Research In Growth Characteristics Of Syzygium Hancei Seedlings Under Different Sunlight

Syzygium hancei is a important tree species of natural vegetation in coastal ecotone of Guangxi, which plays an important role to the ecology environment construction of Beibu gulf. But this kind of plant is hard to natural regeneration and disturbed intensely by human, result in community degradation. This experiment puts shade test on Syzygium hancei, install them under the four levels natural sunlight(NS):100%NS,24%NS,6%NS,1.6%NS, study the change of growth, chlorophyll content, CAT activity, SOD activity, MDA content, photoresponse curve, photosynthetic diurnal variation in order to explore the affect that differenet sunlight reply to the growth of Syzygium hancei. According above, putting forward scientific measure for protecting and renewing to Syzygium hancei. Research conclusion shows:(1)The growth, chlorophyll content, CAT activity, SOD activity, MDA content of Syzygium hancei have changed after shade test. The growth of plant height and ground diameter is fewer as the sunlight weaker, and Syzygium hancei seedlings become dead in6%NS,1.6%NS. The chlorophyll content is highest in24%NS, lowest in100%NS. The CAT activity comes down as the sunlight gets high, and SOD activity is opposite, which grows as the sunlight gets high. MDA content result is1.6%NS>24%NS>6%NS>100%NS, which is affected by CAT activity and SOD activity.(2)The chlorophyll content, CAT activity, SOD activity, MDA content of Syzygium hancei have changed under the different sunlight. The chlorophyll content is highest in24%NS, lowest in100%NS. The CAT activity is up as the sunlight gets high, and SOD activity is same, which grows as the sunlight gets high. MDA content result is1.6%NS>24%NS>6%NS>100%NS, which is affected by CAT activity and SOD activity. The chlorophyll content is lowest under the100%sunlight, which is affected by sunlight. The CAT activity and SOD activity is stronger as the protection is bigger which affect to Syzygium hancei seedlings. And the MDA content is higher as the harm is bigger which affect to Syzygium hancei seedlings.(3)The photoresponse curve of Syzygium hancei has changed under the different sunlight, which includes the max net photosynthetic rate, light saturation point, light compensation point and dark respiration rate. The max net photosynthetic rate, light saturation point, light compensation point comes down as the sunlight gets down, results show is100%NS>24%NS>1.6%NS>6%NS. The trend of three kind of parameter is the same. The dark respiration rate is a little different, results show is100%NS>24%NS>6%NS>1.6%NS. The four levels natural sunlight are100%NS,24%NS,6%NS and1.6%NS. The max net photosynthetic rate of Syzygium hancei are8.400%7.232%5.185and4.652μmolCO2·m-2·s-1. The light saturation point of Syzygium hancei are889.3%841.5%737.6�'�511.8μmol·m-2·s-1. The light compensation point of Syzygium hancei are10.562%10.022%5.643and5.554μmol-m-2·s-1. The dark respiration rate of Syzygium hancei are0.154、0.094、0.031and0.063μmolCO2·m-2·s-1. After different sunlight test, the max net photosynthetic rate, light saturation point, light compensation point and dark respiration rate of Syzygium hancei seedlings show better adaptability to strong sunlight,100%NS is more satisfied for the growing of plant.(4)The photosynthetic diurnal variation of Syzygium hancei has been affected in different sunlight. According to measure the diurnal variation of net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2concentration, the study shows that the diurnal variation of net photosynthetic rate, transpiration rate and stomatal conductance is double-peak curve and the variation law is same. The max numerical value of net photosynthetic rate and stomatal conductance is on8:00-9:00and13:00, the max transpiration rate is on8:00-9:00and12:00, which the variation of this three factors is showing no difference that gets higher as sunlight gets higher. The result is100%NS>24%NS>1.6%NS>6%NS. The diurnal variation of intercellular CO2concentration is a "W" curve, the min value is on8:00-9:00and13:00, contrary to net photosynthetic rate, transpiration rate and stomatal conductance, and the concentration gets lower as sunlight gets higher. The result is6%NS>1.6%NS>24%NS>100%NS. The net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2concentration of Syzygium hancei is accord with other plants’regular, and the net photosynthetic rate reach max when the sunlight is100%NS.Syzygium hancei is light-demanding plant according above conclusions. After compare each target of Syzygium hancei seedlings in different sunlight condition, we can find that Syzygium hancei seedlings is more adaptive to plenty sunlight condition, which grow best under100%NS.