Spatial and temporal variations in salt marsh microorganisms of the Wadden Sea

Abstract

Salt marshes exist at the interface of the marine and the terrestrial system. Shore height differences and associated variations in inundation frequency result in altered abiotic conditions, plant communities, and resource input into the belowground system. These factors result in three unique zones, the upper salt marsh (USM), the lower salt marsh (LSM), and the pioneer zone (PZ). Marine detritus, such as micro‐ and macroalgae, is typically flushed into the PZ daily, with storm surges moving both salt marsh detritus and marine detritus into higher salt marsh zones. Microbial assemblages are essential for the decomposition of organic matter and have been shown to sensitively respond to changes in abiotic conditions such as oxygen supply and salinity. However, temporal and spatial dynamics of microbial communities of Wadden Sea salt marshes received little attention. We investigated the dynamics of soil microbial communities across horizontal (USM, LSM, and PZ), vertical (0–5 and 5–10‐cm sediment depth), and temporal (spring, summer, and autumn) scales in the Wadden Sea salt marsh of the European North Atlantic coast using phospholipid fatty acid (PLFA) analysis. Our results show strong spatial dynamics both among salt marsh zones and between sediment depths, but temporal dynamics to be only minor. Despite varying in space and time, PLFA markers indicated that bacteria generally were the dominant microbial group across salt marsh zones and seasons, however, their dominance was most pronounced in the USM, whereas fungal biomass peaked in the LSM and algal biomass in the PZ. Only algal markers and the stress marker monounsaturated to saturated fatty acid ratio responded to seasonality. Overall, therefore, the results indicate remarkable temporal stability of salt marsh microbial communities despite strong variability in abiotic factors.

The structure of coastal invertebrate communities and their temporal and spatial dynamics

“…However, it declined from the USM to the LSM to the PZ, suggesting that the use of plant-associated resources decreases with decreasing shore height supporting our first hypothesis. These findings are in line with the decline in plant marker PLFAs in soil with decreasing shore height reported by Rinke et al (2022). However, plant biomarker NLFA concentrations in consumers also varied with season.…”

“…Although being generally high across salt marsh zones and seasons, averaging 30.7 % of total marker NLFAs (excluding unspecific NLFAs), bacterial NLFA marker concentration of soil animals was highest in the PZ, implying that bacteria-associated resources increase with inundation frequency. This contrasts the results of Mueller et al (2020) suggesting that soil bacteria density declines at lower shore height, but is conform to earlier findings that generally bacteria dominate the decomposer system in salt marsh soils in particular in the PZ , Rinke et al 2022. Although being generally high, bacterial NLFA marker concentration in each zone varied with season indicating changes in bacterial prey with season.…”

“…Contrasting the general pattern of increased channelling of bacterial resources with decreasing shore hight, the bacterial NLFA marker declined at lower elevations in Amischa sp. and Ochthebius sp., suggesting that the access of bacterial resources in these species declines with inundation frequency, which is consistent with changes in bacterial PLFAs across salt marsh zones (Rinke et al 2022). Presumably, these comparatively large species are more sensitive to removal of litter due to frequent inundations, which detrimentally affects their access to bacterial resources.…”

“…It was highest in October and about 50% lower in April and July, suggesting maximum channelling of fungi to higher trophic levels in autumn. This contrasts low fungal marker PLFAs in soil of the USM and LSM in autumn as reported by Rinke et al (2022), but coincides with the peak of dead organic matter of salt marsh plants in autumn , likely boosting saprotrophic fungi . Therefore, increased channelling of fungi in autumn likely reflects the input of plant litter material with associated saprotrophic fungi contributing to the predominant use of autochthonous resources by the salt marsh food web.…”

“…Contrasting the overall uniform use of fungal resources across salt marsh zones, fungal NLFA marker concentrations declined with decreasing shore height in Mesostigmata, whereas in Amischa sp., Staphylinidae larvae and Ochthebius sp. fungal NLFA marker increased in the LSM, matching soil fungal PLFA patterns (Rinke et al 2022).…”