The Population Differences And Their Responses To Shading After Full Heading In Double Cropping Rice

It is normally cloudy and rainy during the late growth stage in double cropping rice,which can result in yield reduction.In order to analyze the yield change and its relationship with population characteristics under low light stress after full heading, field experiments were conducted in Yong’an Town,Liuyang County.The split-split plot design was applied with two nitrogen treatments(low nitrogen,Nl and high nitrogen, N2) and five density treatments(Dl,D2,D3,D4and D5),which formed ten different population.Half of the formed population were shaded after full heading and then compare the differences of the growth and development,yield formation and physiological and biochemical indices in different population of both the shaded ones and the non-shaded ones.The test purposes are to make sure the responses to low light after full heading in different population in double cropping rice and thus can provide a scientific basis for establishing steady and high yield population in double cropping rice. The main experimental results are as follows:1.There were significant differences in tillers number per unit area, the accumulation of dry matter quantity during the growth period and LAI among different population in double cropping rice. For high density population of N2D1, N2D2, N1D1,N1D2in early rice and high nitrogen population of N2D1, N2D2, N2D3, N2D4in late rice,tillers number, dry matter accumulation and CGR were significantly higher than other population. Population with both high nitrogen and high density in both early and late rice had the highest LAI and had a higher high efficient LAI and high effective leaf area ratio at the same time. Population of N2D1、 N2D5n、 N2D4and NID1had a higher yield in early rice,which indicated that the yield increase were not significant by increasing nitrogen fertilizer application.The yield of high nitrogen population were higher than those of the low nitrogen ones in late rice and N2D2、N2D3and N2D4of high nitrogen population reached10.12t/hm2s10.05t/hm2and10.40t/hm2respectively and N1D3and N1D4of low nitrogen population had a higher yield.2.Shading after full heading had a significant effect on source-sink relationship of different population in double cropping rice.The effects of shading on LAI of different population varied in early and late rice.The LAI of NIDI and N1D5in early rice increased by12.98%and23.08%respectively10days after shading and the LAI of other population decrease.While the LAI of N2D2,N2D4and N2D5in late rice decreased and other population increased,among which N1D2and N1D3increased most,reaching31.70%and 35.95%respectively. Grain leaf ratio is an important indicator whether the source-sink is coordinate. Shading at full panicle stage contributed to great decline of grain leaf ratio: N1D1,N1D2in early rice had the minimum decline,while N1D4,N2D4in late rice were less affected.3.Compared with the control,all of the production,transportation and accumulation of dry matter in different population significantly decreased because of shading after full heading.Besides,RUE of all the population under low light stress in both early and late rice had a variable decline compared with the control. Shading after full heading, photosynthetic performance parameters of the shade population decrease,while the SPAD value increased variably.And shading had a significant influence on chlorophyll fluorescence of lag leaf in late rice:Y (II) and Y (NO) decreased differently among all the population,while Y (NPQ) showed an increase,qN and qP value of late rice among different groups after shading at full panicle improved significantly. NIDI N1D3N1D4and N2D1of late rice had a higher SOD activity, which may be the adaptation mechanism of these population.Low light stress resulted from shading contributed to an increase of the distribution ratio of the dry matter between stem and leaf,and therefore the distribution ratio transported to the panicle substantially reduced.Compared with the control,the dry matter accumulation of the shaded population decreased significantly in both early and late rice,especially for the high nitrogen population. N1D5,N2D1and N2D2in early rice had the most decrease of accumulation of dry matter at maturity and decreased by83.04%、84.74%and88.38%respectively and N2D1,N2D2and N2D3in late rice had the most decrease of accumulation of dry matter at maturity and decreased by139.14%,119.21%and120.13%respectively.Therefore the population with low nitrogen and high density in early rice and those with proper density had a higher yield potential.4.Shading after full panicle changed the MLAI,MNAR and harvest index(HI) of different population in double cropping rice.The MLAI of all the population in early rice decreased variably except for N1D1,N1D5,N2D1and N2D5which increased a little,which was an important reason why these four population had a higher yield. While compared with the control in late rice, the shaded population represented a trend of increase and N2D1,N2D2and N2D4increased most. MNAR of all the shaded population in both early and late rice represented a increase trend,among which high nitrogen population of N2D1,N2D3and N2D4in early population increased most,reaching63.50%,73.75%and60.27%respectively but low nitrogen population of NIDI and N1D5increased by22.69%and23.16%respectively.In contract to early rice,low nitrogen population in late rice increased more and the smaller the density,the more the increase.Harvest index(HI) in both early and late rice decreased significantly.5.Shading after full heading contributed to a substantial decline in yield of all the population in both early and late rice,among which high nitrogen population had a greater decline than low nitrogen population.In early rice,the yield of high nitrogen population N2D1,N2D2,N2D4and N2D5decreased by52.31%,51.40%,52.21%and51.01%respectively compared with the control but the yield of low nitrogen and high density population NIDI and N1D2decreased only44.52%and38.21%respectively.However in late rice,the yield of high nitrogen and high density population N2D1and N2D2decreased by52.76%and53.50%respectively compared with the control but the yield of low nitrogen population N1D2and N1D4decreased only by34.90%and34.35%respectively.The main reason for the substancial decline of yield of different population in both early and late rice was the significant decrease of seed setting rate and1000-seed weight. LAI,panicle number and TDW were very significantly correlated with the decrease margin of yield at full heading stage in late rice,but in early rice only LAI was correlated with the decrease margin of yield.