# Fertilization and Soil Microbial Community: A Review
## 3 Results and Discussion
### Bacterial and Fungal Species Affected by Chemical or Organic Fertilizers
Nutrient addition (both organic and chemical) have been found to enrich copiotrophic taxa affiliated with the _Pseudomonadaceae_ and _Cytopbaceae_ bacterial families but to reduce some _Acidobacteria_[86]. In particular, _Cyanobacteria_ (an active N-fixing group) increased in soils amended with inorganic fertilizers. Manure application, on the other hand, increased the relative abundance of the _Gamma-Proteobacteria_ group (responsible for organic substrate decomposition) and _Nitrosomonadaceae_ (_Beta-Proteobacteria_), which play a vital role in converting ammonium into nitrate [86]. Overall, organic and inorganic fertilizers generally have positive effects on numerous soil bacteria, the most representative of which is _Azotobacter_. The latter is in fact a free-living, nitrogen fixing aerobic soil bacterium able to make available to plants a considerable part of soil nitrogen [132]. For example, the mineral fertilization of an apple (_Malus domestica_) orchard after replanting caused increased number of _Actinomycetes_, _Azotobacter_, proteolytic bacteria and phosphate-solubilizing bacteria [133]. Likewise, the use of inorganic fertilizers on a semi-arid alfisol led to an increase in the numbers of _Azotobacter_, even though the genetic diversity was unaffected [134]. Similar results were obtained in maize cultures [135] and in sugarcane cultures [136]. Chemical N addition was found to increase the relative abundance of oligotrophic bacteria and can have positive effects on some bacterial groups involved in C cycling such as _Ktedonobacteria_ and _Acidobacteria_ in extremely acidic subtropical forests [83]. On the other hand, intensive mineral N fertilization can negatively affect other specific bacterial groups (e.g., _Diazotrophs_, _Beta-Proteobacteria_) that are important rhizosphere microbes with symbiotic N-fixing interactions with leguminous plants. The first step in nitrification (oxidation of ammonia into nitrite) is performed in soil by ammonia-oxidizing archaea (AOA) and AOB (_Beta_- and _Gamma-Proteobacteria_) [137]. AOA,which are 2- to 3000-fold more abundant than AOB in soils [137] and are key players in the N cycle in unfavorable environmental conditions (e.g., low nutrient content, low pH) [138], are more sensitive than AOB to different chemical fertilization treatments in acidic red paddy soil [138]. In this study, the AOA structure was more negatively affected. The long-term application of chemical NPK or N fertilizer has been found to significantly affect soil microbial communities throughout the soil profile and increase the relative abundance of AOA in surface soil (0-40 cm) only in the presence of additional organic fertilization (recycled crop residues or manure) [79; 138]. This implies that the important ecological function of soil nitrification can be promoted only with simultaneous chemical and organic fertilization. Phylogenetic analyses performed in a long-term organic and chemical fertilization experiment in a sandy loam soil in northern China indicated that _Proteobacteria_ was the dominant taxonomic group in the soil, followed by _Acidobacteria_ and _Gemmatimonadetes_[139]. In this study, long-term PK treatment was found to enhance bacterial richness and diversity more than NK, NP, NPK or organic manure addition. [PERSON] and [PERSON] [140] found that the number of spore-forming Gram-positive rods was higher in plots with superphosphate. Specific bacterial groups are enriched by organic fertilization, such as _Alpha-Proteobacteria_, _Gamma-Proteobacteria_, _Nitrospire_, _Bacteriaidetes_ and _Actinobacteria_[141]. This was also found by [PERSON] et al. [142], who studied the effects of different fertilization treatments (no fertilizer added, nitrogen fertilizer and bioorganic fertilizer) on the rhizosphere bacterial community. They found that the soil rhizosphere of winter wheat treated with bioorganic fertilizer had a higher microbial diversity than other treatments.