Moringa oleifera (Horseradish Tree) Leaf Adaptation to Temperature Regimes

Geographical distribution and growth of plants are to a great extent governed by temperature. As Moringa oleifera trees are mainly found throughout the tropics around the world, the extent of their physiological adaptability to lower temperature was the main objective of this study. The successful cultivation of M. oleifera trees in cooler climates would greatly increase their production areas. A total of 264 trees were randomly assigned to three temperature-controlled greenhouses, each with a different fluctuating night/day temperature regime namely; 10/20 degrees C, 15/25 degrees C and 20/30 degrees C. Throughout the trial period, stomatal index, leaf conductance as well as leaf sampling for microscopical analysis were conducted to identify morphological adaptations to lowers temperatures in the leaves across all three temperature regimes. Leaves from the 10/20 degrees C treatment had an average thickness of 0.239 mm, compared to 0.136 mm at 20/30 degrees C. This is a 43.1% increase in leaf thickness, as a result of a mere 10 degrees C decrease in temperature. Leaves were thicker mostly due to a broader spongy mesophyll layer. Despite larger stomata observed at the 20/30 degrees C TR, the lower stomatal index resulted in a significant 18.9% reduction in leaf conductance compared to the 10/20 degrees C TR. Although higher temperatures generally favoured tree growth, plants acclimatized to lower temperatures through physiological adaptations. (C) 2011 Friends Science Publishers