## 4 Discussion
In fact, what distinguishes these two models is how far excitation energy can travel before it is captured at a reaction center or is dissipated by other means [27]. From this perspective, in this study, we worked on some of the most important photo-protective energy dissipation parameters that have been introduced so far. One of the early research on photosynthetic energy partitioning was carried out by [PERSON] et al. [20] which was further elaborated by [PERSON] et al. [19] by introducing the fraction of light absorbed by PSII that is used in photochemistry (\(P\)) and quantum yield of thermal dissipation in the DAS (\(L\)) and LAS (\(D\)). According to the results of energy partitioning, \(P\)values increased by PGPB inoculation and chemical fertilization treatments while decreased under both stress conditions. The inverse results were obtained by application of these treatments for the fraction of absorbed light dissipated thermally, especially the \(D\) value. Nevertheless, there was no significant decrease in \(L\) rate in response to the PGPB inoculation and chemical fertilization treatments in non-stress and salinity conditions. In fact, \(L\) always exists in both healthy and stressed leaves due to its basic physics, as the constitutive non-regulatory (dark) non-photochemical quenching/dissipation [17]. On the other hand, our PGPB strains were able to affect light energy partitioning under both non-stress and stress conditions by increasing \(P\) and decreasing \(D\) values. \(D\) part is related to the non-photochemical quenching, which is formed only upon illumination to regulate the amount of absorbed light as a photo-protection mechanism of plants for energy quenching/dissipation of PSII [17]. It has been proved that the \(P\) rate increases by improving the status of leaf nutrients, including nitrogen, phosphorus, potassium, and zinc, while \(D\) rate decreases [28], which consequently lead to higher grain yield, as confirmed in our research by the significant positive relationship between \(P\) rate with grain yield. According to previous studies, these nutrients, released by microbial activity and chemical fertilizers, can improve the PSII photochemistry functions, electron transport systems, photosynthetic pigments biosynthesis and grain yield under both non-stress and stress conditions [29; 30; 31]. As a consequence of lower \(P\) and higher \(D\) and \(L\) values in plants under stress, as compared to those in non-stress, incoming light energy should be dissipated non-photochemically, as the most important photo-protection mechanism involved in the safe dissipation of excess excitation energy in PSII [5; 32], which resulted in high NPQ and qCN values in stressed plants. On the other hand, owing to the higher \(P\) rate in fertilized plants, the increments in NPQ and qCN values were less than those in unfertilized (control) plants under salinity and non-stress conditions. In fact, the higher rate of \(P\) in the plants grown under microbiological/chemical fertilization, especially PGPB inoculation combined to the chemical fertilizers, indicated that the reaction centers in the thylakoid membrane were open, which led to less activity of NPQ process (lower rate of NPQ and qCN) [6], as compared to the close ones in control plants. Nevertheless, chemical and inoculum treatments did not have a specific effect on NPQ and qCN under drought condition. Another evidence for the discrepancy between plants grown under drought and salinity is the lack of a significant relationship between the NPQ and grain yield in drought stress, while their negative relationship was significant under salinity condition, which may be attributed to their different mechanisms to cope with the drought and salinity stresses, especially the regulation of the photochemical and non-photochemical quenching parameters, which depends on the stress and its severity [33] and a different response of pigments to the environmental stress [34].