Interactive effect of fluorescent pseudomonads rhizobacteria and Zn on the fractionation and availability of Zn in the rhizosphere soil of pistachio seedlings (Pistacia Vera L.) under salinity condition

Background and objectives: Soil salinity and Zn deficiency are among the most important limiting factors for growth and yields of pistachio trees in many regions of Iran, especially in the Rafsanjan area. The use of plant growth promoting rhizobacteria (PGPR) is new strategies to reduce destructive effects of salinity and improvement of nutrient availability. This study investigated the interactive effect of the fluorescent pseudomonads rhizobacteria and Zn on the fractionation and availability of Zn in the rhizosphere soil and uptake of Zn by shoot of pistachio seedlings (cv. Badami) under salinity condition.
Material and methods: A greenhouse experiment was conducted in a factorial experiment based on completely randomized design with three replications in order to evaluate the interactive effect of fluorescent pseudomonads rhizobacteria (pf0 (non-inoculated control), pf1, pf2 and pf3) and Zn application (0 and 5 mg Zn kg-1) on the Zn fractionation in the different levels of soil salinity {0 (1.46 dS m-1), 1000 (7.32 dS m-1) and 2000 (12.0 dS m-1) mg NaCl kg-1 soil} and its relationship with concentration and uptake of Zn in the pistachio seedlings (Pistacia Vera L. cv. Badami) shoot.
Results: The results indicated that salinity and inoculation with fluorescent pseudomonads increased the DTPA- extractable Zn (DTPA-Zn) content and the forms of water soluble plus exchangeable (WSEXC) Zn, carbonate-bound (CA) Zn and organic matter-bound (OM) Zn, while decreased Fe-Mn oxide-bound (FeMnOX) Zn and residual (RES) Zn in the rhizosphere soil. Inoculation by fluorescent pseudomonads increased the DTPA-Zn, WSEXC-Zn, CA-Zn and OM-Zn contents by 52, 26, 29 and 35%, respectively but decreased FeMnOX-Zn and RES-Zn contents by 24 and 3 %, respectively. Also, Zn application significantly increased all forms of Zn (except residual form) in the soil. The results showed that salinity reduced the concentration and uptake of Zn in the pistachio seedlings shoot, while inoculation with fluorescent pseudomonads and treatment with Zn incrased its contents at all salinity levels. However, the combined application of the fluorescent pseudomonads and Zn were more effective. There was a positive and significant correlation between Zn uptakes by shoot and DTPA-Zn, WSEXC-Zn, CA-Zn and FeMnOX-Zn. As well as, soil salinity and inoculation by fluorescent pseudomonads reduced pH value of rhizosphere soil from 7.73 to 7.46 and 7.59, respectively.
Conclusion: The results showed that soil salinity increased Zn availability in the rhizosphere soil, while reduced the concentration and uptake of Zn by pistachio seedlings shoot due to reduce of root volume, water availability and high content of Na+ ion. Thus, the use of superior isolates-especially Zn solubilizing bacteria- can effectively increase the availability of Zn in soil and uptake of Zn by plants through increasing root growth. However, WSEXC-Zn, CA-Zn and FeMnOX-Zn could be used as available fractions of pistachio seedlings.