## 4 Biological Properties of Soils Affected by Biochar  
Several studies have reported beneficial effects of biochar substances--artificially created by charring biological waste and byproducts--on soil productivity in terms of increasing biological activity and the sequestration of greenhouse gases (GHGs) [60; 61; 62]. Among GHGs, the reduction of nitrous oxide (N\({}_{2}\)O) and methane (CH\({}_{4}\)) has been highlighted [54; 57; 62], but carbon sequestration (C) is also a critical property [52]. Biochar as a substance is mainly recommended for acidic soils as it alkalizes the pH and improves nutrient retention through cation adsorption, thereby benefiting soil productivity (Table 3). However, the variety of experiments and sites described in the literature make it difficult to summarize the effects on soil biomass and draw appropriate conclusions. In many cases, the results are contradictory and highlight only one factor of a multifactor system. The conditions for applying biochar depend on the properties of the soil, environmental conditions, raw material, dose, and many other biotic and abiotic factors. Its usage can lead to changes in soil biotic communities that are of interest but also of concern. In the quantitative development of the microbial community, not only plant-growth-promoting rhizobacteria (PGPR), which are favorable for cultivation, but also soil-borne pathogens may potentially multiply [63; 64]. From the point of view of soil protection, such research is important, as the microbiological communities of soil affect both its functions and ecosystem services [65; 66; 67]. The properties that affect functionality are structure and stability, aeration, nutrient cycling, water balance, and the already mentioned carbon sequestration [68]. This refers to soils' suppressive or receptive properties against pathogens, to which biochar can contribute in both positive and negative ways. Overall, increased microbial biomass following biochar supplementation has been determined with various soil-testing methods. The most widely known of these are molecular nucleic-acid-based techniques [69; 70], breeding, and/or the classical colony-counting method [64; 71], substrate-induced respiration [72; 73; 74], fumigation extraction [74], phospholipid fatty acid (PLGA) analysis [70], and microscopic examination of staining particles [75; 76; 77]. In addition, [PERSON] et al. in 2016 [78] and [PERSON] et al. in 2020 [79] found that microbial reproduction rates also increased in biochar-treated soils. The increased microbial activity was further reflected in the CH\({}_{4}\) formed during biodegradation after biochar addition. An increase was observed in the number of anaerobic and cellulose-degrading bacteria as an indirect effect. Thus, there may be a wide variety of microbes, of different types and functions in terms of plant production and protection, food quality, and safety, within each physiological group. The magnitude of these changes differs from species to species and even between strains [12]. Their increasing mass is a common phenomenon with biochar, but its extent and possible maximum are strongly determined by the ecophysiological properties of the studied taxon [80; 81; 82]. This has also been observed in stress-laden saline soils [83]. Biochar, like high-carbon sugars, immobilizes the easily absorbed nitrogen content of the soil and can thus be a successful tool in environmental restoration efforts [84]. In soil-plant systems, the microbiological properties of the rhizosphere have been mainly studied, as is shown in Table 4. [PERSON] et al. in 2010 [85] and [PERSON] et al. in 2019 [86] found that biochar delivered to the rhizosphere increases the number of microbes compared to that in undisturbed/untreated soil. However, generalization is prevented by the fact that [PERSON] et al. [87] reported the opposite in 2010, referring to the strong dose-dependence of the application.