[Effects of postponed basal nitrogen application with reduced nitrogen rate on grain yield and nitrogen use efficiency of south winter wheat]. / å‡é‡æ–½æ°®ä¸‹åŸºè‚¥åŽç§»å¯¹å—æ–¹å†¬å°éº¦äº§é‡å’Œæ°®ç´ åˆ©ç”¨æ•ˆçŽ‡çš„å½±å“.

Excessive nitrogen (N) fertilizer application has led to a reduction of nitrogen use efficiency and environmental problems. It was of great significance for high-yield and high-efficiency cultivation to reduce N fertilizer application with modified application strategies. A two-year field experiment was conducted to study effects of different N application rates at basal and seedling application stages on grain yield and nitrogen use efficiency. Taking the conventional nitrogen application practice (240 kg N·hm-2 with application at basal, jointing, and booting stages at ratios of 5:3:2, respectively) as control, a field trial was conducted at different N application rates (240, 180 and 150 kg N·hm-2, N240, N180 and N150, respectively) and different application times [basal (L0), fourth (L4) and sixth leaf stage (L6)] to investigate the effects on grain yield and nitrogen use efficiency. The results indicated that grain yield decreased along with reducing the N application rate, but it had no significant difference between N240 and N180 while decreased significantly under N150. Nitrogen agronomy and recovery efficiency were all highest under N180. Among different N application stages, grain yield and nitrogen use efficiency were highest under L4. N180L4 had no signifi-cant difference with control in grain yield, but its nitrogen use efficiency was significantly higher. The leaf area index, flag leaf photosynthesis rate, leaf nitrogen content, activity of nitrogen reductase and glutamine synthase in flag leaf, dry matter and N accumulation after jointing of N180L4 had no significant difference with control. In an overall view, postponing basal N fertilizer application at reduced nitrogen rate could maintain high yield and improve nitrogen use efficiency through improving photosynthetic production capacity and promoting nitrogen uptake and assimilation.

[Effects of nitrogen application rates and straw returning on nutrient balance and grain yield of late sowing wheat in rice-wheat rotation].

Field experiments were conducted to study the effects of nitrogen application rates and straw returning on grain yield, nutrient accumulation, nutrient release from straw and nutrient balance in late sowing wheat. The results showed that straw returning together with appropriate application of nitrogen fertilizer improved the grain yield. Dry matter, nitrogen, phosphorus and potassium accumulation increased significantly as the nitrogen application rate increased. At the same nitrogen application rate (270 kg N · hm(-2)), the dry matter, phosphorus and potassium accumulation of the treatment with straw returning were higher than that without straw returning, but the nitrogen accumulation was lower. Higher-rate nitrogen application promoted straw decomposition and nutrient release, and decreased the proportion of the nutrient released from straw after jointing. The dry matter, phosphorus and potassium release from straw showed a reverse 'N' type change with the wheat growing, while nitrogen release showed a 'V' type change. The nutrient surplus increased significantly with the nitrogen application rate. At the nitrogen application rate for the highest grain yield, nitrogen and potassium were surplus significantly, and phosphorus input could keep balance. It could be concluded that as to late sowing wheat with straw returning, applying nitrogen at 257 kg · hm(-2) and reducing potassium fertilizer application could improve grain yield and reduce nutrients loss.

[Responses of wheat seedlings root growth and leaf photosynthesis to drought stress].

Taking drought-sensitive wheat cultivar Wangshuibai and drought-tolerance cultivar Luohan 7 as test materials, a hydroponic experiment was conducted to study the effects of drought stress on root system morphology, physiological characteristics and leaf photosynthesis of wheat seedlings, aimed to elucidate the adaptation mechanisms to drought stress. Under drought stress, the root vitality of the cultivars increased markedly, but the root number and root surface area decreased. Drought stress decreased relative water content and increased the ratio of bound water to free water in leaves of Wangshuibai, but had less effects on Luohan 7. Drought stress decreased, the leaf chlorophyll content, Pn g(s), Ci, and transpiration rate of the two cultivars, but had no significant effects on leaf chlorophyll content and Pn of Luohan 7. Drought stress decreased the leaf area of the two cultivars and the root biomass, shoot biomass, and plant biomass of Wangshuibai, but had no significant effects on Luohan 7. The results indicated that under drought stress, drought-tolerant wheat cultivar was able to compensate decreased root absorption area and retain higher root water uptake capability via enhancing root vitality and maintaining higher root biomass, and further, to keep higher leaf photosynthetic area and Pn to mitigate the inhibition of drought on wheat seedlings growth.

[Effects of atmospheric CO2 concentration enhancement and nitrogen application rate on wheat grain yield and quality].

FACE platform was applied to study the effects of elevated atmospheric CO2 concentration on wheat grain yield and quality under two nitrogen (N) application rates. Elevated atmospheric CO2 concentration and applying N increased the grain yield, spike number, grain number per spike, and biomass significantly, but elevated CO2 concentration had no significant effects on harvest index (HI). Under elevated CO2 concentration, there was a significant decrease in the protein, gliadin, gluteinin, and glutein contents of the grain and the sedimentation value of the flour, and a significant increase in the starch and its components contents of the grain; under N application, an inverse was observed. The dough stability time and the dough viscosity characteristics, such as peak viscosity, final viscosity, and setback value, increased significantly under elevated CO2 concentration and high N application rate. The interaction of atmospheric CO2 concentration and N application rate had significantly positive effects on wheat grain yield and biomass, but less effect on grain quality. Therefore, with elevated atmospheric CO2 concentration in the future, maintaining a higher N application level would benefit wheat grain yield and paste characteristics, and mitigate the decline of grain quality.

[Effects of shading on the nitrogen redistribution in wheat plant and the wheat grain quality].

Taking winter wheat (Triticum aestivum L.) cultivars Yangmai 158 (shading-tolerant) and Yangmai 11 (shading-sensitive) as test materials, this paper studied the effects of shading at the stages from jointing to maturity on the plant N redistribution, grain yield, and grain- and dough quality of the cultivars. The treatments were non-shading, 22% shading, and 33% shading. Under shading, the grain yield and its protein content of Yangmai 158 and Yangmai 11 decreased by 4.1%-9.9% and 3.0%-8.3%, and 15.3%-25.8% and 10.4%-14.1%, respectively, compared with non-shading. With the increase of shading intensity, the grain N content was increasingly dependent on the N accumulated after anthesis. Shading decreased the redistribution of N stored pre-anthesis in the vegetative organs to the grain, but increased the redistribution efficiency of N accumulated pre-anthesis (RENP) in leaves while decreased the RENP in sheathes and stems, and in hulls and rachises. Therefore, the mean RENP in the vegetative organs was not essentially altered by shading. The grain protein content increased significantly under shading, which could be related to the "condense effect", i.e., the decrement of grain protein content was much less than that of grain yield. In addition, shading had less effects on the contents of grain albumin and globulin but increased the contents of grain gliadin and glutinin significantly, and accordingly, the grain wet gluten content, dough development time, and dough stability time increased, while the dough softening degree decreased.

[Morphological and physiological differences of wheat genotypes at seedling stage under water stress].

Taking thirty six wheat cultivars bred in different era and ecological regions as test materials, their seedlings growth under water stress was investigated, and their drought resistance was evaluated by gray correlation grade analysis. Significant difference was observed in the drought resistance among the cultivars. The weighted drought resistance index ranged from 0.6580 to 0.2434. Among the test seventeen morphological and physiological traits, shoot dry mass had the greatest correlation degree (0.9473) with drought resistance, while SPAD had the smallest one (0.5356). The test cultivars were clustered into three groups, among which, eight cultivars belonged to strong drought resistance group, twenty three cultivars belonged to medium drought resistance group, and five cultivars belonged to drought-sensitive group. The shoot dry mass, root dry mass, plant dry mass, plant height, root nitrogen accumulation, leaf area, and tiller number per plant differed significantly among the three groups, which could be used for evaluating the drought resistance of wheat cultivars at seedling stage.

[Effects of shading on wheat grain starch quality and redistribution of pre-anthesis stored nonstructural carbohydrates].

This paper studied the effects of shading in the period from jointing to maturity on the grain yield, starch content, and starch paste traits of two winter wheat (Triticum aestivum L.) cultivars, shading-tolerant Yangmai 158 and shading-intolerant Yangmai 11, and analyzed the relationships of the redistribution of total soluble sugars stored before anthesis in vegetative organs with the grain yield, starch content, and starch paste parameters of the cultivars. The results showed that shading decreased the redistribution of pre-anthesis stored total soluble sugars in vegetative organs to reproductive organ, resulting in the decrease of grain yield, and significantly decreased the amylopectin content but had no effects on the amylose content in grains, inducing a significant decrease in the ratio of amylopectin to amylase content in the grains. Shading also decreased the grain starch peak viscosity of the cultivars. Under shading, Yangmai 11 had a decrease of its grain starch through viscosity and an increase of starch pasting temperature, while Yangmai 158 had lesser responses in the two parameters.

[Effects of salt and waterlogging stress at post-anthesis stage on wheat grain yield and quality].

A pot experiment was conducted to study the effects of salt (ST), waterlogging (WL), and their combination (SW) at post-anthesis on the grain yield and its starch and protein components of wheat cultivars Yangmai 12 and Huaimai 17. Comparing with the control, treatments ST, WL, and SW, especially ST and SW, decreased the allocation of nitrogen and carbon assimilates at pre- and post-anthesis to the grains significantly, resulting in an obvious decrease of grain yield and its protein and starch contents. Both ST and SW had significant negative effects on the glutenin/gliadin and amylase/amylopectin ratios in the grains, compared to CK and WL. Yangmai 12 was more sensitive to ST than SW, while Huaimai 17 was in adverse. WL decreased the accumulation of protein and starch in the grains of the two cultivars. Except that the glutenin and albumin in Huaimai 17 had some increase, the globulin and gliadin in Huaimai 17 and all protein components in Yangmai 12 were decreased under WL.

[Evolution characteristics of flag leaf photosynthesis and grain yield of wheat cultivars bred in different years].

Taking six winter wheat (Triticum aestivum) cultivars, i. e., 'Wangshuibai' and 'Bima 1' bred in 1950s, 'Zhengyin 1' and 'Yangmai 1' bred in 1970s, and 'Yumai 34' and 'Ningmai 9' bred in 1990s, as test materials, field experiments were conducted to study the evolution characteristics of their flag leaf photosynthesis and grain yield. The results showed that compared with those bred in 1950s and 1970s, the cultivars bred in 1990s had higher chlorophyll content, net photosynthetic rate (Pn), PS II maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (PhiPSII), photochemical quenching coefficient (qp) and non-photochemical quenching coefficient (qN) at grain-filling stage, their flag leaf had a longer functional duration and senesced slower, and their harvest indices were higher, with the grain yield increased by 25.90% and 11.29%, respectively. It was suggested that in the evolution process of wheat cultivars from 1950s to 1990s, the improved photosynthetic capacity and the lengthened functional duration of flag leaf after anthesis were the key physiological bases for grain yield enhancement.

[Effects of temperature and illumination on flag leaf photosynthetic characteristics and senescence of wheat cultivars with different grain quality].

Taking wheat cultivars Yumai 34 (high protein content in grain) and Yangmai 9 (low protein content in grain) as test materials, and by the method of growth chamber, this paper studied the effects of different combinations of temperature and illumination on the photosynthetic characteristics and senescence of their flag leaves at grain-filling stage. The results showed that both high temperature and low illumination had negative effects on the photosynthesis. They decreased the net photosynthetic rate (Pn), photochemical efficiency (Fv/Fm), and actual photochemical efficiency (PhiPSII) significantly, but their action mechanisms were differed. High temperature mainly decreased the chlorophyll content (SPAD value) and Pn, while low illumination mainly decreased the chlorophyll fluorescence parameters Fv,/Fm and PhiPSII, and thus, inhibited the activity of PS II. High temperature increased the MDA content and decreased the soluble protein content and SOD activity, resulting in the acceleration of senescence, while low illumination increased the SOD activity and slowed down the senescence. Yumai 34 was more sensitive to high temperature and low illumination than Yangmai 9.

[Effects of drought and waterlogging on flag leaf post-anthesis photosynthetic characteristics and assimilates translocation in winter wheat under high temperature].

With winter wheat varieties Yangmai 9 and Yumai 34 as test materials, this paper studied post-anthesis photosynthetic characteristics in flag leaves, the translocation of assimilates and nitrogen stored in vegetative organs before and after anthesis and their relationships with grain yield and quality under different temperature and water conditions. The results showed that high temperature, drought, and waterlogging all had significant negative effects on photosynthetic rate and chlorophyll content (SPAD value) of flag leaves, and the effects of drought and waterlogging were greater under high temperature than under optimum temperature. The translocation amount and rate of assimilates and nitrogen stored in vegetative organs before anthesis declined in the order of drought > normal soil moisture content > waterlogging under optimum temperature, but normal soil moisture content > drought > waterlogging under high temperature. The amount of post-anthesis assimilates translocated into grain declined in the order of normal soil moisture content > waterlogging > drought under optimum temperature, but normal soil moisture content > drought > waterlogging under high temperature, while that of post-anthesis accumulated nitrogen declined in the order of normal soil moisture content > waterlogging > drought under both high and optimum temperature. The starch and protein contents in grains were the lowest under high temperature x waterlogging, but the highest under optimum temperature x normal soil moisture content. Overall, the decrease of grain mass and starch content under high temperature and water stresses was associated with the lower photosynthetic rate and less post-anthesis assimilates accumulation, while grain protein content was related to the translocation amount and rate of nitrogen stored before anthesis.