Effects of nitrogen input on carbon cycle and carbon budget in a coastal salt marsh

doi:10.17521/cjpe.2020.0353

Abstract

Abstract:

Coastal salt marshes are an effective blue carbon sink to mitigate climate warming, but their ecosystem stability and carbon sink function are threatened by the large amount of nitrogen input caused by coastal eutrophication. Under the action of regular tides, the high nitrogen content in the coastal waters will have a profound effect on the key processes of carbon cycle such as plant photosynthetic carbon fixation, carbon allocation in plant-soil system, and soil carbon release in the salt marsh. This study reviewed the effects of nitrogen input on plant photosynthetic carbon fixation, carbon allocation in plant-soil system, decomposition of soil organic carbon, formation and release of soil dissolved organic carbon (DOC), and carbon sequestration in the salt marsh. Based on the shortcomings of current research, this review proposed the directions of future research, including the effects of nitrogen input on plant photosynthetic carbon fixation and carbon allocation in plant-soil system, the microbial mechanism of soil organic carbon decomposition, production and lateral exchange of soil DOC, and the potential impact of different forms of nitrogen input on soil carbon sequestration in the salt marsh. Overall, this study aims to improve the understanding of impacts of nitrogen input on the key carbon processes and the mechanisms of carbon sequestration in a salt marsh, and to provide new ideas for assessing the potential changes of carbon pools under the influence of eutrophication of coastal waters in the salt marsh wetlands.

Key words: nitrogen input, carbon cycle, carbon allocation, carbon sink, coastal salt marsh, tidal action

HAN Guang-Xuan, LI Juan-Yong, QU Wen-Di. Effects of nitrogen input on carbon cycle and carbon budget in a coastal salt marsh[J]. Chin J Plant Ecol, 2021, 45(4): 321-333.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2020.0353

https://www.plant-ecology.com/EN/Y2021/V45/I4/321

Figures/Tables 4

Fig. 1 Effect of nitrogen (N) input under tidal action on key processes of carbon (C) cycle in a salt marsh. Periodic tides bring N from nearshore eutrophic water into coastal salt marsh ecosystems, changing the stoichiometric relationship of soil nutrient elements in salt marsh wetland. The exogenous N input could have important impacts on the key processes of carbon cycle, such as photosynthesis and respiration of plants, distribution of photosynthetic products, decomposition of soil organic carbon and loss of dissolved organic carbon (DOC). DIC, dissolved inorganic carbon; POC, particulate organic carbon.

Fig. 2 Effect of nitrogen (N) input on decomposition of soil organic carbon in a salt marsh (adapted from Hester et al., 2018 ). Microbial processes are directly or indirectly affected by N input. Plants mainly absorb NH4+-N, which stimulates plant productivity and the deposition of organic matter from the rhizosphere, thus stimulating the material circulation of rhizosphere and the metabolism of rhizosphere microorganisms. Plant derived carbon input and higher N utilization jointly stimulate microbial heterotrophic respiration, and then stimulate the production and emission of CO2 in aerobic condition. In anaerobic condition, excessive NO3--N is converted into NH4+-N, which will inhibit CH4 oxidation.

Fig. 3 Effect of nitrogen (N) input on production and release of dissolved organic carbon (DOC) in a salt marsh. N input is generally accompanied by DOC input, which affects vegetation growth. It alters DOC content in soil and water through plant litter and microbial biomass, thus also interfering with CO2 and CH4 emissions and DOC output.

Table 1 Effect of nitrogen (N) input on carbon sink function of wetland ecosystems

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