High stability of endogenous dissolved organic matter in a karst aquatic ecosystem
The results of this study show that the Auto-DOM has obvious seasonal variation, indicating that the seasonal impact should be considered in the analysis of the contribution of Auto-DOM in the karst aquatic ecosystem. According to the analysis of the relationship between planktonic bacterial community and CDOM, combined with the analysis of microbial function, it is found that C2 may be more difficult to degrade than C1 after the mineralization of planktonic bacteria. The analysis of environmental factors and planktonic bacterial community shows that the karst aquatic ecosystem has a significant impact on the important bacteria related to photosynthesis, which helps to explain the relative stability of the Auto-DOM in the karst aquatic ecosystem, so it can be speculated that C2 may be an important RDOM in this ecology (Figure 3).
In this study, the interaction of discolored dissolved organic matter (CDOM) and its planktonic bacterial communities under five different land use patterns was studied in the Shawan karst water carbon cycle test site in southwest China. The results showed that the Auto-DOM had obvious seasonal changes, indicating that seasonal effects should be considered when analyzing the contribution of Auto-DOM to the karst aquatic ecosystem. Pay close attention to the WeChat public number of "Meige Kefu" and 220927 it backstage to download the original text of this article.
High stability of autochthonous dissolved organic matter in karst aquatic ecosystems: Evidence from fluorescence
High Stability of Endogenous Dissolved Organic Matter in a Sturgeon Aquatic Ecosystem
作者：Fan Xia, Zaihua Liu等
Impact factor: 13.4
abstract of the article
For many years, the biological carbon pump (BCP) in karst areas has received widespread attention due to its contribution to the global carbon sink loss. In particular, the stability of the native dissolved organic matter (Auto-DOM) produced by BCP may play a key role in the carbon sink loss. However, the source of dissolved organic matter (DOM) in inland waters and its consumption by planktonic bacteria are not yet clear. In this study, the interaction of discolored dissolved organic matter (CDOM) and its planktonic bacterial community under five different land uses was studied at the Shawan Karst Water-Carbon Cycle Test Site in southwestern China, and it was found that low-molecular humic fluorophores (C2), as a Auto-DOM component of planktonic bacterial mineralization, may have some characteristics of inert dissolved organic matter (RDOM) and are an important DOM source in karst aquatic ecosystems. In addition, some important planktonic bacteria received the influence of calcium ions and dissolved inorganic carbon in the karst aquatic ecosystem. This study shows that in the karst ecosystem, Auto-DOM may be as important as Allo-DOM carbon sink, but the former is easily mineralized by planktonic bacteria and ignored.
Results and discussion
1. Experimental design
In this study, five different types of land use ecosystems were established, namely bare rock (S1), bare land (S2), cultivated land (S3), grassland (S4) and shrub (S5)(Figure 1). Each ecosystem tank has an artificial pool (P1-P5) to simulate natural karst spring water. In June 2019, marine algae was added to each pool. Water samples were collected in July and October 2020 and January and April 2021. A series of physical and chemical indexes such as temperature, pH, DO and DIC were measured. EEMs measured CDOM three-dimensional fluorescence spectrum, and 16S microbial diversity sequencing identified microbial groups.
Fig. 1. a: location of carbon domestication test site for karst water in shawan; B: 5 land use methods; C: design drawing of test site; D: supporting pool
2. Physical and chemical properties of different pools and changes in CDOM components
The physical and chemical indicators of the supporting pools of different land use ecosystems have obvious seasonal changes, such as TOC in the summer, autumn and winter three seasons are stable, but in the spring showed an upward trend. Four different fluorescent components were identified for different pools, namely, C1 representing the tyrosine fluorophore, C2 of the low molecular humus fluorophore, C3 of the exogenous humus fluorophore and C4 of the microbial humus fluorophore (Figure 2). C1 represents the amino acid of plankton, Fmax of C1 is lower in winter and higher in spring, while C2 changes greatly in the four seasons, is the main fluorescent component in winter and spring, and the change trend of C1 and C2 is similar to TOC. C3 changes very little in the four seasons, while C4 is the main fluorescent component in summer and autumn.
Organic PairMicroorganismsThe resistance of degradation can be defined as its stability. According to this idea, the stability ratio can be defined as the proportion of mineralized organic matter to the total organic matter of each source. The stability of Auto-DOM is low in summer and autumn, the stability of winter and spring is high, and the stability of Allo-DOM is relatively stable in all seasons.
Figure 2. a: changes of four fluorescent components in the four seasons; B: changes of Auto-DOM and Allo-DOM in the four seasons
3. Composition of planktonic bacterial community
A total of 5154 OTUs were obtained by 16S rRNA diversity sequencing and identification analysis, and 25 main bacterial phyla were obtained by species annotation, among which the dominant phyla of proteobacteria, actinomycetes and bacteroides were obtained, but the bacterial community composition of different pools in different seasons was significantly different. The correlation analysis of environmental factors at the gate level showed that temperature, pH and C1 were important factors affecting the composition of the bacterial community, and the correlation network analysis also confirmed that the organic matter and temperature in the aquatic ecology strongly affected the changes of the planktonic bacterial community.
The results of this study show that the Auto-DOM has obvious seasonal variation, indicating that the seasonal impact should be considered in the analysis of the contribution of Auto-DOM in the karst aquatic ecosystem. According to the analysis of the relationship between planktonic bacterial community and CDOM, combinedMicroorganismsFunctional analysis, found that after the mineralization of planktonic bacteria, C2 may be more difficult than C1 degradation. The analysis of environmental factors and planktonic bacterial community shows that the karst aquatic ecosystem has a significant impact on the important bacteria related to photosynthesis, which helps to explain the relative stability of the Auto-DOM in the karst aquatic ecosystem, so it can be speculated that C2 may be an important RDOM in this ecology (Figure 3).
Figure 3. Schematic diagram of carbon sink process of karst aquatic ecosystem