Substrate quality overrides soil salinity in mediating microbial respiration in coastal wetlands

Abstract

As productive and essential ecosystems, coastal wetlands have experienced increased environmental impacts such as saltwater intrusion and eutrophication, resulting in significant shifts in microbially mediated ecosystem functions, such as carbon sequestration and nutrient transformations. The soil microbial respiration, a primary process in the transfer of carbon from soil to the atmosphere, is susceptible to environmental changes. However, studies on how salinity affects soil microbial respiration in coastal wetlands have not been fully explored. Soil samples were systematically collected from divergent sampling sites covering medium‐ and extremely‐saline wetlands along a river‐estuary‐coast continuum to investigate mechanisms controlling soil microbial respiration in coastal wetlands. According to the results, the microbial biomass and carbon‐related extracellular enzyme activities were significantly lower in extremely saline (ECe >15 ds m−1, ES) than medium and highly saline soils (ECe <15 ds m−1, MHS) (p < 0.05), indicating a suppressive effect of salinity on soil microbiota. Meanwhile, high‐salinity soils had lower vector length and soil microbial respiration rates, suggesting that soils with low carbon limitation might cause less carbon loss under higher salinity environments. Moreover, it was showed that increased available phosphorus could alleviate microbial carbon limitations. Changes in the microbial functional community demonstrated that the microbial community in favor of metabolic mediates and secondary metabolites substrates (regarded as labile substrates) were more sensitive to salinity. The partial least square path modeling further confirmed that microbial nutrient limitation and microbial biomass contribute more directly to promoting soil microbial respiration. These results have substantial implications for elucidating carbon dynamics in coastal wetlands ecosystems under increased nutrient discharge and sea‐level rise.

Effect of soil flooding and drying on the metabolic pathways of CO2 fixing microorganisms along an elevation gradient in the Three Gorges Reservoir drawdown area

“…The efficiency of CO 2 fixation pathways is determined by pathway kinetics and energy requirements, which are largely influenced by specific enzymes in the metabolic pathways (Li, Song, et al., 2023). Key enzymes in the rTCA cycle, such as 2‐oxoglutarate synthase (EC1.2.7.3) and isocitrate dehydrogenase (EC1.1.1.42), are known to be highly sensitive to oxygen and are predominantly found in anaerobic and microaerobic environments (Berg, 2011).…”

Effects of Land-Use Type and Salinity on Soil Carbon Mineralization in Coastal Areas of Northern Jiangsu Province

“…Both in the early and late stages, βG had an important driving effect on soil C fractions and microbial biomass; the two active C fractions, DOC and MBC, were indispensable for modeling; MBC had a large direct positive effect on CO 2 release (p < 0.001), with path coefficients of 0.41 and 0.40, respectively. The important function of MBC has been previously reported [57,58].…”

“…However, the mere fact that the high-salinity treatment would inhibit soil respiration and decrease the mineralization potential phenomenon does not lead to the conclusion that saline soils favor soil C sequestration. It has been shown that the effect of substrate quality on soil respiration is greater than that of salinity in coastal wetlands [57], and that the ratio of fungal-bacterial growth is lower when the soil C quality is higher [18], which improves the microbial C use efficiency. The results of enzyme stoichiometry (Figure 5) also showed that site W was significantly more C-limited than the other two sites under the 32‰ treatment, which is one point of evidence that soil C mineralization was limited by the substrate.…”