The Effects Of Elevated CO₂ On Biological Processes Of Maize With Plastic Film Mulching In A Semiarid Region

This experimentwas carried out in field plots for two years,and the maize was grown in open top chambers at ambient and elevated carbon dioxide.Open top chambers were usedto simulate the future situation of elevated atmospheric CO₂ concentration.Our studyaimed to investigate the response of biological processes of maize with plastic film mulching to elevated atmospheric CO₂ concentration in a semiarid region.In this study,the main results obtained are as follows:?1?Two years' field experiment results showed that the addition of plastic film and the increasing of nitrogen fertilizer can promote the increase of 1000-kernel weight and yield of maize,but the elevated atmospheric CO₂ concentration had no significant effect on maize grain number per ear.Under the condition of RN0(Rainfed with 0 kg·N·hm^-2),RN225(Rainfed with 225 kg·N·hm^-2)and MN225(Mulched with plastic film and 225 kg·N·hm^-2),elevated CO₂ concentration promote the increase of 1000-kernel weight,and the impact of elevated CO₂ concentration is reduced with MN290(Mulched with plastic film and 225 kg·N·hm^-2).With the condition of RN0,RN225,MN290,maize yields under elevated CO₂ concentration were significantly improved,and the yield under high CO₂ concentration reached the highest when fertilization for MN290.With the increase of N fertilization,the gap of yield between high CO₂ levels and the natural atmosphere narrowed.The results showed that the impact of elevated CO₂ concentration on maize yield is a positive effect,and it means elevated CO₂ can promote the increase of maize yield,and the influence on yield are closely related to nitrogen condition.Elevated CO₂ concentration had no significant effect on grain number of per ear,but the change trend of 1000-kernel weight was the same as yield.It indicated that the reason for elevated CO₂ concentration increased maize yield was the increase of 1000-kernel weight.?2?Data in 2015 showed that elevated CO₂ concentration can make maize height increase,but it did not reach significant level.Elevated CO₂ concentration at the same time almost had no effect on stem diameter.Data in 2016 showed that elevated CO₂ concentration decreased maize height,and the extent of decline in fertilization for MN225 reached highest.When increasing nitrogen to MN290 the extent of decline had a tendency to decrease.At the sme time,the stem diameter under elevated CO₂ concentration with the condition of MN225 significantly increased.With the condition of MN290,the influence of elevated CO₂ concentration on maize stem diameter is relatively less.With two years' monitoring test of maize height and stem diameter,we found that the influence of elevated CO₂ concentration on the two kinds of agronomic traits in MN225 was relatively significant,and the increase of nitrogen fertilization will weaken the elevated CO₂ concentration's effects on maize height and stem diameter.That suggested that elevated CO₂ concentration and nitrogen level in MN225 may have an "interaction effect".?3?Two years' field experiment showed that elevated atmospheric CO₂ concentration decreased leaf biomass with RN0,but the increase of nitrogen?RN225?and plastic film?MN225?could reduce that negative effects.In 2016 the increase of plastic film?MN225?not only weaken the negative effects of elevated atmospheric CO₂ concentration on maize leaf biomass,but also appeared a positive effect.But with the high nitrogen level?MN290?,the negative effects will continue to weaken.?4?The change trend of dry weight of stem was the same as that in 2015,these results showed that with RN0,elevated atmospheric CO₂ concentration can reduce the accumulation of dry matter of stem.But the increased of nitrogen fertilization?RN225?could reduce the negative effects of elevated atmospheric CO₂ concentration on dry weight of maize stem;On the basis of RN225,to add plastic film?MN225?,it could further decrease the negative effects of high CO₂ concentration,thus it promoted the accumulation of dry matter of stem under high CO₂ concentrations.If we continued to increase nitrogen fertilization?MN290?,it can further reduced the negative effect of elevated atmospheric CO₂ concentration on the dry weight of maize stem,and it even appeared a positive effect,so as to promote the accumulation of dry matter of maize stem.?5?Our study showed that the impact of elevated atmospheric CO₂ concentration on dry weight of kernel and cob varied with nitrogen conditions,it also influenced by plastic film.With the condition of no fertilizer?RN0?,elevated atmospheric CO₂ concentration can promote the accumulation of dry matter of kernel and cob.With the increase of nitrogen fertilization and plastic film?RN225,MN225?,the impact of elevated CO₂ is enhanced.But when we continued to increase nitrogen?MN290?,it will weaken this positive effect.This suggested that the influence of elevated atmospheric CO₂ concentration on accumulation of dry matter of kernel and cob has a certain nitrogen regulation principle.?6?Under the condition of RN0,elevated CO₂ concentration can improve the net photosynthetic rate.The increase of nitrogen treatment and plastic film can promote the positive effect,but the effect was decreased with MN290.Under the condition of RN0,elevated CO₂ concentration decreased stomatal conductance of maize,the treatment with RN225 reduced the negative effects of CO₂ on stomatal conductance and the negative effect was reduced with MN225.But with MN290 the elevated CO₂ reduced the stomatal conductance of corn.