Red Clover Varieties with Nitrogen Fixing Advantage During the Early Stages of Seedling Development

Plant and environmental factors affect root nitrogen (N) exudation dynamics in legumes. To better understand the genotypic variability and plant factors affecting root N release nodulation, plant growth, tissue N content, and root N exudation of six (three diploid and three tetraploid) red clover (Trifolium pratense L.) varieties were evaluated under controlled environmental conditions during the first eight weeks of plant growth after rhizobia inoculation. Genotypic differences were found for nodulation, plant dry weight, leaf area, root attributes (root length, surface area, volume, and diameter), shoot and root N concentration, and N content. Genotypic differences were found for root exudate N content in terms of NO3--N, NH4+-N, and dissolved organic N (DON). In general, root exudate inorganic N content was greater in tetraploid varieties than in the diploids throughout the growth period. Root exudate DON content was greater than the inorganic N content. The NO3--N content in root exudate was positively correlated with root growth attributes and root N concentration while, NH4+-N content was positively correlated with nodule number. Root exudate DON positively correlated with shoot N concentration and average nodule dry weight. These results highlight the existence of genotypic differences among red clover varieties for plant morphological factors affecting root N release during the early stages of plant development.

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