# Fertilization and Soil Microbial Community: A Review
## 3 Results and Discussion
### Bacterial and Fungal Species Affected by Chemical or Organic Fertilizers  
Several authors have demonstrated that the structure of the soil microbial community (composition, diversity, and relative abundance of specific taxa) changes after chemical or organic fertilization [25, 80, 118, 119, 120]. In fact, the latter affects microbial growth and competitiveness because different bacterial and microfungal groups can vary in their ability to use the different nutrient forms found in soil [76, 90, 121]. For example, _Knufa petricola_ and _Zygomycetes_ fungi were found only in the inorganic fertilization of soil. _K. perticola_ is a microcolonial Ascomycete adapted to extreme environments, and _Zygomycetes_ are typical \(r\)-strategists with a rapid growth with simple carbon sources [122]. Moreover, some typical bacteria from organic amendments (e.g., _Firmicutes_ and _Myxococcus_) were found as primary constituents in manured-traded soils [121, 123]. Specific microbial groups (_Firmicutes_, _Proteobacteria_, and _Zygomycota_) are stimulated to grow in organic fertilizer treatments, because they prefer nutrient-rich environments, and are capable of degrading complex organic compounds [76]. Many studies have focused on the impact of different types and regimes of fertilization on the soil microbial communities, and the results are in some case conflicting for chemical fertilizers. For example, [PERSON] et al. [82] focused on the effects of long-term fertilization with NPK or NPK + organic amendments on specific bacterial and archaeal genes involved in the nitrogen cycle. They suggested that the genes for ammonia-oxidization are more sensitive than nitrogen fixers and denitrifiers to fertilization. Although they found that NPK increased soil fertility in terms of genes involved in the nitrogen cycle, the organic amendments induced greater gene abundance. Interestingly, soil available P was the most important factor influencing the abundance of functional communities involved in the nitrogen cycle. Long-term agricultural organic and chemical fertilization significantly affects nitrogen cycling in soils [97; 98; 124; 125; 126]. For example, in calcareous soils, N fertilization increases the potential nitrification rate but reduces the efficiency use of N and changes the beta-diversity of ammonia-oxidizing bacteria (AOB), reducing the relative abundance of _Nitrosospira_ (nitrite-oxidizing bacteria) and increasing the relative abundance of _Nitrosomonas_ (which oxidize ammonia to nitrite) [126]. On the other hand, mineral and organic fertilizer application significantly increased the species richness and alpha-diversity of AOB [125]. In contrast, [PERSON] et al. [78] revealed that the long-term application of manure and chemical fertilizers significantly affected microbial community structure, and specifically, NPK significantly reduced the alpha-diversity of the soil microbial community. The influence of fertilization on the \(r\) to \(K\) member ratio has been reported in some papers. In general, \(r\)-strategists grow fast when the substrate is abundant, and include copi-otrophic bacterial taxa such as _Proteobacteria_ and in particular _Alpha_- and _Beta-Proteobacteria_, _Firmicutes_, _Actinobacteria_ and _Candidatus Saccharibacteria_. \(K\)-strategists can grow when resources are limited and include oligotrophic bacteria such as _Acidobacteria_, _Gamma_- and _Delta-Proteobacteria_, _Gemmatinomatedes_, _Verrucomicrobia_ and _Chlorofexic_[76; 127; 128]. The application of chemical fertilizers has been reported to enrich the \(K\)-strategist bacterial community [76; 93; 129; 130]. It was for example found in a silt loam soil in a long-term experiment with wheat (_Tritcium aestivum_ L.) plantation. [PERSON] et al. [131] in meadow grassland soils reported that N and P fertilizations shifted soil microbes towards an \(r\)-selected community.