Nitrogen form effects on early corn root morphological and anatomical development

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Abstract
Enhanced NH4 nutrition causes thicker roots (higher g/m root length) than NO3 nutrition. This study examined the underlying anatomy of N‐form altered root morphology. Corn (B73xLH51) was cultured in complete nutrient solutions containing NO3‐ or NH4‐N. Plants were harvested four times between 13 and 20 days after germination. Root lengths were measured and photomicrographs taken of primary and nodal root cross‐sections. Plants grew better under the NH4 regime. This was probably due to controlling acidity in the pH 6.0 to 6.5 range using 2.0 mM MES. The primary root system was 16% thicker under NH4‐N. No difference due to N form in the cross‐sectional area of the primary axis base was detected, suggesting that NH4‐N caused thicker laterals. Cross sectional areas of the first tier nodal roots were 27%‐ and 2nd tier roots 10.5%‐ greater under NH4‐N. Changes in the stelar and cortical regions were proportional in 1st tier nodal roots, but the cortex accounted for most of the NH4‐induced thickening in 2nd tier nodal roots. The number of late metaxylem elements was not affected by N form. Possible implications of these morphological and anatomical differences are discussed.