| Shanlan upland rice(Oryza sativa L.),which has been selected by Li people for long period,is a characteristic upland rice in Hainan and a precious germplasm resource in China.It has extremely important economic,cultural value and incredibly suitable for germplasm resources research and utilization.In the past,the original and backward cultivation method was adopted,which lead to low yield and impose pollution om environment.In order to further develop and utilize Shanlan rice,an important tropical rice farming resource,and devote itself to developing new cultivation techniques with high yield,high quality and high efficiency,which not only protect the ecological environment,but also conducive to large-scale agricultural production,the flooding cultivation model of"Shanlan downhill"was studied and proposed by our laboratory.At present,the experiment of flooding cultivation mode of Shanlan upland rice is successful,and the yield increasing is significant.Compared with theNitrogen is the key factor limiting yield formation,but there are no related studies on the effects of nitrogen on the yield and nitrogen utilization of Shanlan upland rice.In this study,we adopted different nitrogen levels with two Shanlan upland rice varieties,and the traditional non-nitrogen application as the control,the yield characters,photosynthetic characteristics and plant nitrogen uptake,the reasonable nitrogen application rate of Shanlan upland rice were determined,and then the effect of nitrogen on yield characteristics of Shanlan upland rice was analyzed.Through the determination and analysis of nitrogen use efficiency,root nitrogen metabolism enzyme activity and rhizosphere microorganism of Shanlan upland rice under different nitrogen application rates,the nitrogen utilization of Shanlan upland rice with different nitrogen levels was explored.The physiological mechanism of nitrogen metabolism and absorption of Shanlan upland rice were analyzed.The main results are as follows:1.Effect of nitrogen level on yield formation of Shanlan rice(1)Compared with non-nitrogen application(CK),increasing nitrogen level significantly increased the yield of Shanlan rice.The yield of two varieties in N3 was the highest,N2 was the second and there was no significant difference between N2 and N3.N1and CK were significantly lower than the former two.In terms of yield components,the number of effective panicles,grain number per panicle and seed setting rate of nitrogen application treatment were higher than that of CK,and the key factor affecting yield under different nitrogen levels was the number of grains per panicle.The 1000-grain weight was not influenced by N levels.(2)the photosynthesis of Shanlan upland rice increased significantly with the amount of nitrogen application,the photosynthetic rate of N3 and N2was higher,and the photosynthetic rate of CK was the lowest.The photosynthetic rate of the two varieties was the highest at booting stage,and decreased in turn at filling stage and mature stage.In the later growth stage,the net photosynthetic rate of N2 treatment still maintained a high level,which could better accumulate dry matter and promote the formation of yield.There was no significant difference in photosynthetic rate between the two varieties(N3 and N2)at grain-filling stage and mature stage,but the net photosynthetic rate of N2 treatment was higher at mature stage.The chlorophyll content was significantly affected by the amount of nitrogen application,and the chlorophyll content of the two varieties treated with N3 was always the highest.There was a significant positive correlation between net photosynthetic rate,chlorophyll and yield traits.(3)Increasing the nitrogen level could increase the nitrogen content and nitrogen uptake of all organs of Shanlan upland rice.The nitrogen content and nitrogen uptake of N3 and N2 treatments maintained a high level.At the mature stage,the nitrogen content of the panicle in N2 was the highest,and the efficiency of nitrogen re-transport and distribution was higher.Although the nitrogen uptake of N3 treatment was the highest,the nitrogen uptake of leaves and stems was also higher,which was not conducive to the redistribution of nitrogen in Shanlan upland rice and affected the formation of yield.2.Effects of nitrogen levels on nitrogen metabolism and rhizosphere microorganisms in Shanlan upland rice(1)The results showed that nitrate reductase(NR),glutamine synthetase((GS)),glutamate synthase(GOGAT)and glutamate dehydrogenase(GDH)were significantly affected by nitrogen levels at different growth stages.The activities of NR,GS and GOGAT were higher at tillering and booting stage,and GDH activities were higher at booting and filling stage.The activities of NR,GS and GOGAT increased with the increase of nitrogen application rate,the activities of N3 and N2 treatments were higher,N1 and CK were lower,GDH decreased with the increase of nitrogen application rate,and CK was the highest.Under different nitrogen application rates,NR,GOGAT and GDH were greatly affected by nitrogen levels,while GS was less affected by nitrogen application.(2)Nitrogen could change the bacterial diversity in the rhizosphere of the two varieties at tillering and grain-filling stage,and the microbial diversity at filling stage was higher than that at tillering stage.Under different nitrogen application treatments,Proteobacteria,Bacteroidetes,Actinobacteria were relatively abundant,which were the dominant bacteria in the rhizosphere of Shanlan upland rice.The performance of nitrifying helicobacterium was different between the two varieties.Shanchuan 24 had higher relative abundance of N2 and CK,while N1 and N2 of Manpozi had higher relative abundance.In the prediction of metabolic function,chemical energy heterotrophic,good oxidizing energy heterotrophic and nitrification were the main metabolic pathways.Nitrogen application changed the relative richness of nitrification metabolic pathway.Shanchuan 24 showed that the abundance decreased with the increase of nitrogen application rate,but the difference of Manpozi was not significant.The relative abundance of nitrate reduction pathway was significantly affected by nitrogen application,which increased at first and then decreased at tillering stage and filling stage,and reached the highest in N2 treatment,but there was no significant difference in Shanchuan 24.In conclusion,increasing the level of nitrogen significantly increased the yield,chlorophyll content and net photosynthetic rate of Shanlan rice,it also significantly increased the nitrogen uptake of leaves,stems and panicles.The the activities of nitrogen metabolism enzymes in root of Shanlan upland rice at each growth stage and the microbial diversity in the rhizosphere were changed significantly by nitrogen levels.Compared with CK,the yield of N2 was significantly higher than that of CK,and there was no significant difference between N2 and N3,which reduced the waste and loss of nitrogen and maintained a higher photosynthetic rate in the later growth stage.The transportation of nitrogen from stem to grain was more efficient in N2 and the enzyme activity of nitrogen metabolism in root was kept higher activity in N2.There are more rhizosphere microorganisms related to nitrogen metabolism enriched in N2.Therefore,this study believes that the N2 level,which means the application of pure nitrogen 180kg/hm~2,is more suitable for Shanlan upland rice. |
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