Abstract: Insect herbivory on leaf is a common phenomenon in forest ecosystems, which strongly affects tree growth, ecosystem structure and processes. However, it is unclear how insect herbivory influences plant photosynthesis, biomass accumulation and allocation of subtropical tree species. In this study, we examined the effects of insect herbivory and artificial defoliation on the growth, leaf photosynthetic characteristics and biomass allocation in seedlings of two subtropical tree species (i.e., Cinnamomum camphora and Cryptomeria fortunei). Our results showed that short-term (i.e., two months) insect herbivory increased net photosynthetic rate, stomatal conductance, initial fluorescence (F₀) of two tree species, but decreased intercellular CO₂ concentration and chlorophyll a and b contents. However, long-term (i.e., six months) insect herbivory inhibited the growth and total biomass of seedlings, but increased root shoot ratio. The effects of artificial defoliation on leaf photosynthetic characteristics were generally lower than that of insect herbivory, but there was no difference with respect to their impacts on biomass and its allocation among plant organs. Cinnamomum camphora biomass had significant negative correlations with F₀. Stem biomass of Cryptomeria fortunei was negatively correlated with G_s, and positively correlated with chlorophyll a content. Our results implied that insect herbivory induced a short-term photosynthetic compensation, and therefore stimulating leaf photosynthesis, but inhibited the long-term growth and biomass accumulation of tree seedlings. In addition, the simulation of insect herbivory using artificial defoliation method might underestimate the impacts of insect herbivory.

Key words: insect herbivory, subtropical forest, photosynthetic characteristics, biomass allocation