The Study Of Compensatory Threshold Of Water Deficit To Economize Water Use In Rice Seedling

Currently, in China, the water resource is extremely scarce and severely contaminated. The agricultural water consumption is the largest and has occupied 65 % of the whole water consumptions. It is necessary to develop the water saving agriculture under the condition of the water shortage and pollution.Compensation effect caused by water deficit is one new technology which makes full use of the adaptation of water deficit and the ability of compensation for economizing water resource. Generally speaking, compensation effect or over-compensation effect is the phenomenon that the growth rate of plant exceeds non-drought group after water deficit. Compensation effect can cause many physiological reactions, including the increase of the ratio of root weight/shoot weight; the increase of the ability of osmotic regulation and flexible regulation; the increase of the accumulation of assimilation products in generative organs; the increase of the excreting of ABA and CTK which would regulate cellular osmosis, stomata behavior. These changes finally brought compensatory effect.The thresholds of compensation effect among different crops are different during the whole stages. The late-seedling stage is transitional stage from seedling to tillering, the growing condition of rice seedling has effect on tillers. In order to investigate the threshold of compensatory effect during rice seedling stage, we planted rice in buckets in Microclimate room and imposed five different water regimes on seedling rice. The results show:1) Compensatory effect is found in every water deficit group, including assimilating compensatory in roots and physiological compensatory in photosynthetic system. That the compensation effect in both D₃ and D₆ is more obvious than others indicates that the threshold (So) of compensation effect in rice seedling stage is 30<6. We can conclude that imposing drought on rice at late seedling stage can change the distribution of assimilation products and the accumulation of nitrogen and then change the osmotic status of plant and induce compensatory effect happening.2) There is sharp decrease in net photosynthetic rate and evaporation rate under water deficit groups, water use efficiency increases because of slower decreasing of photosynthetic rate. More assimilation products are stored in sheathes than those in leaves.3) After re-watering, net photosynthetic rate and evaporation rate come back quickly, especially D3 and D6 groups whose two photosynthetic indexes exceed comparing to D₀ group firstly and return to normal standard after a while. Water use efficiency reduces for the enhancement of evaporation rate and get back to normal standard after 3 days. Nitrogen transfers from leaves to sheaths and stems so as to enhance the growth of these organs.Experimental results make contribution to the investigation on the mechanism of compensation effect and can bring further research on the technology of economizing water resource.