## 4 Biological Properties of Soils Affected by Biochar
Regarding microsymbolents, the presence and biomass of the two most common, arbuscular (AM) and ectomycorrhiza (EM), have also been shown to be positively influenced by the presence of biochar [75; 76; 83]. Both the rate of ectomycorrhizal formation and the level of root colonization increased (by 157%) at the roots of larch (_Larix gmelini_) seedlings [80]. The AM colonization increased by 40% in a wheat rhizosphere two years after biochar application, while a 6% increase in mycorrhizal colonization was observed with 6 t ha\({}^{-1}\) of biochar added to tree plantations [81]. However, we do not know how and to what extent the number of fungi and the extraradical hyphae mass extending beyond the root were affected by the added biochar. This is because the porous biochar can protect against physical damage resulting from soil compaction or a change to the nutrition of the soil fauna through its internal pores. Therefore, the actual surface protection of the microorganisms inside, consistent with their susceptibility to dehydration, is a critical issue in biochar treatment [12]. It has already been mentioned that one of the beneficial effects of biochar is on the surface binding of the gases produced in the soil, such as CO\({}_{2}\). These indirect mechanisms influence the microbiological activity of soils and the composition of microbial groups [14; 25; 36; 48; 55]. However, the result is highly quality-dependent. In 2019, [PERSON] [88] found that the properties of the hydrocarbon produced via the hydrothermal pathway differ significantly from the pyrolyzed version. On one hand, some authors have proposed that hydrothermal carbon better stimulates the germination and colonization of AM fungal spores in the soil due to its higher water content. On the other hand, other authors suggest that AM fungal colonization in hydrothermal char may decrease due to the improved physicochemical soil condition, which ultimately makes symbiosis unnecessary [88; 89]. Decreased AM symbiosis has been observed with the use of high-phosphorus bone-derived biochar [90; 91; 92]. Thus, the essential role of beneficial mycorrhizal fungi that provide live, direct contact (their well-known properties that improve uptake of phosphorus and other elements, or even their stress-buffering capabilities) may be triggered by the use of various biochar products. The direct adverse effects of biochar can even be demonstrated in soils with high salt or heavy metal contents, which inhibit the formation and function of the rhizosphere connection due to their poor chemical properties [93; 94; 95]. Depending on the surface and porosity of the biochar, it can bind not only the contaminants but also the organic nutrients essential for plant nutrition. The absence of these nutrients is of paramount importance in stress-laden soils [96; 97]. In summary, biochar reduces the mutual efficiency of the plant-microbe system, which is an essential element of cooperation and symbiosis. According to previous results, in the absence of biochar, an improvement can be observed in the symbiotic relationships within soils contaminated with saline or heavy metals due to environmental stress [98; 99]. In addition, biochar must be applied while considering the sensitivity of the symbiont relationship, which is why it should only be used with the appropriate expertise. The beneficial effect of biochar can also be reduced by overwhelming the nutrient availability caused by the addition of fertilizer, which can indirectly reduce the growth rates of microbes [16; 82; 90]. Improvement in AM colonization was observed only with the smallest amount of \"starter\" fertilizer application [83]. According to [PERSON] in 2000 [101], the nitrogen dose capable of promoting symbiosis in a low (1.5%) soil content corresponded to 45 kg ha\({}^{-1}\) of nitrogen fertilizer and only 120 kg ha\({}^{-1}\) of phosphorus. Even higher fertilizer doses caused multiple declines in symbiont functionality and economical biological N\({}_{2}\) binding.