| As a substrate of photosynthesis,elevated atmospheric CO2 concentration affects the growth,yield and quality of rice,but there are few reports on whether this effect varies with varieties.Free-air CO2 Enrichment(FACE)technology is used to study crop performance under open-air field conditions.The FACE platform has large experimental space and less human disturbance,which provides an opportunity to accurately evaluate the interaction between CO2 and varieties.Eight high-yield and good-quality rice varieties,HD5,NJ46,NJ5055,GNZ,ZZ39,FYXZ,LLY1988 and YY1540,were treated with two levels of CO2 concentration:Ambient and elevated CO2 concentration(+200 μmol·mol-1,FACE).The effects of elevated atmospheric CO2 concentration on plant height,tiller formation,leaf morphology,dry matter production and distribution,yield and its components,mineral element absorption and distribution,and rice quality were studied.The response of the above traits to high CO2 concentration was compared among rice varieties.The main results are as follows:1.Compared with ambient conditions,the heading date of rice under FACE was not changed or slightly advanced.On average,the maximum tiller number of all varieties increased by 33.4%(P<0.01),but the productive tiller ratio decreased slightly.FACE treatment had no effect on plant height at heading and maturity.2.The total leaf number(+19.5%)and leaf area index(+16.9%)were significantly increased by FACE treatment,but the length,width,area and specific leaf weight of single leaf were not significantly affected.The total leaf number increased,but the morphology of single leaf remained unchanged.3.The above-ground biomass increased significantly by 30.1%in FACE treatment,with significant increase of 32.3%and 28.7%at heading and maturity stage,respectively.The dry weight of leaves,stem sheath and rice panicle increased significantly by FACE at heading and maturity,and the increase of dry weight of stem sheath and panicle was significantly greater than that of leaf.FACE treatment significantly reduced the ratio of leaf to above-ground dry matter(-8.9%),increased the ratio of stem sheath to above-ground dry matter(+4.4%),while the ratio of panicle to above-ground dry matter did not change significantly.The decrease of leaf ratio in FACE rice was greater at heading stage than at maturity stage,while the increase of stem sheath ratio was greater at mature stage than at heading stage.The CO2 by Cultivar interaction was significant at p<0.1for stem sheath dry weight,whole plant dry weight and the ratio of panicle to above-ground dry matter.The CO2 by growth stage interaction was significant for panicle dry weight,whole plant dry weight,the ratio of leaf to above-ground dry matter and the ratio of panicle to above-ground dry matter.The CO2 by Cultivar by growth stage interaction was significant for the dry weight of stem and sheath.4.FACE treatment increased grain yield of all varieties by 23.3%(P<0.01).In terms of yield components,panicles per unit land area,spikelets per unit land area and empty grain rate increased by 21.8%(P<0.01),25.8%(P<0.01),16.4%(P<0.1),respectively.There was no significant FACE effect on spikelets per panicle,filled grain rate and filled grain weight.Various degrees of interaction between CO2 treatment and varieties were found for rice yield,spikelets per panicle,filled grain rate,empty grain rate and filled grain weight.5.Except for Cu and Zn,the concentrations of other nine mineral elements in rice plants showed a trend of decrease under FACE conditions.FACE decreased the concentrations of N,K,Mg,Fe and B by 8.9%(P<0.01),5.6%(P<0.05),6.6%(P<0.01),5.0%(P<0.1)and 6.5%(P<0.01),respectively.In most cases,the decrease of plant element concentration was greater at heading stage than that of mature stage,and the response of element concentration in stem sheath was greater than that of in leaf.From the aspect of element content,the mineral element content of rice shoots was significantly increased by 17.3%- 52.3%under FACE conditions,and the increase in stem sheath and panicle was significantly greater than that in leaf.In terms of element distribution,except for Mn,the proportion of leaf element content in the whole plant decreased(the maximum decrease rate was 15.1%,P<0.01),while the proportion of stem sheath increased(the maximum increase rate was 9.8%,P<0.01).The response of panicle element content varied with mineral elements.The interaction between CO2 treatment and varieties or/and growth stages had significant effects on the concentration,content and distribution of some elements in plants.6.Compared with rice plants grown under ambient CO2 concentration,plants grown under FACE treatment showed a trend of decrease in brown rice percentage,white rice percentage and head rice percentage,but a significant increase in brown rice yield,white rice yield and head rice yield by 23.7%,23.5%and 20.9%,respectively.FACE treatment had little effect on the head rice length,head rice width and the ratio of head rice length to width,but significantly increased the chalky rice rate and chalkiness degree.Averaged across all rice varieties,elevated CO2 concentration increased the chalky rice rate and chalkiness degree by 18.6%and 31.8%,respectively.FACE treatment reduced the amylose concentration and gel consistency on an average by 6.5%and 3.1%,respectively.The response of RVA profile of rice starch to elevated CO2 concentration was also studied.FACE treatment increased the mean value of peak viscosity and breakdown by 1.3%and 6.9%for all varieties,but decreased the mean value of hot viscosity,cold viscosity and setback by 2.2%,5.1%and 65.6%,respectively.The final viscosity and the reduction value reached a significant level.The phytic acid concentration of rice grains was significantly increased by 5.3%on average,whereas protein concentration significantly decreased by 9.9%under FACE conditions.The effects of FACE treatment on the concentrations of elements in milled rice varied with the elements,but the contents of all the 10 elements in milled rice increased with the maximum increase of 50.7%.The response of rice quality traits to high CO2 concentration varied in the direction and magnitude among different varieties.The CO2 treatment by rice Cultivar interaction was found for head rice rate,head rice length,chalky rice rate,chalkiness degree,peak viscosity,hot viscosity and cold viscosityIn conclusion,rice heading date was not changed or slightly advanced under high CO2 concentration.The number of leaves increased but the size remained unchanged.Although high CO2 concentration decreased the concentrations of elements in various organs of plants,it increased plant dry matter production significantly,which led to the rice yield increase.The latter was mainly related to the increase of panicles caused by tillering enhancement.The processing,appearance and nutritional quality of rice in high CO2 concentration environment were deteriorated,but the palatability was improved.The response of rice to elevated CO2 was affected by Cultivar and growth period.The response of yield and grain chalkiness of hybrid rice to elevated CO2 was significantly greater than that of conventional rice. |
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