Sour Orange (Citrus Aurantium L.) Growth is Strongly Mycorrhizal Dependent in Terms of Phosphorus (P) Nutrition Rather than Zinc (Zn)

Abstract

ABSTRACTThe partial sterilization of soil eliminates useful microorganisms, resulting in the reduced growth of mycorrhizae-dependent citrus plants, which are often unresponsive to the application of fertilizer. Research was conducted to test the hypothesis that indigenous mycorrhizae (IM) inoculation is as efficient as selected mycorrhizal inoculation under sterile and non-sterile soil conditions. Rhizophagus clarus and indigenous mycorrhiza spores, isolated from citrus orchards, were used as arbuscular mycorrhizae fungi under greenhouse conditions with sterile and non-sterile Çanakçi series (Typic xerofluvent) soils with low phosphorus (P) fertility. Different P (0 and 100 mg kg−1) and zinc (Zn) (0, 5 and 10 mg kg−1) concentrations were used at the start of the experiments. The shoot, root dry weight (RDW), root colonization, and P, Zn, iron (Fe), copper (Cu) and manganese (Mn) concentrations of the shoot were determined; mycorrhizae dependency (MD) was also calculated.The results indicate that R. clarus and indigenous mycorrhiza in sterile and non-sterile soil conditions considerably increased the growth of citrus plants. Owing to existing beneficial indigenous rhizosphere microorganisms, citrus plant growth without inoculation was better in non-sterile soils than in the sterile soils. In non-sterilized soil, the plant growth parameters of R. clarus-inoculated soils were higher than those of indigenous mycorrhiza-inoculated soils. Mycorrhizae infection increased certain citrus plant growth parameters, such as root infection, biomass and nutrient uptake (P, Zn, Fe, Mn and Cu). In sterile soil, the addition of up to 5 mg kg−1 soil Zn and the inoculation of R. clarus significantly increased plant growth; inoculation with indigenous mycorrhiza produced more dry weight upon the addition of up to 100 mg kg−1 phosphorus pentoxide (P2O5). Under sterile soil conditions, without considering fertilizer addition, MD was found to be higher than that of non-sterile soils. In general, the contribution of the indigenous soil spores is significant. However, indigenous soil mycorrhizae may need to be managed for better efficiency in increasing plant growth and nutrient uptake. The major finding was that the inoculation of citrus seedlings with mycorrhiza is necessary under both sterilized and non-sterilized soil conditions.