Effects of Selected Arbuscular Mycorrhizal Fungi, Rock Phosphate, and Compost on Growth and Nutrient Uptake of Citrus Seedlings

Citrus trees are among the most essential fruit plants grown in southern Turkey. Nutrient uptake in the Mediterranean region is limited by factors such as low organic matter, high soil pH, and limited availability of phosphorus and micronutrients. To evaluate, under greenhouse conditions, how rock phosphate (RP), compost, and different arbuscular mycorrhizal fungi (AMF) species influence growth, root colonization, and nutrient uptake (with emphasis on P, Zn, Fe, Mn, Cu) in Citrus (sour orange) seedlings.The experiment was conducted under greenhouse conditions with three compost levels (0, 20, and 40 g compost/kg soil), three rock phosphate levels (0, 2, and 4 g rock phosphate/kg soil), and seven mycorrhizal species (Control, G. mosseae , G. caledonium , G. etunicatum , G. clarium , indigenous mycorrhiza, and a cocktail mixture) as a completely randomized factorial design with three replications. Before the experiment began, compost and rock phosphate were mixed with the sterilised soil and incubated for 3 weeks. Plants were grown for 10 months. Root colonization, shoot and root dry weights, and tissue nutrient concentrations were determined.Results obtained after 180 days of cultivation showed that mycorrhizal-inoculated plants grew significantly more than control plants. The combination of arbuscular mycorrhizal (AM) fungi species, rock phosphate, and compost application led to a remarkable increase in dry matter production, root colonisation, and nutrient uptake. An increase in RP application resulted in higher MD across all mycorrhizal species and compost treatments. However, increased compost application reduced MD for all mycorrhizal species. Citrus seedlings were colonised by several mycorrhizal species, and the mycorrhizal dependency (MD) of these seedlings was assessed. The highest MD (91%) was observed in seedlings inoculated with G. mosseae and treated with 20 g of compost and 4 g of RP per kg of soil. Citrus seedlings inoculated with G. mosseae exhibited the highest MD (81%), while those inoculated with native mycorrhizal spores showed the lowest MD (59%). Citrus seedlings inoculated with mycorrhiza contained higher levels of phosphorus, zinc, and other micronutrients compared to non-inoculated control plants.AM fungi, particularly G. mosseae , in combination with 20 g kg-1 compost and 4 g kg ^− 1 RP addition, significantly improved citrus seedling growth and P and Zn uptake.Compared with the sterile control, AMF inoculation markedly increased plant height and biomass. Responses differed among fungal species; G. mosseae and the mixed “cocktail” inoculum generally produced the highest growth and root colonization. Higher RP doses tended to suppress colonisation; the effect of compost on colonisation depended on species × dose interactions. AMF treatments raised shoot P concentrations from ~ 0.04–0.07% in control/ineffective-local treatments to ~ 0.08–0.12%, and increased Zn, Fe, Mn, and Cu concentrations. RP and compost alone had limited effects, whereas their combined use with AMF supported both growth and nutrition; the full agronomic effect of RP likely requires a longer incubation period for solubilization.