Nitrogen assimilation and dissimilation in five genotypes of Brachiaria spp.

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Abstract
Five genotypes of Brachiaria spp. were planted in a field experiment with and without nitrate fertilization. Nitrogen metabolism was evaluated by measurements of nitrate reductase (NR) activity in leaves, nitrate accumulation in stems, and nitrogenase activity and dentrification in intact soil–plant cores. There were differences between genotypes in all parameters and a tendency was observed for genotypes with high NR activity and nitrate accumulation to have low nitrogenase activity and vice versa. Brachiaria radicans (Tanner grass) was representative for the first type and B. ruziziensis (CPI 30623) for the second. Denitrification reached 7% of the applied N within 63 h and was lowest in Tanner grass and highest in B. brizantha (FL 902-4). Brachiaria ruziziensis (CPI 30623) plants were able to withstand N stress better than B. radicans as a consequence, possibly, of differences in nitrogenase activity.