Growth of celery (Apium graveolens var. dulce) as influenced by phosphite

Although Phosphite (PO₃; Phi) has recently been marketed as "superior P fertilizer" for a wide range of crops, the claim regarding its potential as a fertilizer is controversial. In this study, effects of Phi at both low (0.2 mM) and high (2 mM) rates on growth and phosphorus (P) supply of celery (Apium graveolens var. dulce) were investigated under either low phosphate (PO₄; Pi) (0.1 mM) or high Pi (0.5 mM) supply. The effect of Phi was found to be strongly dependent on the P nutrient status of the plants. Addition of Phi at both rates did not influence growth of high Pi-supplied plants. However, Phi at 2 mM significantly decreased both shoot and root growth of low Pi-supplied plants. Plants grown in this treatment showed bleaching of young leaves and death of root tips and root hairs as typical toxic symptoms of Phi. Shoot P concentration was highly increased by root application of Phi, suggesting that Phi was well absorbed by roots and mobile inside the plants but also corroborating that Phi did not provide P nutrition to celery plants. No beneficial effect on plant growth was detected from the use of this material.