Interactive effect of salinity and phosphorus availability in plant-soil continuum: Differential responses of Durum wheat (Triticum durum) under contrasting regimes of Orthophosphate and Polyphosphate fertilization

The predicted global population is set to reach 9.6 billion by 2050, which highlights the necessity to increase crop productivity to meet the growing demand for food and nutrition. Nevertheless, this is becoming increasingly challenging due to changing climatic conditions mainly under salinity stress. Soil phosphorus (P) availability and mobility are often limited in salt-affected soils mainly in arid and semi-arid regions. In Morocco, the soils are calcareous and deficient in available P. Hence, it is important to focus on a reasonable and more efficient use of P resources. In the present work, we conducted a series of experiments on durum wheat plants in controlled conditions (Petri dishes, pots, and hydroponic trials) during different stages of plant development. The objective is to evaluate above and belowground changes of wheat plants in response to contrasting P fertilizers doses (0, 30, 45 and 60 ppm of P) and forms: Orthophosphate (OrthoP) and Polyphosphate (PolyP) under salinity. Indeed, different physiological and agronomic traits have been used as key parameters in the enhancement of P fertilizer use efficiency, P acquisition, and crop quality. In the first experiment, we highlighted the effect of P supply on the germination characteristics, seedling growth and their mineral content under salt stress conditions. A second experiment was carried out in hydroponic conditions which focused on the wheat plant's growth using remote sensing technology to measure in vivo physiological parameters such as chlorophyll content index, stomatal conductance, chlorophyll a fluorescence, absorbance, and reflectance with some related parameters. In a pot experiment, we focused on the above-ground part where we assessed the photosynthetic performance and nutrient uptake of durum wheat grown under moderate salt stress. We also investigate if there are any differences between plants’ responses to Ortho-P and Poly-P application in the improvement of the enzymatic and non-enzymatic antioxidant systems to boost ROS detoxification. Similarly, we focused on the below-ground wheat plants’ responses with a special emphasis on how PolyP and P doses alter roots' morphology and their anatomy under salinity. In addition, we emphasized the significance of interconnections between below-ground and above-ground parts of wheat plants for improved P uptake under salt stress conditions. Another pot experiment focused on soil characteristics, major soil enzyme activities, soil nutrient availability and mobility of the rhizospheric and non-rhizospheric soil to improve both the P fertilizer’s use efficiency and soil quality under salinity. Our findings indicate that optimizing phosphorus fertilization management can achieve these goals. Using PolyP not only boosted wheat P acquisition but also coordinated above-below-ground traits, resulting in improved nutrient uptake and photosynthesis efficiency. The best results were observed with Poly-B at a low P concentration of 45 ppm, outperforming OrthoP which showed the best performances at a higher dose (60 ppm) only at moderate salt stress conditions. In conclusion, PolyP could be a favorable option as it gives positive significant responses at lower doses which reduces phosphorus losses over time in salt-affected soils while reducing the frequency of fertilizer application. Furthermore, the micronutrient chelation property enables PolyP fertilizers to enhance simultaneously the uptake of P and micronutrients under salinity where the P availability is reduced. All these findings could enhance the current understanding of durum wheat growth and promote the use of polyphosphates as a sustainable and effective source of phosphorus for crop growth in saline conditions where knowledge is still limited.