## 3 Results
### C and N Dynamics in Soil with MPs: Ecophysiological Indicators  
Ecophysiological indicators were determined to evaluate the changes that MPs could cause in the biological phase of the soil. Regarding the MBC, there were no significant differences (\(p>0.05\)), presenting the following order in concentration: T1 = T2 = T3 = T4 (Figure 7A). Unlike the present study, [PERSON] et al. [88] found that the addition of 1% (w w\({}^{-1}\)) of PE and PLA MPs in clayey and sandy loam soil presented lower concentrations of MBC with respect to the control. They attributed this behavior to a higher respiration rate (C-CO\({}_{2}\)) in treatments with high doses of MPs, which indicated that more MBC was involved in microbial respiration. Similarly, [PERSON] et al. [89] used two non-biodegradable MPs (PE and PVC) and four biodegradable MPs (polybutylene Succinate [PBS], polyhydroxyalkanoates [PHA], polybutylene adipate terephthalate [PBAT], and polypropylene carbonate [PPC]) at concentrations of 1%, 7%, and 28% (w w\({}^{-1}\)) in microcosm-level experiments using silty loam agricultural soil. They found that the MBC content tended to increase when increasing  
Figure 6: Enzyme profiles of the different treatments over 90 days. the MP dose, except for PBS. They mentioned that this was due to the incorporation of C-containing compounds, especially biodegradable plastics, since these compounds break down into nanoplastics and are used to generate new biomass. Although there were no significant differences in this indicator in the present study, it has also been reported that MPs--such as PE, PLA, and PVC--at different concentrations induce changes in microbial activity [74; 75], so it is important to use different types and concentrations of MPs in experiments with agricultural soils to determine the effects of these different MPs on this type of indicator. Regarding the qMIC, there were no significant differences between treatments (\(p>0.05\)), which presented the following order: T1 = T2 = T3 = T4 (Figure 7B). It is important to emphasize that there are few or no studies on the dynamics of this indicator in the presence of MPs. This indicator has been used to estimate microbial activity and OM accumulation in soil [50]. In quality studies using soils (without MPs) from the Mexican Bajio, [PERSON] et al. [50] found qMIC values between 0.01 and 0.09%, values which are below those found in the present study, probably due to the low TOC values in the soils they studied. The TOC values obtained in their study were in a range considered low for agricultural soils, unlike the soil used in the present study, where the TOC values were in the moderate range. On the other hand, the C-CO\({}_{2}\) accumulated during the experiment presented the following order in concentration: T1 = T2 < T3 < T4 (Figure 7C), presenting significant differences between treatments (\(p\leq 0.05\)). Treatment T4 had a concentration that was 11.3% above the control treatment T1. It is interesting to note that the treatments without MPs (T1) and with the lowest concentration of MPs (T2) behaved similarly, without showing significant differences (\(p>0.05\)). [PERSON] et al. [67] found that 0.4% PE foams (w w\({}^{-1}\)  
Figure 7: [PERSON] analysis of variance for ecophysiological indicators with respect to treatments. T1, 0% MPs; T2, 0.5% MPs; T3, 1% MPs; and T4, 5% MPs; (**A**) MBC, microbial biomass carbon (mg C\({}_{\text{mic}}\) kg\({}^{-1}\) dry soil); (**B**) qMIC, microbial quotient; (**C**) C-CO\({}_{2}\), carbon dioxide (mg C kg\({}^{-1}\) dry soil); and (**D**) qCO\({}_{2}\), metabolic quotient (mg C-CO\({}_{2}\) g C\({}_{\text{mic}}\)\({}^{-1}\) h\({}^{-1}\)). The dotted line represents the mean of the indicator. Same letters indicate that there is no significant difference between treatments using a pairwise Wilcoxon rank-sum comparison test with Bonferroni adjustment (\(p\leq 0.05\)). increased microbial respiration compared to soils without PE, a behavior that was observed in the present study in treatments T3 and T4.