Effect Of Nitrogen Rates On Grain Quality Formation In Wheat Under Drought And Waterlogging From Anthesis To Maturity And Its Mechanism

Soil water stress is major ecological factor of limiting grain quality formation in wheat. Elucidating the physiological mechanism and regulation principles for grain quality formation in wheat is of important significance for understanding grain quality physiology and guiding cultural management in wheat. The effects of nitrogen rates on grain yield and quality of two wheat varieties {Triticum aestivum L) differing in grain protein content grown under drought and waterlogging stress from anthesis to maturity were studied in a cement pool culture experiment. Three water treatments were established from anthesis to maturity, i.e. waterlogging, drought (SRWC=45%~50%) and moderate water supply (SRWC=70%~80%), and under each water treatment, two nitrogen levels of 120 and 240 kg'ha'1 were implemented. The effects of nitrogen rates on grain quality formation, carbon metabolism and starch accumulation, and nitrogen metabolism and protein accumulation in two wheat varieties under drought and waterlogging stress from anthesis to maturity were studied. And it was established the function to regulation of the wheat grain quality with nitrogen under drought and waterlogging. The main results were as follows:1. Both drought and waterlogging significantly reduced grain yield, yields of grain protein and starch in wheat, compared with CK. Under CK and drought, nitrogen increased grain yield, and reduced yield under waterlogging. Compared with CK, drought increased the contents of protein, dry gluten and wet gluten, and SDS-sedimentation volume and falling number, while waterlogging reduced the contents of grain protein, dry and wet gluten. Under the same water treatment, nitrogen increased protein content, ratio of glutenin to gliadin, amylopectin content and ratio of amylopectin to amylose. In addition, significant interactions between water and nitrogen on major grain quality traits were observed. The effects of water, nitrogen and their interaction on grain yield and quality varied with different wheat cultivars.2. Effects of nitrogen rates on flag leaf senescence, photosynthetic characteristics andassimilate translocation, the activities of key enzymes for grain starch accumulation and grain starch accumulation in two wheat varieties differing in grain protein content under soil drought and waterlogging from anthesis to maturity were investigated in a cement pool culture experiment. Compared with CK, drought and waterlogging enhanced leaf membrane lipid peroxidation, while content of proline, the osmotic substance increased. Under drought and waterlogging nitrogen increased superoxide dismutase (SOD) activity, contents of soluble protein and proline, while reduced the content of malondiadehyde (MDA) in flag leaf. Under CK and drought, nitrogen increased catalase (CAT) activity in flag leaf while reduced under waterlogging.Compared with CK, drought and waterlogging reduced flag leaf photosynthesis (Pn) and SPAD value, and dry matter accumulation. Nitrogen supply increased under drought while reduced under waterlogging flag leaf Pn and SPAD value. Both drought and waterlogging reduced total soluble sugar concentration in grains. Total soluble sugar contents in leaf and grain decreased under waterlogging while increased under drought. Compared with CK, drought and waterlogging reduced the amounts and remobilization rate of pre-anthesis stored assimilates and grain weight. Under drought and waterlogging nitrogen increased amounts and remobilization rate of pre-anthesis stored assimilates in leaves, hull and rachis, stem and shell. Under CK and drought nitrogen increased total amounts and remobilization rate of pre-anthesis stored assimilates, grain weight and the amounts of pre-anthesis assimilates transferred into grains, while nitrogen reduced them under waterlogging. Nitrogen increased sucrose phosphate synthase (SPS) activities in flag leaf under drought and waterlogging. Drought and waterlogging reduced sucrose synthase (SS) activities in grain. Under CK and drought, nitrogen increased SS activity in grain while nitrogen redu...