## 4 Discussion
### Biomass Production and Yields  
With the exception of three treatment combinations, no impact on plant growth was found after iodine application. There were increases in LFW and LDW biomass following a single application of Cs-KIO\({}_{3}\), which were consistent with results from previous lettuce biofortification studies using KIO\({}_{3}\)[10; 15; 44]. Conversely, there were decreases in HFW and HDW biomass after SDA of Cs-KI, potentially due to the second application direct to the substrate at 15 d.a.t. and subsequent rapid absorption by the plant roots. In addition, there is a high correlation between LFW and LDW (R = 0.9).  
The I\({}^{-}\) anion is known to have greater solubility in soil and better absorption by roots than its IO\({}_{3}\)- counterpart [44]. Reports of greater plant sensitivity to high doses of KI than to KIO\({}_{3}\) applied to the substrate have been published [15; 45]. At low doses (0.013-0.129 mg L\({}^{-1}\)), there are no toxic effects reported for either iodine species [45]. In hydroponic systems, lettuce has demonstrated greater sensitivity to I\({}^{-}\). Phytotoxic effects from excessive iodine accumulation were seen at I\({}^{-}\) doses of 80 uM, while IO\({}_{3}\)- did not affect biomass at doses up to 240 uM [10].  
Considering those previous reports, the iodine concentrations utilized in the present work were well within the ranges used for lettuce cultivation. The best iodine species for biofortification is reportedly IO\({}_{3}\)- [12; 13; 43]. Our study found that Cs-KIO\({}_{3}\) complexes (at 5 and 25 mg I kg\({}^{-1}\)) applied to the substrate led to biomass increases. Compared to KI, that iodine salt is less phytotoxic. Additionally, appropriate doses of chitosan have been found to stimulate plant growth, development, and yields [24; 46]  
The largest improvements to LFW, LDW, and HDW were seen after single applications of Cs-KIO\({}_{3}\) (at 5 and 25 mg I kg\({}^{-1}\)), rather than either Cs-KI or KIO\({}_{3}\). Based on those results, we believe that the complex of Cs and IO\({}_{3}\)- favor improvements in biomass, as there are also other studies that show that Cs and IO\({}_{3}\)- alone have positive effects on plant biomass [9; 22; 47]. Cs by itself is a good source of C, H, O and N for plants, it also works as a chelating agent for metals, which favors chelated elements that are available in assimilable forms for plants, and it has also been related for exercising its function as an elicitor, these and other Cs functions can contribute to plant growth [23; 47]. On the other hand, IO\({}_{3}\)- is less phytotoxic than I\({}^{-}\), as it must first be reduced to I\({}^{-}\) before it can be assimilated. Perhaps this step is a checkpoint for the plant's signaling processes. IO\({}_{3}\)- could also be acting as an elicitor. On the other hand, I\({}^{-}\) is rapidly assimilated by the plant, probably leading to greater accumulation in the chloroplasts while exerting its phytotoxic effects, which have been noted as chlorosis or biomassreductions [10; 15]. However, the mechanisms of iodide and iodate root absorption have not yet been fully elucidated and little is known for sure about the subject [48; 49].