Effects Of Root Traits On Rice Photosynthesis Under Different CO₂ Concentrations And Different Nitrogen Application Levels

The CO₂concentration in the atmosphere is rising at an unprecedented rate.In 2015,the global CO₂concentration exceeded the milestone level of 400?mol mol-1,and the growth rate is getting faster and faster.Increasing concentrations of carbon dioxide and other greenhouse gases are causing changes in the global environment,such as rising temperatures,which are expected to affect major food crop production.Conversely,an increase in CO₂concentration will have a direct and positive impact on crop photosynthesis,thereby increasing grain yield.However,the magnitude of the effects of carbon dioxide fertilization is one of the main sources of uncertainty in global crop yield forecasts.Nitrogen is an important nutrient element that regulates plant adaptation to high CO₂concentrations.Nitrogen generally limits the effects of high CO₂concentrations on plant photosynthesis,biomass production and yield enhancement.In fact,previous rice FACE?Free-Air CO₂Enrichment?experiments have shown that increased yields of cereals grown in high CO₂concentrations are reduced when nitrogen is applied below 80 kg/ha.The nutritional value and appearance quality of cereals are also prone to change under conditions of high CO₂concentration.As a result,it is likely that modification or redesign of nitrogen concentration addition management measures will be required to achieve optimal productivity and quality results under climate change.In this study,OTC cultivation and outdoor pot cultivation were used.Two rice varieties were selected as the low-response rice variety Wuyunjing 30 and the high-response rice variety Yangdao 6 to study different CO₂concentration levels?CO₂concentration in the atmospheric environment and in the atmosphere?.Based on environmental CO₂concentration increase of 200?mol mol^-1)and different nitrogen supply levels?low nitrogen and high nitrogen?through experimental research on rice at different growth stages?tillering stage,jointing stage,heading stage,filling stage and harvesting stage?.The differences in growth and photosynthesis of the two rice cultivars were combined with root system indicators in an attempt to find the effects of root traits on rice photosynthesis under elevated CO₂concentrations and different nitrogen treatments.The main results are as follows:1.Under the condition of high CO₂concentration,high nitrogen treatment had no significant effect on the chlorophyll content and specific leaf area of the two rice varieties grown in the OTC room.Similarly,high nitrogen treatment had no significant effect on the chlorophyll content of the two rice varieties grown outside the OTC.High nitrogen treatment of two rice cultivars growing outdoors in OTC has a certain promotion effect on its specific leaf area.Both high CO₂concentration and high nitrogen treatment promoted 1000-grain weight,but the promotion effect was more obvious for the high-response rice variety Yangdao6.The 1000-grain weight of two rice varieties growing outdoors in OTC had a positive response to high-nitrogen treatment and the outdoor 1000-grain weight is also significantly lower than the indoor 1000-grain weight.2.High CO₂concentration significantly promoted the photosynthesis rate Anet of two rice varieties grown in the OTC room,and high nitrogen treatment only promoted the Anet of the high-response rice variety Yangdao 6 grown indoors and outdoors in OTC.While the high CO₂concentration and high nitrogen treatment in the OTC chamber reduced the stomatal conductance of the two rice cultivars,they also had the same effect on the transpiration rate?Tr?,photosynthetic electron transport rate?ETR?,and photochemical quenching coefficient?q P?.However,the Tr,ETR and q P of the high-response rice variety Yangdao 6 growing outside the OTC all promoted.High CO₂concentration treatment had a positive effect on the WUE of both rice varieties,and high nitrogen treatment had a high-response rice variety Yang The WUE of rice Yangdao 6 has a significant promotion effect in most growth stages.3.The low-response rice variety Wuyunjing 30 growing in the OTC room had a positive response to high CO₂concentration at V_cmaxduring heading stage,while the high-response rice variety Yangdao 6 had a positive response to high CO₂concentration at jointing stage.Response V_cmaxa highly responsive rice variety growing outdoors in OTC,responded positively to high nitrogen treatments.In terms of the response of J_maxto treatment with high CO₂concentration,the two rice varieties growing in OTC indoors are negative for most of their lifespans.The high-response rice varieties growing outdoors in OTC have a positive response to high nitrogen treatment.It was found that nitrogen addition can promote enzyme activity.The stomatal conductance slope values of the two rice varieties grown in the OTC chamber did not respond significantly to different CO₂concentration treatments.It was not found that high CO₂concentration treatments had a regular effect on their stomatal conductance slope values?g1 and m?.High nitrogen treatment did not have regular effects on g1 and m,but g1 and m of two rice varieties growing outdoors in OTC had a positive response to high nitrogen treatment only in the early growth stage.4.From the five-day photosynthetic process of rice,it can be found that high CO₂concentration can promote the photosynthetic rate of both rice varieties.From the tillering stage to the harvesting stage,as the treatment time of high CO₂concentration became longer,both rice varieties showed the phenomenon of light adaptation,and the low-response rice variety Wuyunjing 30 should be faster and more obvious to the light adaptation of CO₂concentration.5.The nitrogen content of leaves and roots of two rice cultivars growing in OTC indoors decreased under high CO₂concentration treatment,but compared to low nitrogen treatments,the nitrogen content of leaves and roots of two rice cultivars of OTC indoor and outdoor under high nitrogen treatments were most of the time.All have a promoting effect.6.Under the condition of high concentration of CO₂,the dry weight of rice root can be increased to some extent.For two rice varieties grown indoors and outdoors in OTC,the high-response rice variety Yangdao 6 has a stronger response to high CO₂concentration than the low-response rice variety Wuyunjing 30 under high nitrogen treatment.High nitrogen treatment There was no significant effect on root length,root width,and root volume of two rice varieties grown in the OTC chamber.Perhaps this is a high nitrogen inhibition of rice root growth,but high nitrogen treatment has a significant effect on the long root volume of the OTC outdoor high-response rice varieties enhancement.Under the condition of high CO₂concentration,high nitrogen treatment promoted the low-response rice variety Wuyunjing 30at its root tip in the early growth stage but inhibited it in the later growth stage,while the high-response rice variety Yangdao 6 was On the contrary,the overall effect was positive.The response of rice varieties grown outside OTC to high nitrogen treatment was similar to that of OTC indoors.7.Under low nitrogen treatment,the root dry weight of the low-response rice variety Wuyunjing 30 was related to its light response phenomenon.The high-response rice variety Yangdao 6 had root projection area,root surface area,root tip number and root volume.The average width of root system and the dry weight of root system are positively related to their light response.Under high nitrogen treatment,the root specific surface area and average root width of the low-response rice variety Wuyunjing 30 were related to its light adaptation phenomenon,and the average root width of the high-response rice variety Yangdao 6 was positively related to its light adaptation phenomenon.The study found that under the condition of high CO₂concentration,the effect of low nitrogen treatment on light response phenomenon of roots of high-response rice cultivars was more obvious,and the effect of high nitrogen treatment on the average width of root system of two rice varieties was relieved.In summary,under the conditions of this test,light adaptation phenomenon appeared in rice under high CO₂concentration treatment,and nitrogen treatment would also compensate for the loss of root bank and ear bank caused by the imbalance of carbon and nitrogen metabolism.Important contribution.