## 3 Results and Discussion
(2015) [31] found that durum wheat inoculation with arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) (alone or in combination) improved plant growth, and N uptake, in comparison with uninoculated controls. According to these results, regarding the use of bacterial inoculants as a sustainable alternative to wheat production, not only is the nitrogen fertilization dose important, but so is fractionation or the N split application (the total N at specific stages of wheat growth). Moreover, in earlier works, we proposed that positive effects on wheat yield in the Yaqui Valley inoculated with the bacterial consortium used in this study are most likely to be observed with total N concentrations of 123-225 kg N ha\({}^{-1}\), considering soil N content and N from fertilization (but with a different N split application: 33% at the souring date, 33% with the first irrigation event, and 33% with the second irrigation) [5]. In this sense, in this crop cycle, the treatments of 120 and 240 kg N ha\({}^{-1}\) applied surpass this range (adding 183 kg N ha\({}^{-1}\) of the soil). It has been observed that as N levels surpass 225 kg N ha\({}^{-1}\), wheat yield and productivity begin to decrease, which may be due to exceeded crop nutrient requirements, as well as adverse effects on the photosynthesis rate and grain filling potential in cereal crops [32]. Thus, high doses of N in the soil, along with low efficiency, can cause toxicity, salinity, and pollution of soils and water bodies [33]. Also, it has been reported that N fertilizer input in the short term altered the soil NO\({}_{3}\)\({}^{-}\) contents, consequently impacting negatively the predominant rhizosphere soil bacterial species [34]. In agricultural soils, high doses of N affect growth and some beneficial effects of plant growth-promoting microorganisms [13] and decrease microbial functional diversity [35]. In general, fertilization changes the activity and community structure of soil microorganisms [36; 34]. In this sense, results of varying carbon and nitrogen in vitro essay (and the inoculation of the BC that was used in the field), showed that the highest sporulation occurred with the highest nitrogen content in the medium, and with the three different C contents (4.90 \(\times\) 10\({}^{4}\) UFC mL\({}^{-1}\), 1.07 \(\times\) 10\({}^{5}\) UFC mL\({}^{-1}\), 4.80 \(\times\) 10\({}^{4}\) UFC mL\({}^{-1}\): low, medium, and high, respectively) (Figure 2). Although this dormant state (endospore formation) is a desirable trait for the development of cost-effective microbial inoculants, microorganisms also produce spores as a survival mechanism to adverse environmental conditions and different types of stress, resulting in a metabolically inactive state [37]. The above could be a factor limiting the BC beneficial effect at high N doses, considering that there are certain important growth stages of wheat where fertilization and the application of the BC are synchronized and where plant growth-promoting activity is crucial to observe positive impacts on plant biometric parameters, yield, and quality. These results suggest that these strains could be forming endospores when high quantities of N are applied to the soil, instead of being in an active state at those specific and critical moments (sowing date, tillering stage, booting stage, among others). Thus, medium rates of nitrogen are required for adequate BC growth, since the consortium strains resulted in 7.40 \(\times\) 10\({}^{7}\) UFC mL\({}^{-1}\) (with low C), 6.90 \(\times\) 10\({}^{7}\) UFC mL\({}^{-1}\) (with medium C), and 1.06 \(\times\) 10\({}^{8}\) UFC mL\({}^{-1}\) (along with high C) cells and spores; also, in 2.80 \(\times\) 10\({}^{3}\) UFC mL\({}^{-1}\) of spores with high C content, and 7.60 \(\times\) 10\({}^{3}\) UFC mL\({}^{-1}\) of spores with medium C content (Figure 2). Other studies have shown how high N fertilization rates affect soil microbial flora. [PERSON] et al.