| Cunninghamia lanceolata is one of the most important fast-growing timber species in southern China.leaf is the most important organ of photosynthesis of C.lanceolata Many researching results on C.lanceolata have achieved.However,research has not been done on the biological process of the new leaf of C.lanceolata and the physiological changes in the process of the development of the new leaf and the change process of the ultrastructure.On the basis of the analysis of the growth of the specific leaf area,dry matter content,nutrient content,enzyme activity and other physiological indexes,the contents of chlorophyll and leaf of different magnesium concentration treatment on the new leaves of C.lanceolata were further analyzed in this paper,based on the laboratory simulated biological culture experiments of 1 a seedlings.The dynamic effects of the photosynthetic parameters such as chlorine fluorescence,photosynthetic rate,key enzyme of photosynthesis and ultrastructure of chloroplast were studied.The results provided a theoretical reference for exploring the biological process of the development of new leaves of C.lanceolata and the role and status of magnesium in the development of new leaves of C.lanceolata.The main results are as follows:(1)The specific leaf area showed a trend of increasing first and decreasing later and the dry matter of leaves showed a trend of continuous increasing respectively with the growth and development of leaves of C.lanceolata,The new leaves growed fastly in early stage and slowly in later stage of growth and development,and the density of leaf tissue increased continuously.(2)The content of malondialdehyde(MDA)in leaves increased first and then decreased,and the activity of superoxide dismutase(SOD)and catalase(CAT)decreased first and then increased,and the activity of peroxidase(POD)increased gradually during the growth and development of new leaves of C.lanceolata.(3)The photosynthetic pigments(chlorophyll a,chlorophyll b and total chlorophyll)increased first and then decreased during the growth and development of new leaves of C.lanceolata The content of photosynthetic pigments in the early growth stage was faster,and the photosynthetic pigment content in the late growth stage was still larger than the photosynthetic pigment content in the new leaves.The photosynthetic rate(Pn)of the new leaf of C.lanceolata was higher and sensitive to high light intensity after 90?120 days growth.but leaf Pn is low and has high adaptability to high light intensity after 90-120 days growth.Gs of leaves decreased with the decreasing of Pn from 30th to 90th day,while Gs increased with the increasing of Pn in 75th day,which meaned the restrictive factors of Pn were non stomatal factors when leaves were in 30?90 days growth.When the leaf growth and development was from 90?120 days,Pa increased and Gs decreased,while Ci increased,which meaned Pn was affected by air pore factors and non stomatal factors.(5)In the process of growth and development of new leaves of C.lanceolata,the activity of Ca2+Mg2+-ATP enzyme increased first and then decreased,and was significantly higher in 90 days and 120 days of growth than that in 30 days and 60 days.The ribulose bisphosphate carboxylase had higher activity and same changing trend with in Pn in 30 days and 120 days of growth.(6)With the prolongation of the growth and development time of the new leaves,the cell wall tended to be smooth and the bending decreased gradually,the structure of thylakoid in the chloroplast turned clear and close.The distribution of chloroplasts along the cell wall tended to be neatly and gradually close to the edge of the cell wall,the degree of chloroplast overlap reduced,and the location of chloroplast in the leaf cells became more beneficial to the chloroplast light,which was much more better for photosynthesis then.(7)During the growth of C.lanceolata,the specific leaf area was higher under magnesium deficiency treatment,while the leaf area was lower under normal magnesium and high magnesium treatments.The dry matter content of C.lanceolata leaves under magnesium deficiency treatment was lower than normal magnesium and high magnesium treatments.The growth rate of C.lanceolata leaves under high magnesium treatment was higher than that by normal magnesium and magnesium deficiency treatments.The addition of magnesium was beneficial to the growth and the accumulation of dry matter of C.lanceolata leaves.(8)The activity of SOD,POD and CAT of C.lanceolata new leaves under different concentrations of magnesium treatments reached a significant difference level.The MDA content of new leaves of C.lanceolata was negatively correlated with the activity of SOD,POD and CAT.and the accumulation of MDA content in new leaves and the temporary increase of SOD and POD activity in the early stage of the development of new leaves.(9)The total potassium content in the whole growth process of C.lanceolata leaves and the C/N ratio at the later stage of growth and development were higher than other magnesium concentrations treatments,and the difference of total potassium content reached a very significant difference level(P<0.01).Normal magnesium and high magnesium treatments were all beneficial to the accumulation of C,N and total Ca in new leaves.(10)The content of chlorophyll a,chlorophyll b and total chlorophyll of new leaves of C.lanceolata increased first and then decreased under different magnesium treatments with the prolongation of culture time.With the culture time prolongating,the difference among chlorophyll a,chlorophyll b and total chlorophyll content of new leaves of different magnesium treatments increased gradually.The difference between chlorophyll a and total chlorophyll content reached significant difference level(P<0.05)in the later period of growth.Magnesium deficiency treatment can cause the decrease of Fv/Fo,Fv/Fm in the new leaves of C.lanceolata and the decrease of leaf quantum yield,hinder the transmission of photosynthetic electron,and reduced the photosynthetic efficiency of plants then.(11)The activity of key enzymes of photosynthesis in new leaves of C.lanceolata leaves decreased gradually,and the activity of key enzymes of photosynthetic key enzymes in the early stage of development of newleaves showed an upward trend,but decreased slightly in the late stage of development,and the activity of Ca2+Mg2+-ATP enzyme in the new leaf of C.lanceolata was on the rise.The activity of RuBP increased with the increase of magnesium concentration.(12)During the growth and development of C.lanceolata,with the decrease of magnesium concentration,the Pn of C.lanceolata leaves decreased,and the Ci of leaves decreased.The main limiting factor of leaf photosynthesis was the non stomatal limit,and the decrease of magnesium concentration directly resulted in the decrease of Pn.The decrease of photosynthesis caused by magnesium deficiency was mainly due to the comprehensive effects of magnesium on chlorophyll content,chlorophyll fluorescence and the activity of key enzymes of photosynthesis.(13)The effects of magnesium on the ultrastructure of chloroplasts in new leaves of C.lanceolata showed different patterns at different stages of growth and development.With the prolongation of development time,the difference in the ultrastructure of chloroplasts increased gradually.When the new leaves grew and developed 120 d,the thylakoid lamellae in the chloroplast began to break and the mitochondria degraded.The rupture of the thylakoid lamellar structure caused by magnesium deficiency would directly affect the effective photosynthesis of the leaves.Thylakoid lamellae in chloroplasts became clear and dense under normal and high magnesium treatments. |
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