Research progresses in carbon budget and carbon cycle of the coastal salt marshes in China

Due to its higher primary productivities and lower carbon decomposition rates,the coastal salt marsh can be as an efficient sink to reduce global warming by sequestering carbon.In recent years,the researches on the function of coastal salt marshes on global climate change have been paid more attention.As an important part of global carbon budget,the research on carbon cycle in the coastal salt marshes will be useful to understand the global carbon cycle and global climate change,and can also provide scientific basis for the use of the coastal salt marshes as a carbon sink to reduce carbon emission.The distribution of the Chinese coastal salt marshes is widespread,and it plays an important role in global change.In this paper,the research progresses on carbon budget and carbon cycle of the coastal salt marshes in China were analyzed and summarized from five aspects,i.e.,the observation methods of carbon cycle,processes and characteristics of carbon budget and cycle,carbon pools and their influencing factors,input and output of gaseous carbon,and the tidal effect on coastal salt marsh carbon budget.The results suggested that carbon cycle in the coastal salt marshes included outer cycle(i.e.,carbon input and output) and inner cycle(i.e.,mineralization and carbon storage).The monitoring methods for each system of the wetland carbon cycle were quite different.The common methods mainly included eddy covariance method,box method and stable isotope method.The primary way of carbon output in the coastal salt marshes was soil and plant respiration releasing CO2 and CH4 to the atmosphere and it was mainly influenced by tidal and soil temperature.Vegetation and soils as the two most important carbon pools for the coastal salt marshes were mainly dependent on vegetation types,invasive alien plants,anthropogenic activities and tidal effect.Besides,tidal effect also was the main factor affecting carbon budget in the coastal salt marshes through direct physical transport.In conclusion,tidal effect was the common and dominant factor affecting both carbon cycle and budget in the coastal salt marshes.Although there have been so many researches on the biogeochemical characteristics of carbon in the coastal salt marshes,but it is deficient in accurately quantifying the carbon sequestration potential of the coastal salt marshes.Thus,there are several suggestions for the future researches on carbon budget and cycle in the coastal salt marshes put forward as follows:(1) to strengthen both the extensive and intensive researches on carbon pools in the coastal salt marshes;(2) to standard the quantization and observation methods of carbon storages and fluxes;(3) to enhance the long-term field observation and laboratory experiments;and(4) to quantify the carbon exchange fluxes between the coastal salt marshes and other adjacent ecosystems.Consequently,the more accurate assessment and long-term monitoring on carbon budget in the coastal salt marshes should be performed before the further understanding of impact of the coastal salt marshes on and its feedback roles in global climate changes,which have important significance to predicting global change and developing the promotion strategy in reserve function of wetland carbon.