## 4 Discussion
Findings in drought experiment also brought out that the amount of grain yield, plant height, and PQ rate in plants under PGPB consortium inoculation, alone (I) or combined with the half dose of CF (I + \(\frac{1}{2}\)CF), were higher than the full dose of CF treatments (CF and I + CF). A possible explanation could be given by salt accumulation in soil because of the intensive application of chemical fertilizers [35] which can contribute to an increasingly negative impact of drought stress. Total quenching of ChIP (qTQ) and total quenching of variable ChIP (qTV) are two other quenching parameters, defined by [PERSON] et al. [21] and [PERSON] et al. [22], reflecting the simultaneous effects of both photochemical and non-photochemical processes during the light induction period. The difference between the two parameters is that the first one (qTQ) is calculated using the maximum ChIP yields in DAS (F\({}_{\text{m}}\)) and steady-state ChIP yield in LAS (F\({}_{\text{s}}\)) while the latter is based on the variable ChIP yields in DAS (F\({}_{\text{v}}\)) and LAS (F\({}_{\text{v}}\)) [9]. In our research, increments in the qTQ rate in fertilization treatmentsby the combined treatments of PGPB and chemicalsindicated an increase in the overall excitation energy consumption by the photochemical and non-photochemical processes in LAS. Similar results observed in qTV showed the higher activation of photochemical and non-photochemical processes in LAS under microbiological/chemical fertilization treatments, which resulted in higher quenching of F\({}_{\text{v}}\). Increment of the total quenching of ChIP (qTQ and qTV), despitethe reduction of non-photochemical quenching (NPQ and qCN), can be related to further increase of the photochemical quenching bychemical and inoculum treatments, especially PGPB inoculation (applied alone or combined with chemicals). This result was confirmed by PQ parameter that was influenced by fertilization (microbiological and chemical) treatments, especially undersalinity conditions. The PQ is defined as a ratio of the quantum yield of actual PSII photochemistry in LAS to the quantum yield of the constitutive non-regulatory non-photochemical quenching [17]. Based on the results, drought condition induced an improvement of root weight as compared to the non-stress, while the salinity condition reduced it. In addition, roots showed a positive response to the application of microbiological/chemical fertilizers. Furthermore, the effect of PGPB inoculums and chemical fertilizers on the increment of the plant height was almost significant as compared to the non-fertilized control plants. This difference between drought and salinity is a morphological adaptation mechanism and an indication of the photosynthetic source-sink balance in plants under various conditions, showing that the photosynthesis assimilation can contribute to growing plant organs by the elongation of the stem (plant height) under salinity and to growing roots, under drought, rather than sink organs such as grain [36; 37; 38]. Drought stress effects induced a biomass allocation into the root organ at the expense of the aerial parts, which can contribute to further absorb water from the soil. The increment of plant height and root weight in response to the PGPB inoculation and chemical fertilization has been already reported in several studies [12; 36]. In the present research, chlorophyll pigments (Chl_a_+_b_) in plants treated by PGPB inoculations and chemical fertilizer were significantly higher than control plants. It has been previously reported that the optimal N, P, and K supply is considered essential for the biosynthesis of photosynthetic pigments, especially under stress conditions [36; 37]. The tendency of the plants to maintain or increase the amount of chlorophyll content under stress conditions is a defense mechanism to conserve the photosynthesis system [29]. On the other hand, the ratio of Chl_a_ to Chl_b_ (Chl_a_/_b_) showed no significant changes under microbiological/chemical fertilization treatments.