JOURNAL OF NANJING FORESTRY UNIVERSITY ›› 2020, Vol. 44 ›› Issue (4): 167-175.doi: 10.3969/j.issn.1000-2006.202001021

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Content and vertical distribution of soil labile organic carbons in different land use types in the tidal flat area

XU Menglu1(), WU Wei1, YAN Zhengming1, CAO Guohua2, SHEN Caiqin2, RUAN Honghua1()   

  1. 1.Co -Innovation Center for the Sustainable Forestry in Southern China, College of Biology and the Environment, Nanjing Forestry University, Nanjing 210037, China
    2.Dongtai City Forest Farm of Jiangsu Province, Dongtai 224200, China
  • Received:2020-01-08 Revised:2020-03-16 Online:2020-07-22 Published:2020-08-13
  • Contact: RUAN Honghua E-mail:xml@njfu.edu.cn;hhruan@njfu.edu.cn

Abstract: Objective

Coastal tidal flats have a high carbon sequestration potential, which may contribute to alleviating the global greenhouse effect.However, they are being reclaimed at an increasing rate because they provide important land for relieving population pressure, promoting regional economic growth, and ensuring food safety. With the largest area of tidal flats in China, a long history of coastal reclamation activities has been existed in Jiangsu Province. Tidal flat reclamation practices change the basic physical and chemical properties of soil, and accelerate changes in the soil organic carbon pool, especially the active organic carbon, which is sensitive to reclamation activities. Meanwhile, the active organic carbon components can be used to characterize the short term changes in the soil organic carbon pool. As such, studying the differences in soil organic carbon and its active components under different land use types in reclamation areas may provide a reference for the rational development and utilization of coastal wetlands. It is also important to elucidate the role of soil carbon in coastal reclamation areas.

Method

A bare tidal flat, paddy field, and area of upland and forest land in the reclamation area in Dongtai, Jiangsu were selected as research sites.At each site, soil samples were collected from different soil depth layers in order to analyze the variations in dissolved organic carbon (DOC), microbial biomass carbon (MBC) and easily oxidized carbon (EOC) under the different land use types.

Result

①With the increase of soil depth, the DOC content increased in soil depths of 0—40 cm soils, but decreased in soil depths of 40—100 cm.Furthermore, the MBC and EOC content decreased significantly in soil depths of 0—100 cm across the four land use types. When tested in the same soil layer, the DOC content of the bared tidal flat soil was significantly larger than that of the soil in the other three land use types. However, the MBC and EOC content descended in the following order: forest land, paddy field, upland,bared tidal flat soil.②With the increase of soil depth, the ratio of DOC to SOC and the ratio of MBC to SOC content followed the same trend in the forest land, the upland and the paddy field; first they increased in soil of 0—40 cm depth, then decreased in soil of 40—100 cm depth. However, there were no obvious changes in the bare tidal flat soil,and the ratio of EOC to SOC content did not show the same trend with the increase of soil depth. Furthermore, in soil depths of 0—40 cm, the ratios of DOC to SOC, MBC to SOC content, and EOC to SOC content in the forest land, upland and paddy field were significantly lower than those in the bared tidal flat. ③The MBC and EOC contents were significantly correlated, and were both significantly correlated with SOC, TN content and pH. However, the correlations with EC and TP content were not significant, and DOC content was not correlated with any of the indices.

Conclusion

Our results indicate that agricultural cultivation measures significantly increased the content of soil organic carbon and its active components, and improved the stability of the soil organic carbon.The forest land and paddy field had more soil active organic carbon than the other sites tested. The forest land in particular had accumulated the most soil organic carbon, indicating that the types of land may play an important role as carbon sinks in the coastal area of Jiangsu, southeastern China.Reclamation had the best effect on decreasing soil pH at the paddy field site, and as the main farming activity which is practiced at the early stages of reclaiming land fromtidal flats, this could quickly lead to desalination and decalcification of the land. In conclusion, the development and utilization of tidal flats can significantly change the natural pathway and models of the carbon cycles in the coastal wet lands, and the impacts of land use designation on the soil carbon cycle during reclamation should be fully considered in future research.

Key words: dissolved organic carbon, microbial biomass carbon, easily oxidized carbon, land use type, reclamation

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