Effect of droughting and chilling on maturation and chemical composition of Townsville Stylo (Stylosanthes humilis)

Abstract

The effects of droughting and chilling on maturing Townsville stylo plants was assessed in terms of growth, seed and leaf shed, nitrogen, phosphorus, and amino acid composition. The major effect was due to droughting. Temperature participated as a small temperature-droughting interaction, in that cold reduced growth and increased proline under moist, but not under dry conditions. With droughting under warm conditions seed and leaf shed were increased and the nutrient content of seed was raised, which resulted in more of the plant's nitrogen and phosphorus being lost in these fractions. Droughting increased soluble nitrogen at the expense of protein nitrogen, but the amino acids fell as a proportion of the soluble nitrogen. The interrelations of nine amino acids were examined by multivariate techniques and it was shown that proline and aspartic acid behaved atypically, and that while other amino acids fell, proline increased some 10-fold under drought or cold stress. These effects indicate that soluble nitrogenous components may both increase and change in composition in the maturing plant as a result of stress, so rendering the plant more susceptible under field conditions to leaching or breakdown caused by dew or by slight showers of rain.