Research Progress and Trend Analysis of Soil Inorganic Carbon Sink Based on Citespace

. To comprehensively understand the research status and development trend of soil inorganic carbon development, this study comprised 441 inorganic carbon pool papers from 1991-2022 in the Web of Science database based on CiteSpace software, and conducted Visualization analysis to explore the research hotspots, research status and development trend in this field. The results show that number of publications has increased year by year, and the clustering results show that the research topics mainly involve terrestrial biosphere, coastal forest ecosystem, forest soil, changed temperature hutrient. The hotspots of research include the blue carbon, soil carbon sequestration and dissolution processes of inorganic carbon. In addition, development trend include the effects of land use change, temperature, organic matter and other changes. soil inorganic carbon sinks, carbon dioxide uptake and the application of isotope technology are the ongoing concerns in this field, which will be the hotspot of soil inorganic carbon sink research in the future period.


Introduction
In recent years, due to global warming problem, the study of carbon cycle in terrestrial ecosystems has been widely concerned [1] .Research findings, Soils have now become the focus of attention due to their huge carbon sink potential [2,3] .However, soil inorganic carbon (SIC) has received increasing attention due to its high temperature, low soil water content, low vegetation, high salinity, and poor microbial activity [4] , and inorganic carbon has become increasingly important in the carbon cycle as it is relatively stable in nature compared to organic carbon, which is dominated by arid and semiarid regions and accounts for about 38% of the total global carbon pool [3,4] .For decades, researchers have studied various aspects of inorganic carbon pools [5][6][7][8] . However, combing through the relevant literature reveals that scholars have mostly focused on the principles of inorganic carbon and carbon storage, and there is a lack of a separate discussion on the research trends of soil inorganic carbon sink. On the other hand, in recent years, research hotspots and trends in a certain research area are often realized by CiteSpace software, which is more intuitive and more scientific in showing the current situation and future trends of research in the field, it has been widely used in different research fields in China and abroad, and is one of the more mature research tools available [9,10] .
In order to effectively understand the current situation of domestic "soil inorganic carbon sink" research and its research trends, this paper uses CiteSpace software and literature analysis methods to review domestic and international research on soil inorganic carbon sink, to comprehensively and systematically analyze the basic features and research dynamics of the literature in this field, and to focus on the main research contents and major issues. It is expected to provide an important reference for future researchers in this field.

data sources
In this paper, "soil inorganic carbon sink" was used as the keyword to search the Web of Science database. The retrieval time was from 1991 to 2022. After screening, a total of 441 literatures were selected as research samples and imported into CiteSpace analysis software for graph analysis.

research method
CiteSpace is a visual analysis software that can help researchers discover the current status of research, research hotspots and research trends in a research field [11] . IIn this paper, CiteSpace, a visualization software, was used to analyze references in the field of soil inorganic carbon sinks. The development direction of inorganic carbon sink research was analyzed by data statistics and formed keyword, keyword co-occurrence, timeline analysis, keyword clustering, and burst analysis graphs in order to understand more intuitively the research hotspots, research status and research development trend in this field. CiteSpace is a visual analysis software that can help researchers discover the current status of research, research hotspots and research trends in a research field.

Evolution in Publication Trends
The number of publications allows us to analyze the trend of changes in their publications, reflect the development stages that the research field has gone through, and assess and predict the development of research. Soil inorganic carbon sink research can be divided into three stages: embryonic stage, the slow growth stage, and the rapid development stage. In the budding stage (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000), the cumulative number of papers published in this stage was 32, with an annual average of 2.9, indicating that soil inorganic carbon sink research has not yet received widespread attention. In the slow growth phase (2000-2011), the number of research publications increased, with an average of 8.15 articles per year and an overall increasing trend year by year. In the rapid development phase (2012-2022), soil inorganic carbon sink research has received extensive attention from researchers, with an average of 25.25 research articles per year, of which the highest number of research papers was in 2021, reaching 41, indicating that researchers have been paying more attention to soil inorganic carbon sink in recent years, and the related research results have gradually increased. In summary, the number of papers published in this field shows a stable growth trend, reflecting the enhancement of research hotspots and great development space.

Keywords co-occurrence analysis
The keyword co-occurrence analysis can visualize the research hotspots in the field of soil inorganic carbon sink and its keyword distribution structure. The keyword "soil inorganic carbon sink" was selected as the node type of CiteSpace and formed the keyword cooccurrence map in Fig1a. From the keyword cooccurrence map, we can see that carbon dioxide, carbon, organic matter, carbon sequestration, organic carbon, climate change, dynamics and other keywords appear most frequently. The keywords carbon dioxide and carbon have the highest centrality (Table 1).

Keywords clustering analysis
The more closely associated keywords in Fig. 2a were clustered to constitute clusters, and finally the keyword clustering map was obtained as shown in Fig. 2b,

Timeline analysis of keywords
To further investigate the vertical span of inorganic carbon sinks and the changing trends of research hotspots, timeline analysis of keywords was drawn based on keyword clustering (Figure 3). Through the keyword timeline analysis, the soil inorganic carbon sink research can be divided into three stages. The first stage was from 1991 to 2007, which was the budding research period. The number of hot keywords and literature in this period was relatively small, and the research content emphasized the impact of global warming and the importance of soil carbon pool research development.
The second phase, 2007-2015, is the period of research development, research continued to deepen the influence of soil respiration, carbon sequestration, and land use change on soil inorganic carbon sinks. The third phase is 2007-2022, the period of research deepening phase, during which the number of papers on soil inorganic carbon sinks grew rapidly and the growth rate reached the highest in history, and the research began to focus on the formation mechanism of soil inorganic carbon and carbon sinks. academic research on blue carbon, carbon sequestration, rivers, responses, and dissolution have become important keywords and research trends.

Bursts analysis of keywords
Using the burst detection function of CiteSpace to explore the frontier dynamics of industrialization development, and the 22 key words with the strongest bursts were obtained. Figure 4 shows that the topic of soil inorganic carbon sink first appeared in 1991, and from the length of emergence time carbon; dissolved organic carbon research is receiving long time attention, and from the intensity of emergence in 2016-2022 organic carbon is the most attention, Strength is 9. From 1991 to the end of 2002, soil used the most topics, indicating that soil inorganic carbon sink in soil became an early research hotspot, and from 2002 to 2008, the frontier of research focused on carbon; dissolved organic carbon forest; nitrogen deposition, which is due to global warming issues gradually attracted the attention of scholars, but researchers focused on the macroscopic perspective. the research frontiers from 2008 to 2016 focused on respiration; microbial biomass; terrestrial ecosystems; terrestrial ecosystems, soil organic carbon, fluxes, indicating that the research perspectives during this period focused on the micro level, such as the effects of soil respiration, biological and organic carbon on soil inorganic carbon sinks. 2018 to 2022 research focuses on carbon sequestration, dissolved inorganic carbon, blue carbon.

Conclusions
Based on the visual analysis of soil inorganic carbon sink research trends from 1991-2022 by CiteSpace, the current research hotspots and trends of soil inorganic carbon sequestration were explored, and on the basis of them, the future research direction and prospect were put forward. the results of the study are as follows: (1) From the basic status of research, soil inorganic carbon sink research at home and abroad began in 1991, and the research has developed rapidly and achieved rich research results, and the number of publications has shown a rapid increase year by year, and the research on soil inorganic carbon sink has received more and more attention, indicating that the current stage is a key stage of soil inorganic carbon research, and the related research should strive to ensure the stability of the quantity, and also hold towards a wide and The research on soil inorganic carbon has been receiving more and more attention.
(2) From the viewpoint of research hotspots, soil inorganic carbon sinks are mainly focused on terrestrial biosphere, coastal forest ecosystem, changed temperature hutrient, carbonate carbon storage and other research fields. With the demand for climate change mitigation, inorganic carbon related research is gradually becoming more comprehensive and expanding, and as the problem of lost carbon sinks is raised, the research on soil inorganic carbon sinks will be further enhanced.
(3) Soil inorganic carbon sink research has gone through three stages, namely, the initial stage from 1991 to 2007, the development stage from 2007 to 2015, and the rapid development stage from 2015 to 2022, with the passage of time, the research mainly focuses on carbon, carbon sequestration, dissolution, and so on. Carbon isotope, which is the process of migration and quantification of soil inorganic carbon, will be an important direction of efforts in the coming period, and the research methods will continue to mature and enrich. The overall development trend is inseparable from global governance, and to a certain extent, it has promoted the advancement of the search for carbon loss sinks.
With the gradual deepening of the research on soil inorganic carbon sink, the understanding of the distribution characteristics, reserves, influencing factors, migration and transformation of soil inorganic carbon is also deepening. Overall, the research on soil inorganic carbon sink at home and abroad is still in the exploratory stage, and we still have more research space to fill. Based on the above content, relevant suggestions are put forward from the following aspects: First, at present, more attention is paid to soil organic carbon, while research on inorganic carbon is still relatively weak. Inorganic carbon sinks involve a wide range of contents. Although some achievements have been made, there are still many problems. Next, after the issue of carbon sink loss was raised, the role and status of soil inorganic carbon in the global carbon cycle became more and more prominent, especially in arid and semi-arid regions where there are huge reserves of inorganic carbon. At present, a large number of studies have been carried out on arid regions, but no accurate conclusions have been reached on the final destination of carbon. At the same time, stable isotope has been widely used as an important means to study carbon migration and transformation. Therefore, exploring the mechanism of atmospheric CO 2 inorganic absorption process and carbon sink based on stable isotope technology is the key to the future study of soil inorganic carbon, and the key to determine the arid desert area is the source of soil carbon sink.