Acclimation To Light Acclimation In Seedlings Of Pinus Koraiensis

In this study, the seedlings of Pinus Koraiensis were used as material to investigateresponses of photosystems to different light environments with photosynthetic parameters,chlorophyll fluorescence, protective enzyme activity and ecologic characteristics whenseedlings of Pinus Koraiensis grew in the different light habitat of natural sunshine andshading, man-made light and man-made shading. The results showed as follows:(1) Seedlings of Pinus koraiensis grown in weak-light were transferred to natural sunshinewith 800μmol·m^-2s^-1 intensity(CK), the maximal yield of photosystemâ…¡photochemistry indark-adapted leaves(Fv/Fm) in seedlings of Pinus Koraiensis were 90.2% and 91.8% and97.6% compared with CK during 2, 3 and 4 days respectively. Seedlings of Pinus koraiensisgrown in weak-light after 2, 3 and 4 days were transferred to man-made light with 200μmol·m^-2s^-1 intensity, Fv/Fm in seedlings of Pinus koraiensis were 91.9% and 94.3% and98.2% compared with CK. So photoinhibition with the photosynthetic apparatus in seedlings ofPinus koraiensis was occurred when seedlings of Pinus koraiensis exposed to high light.(2) Seedlings of Pinus koraiensis grown in 8% natural sunshine with 50μmol·m^-2s^-1intensity transferred to 60% natural sunshine with 600-800μmol·m^-2s^-1 intensity,photoinhibition with the photosynthetic apparatus in seedlings of Pinus koraiensis did nothappened when light intensity increased. Non-photochemical quenching (NPQ) in seedlings ofPinus koraiensis increased with treatment time increasing. After seedlings of Pinus koraiensisgrown in 8% natural sunshine were transferred to 20% natural sunshine with 200μmol·m^-2s^-1intensity, Fv/Fm and photochemical quenching (qP) in seedlings of Pinus koraiensis had nodifference compared to CK, it suggested that photoinhibition in seedlings of Pinus koraiensisdid not happened under 20% natural sunshine.(3) The Fv/Fm of seedlings of Pinus koraiensis was 10.6% after seedlings grown in 8%natural sunshine were transferred to natural sunshine with 1200μmol·m^-2s^-1 intensity.Photoinhibition was occurred. When experimental seedlings had been transferred to shadecondition of 8% natural sunshine again for 5 days, Fv/Fm restored to 0.85 under 8% naturalsunshine. It suggested that photoinhibition in seedlings of Pinus koraiensis caused by naturalsunshine was reversible. And then, when seedlings of Pinus koraiensis was exposed to naturalsunshine for 10 days, Fv/Fm, qP andΦPSâ…¡in seedlings of Pinus koraiensis were very lowcomparede to CK.(4) The apparent quantum yield (AQY) and the carbonoxylic efficiency (CE) in seedlingsof Pinus korctiensis grown under open canopy density of forest were higher than the AQY andCE that of close canopy density of forest. But light saturation point (LSP) and net photosynthetic rate at light saturation point (A₃₅₀) in seedlings of Pinus koraiensis grown underclose canopy density of forest were higher than that of open canopy density of forest, qP andNPQ andΦPSâ…¡of the seedlings of Pinus Koraiesis grown under open canopy density offorest were higher than that of close canopy density of forest. But when the light intensity washigher than 200μmol·m^-2s^-1, qP, NPQ andΦPSâ…¡in seedlings of Pinus Koraiesis grown underopen canopy density of forest were lower than that of close canopy density of forest. Itsuggested that seedlings of Pinus koraiensis grown under natural forest was acclimatized todifferent canopy density of forest by regulation of photosynthetic capacity.(5) During light induction, time of qP andΦPSâ…¡in seedlings of Pinus koraiesis grownunder weak-light to reach steady state was longer than that of high light. It suggested thatinducial rate of photosystems in seedlings of Pinus koraiesis grown in weak-light conditionwas slower than that of high-light condition.(6) The death of a tree in the forest canopy creates a gap and allows light to reach the forestfloor, making way for the establishment and growth of a new generation of trees. However, thisincrease in light intensity can stress otherwise low-light adapted plants. The light environmentin a gap is also characterized by large amplitudes in intensity through the course of a day,another potential stress factor in shade-adapted seedlings. Seedlings of Pinus koraiesis grownunder forest could receive variable light and fluctuate in different time and day, and acclimatesunflecks. The photoinhibition of seedlings of Pinus koraiesis grown close canopy density wasnot occurred easily when seedlings of Pinus koraiesis were exposed suddenly to light intensityof 1200μmol·m^-2s^-1.(7) The plant height, young stem length and basal diameter of the seedlings of Pinuskoraiesis grown under close canopy density were higher than that of open canopy density offorest. So the growth was linear to light intensity.