Abstract:

Objective: This study exploredthe effect of different canopy heights of broad-leaved trees on the relationship between individual leaf mass and leafing intensity of current-year twigs, which is helpful to understand the impact of light environment changes on the twig traits. The main objective of this paper is to provide a theoretical basis for revealing the response mechanism of broad-leaved trees canopy growth to the changes in light environment. Method: In this study, the standardized major axis estimation method was used to determine the allometric growth relationship (the relative growth of a certain part of the tree itself) between individual leaf mass(ILM) and leafing intensity (leafing intensity per unit stem mass or leafing intensity per unit stem volume, Lim and Liv) at the different canopy heights of 69 broad-leaved tree species in Yangjifeng Nature Reserve, Jiangxi Province. The effects of canopy heights (upper canopy height and lower canopy height) on individual leaf mass and leafing intensity relationship of evergreen and deciduous trees in subtropical evergreen broad-leaved forests were analyzed. Result: 1) There were significant differences in Liv, specific leaf area and individual leaf area between evergreen and deciduous trees (P < 0.05), but no significant differences in leaf number, ILM, Lim and stem density (P>0.05). There was significant difference in leaf number, Liv, specific leaf area, Lim and stem density of evergreen tree species at different canopy heights (P < 0.05).However, there were only significant differences in leaf area among deciduous trees at different canopy heights (P < 0.05). 2) The relationship between individual leaf mass and leafing intensity of the current-year twigs was negative isometric among evergreen and deciduous trees at different canopy heights. The canopy height had no significant effect on the allometric growth index (equation slope) of ILM-Lim in evergreen trees (P=0.95), but the allometric growth constant (equation intercept) of the upper canopy ILM-Lim was significantly higher than that of the lower canopy (1.24, 1.05, respectively); The canopy height had no significant effect on the allometric growth index (P=0.65) and allometric growth constant (P=0.83) of the deciduous trees ILM-Lim. 3) The canopy height had no significant effect on the allometric growth index (P=0.43) and constant (P=0.16) of the current twigs ILM-Liv of evergreen trees. The canopy height had no significant effect on the allometric growth index (P=0.69) and constant (P=0.28) of the current twigs ILM-Liv of deciduous trees. Conclusion: The canopy height has no effect on the negative isometric relationships between individual leaf mass and leafing intensity of current-year twigs of evergreen and deciduous trees. However, the canopy height hasa significant effect on the allometric growth constant of evergreen trees. The result indicates that under a certain leafing intensity, the upper canopy has higher individual leaf mass. This may be due to the relationship of resource acquisition strategies between twigs and leaf at different canopy heights.

Key words: canopy height, individual leaf mass, leafing intensity