Improving the Utilization of Legacy P in Animal Manured Soils Using Transgenic Plants that Express a Microbial Phytase

Sustainability of P is a major global issue with the combined effects of variability in costs for mineral fertilisers and their profligate use leading to both limitations and excess of P across different agricultural systems. Systems where animal manures are used for fertilisation often accumulate P to a point beyond where excess P contributes to eutrophication. Increasing the availability of organic forms of P, such as inositol phosphates that can be a significant component of the organic P present in manure and soil, should be an important research target. Here we tested whether transgenic N. tabacum plants which express a fungal phytase gene (phyA from Aspergilus niger), either constitutively or under control of a root-hair P-inducible promoter, were able to acquire more P from soils with long-term supplementation with manures. Plants that constitutively expressed phytase had enhanced root phytase activity and ability to accumulate up to 4.2-fold more P than control plants when grown in soils supplemented with monogastric animal manures. In contrast, the same plants did not accumulate more P in soils supplemented with ruminant manure. These results suggest that P-use efficiency could be improved in systems fertilised with monogastric animal manure by increased phytase activity in the rhizosphere enhancing the use of legacy P and reducing the need for continued addition of inorganic fertilisers.