Effects Of Soil Texture And Nitrogen Rates On Yiled And Quality And The Physiological Basis Of Wheat

The high quality wheat cultivar shannong 12 was used in this experiment under three different soil texture conditions, in order to study starch accumulation characteristics, starch particle size distribution, endogenous hormone levels and enzyme activities related to starch synthesis of different grain position. The protein formation, HMW-GS expression, GMP content and size distribution of GMP particle were studied at the same time, and the relationship between HMW-GS accumulation and GMP size distribution was analyzed. The effects of nitrogen rate on yield and quality under different soil textures and its physiological basis were studied in the experiment. Key findings are as follows:1 Protein accumulation differences at different grain positionsThe protein content and accumulation amount of wheat grain at different position both showed second position grain> first position grain> forth position grain> third position grain. The content of protein components of wheat at different grain positions were different significantly. The upper grains (3,4-Grains) have higher globulin content and lower gliadin content and glutenin content than lower grains (1,2-Grains).There are no significant difference of albumin content between upper grains and lower grains.This study shows that the HMW-GS appeared at 14 days after anthesis of wheat both in superior grain and inferior grain.The HMW-GS content of superior grain was higher than that in superior grain, which indicated that the accumulation ability of HMW-GS was stronger in superior grain. After anthesis, each HMW-GS content changed in the same trend as total HMW-GS content. The content of 5 subunits> 10 subunits> 14 subunits> 15 subunits, each subunits content in superior grain was also higher than inferior grain. The GMP content raised first and then fell down in the process of grain filling.The GMP content in superior gain was also higher than inferior grain. Lower HMW-GS accumulation amount and GMP content maybe one of the reasons for poor quality of inferior grain.This study showed that, the GMP size distribution of wheat was similar in superior grain and inferior grain, the particle diameter ranged for 0.37~245μm. The number of GMP particle mainly composed by <10μm particle (accounting for 99.8%), volume distribution percentage focus on 10-100μm (47.57%~69%), surface area mainly composed by <10μm particle (66.92%~83.23%). The number percentage of 10~100μm and >100μm particle of GMP in superior grain were higher than inferior grain.The volume percentage of >100μm particle of GMP in superior grain were also higher than inferior grain. So superior grain contains more large size GMP particles. This maybe because more small size particles became large size particles in superior grain. The difference of HMW-GS accumulation and GMP size distribution maybe one of the reasons of quality difference between superior grain and inferior grain.2 Starch accumulation differences at different grain positionsThe amylose content of wheat grain at mature increased with the moving up of grain positions,amylopectin content and total starch content of third position grain and forth position grain were higher than that of first position grain and second position grain. The accumulation of amylose and amylopectin and total starch showed second position grain>first position grain>third position grain>forth position grain because of the weight impact. The amylose/amylopectin ratio showed firth position >third position grain>second position grain>first position grain, which may be related to the difference of starch component synthesis.This study showed that, 7-21days after anthesis is the vigorous period of sucrose consumption, which matched with time of starch accumulation rate.The sucrose content in inferior grain was higher than that in superior grain in this period. It is indicated that the substrate of starch synthesis should not be the limiting factor for starch accumulation in inferior grain, which related to starch synthesis efficiency. This study showed that, the activities of SS, AGPase, UGPase, SSS, and GBSS changed in the pattern of a single-peak curve during grain filling. The related enzyme activities in superior grain, which had higher starch accumulation, were higher than those in inferior grain. The simulation with Logistic equation showed that the accumulation rate and initial potential were higher, the accumulation duration was longer, so the starch final amount was higher in superior grain.3 Effects of different soil textures on quality formation of wheatIn this experiment, HMW-GS content and GMP content of wheat under different soil textures showed clay soil> loam soil > sandy soil, which indicated that clay soil was favorable for HMW-GS accumulation and will help to improve wheat quality. The sedimentation volume, wet gulten content and dough development time and dough stability time were highest of wheat from clay soil. That is to say, wheat in clay soil has good dough quality. The results showed that the volume distribution of GMP particle of wheat was two peak curve. The percentage of <10μm and 10~100μm GMP particle volume distribution in sandy soil was highest, while in clay soil was lowest. However, the percentage of >100μm GMP particle volume distribution in sandy soil was lowest, while in clay soil was highest. The number distribution of GMP particle of wheat was single peak curve. Clay soil wheat has higher number percentage of >100μm GMP particle. The surface area distribution of GMP particle of wheat was two peak curve. The surface area percentage of <10μm GMP particle was lower, while 10~100μm and >100μm GMP particle was higher in clay soil. So clay soil was favourble for GMP development and improving of wheat quality. In addition, the difference of HMW-GS content between superior grain and inferior grain was larger under sandy soil, while smaller under loam soil and clay soil. It indicated that the HMW-GS accumulation in inferior grain maybe easily affected by soil conditions. More attention should be paid to the regulation of inferior grain to improve grain quality in wheat production.The results showed that the grain weight of loam soil wheat was larger than sandy soil wheat and loam soil wheat. Sandy soil wheat has higher amylopectin content and higher starch content than loam soil wheat and clay soil wheat but lower starch accumulation amount because of lower grain weight. Clay soil wheat has higher amylose content and lower total starch content. Sandy soil is favorable for starch accumulation, but the starch yield was lower. The starch granule distribution were different among wheat under different texture soils. Wheat in sandy soil has more B-type starch granule and less A-type starch granule. There is no significant difference of starch granule number distribution of wheat among different soil textures. It indicated that clay soil was farvourble for the increase of volume and surface area percentage of A-type granule, because clay soil promoted the development of starch granule possibly, which also consistent with higher amylose of clay soil wheat.4 Physiological basis for effects of different soil texture on wheat qualityNitrogen application increased spike number, kernel number and grain weight under three soil textures, thus increased the yield of wheat. Compared with N0 treatment, the yield increased 15.77% in N1 treatment and 23.22% in N2 treatment respectively under sandy soil, and 10.98% and 18.00% respectively under loam soil, and 5.96% and 19.34% respectively under loam soil. The yield was lowest in sandy soil, but there were largest yield increase of nitrogen application among three soil textures. There was no significant difference of kernel number among three soil textures, but the spike number and grain weight were highest in loam soil. Loam soil has better conditions of air, water and fertilizer, was propitious to increase spike number and kernel weight.This study found that nitrogen accumulation and translocation increased with increasing of nitrogen rate. The nitrogen translation rate was decreased by nitrogen application, but there is no difference among nitrogen treatment. Effect of nitrogen application on nitrogen translocation was higher (an average increase of 56.26%) in sandy soil, while that was lower in loam soil (an average increase of 27.43%) and clay soil (an average increase of 3.58%). Appropriate nitrogen application increased endopeptidases activities and carboxypetidase activities and promoted the decomposition of soluble protein. The endopeptidases activities and carboxypetidase activities of wheat flag leaf in loam soil and clay soil were higher and could keep a long period, which help to keep higher nitrogen translation rate and increase protein content of wheat grain. This study showed that sandy soil wheat has highest root fresh weight in 0-20 cm soil layer while lowest in 20-40 cm soil layer at anthesis. This may be due to loose texture of sandy soil, which increased the proportion of the lower roots. The root fresh weight showed clay soil>loam soil >sandy soil 10 days after the flowering. Because clay soil promoted root growth and delayed the senescence of wheat. The root vigor in 0-20 cm layer soil showed loam soil >clay soil>sandy soil, and clay soil >loam soil>sandy soil in 20-40cm layer soil. It indicated that loam soil and clay soil could help to delay senescence of wheat root.Nitrogen application increased SOD activities of wheat root, and was conducive to remove reactive oxygen species timely. The SOD activities of wheat root in sandy soil were higher than that in loam soil and clay soil. Nitrogen application increased SOD, POD, CAT activities and decreased MDA content of wheat flag leaf, which showed that nitrogen application was conducive to raise wheat active oxygen scavenging ability. The effect of nitrogen application on MDA content of wheat flag leaf was larger in sandy soil. So the active oxygen metaboism of flag leaf in sandy soil wheat was easy to be regulated by nitrogen fertilizer. Therefore, the wheat cultivation in sandy soil can be regulated by reasonable nitrogen application to delay senescence, to obtain high quality and high yield.