Ecophysiological Characteristics Of Phoebe Bournei Young Trees To Different Light Regimes

The purpose of the present study is to explore the adaptive strategy of light environmental heterogeneity and the natural factors contributed to scattered distribution of Phoebe bournei and the strategy of protection and restoration. Thus, characteristics of morphology, photosynthesis, biomass allocation, ecological stoichiometry, non-structural carbohydrate, as well as carbon isotope composition, in response to different light regimes (100%of full sunlight, L100;40%of full sunlight, L40;8%of full sunlight, L8) were investigated in P. bournei young trees. Our results showed that:1) There were statistically significant difference in maximum net photosynthesis rate (Pnmax), apparent quenching efficiency (AQY), light saturation point (LSP), light compensation point (LCP) and dark respiration rate (Rd). Pnmax, LSP, LCP, Rd declined as the light intensity increased while AQY increased with the increase of light intensity, revealing that P. bournei could adapt to dark light condition by lowering LCP and carbon consumption. Furthermore, the largest Pnmax of young trees under L100indicated the full sunlight was in favour of the accumulation of photosynthetic products by the conversion of solar energy to chemical energy to the largest extent.2) There was no statistically significant difference in tree height between L100and L40, but was significant difference (P<0.05) between L100, L40and L8. The height of L8was the lowest.In different light regimes,the values of basal diameter, leaf number, leaf area, specific leaf area, leaf thickness also have significant differences (P<0.05). Basal diameter, leaf number and leaf thickness were all reduced with the reduction of light intensity. Specific leaf area increased with light intensity decreases. Leaf areas were in the order of L4o> Lg>L100.3) Total biomass, leaf biomass, stem biomass and root biomass were largest under L100. Increase in root biomass, fine root biomass in particular, facilitated to maintain normal water absorption and transpiration and keep high photosynthetic rate while increase in leaf biomass and stem biomass was in favour of light capture and construction of supporting and transportation structure separately. In contrast, root to shoot ratio, leaf biomass ratio, root biomass ratio and stem biomass ratio were of no significant difference under three different light regimes.4) The growth of the above-ground part of P. bournei young trees was predominant by dry matter accumulated in leaves and stems. With the decrease in sunlight intensity, a conservative strategy was adopted by slow gain of resource and consumption. In contrast, the measure was taken to capture and consume resource more quickly in P. bournei young tree under full sunlight. Therefore, it was suggested that mixture of P. bournei and Phyllostachys pubescens will help to reduce the canopy density and then promote the renewal of P. bournei young trees in forestation.(5) Leaf carbon and nitrogen content of P. bournei young trees in the spring, summer, and winter, were manifested as increasing with the reduction of the light environment, and the content of leaf phosphorus in the four seasons was manifested as L4o> L8.There were no significant differences of P. bournei young trees in the carbon contents of root and stem, and significant difference (P≤0.05) in the content of P in the three light environments, the value of which increased with light intensity decreases. There were no significant differences of P. bournei young trees in the carbon contents of root and stem, and significant difference (P<0.05) in the content of P in the three light environments, the value of which increased with light intensity decreases. The indicators of ecological stoichiometry in four seasons showed differently. In spring, Pnmax is positively significant correlation (P<0.01) with C and N, but negative with C/N, the correlation between Pnmax and P, C/P, N/P was not significant. In summer, Pnmax was not significant correlation with both of C, N, C/N, C/P, N/P. In autumn, Pnmax was very positive significant correlation (P<0.01) with N, and highly negative significant correlation (P<0.01) with C/N, but not significant correlation (P<0.01) with C, P, C/P. In winter, Pnmax showed very significant positive correlation (P<0.01) with N, highly negative significant correlation (P<0.01) with C/N, but not significant correlation (P<0.01) with C, P, C/P, N/P. P. bournei young trees manifested as the N limit. The values of NUE, in different light conditions, increase in order of L100>L4o> L8, and of PUE increase in order of L100> L40>L8.The variables of P was greater than N in three light environments.(6) The contents of root, stem, leaf total soluble sugar content, starch content, and NSC, in different light conditions, showed decreased with the lower light intensity.(7) In different light environments, the δ13C values of root showed no significant differences, which were minimum of stem and leave in8%of the light environment. In100%light environment, the δ13C values in different organs showed as fine roots (-29.80‰)> coarse roots (-30.06‰)> stem (-30.71‰)> leaf (-31.85‰), fine roots (-30.57‰)> coarse roots (-30.58‰)> stem (-31.89‰)> leaf (-32.98‰) in40%light environment, fine root (-30.16‰) and coarse roots (-31.27‰)> stem (-32.71‰)> leaf (-33.16‰) in8%of the light environment. From the leaves to fine root, the813C values were upward trend, indicating that the813C values of non-photosynthetic organs, as coarse root, fine root, stem, were generally higher than which of photosynthesis organ, as leave.