Photosynthetic induction times and photoinhibition in relation to simulated sunflecks (sudden increase of irradiance from 20 to 1,500 lmol m -2 s -1 ) were examined in leaves of co-occurring Fagus lucida (a deciduous tree) and Castanopsis lamontii (an evergreen tree) saplings grown either in a beech forest understory or in an adjacent open site during a late rainy season. Two hypotheses were tested: (1) understory leaves would display faster photosynthetic induction times and greater photoinhibition than open-grown leaves; and (2) evergreen species would have slower photosynthetic induction times and lighter photoinhibition than deciduous species. Times to reach 90% of maximal CO 2 assimilation rate (t 90%A ) and stomatal conductance ðt 90%g s Þ did not differ between species, but showed faster by 3-5 min in open-grown leaves than understory leaves due to higher initial stomatal conductance (g s initial ) and induction state 1 min into simulated sunflecks (IS 1min ) in the former. Our analysis across the published data on photosynthetic induction of 48 broadleaved woody species again revealed the negative correlations between t 90%A and either g s initial or IS 1min , and the similarity of t 90%A and t 90%g s between evergreen and deciduous species. Measurements of maximum PSII photochemical efficiency (F v /F m ) indicated that photoinhibition occurred in saplings in any of the growth habitats during sunfleck-induced photosynthetic induction. Despite no interspecific differences in the degree of photoinhibition, understory leaves of both species suffered heavier photoinhibition than open-grown leaves, as indicated by a stronger decrease of F v /F m in the former. Dynamic changes in the quantum yields of PSII photochemistry and DpHand xanthophyll-regulated thermal dissipation and adjustments in the partitioning of electron flow between assimilative and non-assimilative processes were functional to resist photoinhibition. However, such photoinhibition, together with stomatal and biochemical limitations, would decrease carbon gain during simulated sunflecks, particularly in understory leaves.

We used leaf economics spectrum (LES) theory to explain the bimodal elevational distribution of evergreen tree species, which is one of the most puzzling biogeographic patterns in the world. Our results suggest that elevation acts as an environmental filter to both select the locally adapted evergreen and deciduous species with sufficient phylogenetic variation and distinct leaf economic strategies and regulate their distribution along the elevational gradient based on their coordinated spreading of phylogenetic divergence and leaf economic variation. If species are filtered from regional species pools, changing climate may affect both the species and leaf economic composition of plant communities.

Indocalamus longiauritus (a dwarf bamboo) dominates forest understory and functions as an ecological filter to hinder the regeneration of canopy tree species in many temperate forests. However, the physiological mechanism underlying the function of ecological filters is not clear. In this study, we measured leaf-level carbon capture ability and use efficiency of the dwarf bamboo and the co-existing Fagus lucida (beech) and Castanopsis lamontii (chinkapin) seedlings in forest understory and small gaps in a beech-chinkapin mixed forest in the summer of 2005. The results indicated that I. longiauritus exhibited greater carbon capture ability, as indexed by light-saturated photosynthetic rate (P max ), maximal carboxylation rate, maximal electron transport rate and carboxylation efficiency, than the co-occurring F. lucida and C. lamontii seedlings in both forest understory and small gaps. Higher carbon capture ability in I. longiauritus was related to its greater partition of absorbed light energy to photochemistry. I. longiauritus had higher photosynthetic nitrogen use efficiency than F. lucida and C. lamontii seedlings in both light environments. However, water use efficiency (WUE) in I. longiauritus was higher than F. lucida but lower than C. lamontii. This intermediate WUE in I. longiauritus was related to its intermediate light-saturated stomatal conductance.In addition, I. longiauritus reduced metabolic cost by increasing the ratio of P max to respiration rate, leading to increased net carbon balance. On the other hand, F. lucida and C. lamontii seedlings had greater plasticity of carbon capture ability and leaf structural traits, which might facilitate colonization of gaps and realization of natural regeneration in these species.Keywords Dwarf bamboo AE Beech-chinkapin mixed forest AE Ecological filter AE Carbon capture ability and use efficiency AE Physiological mechanismList of symbols C a CO 2 concentration external to leaf (lmol mol À1 ) C i CO 2 concentration in the intercellular space (lmol mol À1 ) CE Carboxylation efficiency (lmol m À2 s À1 ) Chl n Ratio of leaf chlorophyll to leaf nitrogen in light-harvesting components (mmol g À1 ) Chl area Area-based leaf chlorophyll content (mg m À2 ) Chl mass Mass-based leaf chlorophyll content (mmol g À1 ) F 0 Minimal fluorescence in the dark F m Maximal fluorescence in the dark F s Steady-state fluorescence in the light F 0 m Maximal fluorescence in the light g smax Light-saturated stomatal conductance (mmol m À2 s À1 ) J max Maximal electron transport rate (lmol m À2 s À1 ) J mc Potential rate of photosynthetic electron transport per unit cytochrome f (lmol lmol À1 s À1 ) K c Michaelis-Menten constant of Rubisco for carboxylation (lmol mol À1 ) K o Michaelis-Menten constant of Rubisco for oxidation (mmol mol À1 ) LCP Light compensation point (lmol m À2 s À1 )LMA Leaf mass per area (g m À2 ) LVPD Leaf-to-air vapor pressure deficit (kPa) N area Area-based leaf nitrogen content (g m À2 ) N mass Mass-based leaf nitrogen content (g g À1 ) OIntercellular oxygen conce...