Effect of Mycorrhizal Inoculation on Rhizosphere Properties, Phosphorus Uptake and Growth of Pine Seedlings Treated With and Without a Phosphate Rock Fertilizer

ABSTRACT

A pot trial was carried out for 10 months to investigate the effects of ectomycorrhizal (ECM) fungal infection and phosphorus (P) fertilization on the growth of newly germinated Pinus radiata D. Don seedling, P uptake by the seedlings and rhizosphere properties. The experiment consisted of two phosphate rock (PR)-P application rates [0 and 100 mg P kg^{− 1} soil supplied as Ben Guire PR (BGPR)] and 5 soil treatments (autoclaved soil, fungicide-treated soil, untreated natural soil, and Rhizopogon rubescens Tul. and Suillus luteus (L. ex. Fr.) S. F. Gray inoculated soils). The results showed that the treatment effects were more striking in P-fertilized treatments. In P-fertilized soils, all the non-autoclaved treatments significantly increased seedling growth and P concentration and P uptake in plant tissues compared with the autoclaved treatment. The ECM inoculation produced greater phosphatase activities, higher oxalate concentration, and more plant-available P (soil solution P and resin extractable P) in the rhizosphere soils than in the bulk soils in P-fertilized soil. Compared with S. luteus, R. rubescens inoculation resulted in greater ECM tip density in seedling roots in P-fertilized treatments, indicating that R. rubescens are more susceptible to infection of radiata seedling roots. Approximately 57–69% of the BGPR added to the soil had been dissolved in 10 months after application and BGPR significantly increased seedling height, ECM root tip density, and P concentration in shoots in both autoclaved and non-autoclaved treatments.

Keywords:

• ectomycorrhizas
• rhizosphere
• oxalate
• phosphatase activity
• phosphate rock

ACKNOWLEDGMENTS

We wish to thank New Zealand Forest Research (Institute Ltd.), Rotorua for providing part financial support through the Centre for Sustainable Forest Management for this study, and Landcare Research New Zealand Ltd. Palmerston North for the analysis of the oxalate concentration of the samples.