Fungal Inoculants for Native Phosphorus Mobilization

Abstract

More than 96% of the total native phosphorus present in any agricultural soils is in unavailable inorganic or organic forms. They may be utilized by the plants through the activity of efficient fungi which are secreting/producing/releasing huge amount of acid phosphatase, alkaline phosphatase, phytase, and organic acids. The important fungi capable of doing the job are in the groups of Aspergillus, Emericella, Gliocladium, Penicillium, Trichoderma, and Chaetomium besides some AM fungi like Glomus and Gigaspora. The three efficient fungi already used as inoculums are Chaetomium globosum, Penicillium purpurogenum, and Emericella rugulosa. Seed inoculation using these fungi is mobilizing 45–60 kg P and 16–25% increase in yield of different crops. They are mainly exploiting from labile and moderately labile fractions of phosphorus. Minimum concentration of organic acid of fungal origin required to solubilize P was found between 0.2 and 0.5 mM. In fungal-inoculated plants, microbial contribution was more than the plant contribution. Fungal extracellular enzymes were more efficient than their intracellular counterpart. P uptake occurs around the root tip into epidermal cells with their associated root hairs and into cells in the outer layers of the root cortex. Phosphate can also be taken up by transfer from mycorrhizal fungi to root cortical cells.