Integrative co-application of citric acid and halotolerant/halophilic citrate-utilizing PGPR enhances leaf ionic homeostasis, productivity, and quality of Vitis vinifera L. in saline-calcareous soils

Abstract Purpose Salinity severelyconstrains viticulture in calcareous soils by disrupting rhizosphere microbial community, nutrient availability, and physio-biochemical homeostasis, thereby reducing fruit yield. This study aimed to (i) assess the effects of soil-applied citric acid (CA) and halotolerant/halophilic citrate-utilizing plant growth-promoting rhizobacteria (CU-PGPR; Bacillus spizizenii and Halobacillus marinus ) on the microbial community and chemical properties of saline-calcareous soil, (ii) evaluate vine physio-biochemical responses to the individual and combined treatments, and (iii) determine their impacts on yield and fruit quality. Methods A 2-field experiment (2023/2024 and 2024/2025) on Vitis vinifera at the Faculty of Agriculture’s Experimental Farm (32°42′ N, 29°75′ E), Fayoum University, Egypt. This study evaluated three CA rates: 0 (CA 0 ), 100 (CA 100 ), and 200 (CA 200 ) g vine⁻¹ season⁻¹ and three inoculation treatments: non-inoculated (NI), H. marinus , or B. spizizenii . Measurements included rhizospheric bacterial counts, soil chemistry (pH, electrical conductivity; EC e , and macro- and micro-nutrient availability), leaf and petiole nutrients, physio-biochemical traits, yield, and fruit quality. Results Co-application of CA 200 × B. spizizenii exhibited the strongest synergistic effects. Total bacterial count and specific functional groups markedly increased. Soil pH declined by 6.1%, while available N, K⁺, Fe²⁺, and Zn²⁺ increased by 817%, 105%, 659%, and 720%, respectively. The CA 200 × H. marinus resulted in the highest available P (310% above CA 0 × NI), though EC e was unaffected. Enhanced nutrient bioavailability improved ionic balance, raising the leaf K⁺/Na⁺ ratio by 78% and the Ca²⁺/Na⁺ ratio by 74.7%, while reducing Na⁺ by 31% compared with CA 0 × NI. Physio-biochemically, CA 200 × B. spizizenii boosted vine water content, osmotic adjustment, antioxidant capacity, and photosynthetic efficiency over CA 0 × NI. Consequently, grape yield, pruning weight, fruit TSS/acid ratio, and firmness increased by 97%, 81%, 99%, and 24%, respectively, averaged across both seasons, over CA 0 × NI. Conclusion Co-application of 200 g CA vine − 1 season⁻¹ with B. spizizenii inoculation effectively revitalizes microbial activity and enhances nutrient bioavailability, offering a promising strategy for sustaining viticulture under saline-calcareous soil conditions.