Effect of Temperature on Total Nitrogen Distribution in Pennisetum Americanum

Abstract

Total N uptake and distribution and relative accumulation of N and dry matter were studied from 26 days after sowing until 50% anthesis in two genotypes of Pennisetum americanum growing at day/night temperatures ranging from 18/13 to 30/25°C. Nitrogen was taken up throughout growth and there was no indication of a net loss of N from the whole plant or from individual organs. Rate of N uptake was closely correlated with dry weight increments until stem elongation: there was a single relationship between uptake and dry weight increment over the three temperatures and two genotypes (41 mg N per g whole-plant dry weight increment). Relative rates of N accumulation and dry weight increment were higher at high temperature and again a single equation related relative accumulation of N to dry weight over all treatments. However, in contrast to the constancy of N uptake per unit dry weight, N distribution within the plant was affected by temperature. Low temperatures resulted in high root N concentrations and relatively high NO3 concentrations in root and stem apices. Temperature did not affect the proportional distribution of N between organs of the top. The results are interpreted as showing that activity of components of the nitrogen pathway are adjusted to maintain a constant rate of N uptake per unit dry weight increment in vegetative growth, but that N distribution within pearl millet is sensitive to temperature.