Contribution of microbial photosynthesis to peatland carbon uptake along a latitudinal gradient

Abstract

1. Phototrophic microbes, also known as micro-algae, display a high abundance in many terrestrial surface soils. They contribute to atmospheric carbon dioxide fluxes through their photosynthesis, and thus regulate climate similar to plants.However, microbial photosynthesis remains overlooked in most terrestrial ecosystems. Here, we hypothesise that phototrophic microbes significantly contribute to peatland C uptake, unless environmental conditions limit their development and their photosynthetic activity.2. To test our hypothesis, we studied phototrophic microbial communities in five peatlands distributed along a latitudinal gradient in Europe. By means of metabarcoding, microscopy and cytometry analyses, as well as measures of photosynthesis, we investigated the diversity, absolute abundance and photosynthetic rates of the phototrophic microbial communities.3. We identified 351 photosynthetic prokaryotic and eukaryotic operational taxonomic units (OTUs) across the five peatlands. We found that water availability and plant composition were important determinants of the composition and the structure of phototrophic microbial communities. Despite environmental shifts in community structure and composition, we showed that microbial C fixation rates remained similar along the latitudinal gradient. Our results further revealed that phototrophic microbes accounted for approximately 10% of peatland C uptake. 4. Synthesis. Our findings show that phototrophic microbes are extremely diverse and abundant in peatlands. While species turnover with environmental conditions, microbial photosynthesis similarly contributed to peatland C uptake at all latitudes. We estimate that phototrophic microbes take up around 75 MT CO 2 per year in northern peatlands. This amount roughly equals the magnitude of | 3425

Contribution of soil algae to the global carbon cycle

“…The positive correlation between soil algal NPP and increasing vegetation cover might be seen as counterintuitive given that plant canopy reduces the light availability at the soil surface. However, most microscopic algae show optimal photosynthesis at low light intensity (Ritchie & Larkum, 2012; Hamard et al ., 2021a) by optimizing light harvesting at low light flux (Perrine et al ., 2012). Given the positive relationship between total microbial abundance and metabolic rates in soils (Johnston & Sibly, 2018), our results further presume a simultaneous increase in soil algal abundance and productivity with increasing environmental favorability, which corroborates previous findings in aquatic systems (Y. Liang et al ., 2017).…”

“…Despite their apparent global distribution, our understanding of the ecological preferences of soil algae across broad spatial scales remains limited. Though some previous work has suggested that soil moisture availability is a key driver of soil algal net primary productivity (NPP) (Brostoff et al, 2005;Yoshitake et al, 2010;Hamard et al, 2021a,b), other studies have highlighted the importance of temperature (Shimmel & Darley, 1985;Dettweiler-Robinson et al, 2018) or plant community composition (Hamard et al, 2021a), and it remains unclear how predictable soil algal NPP is at larger spatial scales. As a result, quantitative information on soil algal C fixation remains mostly restricted to drylands (Rodriguez-Caballero et al, 2018) and is not readily available at the global scale.…”

Peatland microhabitat heterogeneity drives phototrophic microbe distribution and photosynthetic activity

“…In total, we identified 129 phototrophic OTUs distributed in nine phyla. This richness is lower than the one found in peatland lawns along a 3000 km latitudinal gradient (351 OTUs and 11 phyla with 16S/18S metabarcoding; Hamard et al ., 2021) or than the one found in a peatland along a gradient of drainage (794 OTUs with 18S metabarcoding; Heger et al ., 2018). The 23S metabarcoding analyses should perform better than the 18S or 16S analyses to reveal the presence of phototrophic OTUs (Marcelino and Verbruggen, 2016).…”

“…organisms combining photoautotrophy and heterotrophy such as some Ciliophora, Lobosa, many Alphaproteobacteria or Cyanobacteria), or photoheterotrophs species (e.g. Chloroflexia) (Jassey et al ., 2015; Nowicka and Kruk, 2016; Hamard et al ., 2021). Only a handful studies suggest that phototrophic microbes fix significant amounts of atmospheric C in northern peatlands (Goldsborough and Robinson, 1996; Gilbert et al ., 1998b; Wyatt et al ., 2012; Jassey et al ., 2015; Hamard et al ., 2021).…”

“…Phototrophic microbes are very abundant in northern peatlands (Hamard et al ., 2021) where the dominant plants, Sphagnum mosses, provide a suitable habitat for microbial communities (Gilbert and Mitchell, 2006; Bragina et al ., 2012), and moist conditions foster phototrophic growth (Starks et al ., 1981). Phototrophic microbes live either freely in pore water or in Sphagnum dead cells (Gilbert et al ., 1998b) and show a tremendous diversity of taxa and life styles (Gilbert and Mitchell, 2006; Lara et al ., 2011; Hamard et al ., 2021). Not all phototrophic microbes in peatlands are strict autotrophs.…”