Study On Water-saving And Mechanism Of Yield Response Of Paddy Rice To Upland Condition

Field experiments, pot experiments and 3H-glucose trace technique were applied to study the yield response and transportation and allocation of assimilation products in early stage and during filling stage of normal paddy rice (T11) and normal paddy rice cultivated under upland condition with plastic film mulching (T12), rice straw mulching (T13) and without mulching (T14). Results of the study were expected to find out why the grain yield of the upland rice (T13) decreased without significant loss of biomass in order to provide knowledge to increase yield of upland rice. The main results are as followings.Amount of water consumed by T11 was 545.40 mm, which was significantly higher than that of upland treatments. Comparing with T11 the water saving efficiency (WSE) of T12, T13 and T14 was 35.1% , 22.8% and 21.2% respectively. Comparing with T14 the WSE of T12 was 17.7%, and water consumption of T13 was almost the same as T14. The effective water saving period of upland cultivations was the first two months after transplanting and after then there was no significant effect. The water use efficiency (WUE) calculated by grain yield and total water consumption of upland cultivations weas significantly higher than that of normal paddy rice. The WUE of T12, T13, T14 and T11 was 1.47 g/kg, 1.31 g/kg, 1.21g/kg and 1.05g/kg respectively. The pattern of WUE of each treatment calculated by biomass and total water consumption was same as WUE calculated by grain yield and total water consumption.Shifting normal paddy to upland condition the rice grain yield decreased from 3% to 12.5%. Among upland treatments the yield of T13 was the highest and T14 was the lowest. However, there was no significantly difference between straw biomass or total aboveground biomass of upland rice and normal normal paddy rice. The main reason of grain yield decrease of upland rice was that number of filled grains per panicle and harvest index decreased by use of correlation analysis and path analysis.Labeling at late tillering stage, the total radioactivity was 55.64±1.91×105 dpm in upland rice plant and 44.13±3.68×105 dpm in paddy rice at flowering stage. There was more radioactivity in sheath than the other organs and in it the relative percentage of radioactivity of paddy rice and upland rice was 47.0% and 61.6% respectively. Then the second leaf from the top took the second place and the relative percentage of radioactivity of paddy rice and upland rice was 26.6% and 21.0% respectively. Radioactivity in panicles of paddy rice increased by 6.14×105 dpm from flowering stage to harvest and it derived mainly from sheath and flag leaf. Radioactivity in panicles of upland rice increased by 6.14×105 dpm and it derived mainly from sheath and the second leaf and stem. Though there was more non-structural labeled substance in upland rice at flowering stage, the translation and allocation efficiency of it was much lower than that of normal paddy rice during grain filling. Labeling at the early grain-filling stage, the relative percentage of radioactivity in spiklet of paddy rice and upland rice was 88.36% and 77.05% respectively one day after labeling, and 94.45% and 92.05% respectively at harvest. However, the amount of radioactivity of upland rice was much lower than normal paddy rice. The efficiency of absorption of labeled substance of upland rice was much lower than that of normal paddy rice. In the process of translocation of assimilation products to spiklet the labeled assimilate in upland rice staying in sheath and stem for a longer period than normal paddy rice and the allocation efficiency was lower than the latter. Labeling at the mid grain-filling stage the two treatments have the same dynamic changes of radioactivity in rice after mid filling stage, but the amount of radioactivity in upland rice was only 50%-60% of normal paddy rice. With time extending the radioactivity in rice plant declined. From the next day of labeling to harvest the total amount of radioactivity decreased by 31.56% in normal paddy rice and 31.34% in upland rice. More than 85% of total radioactivity in rice plant distributed to spiklet in this period. However, total radioactivity in spiklet decreased with rice growth during this stage.Two treatments, being normal paddy rice and upland cultivation of the normal paddy rice with straw mulching (stands for upland rice), was applied in the experiment to study the assimilates partitioning during grain-filling stage. In both the first and the second season the changes of organs biomass from flowering to ripen were as followings. The spiklet biomass of normal paddy rice was significantly larger than that of upland rice whereas the sheath biomass of the former was smaller than the latter. In the first season biomass of leaf and stem of paddy rice were larger than that of upland rice at initial and mid filling stage, but no difference between two treatments was found at harvest. In the second season the change of biomasses of stem and leaf between treatments was not regularly. Decrease of grain/straw ratio at harvest was mainly caused by increase of biomass of sheath in upland rice. During grain-filling stage in the first season, both of the concurrent photoassimilate and the export of reserved assimilates of normal paddy rice were larger than that of upland rice. In the second season there was no significant difference of the export of reserved substance between treatments and the weight of spiklet detpended mainly on concurrent photoassimilate. The contribution of concurrent photoassimilate in upland rice was less than that in normal paddy rice. At flowering stage the soluble carbohydrate contents in leaf and sheath of upland rice were lower than that of paddy rice and the difference was little in stem between the two treatments. The soluble carbohydrate content in leaf, sheath and stem declined gradually with rice growth. In most of the time the soluble carbohydrate content in leaf of upland rice was higher than that of paddy rice. The soluble carbohydrate in stem of upland rice was lower than that of the latter. The soluble carbohydrate content in sheath of upland rice was higher than that of paddy rice in the mid-late stage of grain-filling. In spiklet and root the soluble carbohydrate content were very low and there was no much difference between treatments, and there was no big changes from flowering to harvest.The root/shoot ratio of upland rice was 23.2% higher than that of normal paddy rice. The maximum deepth of rice root was 28cm for normal paddy rice and 35cm for upland rice. From paddy to upland condition the respiration intensity of rice root increased obviously during grain-filling period. In the first season the range of yield decrease of root-cutting treatments for normal paddy rice was from 15% to 23%. However, the yield of upland rice with 1/4 root-cutting treatment increased about 20%. In the second season the yields among treatments with root-cutting for normal paddy rice were not significantly difference, but for upland rice the yields declined with the degree of root cut off. The yield in treatment of 3/4 of root-cutting in upland rice decreased about 20.41% and the difference was significantly. In the first season root-cutting was in disadvantage of export reserved assimilate but was in advantage of concurrent photoassimilate accumulation. At last the weight of spiklet of upland rice increased with root-cutting whereas normal paddy rice decreased. In the second season, for upland rice the export of reserved assimilate decreased with root-cutting, whereas the concurrent photoassimilate increased with 1/4 root cutting-off. Excessive root-cutting would bring down the accumulation of concurrent photoassimilate and result in the decrease of spiklet. For normal paddy rice root-cutting did not have much effect on the reserved assimilate export and concurrent photoassimilate increased with 1/4 root cutting treatment, but excessive root-cutting brought down the net accumulation of concurrent photoassimilate.