Effects Of Shading And Fertilizing On Photosynthetic Characteristics Of An Endangered Plant Sinomanglietia Glauca

Sinamanglietia glauca,a species of state key protected plant(Class I),was found only in Yichun City of Jiangxi Province and Yongshun County of Hunan Province,China.And part of S.glauca population is sharply decreased because of the interference of Phyllostachys edulis expansion.We hypothesized that the changes of community light and soil nutrient due to the P.edulis expansion might be the main reason.Therefore,we performed an orthogonal experiment with double factors to simulate how light and soil nutrient affect the growth of S.glauca.Light levels were 10 0%,50 % and 25 % of complete light,marked as L100,L50,L25.Nutrient addition with 0.24 %NH4NO3 and 0.12 %KH2PO4 and no addition were marked N1P1 and N0P0,respectively Schima superba and Cyclobalanopsis glauca were chosen as references The growth indicators including height and base diameter were measured.The physiological and ecological indicators,light response curve and diurnal variation process and related environment factors were monitored to reveal the endangered mechanism of light and nutrients influencing the photosynthetic physiology of S.glauca.The results were as follows.(1)The growth of S.glauca sapling was significantly correlated with light but not with soil nutrient.From L100 to L25,the height,basal diameter and LDMC of S.glauca decreased,LSA increased;and those of the S.superba and C.glauca changes were not obvious.(2)The maximum net photosynthetic rate,light saturation point and light compensation point of S.glauca decreased by 56.50%,69.67% and 61.93%,from L100 to L25,respectively,while dark respiration rate increased by 64.85 %.However,the photosynthetic indexes for S.superba and C.glauca showed little changes with light and nutrient.(3)Leaf chlorophyll content of S.glauca had significant correlation with shading treatment,with L50>L25>L100,but fertilizing and the interaction with shading had no significant influences.Furthermore,the ratio of N to P of leaf increased from 12.19 to 18.28 with L100 to L25,indicating that the nutrient limitation S.glauca changed from N to P.(4)The net photosynthetic rate(Pn)showed a " parabola single peak" trend,with the peak under L100 appearing at 10:00 am,and being delayed under the shading treatment.The “lunch break" phenomenon was not found.The average net photosynthetic rate under six treatments was 10.00,9.64,4.45,4.20,1.26,1.25 ?mol·m-2·s-1,respectively.The stomatal conductance(Cond)and transpiration rate(Tr)also showed a trend of parabola.And the intercellular CO2 concentration(Ci)was higher in morning and evening and was lower in middle.The changes of S.superba and C.glauca were consistent with S.glauca.(5)Pn showed significant positive correlation between Cond and Tr,but had no significant correlation with Ci and water use efficiency(WUE)under the condition of full light(p<0.01).However,Pn was significantly negatively correlated with Ci and positively correlated with WUE under shading.(6)The regression equation of net photosynthetic rate with environmental factors showed that net photosynthetic rate of S.glauca was influenced by multi-environment factors including photosynthetic active radiation,relative air humidity,air CO2 concentration and air temperature under L25,but S.superba and C.glauca were influenced only by PAR.In conclusion,the light saturation point of S.glauca was higher,changes of light can exert great influences on the physiological and ecological characteristics of S.glauca,and change the diurnal change of photosynthesis,But fertilization were not significantly affect to S.glauca.For Phyllostachys edulis expansion can significantly increase of the canopy closure and decrease the light level,thus,photosynthesis of S.glauca may be more susceptible.There was not enough nutrient to supply the growth,nutrient limitation changed,and the more vulnerable to environmental factors influence,which causes the difficulty in recruiting population.Our research findings can not only provide a theoretical reference for the endangered mechanism for S.glauca,but also offer an insight to biodiversity protection.