## 4 Limitations of Using Plant Products as Bioherbicides
### Effect of Nepetalactone and Phloretin on Non-Target Organisms
#### 4.3.2 Effects on Soil Microbiota  
Bioherbicides, in addition to being effective in controlling the germination and growth of weed species, should not have negative effects on soil microorganisms. The soil microbiome is a complex community of microorganisms, including bacteria, fungi, archaea, viruses, and protozoa. These microorganisms play a vital role in organic matter decomposition, nutrient cycling, nitrogen fixation, and the establishment of symbiotic relationships with plants, all of which directly influence soil fertility and plant health [308]. To date, the effects of NL, a potential bioherbicide from _Nepeta_ sp., as well as EOs, water emulsions, and extracts from this plant, on the biogeochemical properties of soil and key microbial groups have not been studied. This will be a critical focus of future research to enhance our understanding of _Nepeta_'s potential in sustainable agriculture and ecosystem. However, few studies have investigated the impact of EOs from the _Lamiaceae_ family on soil microorganisms. While _Nepeta_ sp. EOs and extracts are widely recognized as antimicrobial agents [55; 309], some microorganisms can be stimulated by their presence and utilize them as a source of carbon dioxide and energy. [PERSON] and [PERSON] [310] discovered that EOs extracted from _Origanum vulgare_, _Rosmarinus officinalis_ L., _Mentha spicata_ L., and _Coridohymus capitatus_ (L.) Rchb.f enhanced microbial respiration. Similarly, EOs from _Lavandula stoechas_ L. increased microbial respiration due to bacterial growth stimulation [311]. In contrast, [PERSON] et al. [312] reported a decrease in microbial biomass and activity following treatment with emulsions of _Oximum basilicum_ and _Mentha arensis_ L. EOs. [PERSON] et al. [313] demonstrated that EOs from _Thymbra capitata_ L. at concentrations of 8 and 12 \(\mu\)L mL\({}^{-1}\), when added to soil, and _Mentha \(\times\) pipertia_ EO at a concentration of 20 \(\mu\)L mL\({}^{-1}\) have herbicidal potential against _Avena fatua_, _Echinochloa crus-galli_, _Portulaca olerca_, and _Amarantlhus retroflexus_. The same authors also investigated the effects of different concentrations and exposure durations of EOs on the biochemical properties of the soil and the main microbial groups. The addition of _T. capitata_ EO stimulated soil microorganisms, with the effects varying depending on the applied dose and the duration of the incubation period. An increase in microbial biomass carbon and nitrogen, as well as respiration, along with a reduction in extractable carbon, occurred immediately after the addition of the lowest EO dose (4 \(\mu\)L mL\({}^{-1}\)). This suggests that the carbon substrates available in the soil, together with those added by the EO treatment, were simultaneously immobilized and mineralized by the soil microorganisms. In contrast, as the EO dose increased, the stimulation initially affected only microbial respiration. Towards the end of the incubation, the stimulatory effects of the two lowest doses of _T. capitata_ (8 and 12 mL mL\({}^{-1}\)) disappeared, while the highest oil dose (12 mL mL\({}^{-1}\)) led to a reduction in microbial biomass carbon and microbial activity. This suggests that the highest dose of _T. capitata_ EO destroyed some of the soil microorganisms, and the remaining microorganisms were unable to utilize cytoplasmic materials released from the cells, as confirmed by the increased extractable carbon and low respiration rate compared to the control. The results indicate that _T. capitata_ EO at the highest concentration can be harmful to soil microorganisms, and these negative effects become apparent after approximately two months. Both bacteria and fungi were slightly reduced upon the addition of _M. \(\times\) piperita_ EO compared to the control at all doses of the oil (12, 16, and 20 mL mL\({}^{-1}\)). However, by day 50, all microbial groups did not show significant deviations from the control.