No abstract

Coastal scientists postulate that salt marshes are significantly affected by dynamics of global climate. However, few studies have explicitly proposed a perspective that regards salt marshes as potential indicators of climate change. This review article evaluates the possibility of salt marshes as indicators of global climate change, focusing upon three major aspects: sedimentary, vegetation, and biogeochemical dynamics. The previous literature concerned with these aspects commonly argues that the primary impact of climate change on salt marshes occurs via sea‐level variations, because hydrologic fluctuations regulate the frequency, duration, and depth of over‐marsh flooding events. Sedimentary, floristic, and biogeochemical dynamics prove to be significantly influenced by sea‐level changes regardless of climate zones, and hence, undoubtedly possess a potential for indicating climate signatures. However, where plant‐plant interactions such as facilitation and competition are important, vegetation dynamics in salt marshes may not be an immediate, sole function of sea‐level and climate variations. Also, specifically in the field of salt marsh biogeochemistry, enough long‐term data have not been collected to convincingly conclude that biogeochemistry is a useful indicator of climate change. Therefore, while this review is concerned mainly with the possibility of salt marshes as indicators of climate change, their suitability or usefulness is a different matter to be resolved through further data collection and discussion in future investigations.

Atmospheric CO 2 concentrations have increased exponentially over the last century and, if continued, are expected to have significant effects on plants and soil. In this study, we investigated the effects of elevated CO 2 on the growth of Pinus densiflora seedling and microbial activity in soil. Three-year-old pine seedlings were exposed to ambient as well as elevated levels of CO 2 (380 and 760 ppmv, respectively). Growth rates and C:N ratios of the pine seedlings were also determined. Dissolved organic carbon content, phenolic compound content, and microbial activity were measured in bulk soil and rhizosphere soil. The results show that elevated CO 2 significantly increased the root dry weight of pine seedling. In addition, overall N content decreased, which increased the C:N ratio in pine needles. Elevated CO 2 decreased soil moisture, nitrate concentration, and the concentration of soil phenolic compounds. In contrast, soil enzymatic activities were increased in rhizosphere soil, including β-glucosidase, N-acetylglucosaminidase and phosphatase enzyme activities. In conclusion, elevated CO 2 concentrations caused distinct changes in soil chemistry and microbiology.

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.