Interactive effects of wind and light on growth and architecture of poplar saplings

Abstract

AbstractTo explore the interactive effects of wind and light on growth and morphogenesis, poplar saplings were subjected to two different levels of wind and light. Morphogenesis, growth, water relations and gas exchange were examined in a factorial experiment. The results showed that wind reduced both shoot height and root growth but did not affect shoot diameter or root/shoot ratio, while light promoted both shoot and root growth, and the root/shoot ratio. However, light and wind consistently increased stem taper. Wind and light reduced leaf water potential and increased stem xylem cavitation at midday. Lateral shade decreased root and stem hydraulic conductance, while wind reduced stem hydraulic conductance without influencing root hydraulic conductance. Wind and light reduced the vulnerability of poplar saplings to xylem cavitation. Lateral shade strongly reduced the CO2 assimilation rate and stomatal conductance. Wind reduced the assimilation rate at midday under full sunlight. In summary, both light and wind increased stem taper, although the two environmental factors had opposite effects on the growth of poplar saplings. Lateral shading reduced the growth of shoots and roots of poplar saplings by restricting assimilation, and light promoted greater allocation of carbon to roots than to shoots, and to a lower rather than upper portion of the stem, leading to increased root/shoot ratio and stem taper. At the sapling stage, wind reduced shoot height and root growth primarily by interrupting water balance, and also induced thigmomorphogenic responses, such as increased taper. Finally, lateral shading did not suppress the thigmomorphological responses to wind.