# Fine Root Length of Maize Decreases in Response to Elevated CO2 Levels in Soil
## 1 Introduction  
Carbon capture and storage (CCS) can capture up to 90% of the carbon dioxide (CO2) emissions generated by fossil fuels in power generation and industrial processes, thereby reducing the amount of CO2 entering the atmosphere [1]. Moreover, there are seventeen large-scale facilities that are already successfully in operation around the world (with four more scheduled to come online in the near future), which are currently capable of capturing more than 30 million tons of CO2 per annum [2]. However, an unavoidable issue associated with CCS is the leakage of CO2 from geological storage sites into the soil and atmosphere [3, 4].  
Many tests of CO2 injection into soil have been carried out to assess the potential impacts on agro-ecological systems and plant growth [5, 6, 7]. Currently, injected CO2 has been proven to reduce the soil O2 concentration and decrease soil pH, which have negative impacts on plant growth [8, 9, 10, 11]. For example, this was demonstrated at the ASGARD (Artificial Soil Gassing and Response Detection) facility site, where injected CO2 significantly limited productivity in both grass and clover, visible stress symptoms were observed in plants exposed to high soil CO2 concentrations, and the spectralreflectance also changed [12; 13]. This has also been shown in Korea, where a medium CO\({}_{2}\) treatment (i.e., with a soil CO\({}_{2}\) concentration of 12%) retarded plant germination, and no seeds germinated with a high CO\({}_{2}\) concentration (29.4%) [14]. Many assessments of the effects on plants due to CO\({}_{2}\) leakage have mostly focused on plant responses. A previous study demonstrated that, in response to a leakage treatment with a CO\({}_{2}\) flux of 2000 g m\({}^{-2}\) d\({}^{-1}\), the height of maize and alfalfa decreased by 35.71% and 52.25%, respectively, compared with the control, while similar responses to leaked CO\({}_{2}\) in terms of the number of visible leaves, unfolded leaves, and leaf area were also found [15]. Moreover, [PERSON] et al. found that the chlorophyll content (i.e., a unitless measure) of dandelions decreased significantly from 9.49 to 1.91 (i.e., by 80%) in response to the intentional release of 0.15 ton day\({}^{-1}\) CO\({}_{2}\) through a horizontal injection well that was 100 m long and 2.0-2.3 m deep [16]. Furthermore, elevated soil CO\({}_{2}\) lowered the net photosynthetic rate, transpiration rate, and stomatal conductance of plants [17; 18]. These aforementioned results provide useful evidence regarding the inhibition of plants due to leaked CO\({}_{2}\).  
Some work has also been undertaken to explore the below-ground root system response to CO\({}_{2}\) leakage from CCS. It has been shown that an increased soil CO\({}_{2}\) concentration inhibits root respiration and decreases root density [19; 20] and that the root lengths of plants, such as clover, maize, alfalfa, and teosinte, were significantly affected by CO\({}_{2}\) leakage [21]. The total number of roots of oilseed rape decreased at depths below 20 cm in soil with high CO\({}_{2}\) levels compared to those grown in soil with no elevation of CO\({}_{2}\)[22]. Moreover, the root responses to stress have being revealed in depth. [PERSON] et al. concluded that drought significantly decreased the root length and root density while increasing the root diameter, as evidenced by a meta-analysis of 128 published studies [23]. Mild water stress can decrease the root length and increase the root diameter of maize [24]. Root systems play a key role in the uptake, transportation, and accumulation of water and nutrients in farmland ecosystems [25]. Despite the fact that roots are the first to be affected by CO\({}_{2}\) leakage, there is minimal understanding of plant root morphology under such conditions.  
In this paper, pot experiments simulating CO\({}_{2}\) leakage with three treatments were conducted to study the response of root systems to elevated soil CO\({}_{2}\). The specific objective was to reveal how plant root systems respond to CO\({}_{2}\) leakage from CCS.