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Symbiotic nitrogen-fixing trees often grow rapidly and can greatly increase carbon storage in forests, provided other essential nutrients such as phosphorus are abundant.

Nitrogen-fixing trees require large amounts of phosphorus uptake from soil, some of which can be released from organic matter by a nitrogen-based enzyme called phosphatase. It has long been thought that symbiotic nitrogen fixing trees produce more phosphatase enzymes than non-fixing trees but coordinated field tests of this idea across sites are rare. Researchers compared soil phosphatase activity under N-fixing and non-fixing trees grown in multiple locations across the U.S. The team found no evidence that soil phosphatase is higher under N-fixing trees. Fertilization with large amounts of N also did not stimulate phosphatase production. The results of this study add to the growing evidence that there is no connection between rates of N fixation and phosphatase activity. 

Jager, E., Quebbeman, A., Wolf, A.A., Perakis, S.S., Funk, J.L., and Menge, D.N., 2023, Symbiotic nitrogen fixation does not stimulate phosphatase activity in soils under temperate and tropical trees: Oecologia, Online.