Responses Of Rice Root Anatomy Characters To Water And Nitrogen Supply And Its Relatinships With Water And Nitrogen Absorptions

Water and nitrogen are the two main factors in rice growth and production; many studies have focused on the interaction of water and nitrogen applications and its effects on water and nitrogen absorption. In order to understand the responses of rice root anatomy to water and nitrogen application and its associations with water and nitrogen absorption, three rice genotypes, Liangyoupei 9, Shanyou 63, Hanyou 3, were grown hydroponically. We designed three water treatments: well watered condition, moderate water deficit condition(PEG6000, 7.5% w/v), severe water deficit condition(PEG6000, 15% w/v), and each water treatment contains three nitrogen conditions: low nitrogen(20 ppm), moderate nitrogen(40 mg·L-1) and high nitrogen(80 mg·L-1). Biomass, water and nitrogen absorption, root anatomy characteristics were measured. The main results are as follows:1. The shoot biomass deceased by 11.9%-20.7% under moderate water deficit conditions and decreased by 20.1%-36.2% under severe water deficit conditions. Compared with low nitrogen condition, moderate and high nitrogen increased the shoot biomass by 11.2%-53.1% and 35%-96.6%, respectively, in three rice genotypes. Under well watered condition, the shoot biomass was highest with high nitrogen supply; under severe water deficit condition, the shoot biomass was lowest with low nitrogen supply. Under moderate and severe water deficit conditions, photosynthetic rate decreased by 4.8%-13.1% and 10.8%-24.8%, respectively; under moderate and high nitrogen conditions, photosynthetic rate increased by 14.7%-29.7% and 40.4%-63.5%, respectively, in three rice genotypes. Under well watered condition, the photosynthetic rate was highest with high nitrogen supply; under severe water deficit condition, the photosynthetic rate was lowest with low nitrogen supply. Therefore, water deficit stress inhibits rice photosynthetic rate, reduce biomass accumulation; high nitrogen increases rice photosynthesis and biomass accumulation.2. Ratio of stele diameter to root diameter increased under both water deficit and high nitrogen conditions. Root aerenchyma and sclerenchyma cell diameter increased significantly under water deficit condition, but decreased significantly when expose to high nitrogen condition. Passage cell(%) decreased significantly under water deficit condition, but increased significantly when exposured to high nitrogen condition. These root anatomy characteristics diversifications were accompanied by the changes in root water and nitrogen absorption ability. There were a significant decrease in total water uptake rate, water uptake rate via apoplastic pathway, water uptake rate via cell-to-cell pathway and total nitrogen uptake under water deficit condition in three rice genotypes; but increased under high nitrogen condition. Suggest that nitrogen can enhance root water uptake capacity under water deficit condition.3. Root aerenchyma and sclerenchyma cell diameter were significantly and negative ly correlated with total water uptake rate, water uptake rate via apoplastic pathway, water uptake rate via cell- to-cell pathway and total nitrogen uptake. Passage cell(%) showed significantly positive correlation with total water uptake rate, water uptake rate via apoplastic pathway, water uptake rate via cell- to-cell pathway and total nitrogen uptake. Our results indicated that root aerenchyma and sclerenchyma cell formation impede water and nitrogen transport, passage cell formation enhances water and nitrogen transport.4. This study found the interactions between water and nitrogen application on root aerenchyma, sclerenchyma cell diameter, total water uptake rate, apoplastic water uptake rate and total nitrogen uptake, indicated that water application and nitrogen level affect root absorption ability by modifying rice roots anatomy traits.