Phosphorus deficiency affects the rate of emergence and number of maize adventitious nodal roots

Root growth Is critical for P uptake, especially when soil P availability i s low. We studied the effects of P deficiency on the rate of appearance and number of adventitious nodal roots of field-gown maize plants (Zea mays L. ). Experiments were conducted in 1995, 1996, and 1997 on a long-term P fert ilization trial with three P fertilization regimes, located on a sandy soil in southwest France, Phosphorus deficiency Bad a negative effect on leaf a rea index (LAI), The amount of photosynthetically active radiation (PAR) ab sorbed by the canopy and plant growth were reduced, especially during the f irst phases of the crop cycle (between the 7- and 14-visible-leaf stage). T he emergence of adventitious roots was delayed for P-deficient plants, but the synchrony between root and leaf emergence was not disturbed. The final number of roots was significantly lower for P-deficient plants for phytomer s 4 to 7. These phytomers were those for which root differentiation occurre d when the PAR absorbed by the canopy was most severely reduced relative to the fertilized P treatments. A unique relationship was found for all years and P treatments between the cumulative amount of PAR absorbed by the plan t and the number of emerged adventitious roots. We concluded that the reduc ed number of adventitious roots for phytomers 4 to 7 on P-deficient plants may be caused by the negative effect of P deficiency on LAI and its subsequ ent effect on PAR absorption and C nutrition of plants during the period of root emergence from specific phytomers.