*4.2. Counts and Diversity of Soil Bacteria*

The present study demonstrated that the analyzed grass species modified the soil bacteriobiome to various extents, which was mainly due to the development of their root system [71–73] and chemical composition of their root secretions [13]. According to Berg and Smalla [74] and to Murphy [75], plants may contribute to the establishment of unique communities of soil microorganisms. Among all analyzed grass species, *Lolium* x *hybridum* Hausskn (Lh) contributed to the greatest increase in the population number of organotrophic bacteria compared to the control soil, whereas *Poa pratensis* (Pr), *Lolium perenne* (Lp), *Phleum pratense* (Pp), and *Festuca rubra* (Fr) significantly suppressed their proliferation. The analysis of study results demonstrates that the fodder grasses had a more beneficial effect on the proliferation of organotrophic bacteria and actinobacteria than the lawn grasses had. As reported by Deru et al. [71] and Saleh et al. [73], this could be due to the genetic determinants of individual grass species, which affect development of their root system; whereas the root system influences the development of rhizosphere microbiome by the mineral and organic compounds it secretes [13,74]. Singh et al. [76] emphasized that greater amounts of root secretions produced by young plants contribute to a better availability of carbon and energy sources to microorganisms. In addition, these secretions facilitate rhizosphere colonization by microorganisms [77]. This, in turn, leads to cooperation between the plant and the bacteriobiome, because part of rhizospheric bacteria penetrate inside plant tissues through damaged tissue or due to the release of enzymes capable of increasing solubility of nonabsorbable elements [73].

Although fodder and lawn grasses sown onto the soil elicited changes in the counts of organotrophs and actinobacteria, they did not improve their ecophysiological diversity index (EP). A shift could, however, be noticed in bacteria development towards the k strategists, i.e., slow-growing bacteria, which was indicated by decreased values of the colony development index (CD) caused by both fodder and lawn grasses. These results confirm earlier findings reported by De Leij et al. [61], and Murphy et al. [75], who also observed that the microbiome of the rhizosphere of plants changes along with the prolonging growing season, and that the population of r-strategists turns into k-strategists. Marschner et al. [78], Murphy et al. [75], and Kielak et al. [79] demonstrated that bacterial communities of the rhizosphere are initially predominated by *Proteobacteria* r-strategists. Also in our study, the *Proteobacteria* and *Actinobacteria* were the prevailing phyla on all pots; whereas the prevailing classes included: *Alphaproteobacteria* and *Actinobacteria*; the prevailing orders were: *Actinomycetales*, *Sphingomycetales*, and *Rhizobiales*; the prevailing families included: *Sphingomonadaceae* and *Hyphomicrobiaceae*; and the predominating genera were: *Kaistobacter*, *Rhodoplanes*, *Teracoccus*, and *Flavobacterium.* These results correspond with literature data [22,33,80–83]. In general, a richer bacteriobiome in terms of diversity was demonstrated in the soils sown with grasses than in the control soil without grasses. In the case of the fodder grasses, the greatest diversity occurred in the rhizosphere of *Poa pratensis* (Pr), whereas, in the case of lawn grasses, it was in the rhizosphere of *Phleum pratense* (Pp).

The response of *Proteobacteria* and *Actinobacteria* to sowing grasses onto soil varied. Greater OTUs of *Proteobacteria* were demonstrated in the soils sown with grasses, regardless of their functional type, than in the control soil, whereas the OTU number of *Actinobacteria* in the soil was reduced by both groups of grasses. Changes at the level of phylum and other taxonomic units in the soil sown with various species of legumes and grasses were also observed by Zhou et al. [47] and Singh et al. [76]. A special trait of *Actinobacteria* is their resistance to extreme environmental conditions [22,33,82]. This phylum was described as a promising taxon of plant growth promoters [83].

According to Delgado-Baquerizo et al. [80], the most abundant class of bacteria in soils of the world is *Alphaproteobacteria*, which includes *Bradyrhizobium*, *Sphingomonas*, *Rhodoplanes*, *Devosia*, and *Kaistobacter* genera; whereas among *Actinobacteria*, there are the *Streptomyces*, *Salinibacterium*, and *Mycobacterium* genera. In our study also, the *Kaistobacter* and *Rhodoplanes* genera were found to prevail, but other major genera included *Terracoccus, Candidatus Koribacter*, and *Devosia*.

Both the results of this study and literature data [21,22,33,80,82] indicate that investigations addressing the genetic biodiversity of bacteria should be continued in various soil ecosystems.

### *4.3. Activity of Soil Enzymes*

Being sensitive indicators of soil quality, enzymes are strongly associated with the microbiological activity and species colonization of plants [4,84]. In the present study, grasses stimulated the biochemical activity of soil. This is due to their beneficial effect on the soil bacteriobiome, as indicated by results of this study and by literature data [51,52,84–86]. The association between the activity of soil enzymes and microbiome quality is due to the origin of enzymes [38,50,53,84]. In soil ecosystems, they are mainly derived from microorganisms and, to a lesser extent, from plants and other soil organisms [87–90]. The positive correlation between the activity of soil enzymes and the activity of microorganisms has been demonstrated by many experts in soil science [91–93]. In our own research, the higher activity of soil enzymes in soil sown with fodder grass is mainly associated with a greater diversity of bacteria at the family and genus level in soil from below these plants than in soil from below lawn grasses. The values of the Shannon-Wiener and Simpson indicators prove this. Nevertheless, the more beneficial effect elicited by the fodder than by the lawn grasses on the biochemical properties of soil proves that, by activating the microbiome, the plants can intermediately affect enzymatic activity. This hypothesis was corroborated by other authors [3,86,91–94].
