## 1 Introduction
Among them, the I form of RubisCO is the most dominant, whose large subunit contains catalytically active amino acid residues encoded by the \(cbbL\) genes [22]. In recent years, RubisCO and the encoded \(cbbL\) genes have been widely valued and studied in aquatic, terrestrial, and wetland ecosystems. [PERSON] et al. (2013) studied the community structure and diversity of the autotrophic bacteria in agricultural soil and paddy systems, and indicated the significant effects of different land use, and also showed that the synthesis rates of soil organic carbon ranged from 0.0134 to 0.103 g\(\cdot\)C\(\cdot\)m\({}^{-2}\)-day\({}^{-1}\)[23]. [PERSON] et al. (2017) showed the different amounts of RubisCO activity in the rhizospheric sediments of Poyang Lake, as well as the significant and positive correlations between RubisCO activity and organic carbon fractions [24]. [PERSON] et al. (2014) also showed the significantly higher \({}^{14}\)C-OC in surface soil than in subsurface soil after 80 days of \({}^{14}\)C-CO\({}_{2}\) incubation, and the wetland sediments presented notably higher CO\({}_{2}\) fixation rates than upland sediments [25]. Thus, the CO\({}_{2}\) fixation process and RubisCO activity are very sensitive to surroundings and soil properties, and wetland sediments potentially present certain advantages. From the previous reports, we deduced that exogenous carbon addition could also have certain effects on the RubisCO activity and composition of _cbbl_. gene-containing bacterial communities. Based on the chemical stability and soil density, OM can be separated into light fraction and heavy fraction organic matter (LFOM and HFOM). LFOM, mainly the undecomposed or partly decomposed residues of animals, plants, and microbes, basically accounts for about 1-5% and is sensitive to land use and climate changes [26]. HFOM is the dominant component of the OM reservoir pool in wetland sediment, accounting for more than 60% of total amount [27]. It presents a complex chemical structure and stable physico-chemical properties, and is not easily affected by biological activities or environmental changes [28]. Several studies have expounded the effect of land change, upland types, different rhizosphere sediments, and human activities on the dynamic changes of LFOM and HFOM [26; 27; 28], while the effect of exogenous carbon addition on the OM fractions is still not clear. Although the global wetland area only accounts for 4-6% of the land area, it contains more than 30% of the global carbon reserves, and plays an important role in the process of the land and global carbon cycle. The impacts of exogenous carbon degradation on carbon composition and contents, abundance, and composition of cbbl gene-containing bacterial communities can directly relate to the carbon cycle in wetlands, thus reducing the carbon fixation potential. To explore the detailed affecting dynamics and internal mechanism of exogenous carbon addition, this experimental research is conducted. As the most typical constituent of small-molecule OM, glucose is selected as the representative. We designed the control experiment of glucose addition into wetland rhizosphere sediments and bulk sediments, and conducted the subsequent study. This study aims to (1) analyze the effects of glucose addition on LFOM, HFOM, as well as the changes of typical chemical bonds in LFOM, (2) present the changes of RubisCO activity and its relations with _cbbl_ gene abundance, and (3) show the composition characteristics of _cbbl_-encoded bacteria during the glucose degradation. This study firstly revealed the responses of the CO\({}_{2}\) assimilation process to the glucose addition in wetland, which is of great significance to clarify the soil carbon cycle in wetland ecosystem.