Interaction of Photoperiod and Vesicular‐arbuscular Mycorrhizae on Growth and Metabolism of Sweet Orange

Summary Vesicular‐arbuscular (VA) mycorrhizal infection and growth of Citrus sinensis were increased by longer photoperiods. Photosynthesis and stomatal conductances were greater for mycorrhizal plants, but were unaffected by daylength. Phosphorus levels in leaf tissue from mycorrhizal plants were threefold greater than those in non‐mycorrhizal plants and P levels were slightly greater in plants grown under long‐day photoperiods. Root exudation of reducing sugars was greatest for non‐mycorrhizal plants grown under long day photoperiods, but exudation of amino acids was variable. The results suggested that plants grown under long‐day photoperiods have greater basipetal transport of photosynthates resulting in improved mycorrhizal infection and plant growth response.