Delayed leaf greening (e.g. young leaves with red coloration) is common in subtropical forests. But its roles in leaf herbivory, seedling survival, and biodiversity maintenance are not clear. Delayed greening leaves may suffer weaker herbivore damage due to their less visibility to insects lacking a red photoreceptor or higher chemical defense. Leaf herbivore damage and seeding mortality may also be higher in sites with more conspecific neighbors. This conspecific negative density dependence (CNDD) effect is an important mechanism for biodiversity maintenance. However, it is not well understood how CNDD vary across species with different degrees of delayed leaf greening. To assess the effects of delayed greening on leaf herbivore damage, we calculated young leaf color (RGB channel) and herbivory damage of 35 common species through digital photos taken from 600 seedlings plots within a 3 ha permanent forest plot in a subtropical evergreen broad-leaf forest at Heishiding Nature Reserve, Guangdong Province, in the spring of 2018. Species were separated into different delayed greening groups based on young leaf colors. Using a decade-long census data (from 2007 to 2018), we assessed the variation of CNDD effects on seedling survival across species with different degrees of delayed leaf greening.
Results/Conclusions
R:G ratio (the ratio of red color to green color) of every observed leaf was representative of the degree of delayed greening at individual level. Different species were divided into three coloration categories represented strong (red color), weak (light blue or light green) and no delayed greening (green). We found that insect herbivore damage was lower in young leaves of the species with strong delayed greening. Larger R:G ratio had an positive effect on reducing insect herbivory at individual level. Seedlings of strong delayed greening group suffered weaker CNDD while others relied more on heterospecific protection. We concluded that delayed leaf greening decreased insect herbivory and seedlings with delayed greening leaves suffered weaker conspecific negative density dependence.