Stronger plasticity of leaf characteristics is associated with better shade adaptation in Calycanthaceae.

To understand how Calycanthaceae species adapt to different light levels, we examined the responses of leaf structure, chlorophyll (Chl) content, and Chl fluorescence of five Calycanthaceae species to different light conditions. With the reduction of light irradiance, total leaf thickness of Sinocalycanthus chinensis significantly decreased, and that of Chimonanthus nitens was generally the same. The other three species, Ch. praecox, Ch. salicifolius, and Calycanthus floridus var. glaucus, showed moderate plasticity of leaf structure. With shade treatments, the Chl a content in the leaves of Ch. nitens increased, while that in Ch. salicifolius decreased. However, the Chl a content in Ch. praecox, Ca. floridus var. glaucus, and S. chinensis was not changed with decreased light levels. Leaves of four species (except Ch. salicifolius) showed higher Chl b content and total Chl content, and leaves of all five species showed a lower Chl a/b ratio in shade. The maximal quantum efficiency of photosystem II (PSII) (F_v/F_m) and the effective quantum yield of PSII (Φ_PSII) in S. chinensis were the same regardless of the light regime, but those of the other four species were significantly lower in full sunlight. Another Chl fluorescence parameter, non-photochemical Chl fluorescence quenching, was significantly higher in full sunlight. Our results revealed that among the five Calycanthaceae species, S. chinensis exhibited the highest plasticity of leaf structure in response to different irradiances and Ch. nitens was considered to have the highest shade tolerance. [ABSTRACT FROM AUTHOR]