Abstract
Quercus aliena var. acuteserrata and Fagus engleriana are important species in the temperate and subtropical middle-elevation mountainous areas of China. In this study, we investigated the regeneration dynamics, diameter size class distributions, and the light response curve of these two species to better understand the effects of light availability on the regeneration of Q. aliena var. acuteserrata and F. engleriana. The results showed that both species had a high abundance of seedlings in the field, but the survival rate from seedling to sapling stage was nearly zero for Q. aliena var. acuteserrata and only 6%-8% for F. engleriana. In the mixed-forest that contained both species, the population of F. engleriana showed a stable pyramidal age structure, but the size structure of Q. aliena var. acuteserrata was dominated by a few cohorts of trees that were able to establish within a short time period. From the light saturation response curve of the two-year old cohort, Q. aliena var. acuteserrata seedlings in gaps had a higher maximum photosynthetic rate (4.61 #mu#mol·m~(-2)·s~(-1)) than F. engleriana (4.16 #mu#mol·m~(-2)·s~(-1)) and, for the seedlings under canopy, F. engleriana had higher maximum photosynthetic rate (3.89#mu#mol·m~(-2)·s~(-1)) than Q. aliena var. acuteserrata (3.68 #mu#mol·m~(-2)·s~(-1)). Moreover, seedlings of F. engleriana reached maximum photosynthetic rates with lower photosynthetic photon flux density than Q. aliena var. acuteserrata. The light induction curve indicated that both the response speed and the maximum photosynthetic rate of Q. aliena var. acuteserrata understorey seedlings were lower than that of F. engleriana, which demonstrated different competitive abilities and shade-tolerance characteristics of the two species. Resource allocation experiments showed that Q. aliena var. acuteserrata seedlings allocated more biomass to above-ground growth whereas F. engleriana seedlings allocated more biomass to under-ground growth. These results are consistent with the different light use strategies of the two species.
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