Trade-off relationship between light interception and leaf water shedding at different canopy positions of 73 broad-leaved trees of Yangji Mountain in Jiangxi Province, China

Abstract

<p indent=0mm>As light interception and leaf water shedding may require different leaf traits, trade-offs may exist between the leaves’ abilities in light interception and leaf water shedding. Moreover, such trade-offs may vary with the vertical canopy position as leaf traits vary with tree height. We studied the variations in leaf traits at different canopy positions to study how canopy positions would affect the trade-off between the traits related to light interception and leaf water shedding in subtropical broad-leaved trees. We used the standardized major axis regression method to analyze the relationships among leaf morphological traits (leaf thickness and leaf length/width ratio), configuration traits (leaf angle and leaf drip tip length), and physiological traits (photosynthesis-light saturation point and photosynthesis-light compensation point) between sun and shade leaves. The results are as follows: (i) There was no significant difference in the leaf thickness and leaf length/width ratio at different canopy positions (<italic>P</italic>>0.05). The leaf angle (34.92°±1.15°), light saturation point ((954.89±27.86) µmol/(m²·s)), and light compensation point ((29.45±1.02) µmol/(m²·s)) at the upper canopy were significantly higher than those at the lower canopy (leaf angle: 16.66°±0.50°, light saturation point: (520.74±15.47) µmol/(m²·s), and light compensation point: (12.54±0.38) µmol/(m²·s); <italic>P<</italic>0.05). However, the leaf drip tip length was significantly shorter at the upper canopy position ((4.26±0.15) mm) than at the lower canopy position ((7.18±0.22) mm; <italic>P</italic><0.05). (ii) There were significant correlations among leaf angle, leaf drip tip length, light saturation point, and light compensation point at different canopy positions (<italic>P</italic><0.05), but the leaf drip tip length and leaf length/width ratio were only weakly correlated at the upper canopy leaves (<italic>P</italic><0.05). (iii) Common slope (<italic>P</italic>>0.05) and isometric scaling existed among the leaf angle, light saturation point, and light compensation point at different canopy positions, but there was no common constant (<italic>P</italic><0.05). These results indicated that the canopy position does not alter the trade-off strategy between light interception and leaf water shedding. The leaf drip tip length and inclination were mainly affected by the light saturation point and light compensation point.