Effects of elevated CO₂on organic matter decomposition capacities and community structure of sulfate-reducing bacteria in salt marsh sediment

Abstract

Increasing atmospheric CO 2 affects the soil carbon cycle by influencing microbial activity and the carbon pool. In this study, the effects of elevated CO 2 on extracellular enzyme activities (EEA; β-glucosidase, N-acetylglucosaminidase, aminopeptidase) in salt marsh sediment vegetated with Suaeda japonica were assessed under ambient atmospheric CO 2 concentration (380 ppm) or elevated CO 2 concentration (760 ppm) conditions. Additionally, the community structure of sulfate-reducing bacteria (SRB) was analyzed via terminal restriction fragments length polymorphism (T-RFLP). Sediment with S. japonica samples were collected from the Hwangsando intertidal flat in May 2005, and placed in small pots (diameter 6 cm, height 10 cm). The pots were incubated for 60 days in a growth chamber under two different CO 2 concentration conditions. Sediment samples for all measurements were subdivided into two parts: surface (0-2 cm) and rhizome (4-6 cm) soils. No significant differences were detected in EEA with different CO 2 treatments in the surface and rhizome soils. However, the ratio of β-glucosidase activity to N-acetylglucosaminidase activity in rhizome soil was significantly lower (P < 0.01) at 760 ppm CO 2 than at 380 ppm CO 2 , thereby suggesting that the contribution of fungi to the decomposition of soil organic matter might in some cases prove larger than that of bacteria. Community structures of SRB were separated according to different CO 2 treatments, suggesting that elevated CO 2 may affect the carbon and sulfur cycle in salt marshes.

Impact of Elevated Atmospheric CO2 in Spartina maritima Rhizosphere Extracellular Enzymatic Activities

“…In addition, an increase in DOC concentrations can also lead to an enhancement of the activity of several extracellular enzymatic activities and, subsequently, nutrient mineralization [55]. Generally, rhizospheres accumulate higher labile carbon amounts than bulk sediments due to photosynthesis products (including extracellular enzymes) released through exudation into the rhizosphere [10,56]. Beyond the potentially enhanced production of extracellular enzymes by the plant, this DOC increase in the rhizosphere additionally enhances microbial activities, breaking the typical C limitation [10].…”

“…Generally, rhizospheres accumulate higher labile carbon amounts than bulk sediments due to photosynthesis products (including extracellular enzymes) released through exudation into the rhizosphere [10,56]. Beyond the potentially enhanced production of extracellular enzymes by the plant, this DOC increase in the rhizosphere additionally enhances microbial activities, breaking the typical C limitation [10]. Another key factor in regulating sediment carbon pools under elevated CO 2 is nitrogen concentration.…”

“…Water 2023, 15, 2667 2 of 15 due to an increase in starch content and reduction in N-compounds [8], leaf litter chemistry did not show changes under elevated CO 2 [9]. Therefore, the predicted effects of high CO 2 concentrations on soils will probably be due to interactions between root and microbial communities, rather than by differences in plant litter chemistry [10].…”

“…Changes in primary production in these estuarine ecosystems will have inevitable consequences, not only in the salt marsh community itself but also in the adjacent areas [10]. About 30-60% of the net photosynthetic C is allocated in the root system, from which about 40-90% enters the sediments through rhizodeposition [13,21,29,30].…”