ABSTRACT
As a unique hydrological characteristic, the tidal action can strongly affect carbon balance in a salt marsh despite their short duration. Using the eddy covariance technique, we measured the net ecosystem CO2 exchange (NEE) and its environmental factors and tidal change over a salt marsh in the Yellow River Delta. It aimed to investigate the effect of tidal process and drying and wetting cycles induced by tides on NEE. The results showed that the tidal process promoted the daytime CO2 uptake, but it didn't clearly affect the nighttime CO2 release. Tidal inundation was a major factor influencing daytime NEE. The diurnal change of NEE showed a distinct U-shaped curve on both drought and wet stages, but not with substantial variation in its amplitude during the drought stage. The drying and wetting cycles enhanced the absorption of daytime CO2. Under drought stage, the mean of the maximum photosynthetic rate (Amax), apparent quantum yield (α) and ecosystem respiration (Reco) were higher than those in wet stage. In addition, the drying and wetting cycles suppressed the nighttime CO2 release from the salt marsh but increased its temperature sensitivity.
Subject(s)
Carbon Dioxide , Ecosystem , Wetlands , China , Rivers , Tidal WavesABSTRACT
Soil respiration (Rs) is the main efflux of carbon pool from soil to atmosphere. Increasing Rs caused by rising temperature can result in significant change in the global carbon balance. Global mean land-surface temperature is predicted to rise by 0.3-4.8 â by the end of 21 century. Therefore, how Rs responds to simulated experimental warming in the natural field is one of the critical issues in global change research. Here, we reviewed the response characteristics of Rs to simulated warming under different temporal and spatial patterns. Experimental warming can increase Rs at the short time scale, but there was no uniform law in the long-term warming experiments, and there were differences among different ecosystems. This paper also reviewed the mechanism underlying the simulated warming response of Rs. Warming can directly affect Rs, and warming can also affect Rs indirectly by affecting the environmental factors (e.g., soil water, soil salt, soil physical and che-mical properties), and the regulation of biological factors (e.g., photosynthesis, litter decomposition). Furthermore, we synthesized the formation mechanism of adaptability of Rs to warming, including adaptability of microbes, roots and enzymes to warming, water restriction, and regulation by excessive nitrogen and the substrate supply. Finally, the future research directions were proposed. The study of micro-ecosystem of rhizosphere, characteristics and mechanism of Rs under asymmetric warming should be strengthened. Also, more attention should be paid to the measurement of Rs in typical phenological periods and typical weather in different seasons. The research network of Rs response to simulated warming should be constructed for networking test.
Subject(s)
Carbon Cycle , Climate Change , Ecosystem , Soil/chemistry , Atmosphere , Carbon , Carbon Dioxide , Nitrogen , Photosynthesis , Plant Roots , Rhizosphere , Seasons , Temperature , WaterABSTRACT
Using the Li-8150 multichannel automatic soil CO2 efflux system, soil respiration was measured continuously over a one-year period in a coastal wetland in the Yellow River Delta, China. Environmental and biological factors were measured simultaneously, including temperature, soil water content, aboveground biomass and leaf area index. The results showed that the diurnal variation of soil respiration presented a single-peak curve, but it appeared as multiple peaks when disturbed by soil freezing and surface flooding. Soil respiration showed obvious seasonal dynamics and a single peak curve. The average annual soil respiration was 0.85 µmol CO2·m-2·s-1, and the mean soil respiration rate was 1.22 µmol CO2·m-2·s-1 during the growing season. On one-year scale, soil temperature was a major factor influencing soil respiration in the coastal wetland, which explained 87.5% of the variation in soil respiration. On the growing season scale, soil water content and leaf area index accounted for 85% of the seasonal variation of soil respiration.
