## 3 Results
### C and N Dynamics in Soil with MPs: Ecophysiological Indicators
However, these researchers also observed that other forms of PE MPs--such as films or fragments--did not have a significant effect on microbial respiration. They concluded that the positive effect of PE foams on microbial respiration may have been due to their spongy structure, which tended to increase soil aeration [90]. Something similar may have occurred in the present study, since the increase in C-CO\({}_{2}\) as a function of the MP concentration in the soil could be attributed to the fibrous structure of PP, which increased soil aeration and, therefore, favored the activity of aerobic microorganisms [90]. Another reason could be a change or increase in the soil porosity, as reported by other authors [75; 77]. Depending on the type, size, and spatial arrangement of PP, it can increase or generate channels or air flows between soil microaggregates, favoring the arrangement of OM, thus increasing the respiration rate of aerobic microorganisms via the mineralization of OM [91]. [PERSON] et al. [74] reached the same conclusions by establishing that, due to the low density of PP, it promotes or induces a decrease in soil density, thus increasing aeration, favoring the activity or respiration of aerobic microorganisms. In the present study, using high doses of MPs in the systems or microcosms may have also induced the same events, i.e., modifications in the orientation or structure of the microaggregates, favoring changes in soil porosity and, in turn, facilitating the availability of organic compounds, causing a higher concentration of C-CO\({}_{2}\) via the aerobic mineralization of available C and N sources over time, as could be observed in the N\({}_{\text{min}}\) indicator. In the same context of ecophysiological indicators, qCO\({}_{2}\) is an indicator that is widely used to evaluate the physiological state of the biological phase of a soil. The qCO\({}_{2}\) indicator has been related to cellular respiration and has been used as a measure of the ecophysiological state of microorganisms [50]. In the present study, this indicator did not show significant differences between treatments (\(p>0.05\)), presenting the following order: T1 = T2 = T3 = T4 (Figure 7D). There are a few studies where this indicator has been quantified in soils containing MPs, for example, the study by [PERSON] et al. [88], who found that PE and PLA at concentrations of 1% (w w\({}^{-1}\)) tended to increase C-CO\({}_{2}\) production and decrease MBC, which increased qCO\({}_{2}\), presenting significant differences between treatments. Since there were no significant differences (\(p>0.05\)) in the present study with respect to the MBC concentration, this could be one of the reasons why no significant differences were found regarding qCO\({}_{2}\), despite the fact that significant differences were observed for the C-CO\({}_{2}\) indicator. Although the MBC and qCO\({}_{2}\) indicators did not present significant differences between treatments in the present study, they are of the utmost importance for future research related to MPs in soils, since they give a general diagnosis of the changes that a system suffers in its biological phase once elements foreign to the system--such as MPs--are incorporated.