| Nitrogen (N) and sulphur (S) play significant roles in physiological processes andgrowth performance in wheat crop. However, with the changes in fertilizer species andincreases in grain yield, there is an imbalance between N and S under excessive N supplyconditions, which must bring some great effects on grain yield and quality of wheat. Thus,the present study was conducted to investigate the effects of S and S/N interaction on gainyield and main quality traits in winter wheat, with a series of experiments in two years. Thechanges in the key enzymes for N and S assimilation, photosynthetic characteristics,accumulation and transport of dry matter, and properties of grain protein and starch wereelucidated under the different supply conditions of N and S. The regulative effects ofdifferent S applying levels on grain yield and quality traits were clarified in wheatproduction. These results helped to provide theoretical evidence and practical experiencefor attaining high yield, high quality and high fertilizer efficiency in winter wheat. Theprinciple results are as follows.1. The effects of different N levels on the key enzymes of N and S assimilation in flagleaves of winter wheat were studied using two cultivars with different grain proteincontents, i.e. Yumai 34 (high protein) and Yumai (low protein). With regards to Yumai 34,under a high N rate (330 kg N ha-1) nitrate reductase (NR) activities decreased with amountof S application, and glutamic-pyruvic transaminase (GPT) had the similar trend as NRactivities at the middle filling stage, but glutamine synthetase (GS) activities increasedwith S application. Under an appropriate N rate (240 kg N ha-1), NR activities increasedwith S application, and GS activities with 60 kg S ha-1 treatment were markedly higherthan any other S treatment, but GPT activities between different S treatments were notobviously different. These results indicated that S application might inhibit NR activitiesbut could increase the activities of GS and GPT under N application conditions, and underthe appropriate N rate, supplying S fertilizer could increase the activities of NR and GS.Furthermore, the activities of O-Acetylserine thiollyase (OAS-TL), the key enzyme of Sassimilation, decreased with S application under two N rates, especially the flag leaves of the treatment with high N combined with low S had relatively higher OAS-TL activities.Regarding the Yumai 50, there were the higher NR activities of S treatment comparingwith control (no S application). Under the high N rates, there were peak values of NRmarkedly higher than that of appropriate N application, and the activities of GS and GPTsignificantly higher than control, but there were not significant differences in the. OAS-TLactivities among all treatments. However, the OAS-TL activities in no S application werehigher than that of S application treatment under the appropriate N rate. The N assimilationenzymes in flag leaves of Yumai 34 were obviously correlated with kernel weight, grainyield, grain protein and starch contents, respectively, but correlations were not found to theS assimilation enzymes. Only a few N assimilation enzymes of Yumai 50 had obviouscorrelations with grain yield and some quality traits, but significant positive relationshipsexisted between final total starch content and the OAS-TL activity of prophase andmetaphase at grain filling stage.2. Based on the above experiments, a multiple-spike Yumai 49 and a large-spike Yumai66 were taken as trial cultivars to study the effects of S application on photosynthesischaracteristics in wheat leaves. The results suggest that, comparing with control, either of Sapplication as basal fertilizer or as basal and topdressing at jointing stage in 5:5 ratio couldsignificantly increase the canopy apparent photosynthesis (CAP), flag leaf transpiration (Tr)and flag leaf's chlorophyll (Ch1.) content, while the net photosynthesis (Pn) in flag leafwas significantly increased. With treatment of 120 kg S ha-1 for basal application, CAP, Pn,Tr. and Chl. content were lower than those with other treatments. Furthermore, Sapplication could increase chlorophyll SPAD and soluble protein content of flag leaves intwo wheat cultivars. Comparing with no S supply, S application under the appropriate Napplication level could significantly improve flag leaf's Pn and also increase dry matteraccumulation, which could provide basis for increasing wheat yield.3. The effects of S application on dynamics and fractions of S accumulation, andassimilation and translocation of carbon and nitrogen were also studied in two glutencultivars under different N levels. The results indicated that over growth progress Saccumulation in wheat spike increased up to maturity stage. A supply could increase theamounts of S accumulation in leaf, stem and sheath as compared with control, especiallymore accumulation after filling stage. Before the filling stage, the leaf presented thehighest amount of S accumulation, followed by spike＞stem＞sheath, but at maturitystage S accumulation in the spike was the highest, followed by stem＞leaf＞sheath. The results also showed that in Yumai 34 S content in leaf, stem and sheath gradually increasedafter the jointing stage, then decreased after booting and anthesis stages, whereas Saccumulation in stem of Yumai 50 gradually increased with growth process. As a result, Sapplications with both cultivars could increase the grain weight and grain N accumulationof single stem, the transfer amount of dry matter and N to grains before anthesis and thecontribution of transferred dry matter and N to grain.4. Combined with topdressing S fertilizer in Yumai 70 (middle gluten type) at thejointing stage in sandy soil, the effects of S application on grain yield and its componentsof winter wheat were evaluated. The results showed that topdressing S could obviouslyincrease grain yield in sandy soil, with highly significant level (P<0.01) between Sapplication and control. The grain yields in treatments of sulphur application were higherthan those in no sulphur fertilizer, and S3 (60 kg.ha-1 sulphur for basal application) ofYumai 49 and S1 ( basal application and topdressing at jointing stage in 5:5 ratio ) and S3of Yumai 66 were significantly different from the control at the 0.01 probability level.Moreover, S application could also obviously increase grain yield of two different glutencultivars, with the significant effects of N and N/S interaction on grain yield (P＜0.05), andthe very significant S effect (P＜0.01). Further studies on yield components suggests thatincrease of Yumai 34 yield was mostly due to increased 1000-kernel weight, then due tothe contribution of increasing spike kernel number and spike number, while increase ofYumai 50 yield was mostly contributed to increased spike kernel number and 1000-kernelweight. In addition, from observations of spike and flower development in wheat cultivars,as compared With no S supply, S application prolonged the process of floret developmentand increased the rate of fertile florets, and could also postpone peak time of maximumgrain filling, which in turn increased the 1000-kernel weight.5. At the same time, the effects of S supply on the grain quality traits of winter wheatwere also studied under varied S fertilization. The results revealed that S application couldhardly increase total grain protein content but could increase sulfurous protein content (e.g.albumins and globulin), especially with marked increases in glutenin macrpolymer (GMP)content and disulfide bond content. Further analysis on different storage proteincomponents and their proximate rates, using the methods of reverse phase highperformance liquid chromatography (RP-HPLC), showed that S application could reduceω-gliadin content and increase the rates of the X types of HMW-GS and X/Y HMW-GS,and also increase the contents ofα/β,γand grain starch and amylopectin in flour of two cultivar types. Among them, at 330 kg N ha-1 rate, S application with 100 kg S ha-1 inYumai 34 could significantly increase the content of amylose and proportion of amyloseand amylopectin, and the same N and S application in Yumai 50 could also significantlyincrease grain starch content. Although S application with 100 kg S ha-1 in Yumai 50 under240 kg N ha-1 rate could also increase the content of amylose and proportion of amyloseand amylopectin, the content of grain starch and amylopectin had lower values than control,implying that regulation on starch properties via S fertilizer supply was dependent on bothwheat cultivars and N rates. In addition, the texture analysis showed that flour farinogramsand extensograms were improved with sulphur application, and hardness, gumminess andchewiness were enhanced with the increased sulphur rate. For the parameters relevant tonoodle properties, the highest values were observed in the treatments of S100 in bothwheat cultivars.
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