The Response And Acclimation Of Two Different Plant Functional Groups To Different Light Regimes In Subtropical Evergreen Broad-leaved Forest

As a result of special geographical environment, China has the largest area and typical-developed evergreen broad-leaved forest in the world. The function and effect of evergreen broad-leaved forest are not clearly recognized for a long period, so large area of forest was destroyed and exploited, which caused serious ecocatastrophe.Light is one of the most important environmental factors, it limits the subsistence and growth of plant grown in the forest. Studies on the response and acclimation of different plant functional groups to different light regimes, first of all, it makes us understand the physiological demand and ecological trait of dominant species at the period of seedling period of evergreen broad-leaved forest. Second, ecophysiological methods can be used to research the forest regeneration, the dynamic of community and the intrinsic drive-mechanism of succession on the individual level.The seedlings of evergreen broad-leaved species Liquidambar formosana and deciduous broad-leaved species Gordonia acuminata were chosen to plant in different light regimes (Open,Gap,Understory). The microclimate of different light regimes and the change of the net photosynthetic rate (P_n), chlorophyll fluorescence, leaf trait, growth and biomass allocation in different light regimes were compared, the results of the experiments showed that:1) The microclimate was significantly different in different light regimes, the diurnal mean photosynthetic active radiation (PAR) in Open was about 1200μmol·m^-2·s^-1, which was 2.1 and 36.4 times than Gap and Understory, respectively. Besides, the daily mean land surface temperature was significantly higher than in Gap and Understory, but the daily mean relative humidity was significant lower than in Gap and Understory.2) The photosynthetic capacity (P_s) of Liquidambar formosana seedling was largest than Gordonia acuminate in Open, the P_s about 13μmol·m^-2·s^-1, which was 4 times than Gordonia acuminate seedling in Open. The P_s of Liquidambar formosana and Gordonia acuminata seedling in Gap was high, about 12 and 8.2μmol·m^-2·s^-1 respectively, but the P_s of Gordonia acuminate seedling was 1.2 times than Liquidambar formosana seedling in understory. With the decreasing of PAR, the light saturate point (LSP), light compensation point (LCP), CO₂ compensation point (Γ) and dark respiration rate (R_d) of two seedlings significantly decreased.3) The maximal photochemical efficiency of PSâ…¡(Fv/Fm) of Liquidambar formosana seedling were 0.82 and 0.84 in Open and Gap respectively, but it was 0.78 in Understory. The Fv/Fm of Gordonia acuminata seedling increased with the decreasing of PAR, it was about 0.72 in Open, but it was 1.2 times in Undertory than in Open. Besides, the correlation analyze showed that: under different light regimes, the actual photochemical efficiency of PSâ…¡(Yield) and the photochemical quenching coefficient (qp) of Liquidambar formosana and Gordonia acuminate seedlings had negative correlation with the PAR, but the electron transport rate (ETR), the relative limit of photosynthesis (L_PAR) and the non-photochemical quenching coefficient (qN) had positive correlation with the PAR significantly.4) The chlorophyll content of Liquidambar formosana seedling was highest in Gap, and lowest in Open, but the chlorophyll content of Gordonia acuminata seedling increased with the PAR decreasing, it was 1.6 times in Understory than in Open. Under different light regimes, the change of leaf angle of Liquidambar formosana seedling was significantly larger than Gordonia acuminate seedling. The leaf mass per unit area (LMA) of Liquidambar formosana and Gordonia acuminate seedling decreased with PAR, but single leaf area (L_s) of that two species were not changed regularly. Besides, the petiole length of Liquidambar formosana seedling was 18～30 times longer than Gordonia acuminate seedling, and the variety was significant under different light regimes. The stomata length, width, area and density of Liquidambar formosana and Gordonia acuminate seedling decreased with PAR. Compared to Gordonia acuminata, palisade mesophyll of Liquidambar formosana seedling in Open was developed better, which showed distinctly xeromorphic leaves, for the leaf of Liquidambar formosana, the ratio of the palisade mesophyll to spongy mesophyll (P/S) was largest (about 1.87) in open, which was about 4.8 times than in Understory, but the P/S of Gordonia acuminate seedling was largest in Gap (about 0.55), it was smallest in Open, about 0.36. Besides, the shape of palisade cell of Liquidambar formosana leaf changed from slight to podgy, but the palisade cell of Gordonia acuminate leaf did not have regularly variety. In conclusion, the plasticity of leaf traits of Liquidambar formosana seedling is larger than Gordonia acuminate seedling under different light regimes.5) The plant height, total leaf number, crown-width and total leaf area of Liquidambar formosana and Gordonia acuminate seedling was highest in Gap, but these indexes of Liquidambar formosana seedling were lowest in Understory and Gordonia acuminate seedling were lowest in Open. The vertical growth rate and the growth rate of total leaf area of Liquidambar formosana and Gordonia acuminate seedling was highest in Gap, and the rate of Liquidambar formosana seedling was larger than Gordonia acuminate seedling significantly. The growth rate of stem diameter of Liquidambar formosana seedling was highest in Open, about 0.36cm·M^-1, but for Gordonia acuminate seedling, it was highest in Gap, about 0.26cm·M^-1. The total biomass of Liquidambar formosana seedling decreased with PAR, which in Open was 4 times than in Understory, but the total biomass of Gordonia acuminate seedling was highest in Understory, it was lowest in Open and was about 0.45 times than in Gap. The root to shoot ratio (R/S) of Liquidambar formosana and Gordonia acuminate seedling increased with PAR, but their leaf weight to total weight ratios were all highest in Gap. The relative growth rate (RGR) of Liquidambar formosana seedling was highest in Open, about 7.90 mg·g^-1·day^-1, which is 39.5 times than in Understory. But the RGR of Gordonia acuminate seedling was highest in Gap, it is about 16.7 times higher than in Open. Besides, under different light regimes, the growth plasticity of Liquidambar formosana seedling was higher than Gordonia acuminate seedling.In general, the results showed that:â‘ . The difference of light environment is the main driving force of the change of different function group adaptability.â‘¡. Deciduous broad-leaved species Liquidambar formosana can grow fast in high light intensity habitats, it is difficult to survive in understory. Evergreen species Gordonia acuminata can grow better in Gap, it also can survive in low light regime, but it can not acclimate to the extreme high light.â‘¢. The acclimatization difference to light regimes, which make the broad-leaved species Liquidambar formosana become the pioneer species of evergreen broad-leaf forest, this kind of species played a very important role in community succession and vegetation restoration. Evergreen species Gordonia acuminate is moderate shade-tolerant species and the succession seral spices.â‘£. Deciduous broadleaved species is dominant species in evergreen broad-leaved forest, which has important effects in the succession of ever green broad-leaf forest. Deciduous broad-leaved species can be considered to be used in rehabilitating and restoring subtropical evergreen broad-leaved forest as pioneer population.