human impacts (=anthropogenic desilication).
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Current address: Institute of Integrative Biology, University of Liverpool, L69 7ZB, UK.