## 2 Materials and Methods
### Soil Pre-Incubation  
Prior to the C and N mineralization dynamics experiments, the pre-incubation of the soil samples was performed. This was conducted under controlled humidity conditions for a period of 7 days. The purpose of this was to reduce the effect of the sampling and handling of the soil samples in the laboratory and to homogenize the soil conditions in all treatments, especially the activity of the biological phase. The soil was adjusted to a WHC of 40% at room temperature and placed in plastic containers, along with a bottle of distilled water to prevent drying. In addition, amber bottles with 1.0 M sodium hydroxide (NaOH) were placed in each of the plastic containers with soil to capture the C-CO\({}_{2}\) produced by the activity of the microorganisms present in the soil [38]. C and N Mineralization Dynamics in Soil with MPs: Physicochemical, Enzymatic, and Ecophysiological Indicators  
The physicochemical indicators analyzed during the experiment were pH, EC, TOC, OM, TN, C/N, N-NO\({}_{2}\)-, N-NO\({}_{3}\)-, and N-NH\({}_{4}\)+, using the methodology described in Section 2.2. Additionally, the net mineralizable N (N\({}_{\text{min}}\)) was determined, which represents the net mineralization of N. This was determined by the sum of the indicators of N-NO\({}_{2}\)-, N-NO\({}_{3}\)-, and N-NH\({}_{4}\)+ [46]. High values of N\({}_{\text{min}}\) represent a tendency towards nitrification [47]. Also, the nitrification index (NI) was determined, which was obtained from the quotient of the indicators of N-NH\({}_{4}\)+ and N-NO\({}_{3}\)-, representing the partial flow of the inorganic N cycle. High NI values have been linked to denitrification processes and low values to nitrification processes [48]. Within the group of biological indicators, the enzymatic activities of UA, DHA, and FDA were analyzed, using the methodology described in Section 2.3. At the same time, a synthetic enzymatic index (SEI) was determined, which included the sum of the enzymatic activities of UA, DHA, and FDA, reflecting the overall enzymatic activity in the soil [49]. The results obtained are reported in mg kg\({}^{-1}\) soil h\({}^{-1}\). As a supplementary and innovative tool in this study, another set of enzymatic activities was determined using the API ZYMenzymatic system (bioMerieux; Marcy-I'Etoile, France), which is a fast and useful tool used to establish enzymatic profiles in complex matrices such as soil and link them to soil processes at a semi-quantitative level [50]. The APIZYM(r) allowed for the simultaneous evaluation of 19 enzymatic activities from 2 g moist soil samples following the supplier's instructions [51]. The enzymatic activities evaluated were Alkaline and Acid phosphomoesterase, Phosphohydrolase, Esterase, Esterase lipase, Lipase, Leucine arylamidase, Valine arylamidase, Cysteine arylamidase, Trypsin, \(\alpha\)-Chymotrypsin, \(\alpha\)-Galactosidase, \(\beta\)-Galactosidase, \(\beta\)-Glucoronidase, \(\alpha\)-Glucosidase, \(\beta\)-Glucosidase, \(\beta\)-Glucosaminidase, \(\alpha\)-Mannosidase, and \(\alpha\)-Fucosidase. The ecophysiological indicator MBC was also determined using the methodology described in Section 2.3. Another ecophysiological indicator that was evaluated was the microbial quotient (qMIC), which indicates the efficiency of the conversion of C into microbial biomass in the soil. This indicator was determined by the MBC quotient and the TOC content in the analyzed samples. Another important ecophysiological indicator was the accumulated C-CO\({}_{2}\), a direct indicator of the biological activity of aerobic microorganisms. The accumulated C-CO\({}_{2}\) indicator was determined by the volumetric titration of 5 mL of 1.0 M sodium hydroxide (NaOH) with 0.1 M hydrochloric acid (HCI) and phenolphthalein as an indicator [45]. Finally, the ecophysiological indicator known as the metabolic quotient (qCO\({}_{2}\)) was calculated by the quotient of the value of the C-CO\({}_{2}\) emitted and the MBC.