Dissolved organic matter (DOM) represents the largest carbon reservoir in aquatic ecosystems. The priming effect (PE) significantly influences the dynamic changes in DOM reservoirs and its exchange across land-ocean aquatic continuum (LOAC) interfaces. Therefore, it plays a crucial role in the transformation, degradation, and carbon cycling of DOM. Various external factors, such as human activities and land use types, continuously affect the direction and intensity of the PE at the LOAC interface.
Recently, Professor Qi Yulin's research group from the Biogeochemical Cycling Research Center of our institute has conducted studies on the degradation patterns of organic carbon at the LOAC interface in the Bohai Rim region under the influence of special events such as rainfall, wastewater discharge, and pollutant release. Through laboratory experiments combined with spectroscopic, chromatographic, mass spectrometric, and isotopic techniques, the group quantified the priming effect of organic carbon in the Haihe River Basin and revealed the changes in the sources, molecular composition, and structural characteristics of organic carbon caused by the PE. The research results indicate that: the PE widely occurs in aquatic system, especially in estuary zone and under the rainfall condition, and the impact of emerging contaminants on the PE cannot be ignored as well. Estuary zone serves an important region for the research of carbon budget imbalance due to its strong PE, while the negative PE in the offshore zone contributes the stable carbon sink in the ocean. During the PE process, DOM tend to shift from humus-like substances to small molecular weight and protein-like substances, and the carbon sources gradually transform from terrestrial to microbial. In addition, the molecular structures also play crucial roles in carbon sequestration in the coastal area. DOM containing carboxylic and heteroatoms functional groups are more sensitive and prefer to be degraded in aquatic system, and humus-like substances contribute to a positive PE while tyrosine can slow down the DOM degradation. Finally, special parameters such as BDOC, AI-mod, Corg/Ntotal, along with the humus-like substances and specific molecular markers can be utilized to track the occurrence of the PE.
Figure 1 Schematic showing the entire research approach of this work, including the sampling area, incubation experiment, sample measurement, and data analysis.
Figure 2: Structure, sources, molecular composition, and degradation patterns of organic carbon under the influence of the PE.
Overall, this study summarizes the compositions, variations, and molecular signatures of DOM during the PE process. At present, the understanding of the river and ocean carbon cycling is not sufficient, and there is a gap between the estimated and measured organic carbon flux. Our data here indicate such a carbon budget imbalance in aquatic system could be partially explained from the perspective of the PE. These findings provide both theoretical and experimental support for carbon turnover in river-ocean system and give scientific insights to understand the carbon cycling in the coastal area.
The related study has been published in the internationally renowned environmental journal Environmental Science & Technology. Yao Wenrui, a master student, is the first author of the paper, with Professor Qi Yulin serving as the corresponding author. Professors Fu Pingqing, Li Siliang, Liu Xueyan, and Researcher Zhang Zhiyang from the Yantai Institute of Coastal Zone Research jointly supervised this study. The research was supported by the National Natural Science Foundation of China (Grants 42221001 and 42277456).
About the paper: Wenrui Yao, Yuanyuan Dong, Yulin Qi*, Yufu Han, Jinfeng Ge, Dietrich A. Volmer, Zhiyang Zhang, Xue-Yan Liu, Si-Liang Li, Pingqing Fu. Tracking the changes of DOM composition, transformation and cycling mechanism triggered by priming effect: insights from incubation experiments. Environmental Science & Technology. https://pubs.acs.org/doi/10.1021/acs.est.4c03784.
