Linkages between the molecular composition of dissolved organic matter and soil microbial community in a boreal forest during freeze–thaw cycles

Abstract

Soil dissolved organic matter (DOM) plays a vital role in biogeochemical processes. Global warming leads to increased freeze–thaw cycles (FTCs) in boreal forest soils, which can change DOM production and consumption. However, the interactions between the chemical composition of DOM molecules and the microbial communities that drive C decomposition in the context of freeze–thaw are poorly understood. Here, a FTCs incubation experiment was conducted. Combined with pyrolysis gas chromatography–mass spectrometry and high-throughput sequencing techniques, the relationships between DOM chemodiversity and microbial community structure were assessed. Results indicated that both low-frequency (2FTCs) and high-frequency freeze–thaw cycles (6FTCs) significantly increased soil dissolved organic carbon (DOC) contents in the surface (0–10 cm) and subsurface (50–60 cm) soil layers. In the topsoil, FTCs significantly reduced the relative abundance of aromatic compounds, but increased the relative proportions of alkanes, phenols, fatty acid methyl esters (Me) and polysaccharides in the DOM. In the subsuface soil layer, only the relative abundance of Me in the 6FTCs treatment increased significantly. The response of bacterial communities to FTCs was more sensitive than that of fungi, among which only the relative abundance of Gammaproteobacteria increased by FTCs. Moreover, the relative abundance of these taxa was positively correlated with the increment of DOC. Co-occurrence networks confirmed DOM-bacterial interactions, implying that specific microorganisms degrade specific substrates. At class level, Gammaproteobacteria were significantly positively correlated with labile C (polysaccharides and alkanes), whereas other bacterial classes such as Actinobacteria, Alphaproteobacteria, and Thermoleophilia were significantly positively correlated with aromatic compounds in the topsoil. Collectively, FTCs tended to activate DOM and enhance its biodegradability of DOM, potentially hampering DOC accumulation and C sequestration. These findings highlight the potential of DOM molecular mechanisms to regulate the functional states of soil bacterial communities under increased FTCs.

From green to brown: two decades of darkening coastal water in the Gulf of Riga, the Baltic Sea

“…The effect of FTC on DOM mobilisation has been highlighted also in more recent studies, (e.g., Speetjens et al, 2022;Yang et al, 2023). Moreover, these studies suggest that the altered composition of DOM, influenced by changes in soil microbial activity due to freeze-thaw cycles (Feng et al, 2007;Yang et al, 2023), has the potential to shift the optical properties of DOM and increase its humification index (Speetjens et al, 2022). This phenomenon underscores the intricate relationship between climate-induced freeze-thaw dynamics and the composition of dissolved organic matter, most likely impacting the water optical properties observed in the Gulf of Riga over the past two decades.…”

“…Furthermore, the greatest FTC effect has been observed at mild frost conditions. The effect of FTC on DOM mobilisation has been highlighted also in more recent studies, (e.g., Speetjens et al, 2022;Yang et al, 2023). Moreover, these studies suggest that the altered composition of DOM, influenced by changes in soil microbial activity due to freeze-thaw cycles (Feng et al, 2007;Yang et al, 2023), has the potential to shift the optical properties of DOM and increase its humification index (Speetjens et al, 2022).…”

Boreal moss-microbe interactions are revealed through metagenome assembly of novel bacterial species

“…F420 is a co-enzyme that is costly to synthesize; nevertheless, Ney et al [89] found that it was commonly synthesized by aerobic bacteria. Meanwhile, coenzyme M is found in methanotrophic archaea and used by bacteria in metabolizing of different substrates, for example alkenes [90], which are found in boreal forest soils [91]. More interestingly, alkenes are known to be produced by bacteria associated with lichens [92].…”

Table_1.xlsx

“…The effect of FTC on DOM mobilisation has been highlighted also in more recent studies, (e.g., Speetjens et al, 2022;Yang et al, 2023). Moreover, these studies suggest that the altered composition of DOM, influenced by changes in soil microbial activity due to freeze-thaw cycles (Feng et al, 2007;Yang et al, 2023), has the potential to shift the optical properties of DOM and increase its humification index (Speetjens et al, 2022). This phenomenon underscores the intricate relationship between climate-induced freeze-thaw dynamics and the composition of dissolved organic matter, most likely impacting the water optical properties observed in the Gulf of Riga over the past two decades.…”

“…Furthermore, the greatest FTC effect has been observed at mild frost conditions. The effect of FTC on DOM mobilisation has been highlighted also in more recent studies, (e.g., Speetjens et al, 2022;Yang et al, 2023). Moreover, these studies suggest that the altered composition of DOM, influenced by changes in soil microbial activity due to freeze-thaw cycles (Feng et al, 2007;Yang et al, 2023), has the potential to shift the optical properties of DOM and increase its humification index (Speetjens et al, 2022).…”