We compared variation in sun-canopy leaf anatomy, morphology and photosynthetic rates of coexisting woody species (trees and lianas) in an 8-year-old secondary forest (SF) and mature forest (MF) in the wet season in Xishuangbanna, SW China. Variability of leaf traits of 66 species within growth-form groups in each forest was quantified using coefficients of variation (CV). For the mean values, the woody species in the SF had significantly higher leaf thickness and stomatal density, but lower nonmesophyll/mesophyll ratios than those in the MF. The average leaf area and leaf mass area (LMA) in the studied woody species did not change greatly during the successional process, but differed significantly between the growth forms, with trees having higher values than lianas. The light-saturated photosynthetic rate per unit leaf area (Aa) of the woody species in the SF ranged from 11.2 to 34.5 μmol m-2 s-1, similarly to pioneer tree species from literature data in southeast Asia. The Aa and photosynthetic nitrogen-use efficiency (PNUE) were significantly higher than those in the MF; whereas Aa in the MF ranged between 9 to 21 μmol m-2 s-1, with similar values between lianas and trees. For all woody species in both SF and MF, there were no significant differences in the average values of the CV of all measured variables for both lianas and trees. However, considerable variation in leaf anatomy, morphology, and photosynthetic rates within both growth forms and forests existed, as well as substantial variation in leaf size and stomatal density. We concluded that the tropical woody species formed a heterogeneous functional group in terms of leaf morphology and physiology in both secondary and mature forests. and L. Han ... [et al.].
The ability to modulate photosynthesis is essential for plants to adapt to fluctuating growing conditions. Populus species show high tolerance to various and highly variable environments. To understand their response strategies against fluctuating environments, this study investigated the morphological and physiological differences of white poplar (Populus alba) leaves when grown in a phytotron, glasshouse, and field. Our results show that the palisade cells were elongated in the field, which would enhance intercellular CO2 exchange. Photosynthetic capacity was the highest in the field leaves, as shown by higher electron transport rates (1.8 to 6.5 times) and carbon assimilation rates (2.7 to 4.2 times). The decrease of PSI acceptor-side limitation and increase of PSI donor-side limitation suggests changes in PSI redox status may contribute to photoprotection. This plasticity of white poplar allows adjusting its structure and photosynthesis under fluctuating conditions, which may partly enable its outstanding tolerance against environmental changes.