Effects Of Doubling CO₂ Concentration And Applying Phosphorus Fertilizer On Pepper Growth And Element Absorptio

Since the Industrial Revolution,the massive burning of fossil fuels has increased the concentration of CO₂in the atmosphere.CO₂is an essential raw material for plant photosynthesis,which has an important impact on plant growth and development.However,the increase of CO₂concentration will reduce the absorption of mineral elements（such as phosphorus,P）by plants,which is an essential nutrient element for plant growth and development.Phosphorus deficiency in soil has become one of the main factors limiting crop growth.How does the interaction between CO₂concentration and phosphorus affect plant growth and development,physiological and biochemical processes?In this study,Yanjiao 425,a pepper（Capsicum anmuum L.）with a wide planting range in Guizhou Province,was selected as the research object.Pot control experiment was carried out,and two CO₂levels（natural CO₂concentration:）were set by means of four automatic artificial climate incubator which could control CO₂concentration.400±30μmol·mol^-1,CO₂concentration multiplied:800±30μmol·mol^-1),three phosphorus supply levels（0,50,250 mg/kg）were set,and the natural CO₂concentration and phosphorus supply level were 0 mg/kg as control.To study the effects of doubling CO₂concentration and applying phosphorus fertilizer on pepper growth,chlorophyll content,biomass accumulation and distribution,root morphology,root acid phosphatase activity,nutrient element absorption and distribution,and ecological stoichiometric ratio,in order to provide theoretical basis for improving pepper growth in the future.The main results are as follows:（1）Plant height,stem diameter,crown width,leaf area,total root length,taproot diameter,root surface area,root volume,number of root tips and number of bifurcation increased significantly when CO₂concentration alone was multiplied.Under the condition of natural CO₂concentration,plant height,stem diameter,crown width,leaf length,leaf width and leaf area increased with the increase of phosphorus application rate.Plant height,stem diameter,crown width,leaf length,leaf width,leaf area,leaf circumference,total root length,principal root diameter,root surface area and root volume reached the maximum under the reciprocal treatment of CO₂concentration doubling and P supply level of 250 mg/kg.The results showed that the morphological growth of capsicum could be promoted by doubling CO₂concentration alone or applying phosphorus fertilizer alone,and the root growth of capsicum could be synergically promoted by doubling CO₂concentration and applying phosphorus fertilizer alone.（2）Root,stem,leaf and total biomass increased significantly,root biomass ratio increased but did not reach a significant level,stem biomass ratio increased significantly,leaf biomass ratio decreased significantly,root/shoot ratio increased significantly.Under the condition of natural CO₂concentration,the root,stem,leaf and total biomass increased significantly,the ratio of root to stem biomass increased,the ratio of leaf biomass decreased,and the ratio of root to shoot increased significantly after the application of P fertilizer.Under the interaction treatment of CO₂doubling and P supply level of 250 mg/kg,the root,stem,leaf and total biomass reached the maximum.Under the interaction treatment,the root,stem biomass ratio and root/shoot ratio increased significantly compared with the control,while the leaf biomass ratio decreased significantly.（3）The content of chlorophyll in leaves increased but did not reach a significant level,and the change of acid phosphatase activity had no obvious rule.Under the condition of natural CO₂concentration,the chlorophyll content reached the maximum at 250 mg/kg P application level,and the activity of acid phosphatase decreased significantly with the increase of P application,and the decrease was up to 45.11%compared with no P application.Compared with the control,the chlorophyll content increased significantly and the activity of acid phosphatase decreased significantly under the interaction treatment of doubling CO₂concentration and applying phosphate fertilizer.The activity of acid phosphatase is mainly affected by the phosphorus supply level,and the two are negatively correlated.（4）Under the treatment of doubling CO₂concentration alone,the content of C in the roots,stems and leaves of pepper increased significantly,while the content of N,P and K decreased significantly,so that C/N,C/P and C/K increased significantly.Under the condition of natural CO₂concentration,the content of C and P in the roots and leaves of pepper increased after the application of P fertilizer,and the absorption of P was greater than that of C,so the C/P in the roots and leaves was significantly lower than that without the application of P fertilizer,and the N/P in the roots and leaves was also significantly reduced due to the application of P fertilizer.Under the interactive treatment of doubling CO₂concentration and applying phosphorus fertilizer,the content of C in roots,stems and leaves reached the maximum value,while the content of N,P and K in general was significantly lower than that of the control.（5）The contents of Ca and Mg in roots increased significantly,while the contents of Fe,Mn and Zn decreased significantly with the multiplication of CO₂concentration alone;The contents of Ca and Mg in stems decreased significantly,while the contents of Fe,Mn and Zn increased significantly.The contents of Ca,Fe and Zn decreased significantly,while the contents of Mg and Mn increased significantly.Under the condition of natural CO₂concentration,the contents of Ca,Mg and Fe were significantly increased and the contents of Mn were significantly decreased after applying phosphorus fertilizer compared with the control.The contents of Ca and Mg in stems decreased first and then increased,while the contents of Ca and Mg in leaves significantly decreased and increased.The contents of Ca and Mg in roots increased significantly,but the contents of Fe,Mn and Zn had no obvious rule under the interactive treatment of doubling CO₂concentration and applying phosphate fertilizer.The contents of Ca and Mg in stems decreased significantly,while the contents of Fe,Mn and Zn increased significantly.The contents of Ca,Fe and Zn in leaves decreased significantly,while the contents of Mg and Mn increased significantly.These results indicated that the effects of doubling CO₂concentration and applying phosphorus fertilizer on the absorption of nutrient elements in plants were different,and the absorption of different elements in different organs were different,with positive and negative effects.In summary,doubling CO₂concentration or applying phosphorus fertilizer can promote the growth of pepper.Doubling CO₂concentration can reduce the absorption of most nutrient elements by plants,while applying phosphorus fertilizer can alleviate this negative effect.However,different parts have different absorption performances of different nutrient elements,and there are positive and negative effects.In the process of pepper planting,it is necessary to pay attention to the supply of fertilizer,apply fertilizer appropriately and consider the combination of fertilizer,so as to promote the absorption of nutrient elements of pepper and ensure that the growth and development of plants are not restricted.