Effects Of Elevated CO₂ Concentration On Photosynthesis -Carbon Metabolism,Nitrogen Uptake And Utilization And Absortion Of Trace Elements In OilseedRape（Brassica Napus L.）

Elevation of atmospheric CO₂ concentration has become an inevitable trend, it is indicated that atmospheric CO₂ concentration would reach 700 μmol/mol at the end of 21st century. Carbon dioxide is the raw material for photosynthesis, its change will affect plant photosynthesis and growth. The study on the response mechanism of plant growth to elevated CO₂ concentration and effects of nutrients on plant growth will play an important role in promoting crop production potential and improving nutrient use efficiency and has great significance in economy and environment.In this thesis, oil seed rape varieties highlighting in carbon and nitrogen metabolism contradiction was used as target plant, and the variations of photosynthetic carbon metabolism, the distribution and redistribution of nitrogen absorbed by plants, carbon and nitrogen components in phloem and root exudates, the content of endogenous hormones in leaves and trace element uptake in response to elevated CO₂ concentration were studied. Results presented in this thesis provided important information on the exploration of the mechanism of oilseed rape to elevated CO₂ concentration and the effects of nitrogen on it. The results showed as follows:1. Results of elevated CO₂ concentration on photosynthetic carbon metabolism showed that photosynthesis （Pn） increased under CO₂ concentration in a short-term treatment, and along with the extension of treatment time, photosynthetic acclimation occurred, that is, Pn were decreased under two nitrogen application levels, but the time of photosynthetic acclimation is later under normal-N than that of limited-N. Under elevated CO₂ concentration for longer time,the largest electron transfer rate and the transport rate of triose phosphate（TPU） were restricted. Sufficient nitrogen supply can alleviate these restrictions.Starch accumulated in chloroplast when expose to elevated CO₂ concentration and limited nitrogen conditions for a long time, resulting in the breakage of chloroplast thylakoid membrane.Elevated CO₂ concentration and sufficient nitrogen application are both beneficial for increasing photosynthesis and CO₂ use efficiency of oil seed rape. The former has greater impact than the later. Sufficient nitrogen application can improve CO₂ use efficiency of oil seed rape under elevated CO₂ concentration; limited nitrogen restricted CO₂ use efficiency of oilseed rape. Grain yield per plant both increased of two nitrogen application levels under doubled CO₂ concentration conditions.2. Effects of elevated CO₂ concentration on dry biomass,nitrogen accumulation and distribution were studied.The results showed that, under elevated CO₂ concentrat-ion conditions,the dry biomass of different organs（root,stem,leaf）accumulated in both limited N and normal N treatment.The difference of total nitrogen per plant is not significant in both normal CO₂ and elevated CO₂ treatments. Elevated CO₂ treatment can distribute more nitrogen to root than that to stem or leaves at bolting stage; in the reproductive stage, elevated CO₂ reduced the nitrogen distribution proportion in stem and root of normal nitrogen treatments and increased that in pod,whereas,the nitrogen distribution proportion reduced in pod and root of limited nitrogen treatments while increased that in stem.The distribution of nitrogen absorbed during bolting stage indicated that under elevated CO₂ condition,more nitrogen absorbed before bolting stage（including bolting stage）was redistributed to root and pod than that to stem of normal-nitrogen treatment.. In addition, more nitrogen was redistributed more to root and stem than that to pod under limited-nitrogen condition.Under elevated CO₂ condition,the redistribution proportion of nitrogen absorbed after bolting stage was decreased in root while increased in stem and pod in both two nitrogen application levels.Effects of elevated CO₂ concentration on the transfer amount and rate of nitrogen and nitrogen use efficiency showed that the transfer amount and rate of nitrogen under ambient CO₂ was higher than that of elevated CO₂,while the loss rate was lower and loss amount was higher. Nitrogen use efficiency of normal N in both two growth stage was higher than that of elevated CO₂.3. The result of carbon and nitrogen compounds determination in phloem sap showed that:NH4+, free amino acid and soluble protein in phloem sap were increased with no nitrogen supply and were decreased with nitrogen supply by elevated CO₂; however, the content of NO3- was reversal to that.No matter nitrogen supply level, the contents of soluble sugar in phloem sap was increased and organic acid was slightly changed by elevated CO₂ with no nitrogen supply and they were decreased with nitrogen supply.4. Study in effect of elevated CO₂ concentration on hormones in leaves showed that,the elevated CO₂ concentration increased the content of IAA and zeatin （Z） in leaves under non-nitrogen application treatment but reduced IAA and zeatin content under nitrogen application treatment which reduced ABA content with two nitrogen levels.Under elevated CO₂ concentration,IAA/ABA,Z/ABA and （IAA+Z）/ABA were significantly increased for non-nitrogen treatment,respectivly;but Z/AB A was Increased and IAA/ABA,（IAA+Z）/ABA changed slightly for non-nitrogen treatment, respectivly.5. The results of nitrogen and carbon composition in root secretion showed that, production of free amino acids were increased in both of seedling and bolting stages for two nitrogen levels treatments by CO₂ elevation;soluble protein secretion were both reduced for a third normal nitrogen treatment and increased for normal treatment in seedling and bolting stages;the change of secretion NH4+was the same with soluble protein in bolting period but reversed in seedling stage;NO3- production showed a same trend with that of soluble protein at seeding stage but reversed in bolting stage. Total nitrogen are decreased in seedling while increased in bolting stage for two nitrogen levels treatment;Elevated CO₂ increased soluble sugar,total organic acids and total carbon in two growth period under two nitrogen supply,respectivly.No matter for CO₂ concentration,production of free amino acid,total nitrogen, soluble sugar, total organic acids and total carbon are all increased by high nitrogen supply in two growth period,which reversed for NH4+ production.NO3- production change at seedling stage as same NH4+ production change,that at bolting stage instead. Soluble protein production are both increased at seedling and bolting stage under the condition of elevated CO₂ concentration but unchanged at seedling stage and decreased at bolting period for ambient CO₂ concentration,respectivly.Effects of elevated CO₂ on the absorption and transportation of secondary nutrient elements （calcium,magnesium,sulphur） and micronutrient elements （iron, manganese,zinc,molybdenum and boron） in oilseed rape at stem elongation stage were studied by greenhouse simulated method.Compared with ambient CO₂ concentration,the content of Zn in stem was increased and the others nutrient elements were decreased under the elevated CO₂ and no nitrogen application treatment;the contents of Ca,S,B and Zn were increased,and the contents of Mg,Mn,Mo and Fe were decreased under the elevated CO₂ with N application treatment;while the content of Mo in leaves was increased,the contents of others nutrient elements were decreased under the elevated CO₂ and the two N application levels.Accumulation amount of Ca,S,B,Zn in stems were increased under elevated CO₂,while Mg,Mn,Mo,Fe were decreased;Accumulation amount of S,Mn,Mo,Zn in leaves showed an increased trend under elevated CO₂,while B,Zn were decreased. Compared with ambient CO₂ concentration,the amount of Ca and S in stem account for total secondary nutrient elements and the amount of B and Zn in stem account for total micronutrient elements were increased under the elevated-CO₂ treatment and two nitrogen levels,and the corresponding values of Mg,Fe,Mn and Mo were decreased;no-N application treatment increased the proportion of Ca distributed into the leaves, and the proportion of Mg distributed into leaves was increased by the normal-N application level; the proportion of Mn, Zn and Mo distributed into the leaves were increased under the both N application levels. Under no-N application treatment, the transport coefficients of Sca,Mg,SMn,Mo,SMn,Fe and SMo,Fe under elevated-CO₂ were higher than that observed at the ambient CO₂ concentration, but the transport coefficients of SMg,S,SCa,S,SMn,B,SB,Zn and SMn,Zn under elevated-CO₂ were lower than that in plants grown under the ambient CO₂ concentration, indicated order that the proportion of elements transported into the upper part of plant tissues was Mg>Ca>S,Fe>Mo>Mn>B>Zn;Under normal-N application treatment, the transport coefficients of SCa,Mg,SCa,S,SMn,Mo,SB,Zn and SMn,Fe under elevated-CO₂ were higher than that observed under theambient CO₂ concentration,but SMg,S,SMn,B,SMn,Zn and SMo,Fe under elevated-CO₂ were lower than in plants grown under the ambient CO₂,indicatedMg>S>Ca,Mo>Fe>Mn>Zn>B.