## 3 Results and Discussion
### Metagenomic Analysis of Soil Samples with and Without Hydroinfiltrators
The proportion of _Sphingomonas_ was also predominant in soils with hydroinfiltrators (Figure 6), although differences were observed according to soil depth. Its proportion is somewhat lower in soils with hydroinfiltrators (SH20) (5.5%) compared to the control soils at the same depth (SC20) (6.5%). However, the relative abundance increased considerably in soils with hydroinfiltrators (SH40) (6.0 5) compared to the control soils, both collected at 40 cm (SC40) (0.9%). The genus _Sphingomonas_ actively participates in N and P biogeochemical cycles [48]. Some species facilitate P solubilisation [49], while others contribute to nitrogen fixation [50]. Additionally, some cases involving the bioremediation of contaminated soils and the degradation of polycyclic aromatic hydrocarbons (PAH) have also been described [51; 52]. Furthermore, certain strains are considered extremophiles due to their tolerance to drought, high salinity, and elevated heavy metal concentrations [53; 54]. _Steroidobacter_ and _Blastococcus_ also showed the highest relative abundance in soil with hydroinfiltrators (Figure 6). The presence of _Steroidobacter_ was larger in soils with hydroinfiltrators compared to control soils, with higher abundance at 20 cm depth (SH20) (2.4%) than at 40 cm (SH40) (1.5%). Similarly, _Blastococcus_ showed a greater abundance in soil with hydroinfiltrators only at 40 cm depth (SH40 vs. SC40) (1.4% vs. 0.13%), although its presence slightly decreased to 20 cm (SH20 vs. SC20) (2.3% vs. 3.2%). Microorganisms belonging to _Blastococcus_ perform various beneficial functions for soil and plants. This genus can promote the bioremediation of contaminated soils [55]. Some species are involved in the degradation of organic substrates [56], while others exhibit PGP properties [57]. Additionally, certain strains are resistant to extreme conditions of drought, salinity [58], and alkalinity [59], and demonstrate broad tolerance to heavy metals [60]. Similarly, the genus _Steroidobacter_ is also effective in the bioremediation of contaminated soils [61]. Some species play a key role in the degradation of PAH, while others are efficient in the uptake of heavy metals [62]. The use of hydroinfiltrators, on the other hand, has a negative impact on the development of some soil bacterial populations. The relative abundances of _Cutibacterium_ (1.3%), _Ramlibacter_ (1.2%), _Blautia_ (1.0%) and _Weissella_ (1.4%) decreased in soil with the hydroinfiltrators (Figure 6). Specifically, for _Ramlibacter_, its proportion was considerably lower in SH20 soils (0.1%) compared to SC20 4.5 soils (4.5%). However, at 40 cm depth, similar proportions were observed between SH40 (0.19) and SC40 (0.1%). A negative effect was also noted on some genera of non-culturable bacteria and others corresponding to unassigned environmental taxa. Nevertheless, these findings differ from other studies involving the application of biochar to soil, reporting beneficial effects for several genera such as _Cutibacterium_[63] and _Ramlibacter_[33]. The genus _Ramlibacter_ is involved in P solubilisation, and precipitation processes and exhibits PGP properties [64; 65]. Some species promote the degradation of organic compounds (e.g., PAHs) and participate in the bioremediation of contaminated soils [33; 66]. Additionally, certain strains are tolerant to stress conditions such as high temperature, aridity, and nutrient scarcity [67]. As previously mentioned, soil depth is a key factor influencing the structure of bacterial communities, although this effect is less pronounced in soil with the hydroinfiltrators (Figure 6). However, the genera _Skernanella_ and _Microvigra_ are notably more abundant in SH20 soils compared to SH40 soils (Figure 6). These genera are actively involved in the nitrogen cycle and are capable of degrading organic compounds [68; 69; 70; 71]. In addition, _Skernanella_ also participates in the P cycle through the production of alkaline phosphatase [72; 73].