Effects Of Different Light Quality Ratios On Photosynthetic Characteristics Of Cunninghamia Lanceolata Seedling Clones

Cunninghamia lanceolata is one of the important timber and afforestation tree species in southern China.It has extensive market demand and has an important impact on China's timber economy.It is one of the effective ways to realize the fast-growing,high-yield and high-quality C.lanceolata plantation,and to improve the photosynthesis ability of C.lanceolata.In this thesis,we use the 020 cutting seedlings of1 year old excellent clone as the experimental material,select the main light quality red and blue light absorbed by the plant photoreceptor,and use the LED light quality to set 4 different light quality ratios?W,R:B=1:0,R:B=0:1,R:B=1:1,where W,R,and B represent white light,red light,and blue light,respectively.?to study the changes of antioxidant enzyme activity and MDA content,photosynthetic pigment content,chlorophyll fluorescence parameters,photosynthetic parameters and chloroplast ultrastructure of the new leaves of C.lanceolata seedlings under different treatments during different developmental days,and the changes of nutrient accumulation.The research results from plant physiology,plant nutrition and cytology not only explore the biological process of new leaf development of C.lanceolata seedlings under different light quality treatments and reveal the role and position of different light quality in the development of new leaf of C.lanceolata seedlings,but also provide theoretical reference for the improvement of the photosynthesis of C.lanceolata and the productivity of C.lanceolata plantation.The main research results are as follows:?1?There are differences in the influence of light quality on the content of antioxidant enzymes and MDA.Under the white light treatment,the activities of SOD,POD and CAT are all reduced,but it is conducive to the accumulation of MDA content.Red light treatment results in less accumulation of MDA content,but POD activity increases significantly.The blue light treatment is beneficial to the accumulation of MDA content and the temporary increase of SOD and CAT activities.The SOD and CAT activities also increase under the red-blue combination light treatment,but it is not conducive to the accumulation of MDA content.This shows that the leaf senescence is faster under blue light treatment than other treatments,and the combination of red and blue light treatment delays leaf senescence.Compared with white light treatment,red-blue combined light,blue light,and red light treatment can increase the antioxidant enzyme activity of new leaves of C.lanceolata seedlings,of which red and blue combined light is more beneficial to enhance the antioxidant enzyme activity of new leaves of C.lanceolata seedlings.Under the blue light treatment,the cells produce free radicals,which causes the lipid peroxidation of the unsaturated fatty acids in the membrane,and the structure is damaged to a certain extent,which will cause the accumulation of MDA content.The accumulation of content delays the senescence of the leaves.Under different light quality treatments,the MDA content of new leaves is negatively correlated with POD activity,and positively correlated with SOD and CAT activities.?2?With the development of new leaves of C.lanceolata seedlings,the differences in chlorophyll a,chlorophyll b,total chlorophyll,carotenoid and chlorophyll a/b of new leaves of C.lanceolata seedlings under different light quality treatments gradually increase.With the development of new leaves,the difference of chlorophyll a between the treatments reaches a significant level?P<0.05?,except for white light treatment,chlorophyll a is the largest under red light treatment.Chlorophyll b is not significantly different between treatments at the early stage of development?P>0.05?.From the whole development days,chlorophyll b is higher than other treatments under red light treatment.Under the white light treatment,the total amount of chlorophyll increases obviously in the later stages of new leaf development,and is significantly higher than other treatments after 180 d?P<0.05?.Carotenoids are generally higher under white light treatment,especially when the new leaves develop after 60 days and 180 days they are significantly higher than other treatments?P<0.05?.Under red light treatment,chlorophyll a/b is lower during the whole period of new C.lanceolata leaf development.Overall,red light is beneficial to the synthesis of chlorophyll b in new leaves of C.lanceolata seedlings.For chlorophyll a,in addition to white light treatment,red light treatment is also more conducive to the synthesis of new leaf chlorophyll a of C.lanceolata seedlings.The chlorophyll a/b is the smallest under red light treatment.White light treatment is beneficial to the synthesis of chlorophyll content and carotenoids.?3?Chlorophyll fluorescence parameters F_m,F_v,F_t,F_v/F_mand F_v/F_ohave different changes in different developmental days under different light quality treatments.Under white light treatment,F_mis higher during the whole period of new leaf development of C.lanceolata seedlings,especially in the middle development period,which is significantly higher than other treatments?P<0.05?,which indicates that white light treatment is most conducive to PS?electron transfer.The red and blue combination light treatment of F_vin the whole period of new leaf development of C.lanceolata seedlings is lower than other treatments,indicating that the red and blue combination light treatment can produce different levels of inhibition on the reduction of PS?original electron acceptor Q_A.The F_tis generally higher under red light treatment,especially when the new leaves of C.lanceolata seedlings develop after150 d and 180 d it is significantly higher than other treatments?P<0.01?,indicating that photosynthesis treated by red treatment when dark reaction and light reaction reach equilibrium,the fluorescence output is the largest.Under the white light treatment,F_v/F_mand F_v/F_oare higher than those of other treatments in the whole period of new leaf development of C.lanceolata seedlings.When the new leaves develop up to 180 days,the difference between the blue and red and blue light treatment reaches a very significant level?P<0.01?,followed by red light treatment.In addition to white light treatment,the PS?of new leaves of C.lanceolata seedlings under red light treatment has higher primary light energy conversion efficiency and potential activity,that is,new leaves of C.lanceolata seedlings under red light treatment have higher photochemical efficiency and potential activity.?4?Chlorophyll fluorescence parameters NPQ,Rfd and _qP are regulated by different light qualities during the development of new leaves of C.lanceolata seedlings.From the whole stage of new leaf development of C.lanceolata seedlings,NPQ and Rfd under red light treatment are lower than other treatments,while red and blue combination light treatments are higher than other treatments.Under the white light treatment,_qP is lower than that of other treatments during the whole period of new leaf development of C.lanceolata seedlings,and under the blue light treatment,the _qP is the largest during the whole development days.In general,the NPQ and Rfd values of new leaves of C.lanceolata seedlings under red light treatment are significantly lower than those of other treatments,so it can be speculated that the new leaves of C.lanceolata seedlings under red light treatment have low heat dissipation capacity and could not consume excess energy.Therefore,the red light treatment may cause certain damage and inhibition to its photosynthetic system and normal growth of new leaves.The new leaves of C.lanceolata seedlings under the red-blue combination of light treatment increase dissipation,which is conducive to the protection of the photosynthetic reaction center.Under the blue light treatment,the new leaves of C.lanceolata seedlings have the largest _qP value,that is,the degree of openness of PS?is greater.The greater the amount of Q_Areoxidized to form Q_A,it also reflects that the transfer activity of new leaf PS?is greater.It shows that the new leaves of C.lanceolata seedlings can dissipate excess energy to protect the photosynthetic system from light damage under blue light treatment.?5?During the development of new leaves of C.lanceolata seedlings,compared with other treatments,white light treatment promotes the opening of new leaf stomatal leaves of C.lanceolata seedlings and increases the amount of CO₂entering the leaves,thereby increasing C_iand T_r,and also accompanied by the increase of P_nHigh,indicating that the change of photosynthetic rate under white light treatment is the result of the effect of stomatal factors.Under red light treatment,the G_sof new leaves of C.lanceolata seedlings is lower than that of other treatments,and C_iis second only to white light treatment;under the combination of red and blue light treatment,G_sis second to white light treatment,but C_iis lower than other treatments.That is the change direction of G_sand C_iis opposite,and the change of photosynthesis rate is the result of non-stomatal factors.This also shows from another aspect that the decline in photosynthetic capacity under the combined treatment of red light and red-blue light is mainly the result of the combined action of photosynthetic pigments,chlorophyll fluorescence,and photosynthetic key enzyme activities.?6?Light quality affects the activity of the key photosynthetic enzyme Rubisco.As a key enzyme in plant photosynthesis,Rubisco affects both the direction of C₃plant photosynthetic carbon metabolism and the efficiency of photosynthetic metabolism.At the same time,Rubisco activity is also closely related to the photosynthetic rate.During the development of new leaves of C.lanceolata seedlings,there is a strong correlation between photosynthetic parameters and Rubisco activity.Rubisco activity increases under white light treatment,Rubisco activity decreases under red light treatment,P_nis the largest under white light treatment,and P_nis the smallest under red light treatment,indicating that changes in Rubisco activity will affect P_n?7?The influence of light quality on the chloroplast ultrastructure of new leaves during the development of new leaves of C.lanceolata seedlings shows different changes at various stages of new leaf development.Under white light treatment,when the new leaves of C.lanceolata seedlings develop for 60 days,the starch granule volume is relatively large;after 120 days,the osmium granules appear more and distribute widely;after 180 days,the starch granules become larger and the osmium granules are more abundant.There is an increase in the number of base particles and substrate layers,and the structure of base particles and substrate layers is obvious.Under the treatment of red and blue light,when the new leaves of C.lanceolata seedlings develop for 60days,the structure of the base grain layer and the base layer layer is clearly visible,and the base grain stack is neat and tightly ordered;after120 days,the number of chloroplasts increases significantly,followed by the number of starch granules decrease;after 180 days of development,the cell wall structure is more complete,and osmium granules appeare in large numbers.From the perspective of the entire development days,the combination of white light,red and blue light treatment has a large number of base particles and substrates,and the structure of the base particles and substrate sheets is clear and neatly arranged,indicating that the combination of white light,red and blue light treatment is conducive to maintaining normal chloroplast development.?8?Light quality has a certain effect on the accumulation of nutrient elements.Blue light is beneficial to the accumulation of Mn,Zn,Cu,Fe,and N elements in the new leaves of C.lanceolata seedlings;Ca content and Mg content of the new leaves of C.lanceolata seedlings under red light treatment are significantly higher than those in other developmental days during 60-120 d and 90-120 d,respectively Treatment?P<0.05?showes that red light increases the content of Ca and Mg nutrients in the new leaves of C.lanceolata seedlings;the P content and K content of the new leaves of C.lanceolata seedlings under white light treatment are significantly higher during 120-150 d and 90-150 d All other developmental days?P<0.05?,and also significantly higher than other treatments at the same developmental period?P<0.05?,indicating that white light treatment has a certain promoting effect on the content of nutrients P and K.The enhanced activity indicates that P and K activate photosynthetic enzymes and promote photosynthesis.Nutrient elements P content and K content have significant or extremely significant positive correlations with P_n,G_sand T_r.In summary,the mechanism of light quality affecting plants is more complicated.Light affects plant growth,photosynthetic enzyme activity,photosynthetic pigments,photosynthetic characteristics,chloroplast ultrastructure,stress resistance and aging.This study finds that white light treatment is conducive to the accumulation of some nutrients and promotes the growth of new leaves of C.lanceolata seedlings;it is also conducive to the increase of photosynthetic rate and the increase of carotenoid content of new leaves of C.lanceolata seedlings,and can also activate key photosynthetic enzymes and promote C.lanceolata seedlings normal development of new leaf chloroplast ultrastructure.The combination of red and blue light can enhance the antioxidant enzyme activity of the new leaves of C.lanceolata seedlings and delay the senescence of the leaves.At the same time,the combination of red and blue light treatment increases the dissipation of the new leaves of C.lanceolata seedlings,which is beneficial to protect the photosynthetic reaction center and promote the photosynthetic rate.To a certain extent,it also promotes the normal development of chloroplast ultrastructure of new leaves of C.lanceolata seedlings.Comprehensive analysis shows that compared with red light and blue light,white light and a certain ratio of red and blue combined light are more conducive to the growth of new leaves of C.lanceolata seedlings.