Effects Of Elevated Atmospheric CO₂ Concentration On Yield Formation And NPK Absorption And Utilization In Different Types Of Rice Varieties

Rice is one of the most important food crops in the world.Its growth and development aredrastically altered by the atmospheric CO₂ concentration and mineral nutrients such as nitrogen（N）,phosphorus（P）and potassium（K）.The increasing human activities have led to a consistent increment of CO₂ concentration in the atmosphere,which in turn affects the growth,development,yield and grain quality of rice plant.Previous studies employing FACE（Free Air CO₂ Enrichment）have generated many reports on the response and adaptation of rice.However,most of the studies use single rice variety and deal with one of the major macronutrients.Yet,rice varieties in China differ very much in genotypes.Each type of rice has its unique adaptation region or season and scale,which is irreplaceable by others in a near future.Therefore,it is very important to expand investigating their responses,systematically study the growth and development,yield formation,uptake and utilization of the major nutrients such as N,P and K,photosynthetic characteristics of leaves and the N metabolism enzymes,their relationships with yield formation under FACE condition.The current study took advantage of the first rice-wheat rotation FACE research platform in China,analyzed the yield formation,uptakes of N,P and K of different types of rice varieties,including conventional japonica rice（Wuyunjing 21,Yangfujing 8）,conventional indica rice（Yangdao 6,Yangfuxian 6）and hybrid indica rice（Shanyou 63,Liangyoupeijiu）.Clarifying their differential responses in yield formation,nutrient uptake and utilization under the elevated CO₂ concentration could provide practical basis for the variety selection and production management for the future.Results have shown that:1.Under FACE condition,1)the heading date of rice was promoted by 0.97 days earlier.The whole growth duration shortened by 0.75 days.The plant height increased by 0.69 cm.These vary significantly among varieties.2)The maximum tiller number increased by 8.61%and the effective panicle percentage decreased by 3.67%,with the largest change observed in indica hybrid rice.3)The leaf area coefficient（LAI）increased by 11.50%,and the sink capacity enlarged by 18.38%,with the largest LAI and sink capacity increment observed in the hybrid indica and conventional japonica rice respectively.4)Dry matter weight at maturity increased by 25.15%,with the maximum increment observed in hybrid indica rice.The differences between treatments and varieties were significant.The harvest index（HI）increased 0.72%in conventional j aponica rice,while showing a reduction of 2.29%and 0.44%in hybrid indica and conventional indica,respectively.5)Correlation analysis revealed that LAI at heading stage,sink capacity,dry matter weight at maturity and HI all significantly positively correlated with the yield.Sink capacity and dry matter weight displayed closer relationship with yield than their respective counterparts did.2.Under FACE condition,1)it significantly increased rice yield by 24.17%averagely,being 19.38%in conventional japonica,24.02%in hybrid indica,and 29.10%in conventional indica rice.2)The number of panicles per unit area displayed a 16.37%increment,with the maximum increment observed in the conventional japonica rice.3)The grain number per panicle increased in hybrid indica and conventional indica rice.4)Seed setting rate and 1000-grain weight showed limited responses to the FACE.However,varietal differences were significant.In general,all of the four yield components had significant contribution effects to the yield increase,with the number of grains per panicle and panicle number being more effective.3.Under FACE condition,1)the average N content of rice plants at maturity decreased by 3.57%,with the maximum reduction found in the conventional japonica rice.However,the total N uptake increased by 21.61%averagely,being 13.69%,25.79%and 24.32%in conventional japonica,hybrid indica and conventional indica rice,respectively.2)The N uptake in the culm and sheath,and leaf increased,whereas it decreased in the panicle.The largest increase（51.86%）was in the leaf.3)N uptake increased at every growth duration,with the largest increase of 58.04%between heading and maturity.Conventional indica rice showed the most N uptake increment than others.4)N uptake per panicle in conventional indica rice and hybrid indica rice increased 10.79%and 13.93%,respectively,whereas it decreased in japonica rice by 9.60%.5)The N absorption intensity of the population increased by 22.62%at maturity,with the largest change in hybrid indica rice.6)The N proportion in the culm and sheath,and leaf at maturity stage increased significantly,whereas it decreased in the rice panicle.The apparent relocation of N to the panicle,and from culm and sheath during grain filling stage reduced at 6.62%and 32.41%,respectively.7)N use efficiency for yield increased by 4.72%averagely,being 6.90%,9.44%,and 5.31%in conventional japonica,hybrid indica and conventional indica rice,respectively.Generally,higher plant dry matter weight,N uptake during grain filling,N uptake per panicle,N uptake intensity,and N uptake in leaf all contributed positively to total N uptake at maturity.Total N uptake and use efficiency for yield both contributed positively to increasing grain yield,with the former showing greater impact.4.Under FACE condition,1)the plant P content increased by 6.07%at maturity,the biggest change occurred in conventional japonica rice.The total P uptake increased by 31.97%averagely,being 28.84%,42.07%and 24.81%in conventional japonica,hybrid indica and conventional indica rice,respectively.2)P uptake in culm and sheath,leaf,and panicle at maturity increased.P uptake increased the most in the panicle,by 32.95%.The largest change was in the indica hybrid rice.3)The P uptake increased in every growth stage,with the biggest increment occurred during grain filling,averagely by 63.44%.The largest increment was in the conventional japonica rice 4)The P uptake per panicle increased by 11.16%at maturity,and the largest increase was in the conventional indica rice.5)P uptake intensity of rice population increased by 33.16%averagely,and the largest was in conventional japonica rice.6)The proportion of P in culm and sheath,and leaf decreased,whereas that increased in the panicle.FACE treatment increased the relocation of P to panicle and P transport from culm,sheath and leaf during grain filling stage by 25.45%and 36.23%,respectively,with the largest increase observed in the conventional indica rice.7)P use efficiency for grain yield and P use efficiency for dry matter production efficiency reduced by 3.49%and 2.95%,respectively,with the largest reduction in conventional japonica rice In general,plant P content,P uptake during grain filling,P uptake in panicle,P uptake per panicle,P uptake intensity all positively affected total P uptake at maturity.Total P uptake and P use efficiency for grain yield are both important P factors to improve yield,with the former showing greater contribution.5.Under FACE condition.1)the K content of rice plants reduced by 8.81%averagely at maturity.The largest reduction occurred in the conventional indica rice.The K uptake at maturity increased by 18.25%averagely,being 13.65%,23.47%and 16.51%in conventional japonica.hybrid indica and indica rice,respectively.2)The K uptake in culm and sheath,and panicle increased significantly,while that in leaf decreased slightly.3)The K uptake at every growth duration was promoted with the largest increase occured during heading to maturity,averagely by 23.1 1%.The most significant change was in the hybrid indica rice.4)K uptake per panicle increased significantly by 2.54%at maturity,and the largest one was in the hybrid indica rice.5)K absorption intensity of rice population increased by 20.50%during grain filling stage.6)The proportion of K in culm and sheath,and panicle increased,while it reduced in the leaf.The translocation of K to panicle,and from culm and sheath increased by 55.43%and 44.04%,respectively.The largest translocation to panicle was in the conventional japonica rice,whereas the largest translocation of K from culm and sheath was in the hybrid indica rice.7)The K use efficiency for grain yield increased by 12.91%,6.64%and 16.85%in conventional japonica,hybrid indica and conventional indica rice,respectively.In general,plant K content,K uptake from transplant to tillering stage,K uptake in culm and sheath,K uptake per panicle,K uptake intensity all positively affected total K uptake at maturity.The total K uptake at maturity and K use efficiency for grain production were both important contributors to grain yield,with the former showing greater impact.6.Under FACE condition,1)the content of chlorophyll a,b and a/b decreased by 4.19%,4.27%,4.20%at jointing stage,and 5.17%,7.12%and 5.50%at 20 days after heading,respectively.The largest change was in the indica hybrid rice.The content of chlorophyll a,b,a/b at heading stage increased by 3.79%,3.78%and 3.79%,respectively.The largest changed was in the conventional japonica rice.2)The leaf net photosynthetic rate at jointing stage and 20 days after heading decreased by 5.98%and 4.97%,respectively.The largest decrease was in the indica hybrid rice and conventional japonica rice.Whereas the net photosynthetic rate at heading stage increased by 4.31%,with the largest increment observed in conventional japonica rice.3)The leaf soluble protein content at jointing stage,heading stage and 20 days after heading decreased by 4.94%,12.04%,and 19.13%,respectively.The largest decrease at jointing stage and heading stage was in the conventional japonica rice,whereas the largest decrease after heading stage was in the indica hybrid rice.4)The GS activity in leaf at jointing stage,heading stage and 20 days after heading decreased by 15.72%,10.82%and 7.49%,respectively,and there was no significant difference among varieties.The GOGTA activity decreased by 0.91%,3.71%,and 0.79%,respectively.The largest decrease at jointing stage and after heading stage was in the conventional indica rice,whereas the largest decrease at heading stage was in the conventional japonica rice.5)Correlation analysis revealed that a significant linear positive correlation between leaf chlorophyll content and net photosynthetic rate,and similarly between leaf soluble protein content at heading and its N metabolism enzyme activity.In summary,FACE treatment significantly increased the yield in different types of rice varieties,and the varietal differences were significant.The total uptake of N,P and K at maturity increased significantly,and differences were significant among varieties.The N and K use efficiency for grain yield improved,whereas the P use efficiency for grain yield reduced in most of the varieties.The N and K content of rice plant at maturity decreased,yet the P content increased.The NPK uptake and their use efficiency for grain yield all affected grain yield,with the former played a greater impact.Among those different types of rice varieties,indica rice varieties were more responsive to the elevated atmospheric CO₂ concentration than those japonica varieties.In other words,indica varieties may show more yield potential than the japonica rice varieties in future CO₂ condition.