Relationships of 'water requirement- photosynthesis- production' for paddy rice using structural equation modeling

Abstract: The yield formation of rice is affect by the relation between source and sink, and the variation of water level is important to relationship between source and sink. Under the water management of paddy rice, yield and population quality can be controlled effectively, which is important to the relationship between moisture and yield studies. Structural equation modeling (SEM) is a method of multivariate statistical analysis. Through structuring generalization of the theoretical models and path diagrams, causal relationships and effect value among the multivariable can be achieved. Based on source-sink theory of rice, this study analyzed the relationships of "water requirement-photosynthesis-population quality-production" for paddy rice under water level control using structural equation modeling method. Tests were implemented in the experimental station of Jiangning campus of Hohai University (Efficient Irrigation and Drainage and Environment of Agriculture Water and Soil of South Area Key Laboratory of The Ministry of Education) from May to October in 2009 and 2010. Those tests were carried out in fixed cubic lysimeters (28 with closed bottom and 2 without bottom) with specifications for the length × width × depth = 2.5m×2m×2m, and processing scheme of drought and waterlogging in different growth stages of rice was designed. Dynamic variation rule of water level in paddy fields and rice growth and physiological indexes were observed, rice water requirement during whole growth stages and total amount of canopy photosynthesis under water level control were calculated. Then, we chose some population quality indexes (maximum LAI, root-shoot ratio, plant height, stem weight) and yield components indexes (effective panicles, grains per panicle, 1000-grain weight, seed setting rate) as observation variable, and analyzed the relationships among water requirement, photosynthesis, population quality and yield components of rice under water level control using structural equation modeling method. The results showed that: the first three total effect value (absolute value) of total water requirement to the factors were 1000-grain weight(0.717), effective panicles(0.650), grains per panicle(0.459). And the fist three total effect value (absolute value) of canopy gross photosynthesis to the factors in order were stem weight (0.631), maximum LAI(0.437), plant height(0.437). It showed that total water requirement played an important role in yield formation, moreover, canopy photosynthesis focused on the effect of rice development status. Source and sink correlation showed moderate positive correlation with the coefficient of 0.44. Both the direct and indirect effects from total water requirement and canopy gross photosynthesis were positive. Total effect value (0.552) of total water requirements on yield is greater than the total canopy photosynthetic capacity (0.201), and the effect of total water requirement on yield came indirectly from the function of yield components factors.