Abstract:

Four common shrubs (Lespedeza bicolor, Spiraea triblobata, Ostryopsis davidiana and Rosa xanthina) were selected in Guancen Mountains to study the physiological and morphological acclimation to three different light environments (10%-20%, 30%-50% and 100% transmittance levels)in the field. Photosynthetic parameters, chlorophyll contents, SLR, LAR, biomass allocation patterns and phenotypic plasticity indices were measured. The results showed that in 10%-20% forest light environment, the adult plants of Spiraea triblobata did not respond to the understory light environments. Their photosynthetic, Chla contents, morphological and most biomass allocation traits remained the same as those growing under full light. Their SMR decreased, but AQE and Chlb content were 30%-50% higher than that in full light levels. The low light responses of Lespedeza bicolor were also limited. Its photosynthetic LAR, LMR and AB were the same as those growing under full light. Its SMR also decreased in 10%-20% light level, while Chlb, SLA and RMR increased. In contrary, the adult plants of Rosa xanthina and Ostryopsis davidiana responded relatively stronger to understory light environment. In 10%-20% light level, the A_max, LSP and RMR decreased, and Chla and b contents, SMR and AB increased. Meanwhile, the AQE of Rosa xanthina and the SLA and LAR of Ostryopsis davidiana also significantly increased. In addition, the morphological plasticity indices of Rosa xanthina and Ostryopsis davidiana were generally higher than that of Spiraea triblobata, which supported the hypothesis that there is a close relationship between morphological plasticity and shade tolerance, but not the relationship between physiological plasticity and high light environment acclimation. The differences in ecophysiological responses and phenotypic plasticity indices of adult plants of these four naturally-regenerated shrubs under different forest light environments will significantly affect their niches in different forest communities within their distribution ranges, thus the restoration and protection of montane forest ecosystems should consider the light acclimation characteristics of naturally-generated shrubs.

Key words: naturally-regenerated shrubs, understory light environments, photosynthesis, chlorophyll contents, SLA, biomass allocation, phenotypic plasticity