Nitrogen Accumulation and Transport Characteristics and Grain Protein Content of Wheat Varieties with Different Nitrogen Efficiencies and Their Responses to Irrigation

Weina HE

Xinxiang City Agricultural Technology Extension Station, Xinxiang 453000, China

Abstract [Objectives]To explore the differences in nitrogen accumulation and transport characteristics and grain protein content of wheat varieties with different nitrogen efficiencies and their responses to irrigation.[Methods]Under field conditions, using nitrogen-inefficient varieties Luohan 17 and Xinhua 818 and nitrogen-efficient varieties Bainong 418 and Bainong 419 as materials, this paper studied the nitrogen accumulation and transport characteristics, grain protein content and protein yield of wheat with different nitrogen efficiencies under rainfed and irrigated conditions.[Results]Compared with the nitrogen-inefficient wheat varieties, the pre-flowering nitrogen transport and the shoot nitrogen accumulation at the mature stage of nitrogen-efficient wheat varieties decreased by 15.08% and 28.25%, respectively, and the grain protein content decreased by 11.66%, under rainfed conditions.Compared with rainfed conditions, nitrogen accumulation in shoots of nitrogen-inefficient wheat varieties and nitrogen-efficient wheat varieties at the mature stage increased by 6.59% and 67.05%, respectively, and grain protein content decreased by 13.50% and 3.47%, respectively, under irrigated conditions.The two nitrogen efficiency types of wheat had different responses to irrigation after flowering.After irrigation, the nitrogen accumulation of nitrogen-efficient varieties increased by 274.80%, while that of nitrogen-inefficient varieties decreased by 51.15%.Finally, the grain protein yield of nitrogen-inefficient wheat varieties remained stable, while the grain protein yield of nitrogen-efficient wheat varieties increased by 40.37%.[Conclusions]The nitrogen accumulation and transport characteristics and grain protein content of wheat varieties with different nitrogen efficiencies are different under different irrigation conditions.In production, it is necessary to take different irrigation measures in accordance with the difference in nitrogen efficiency of wheat varieties, so as to increase the protein content of wheat grains.

Key words Irrigation, Wheat, Nitrogen efficiency, Nitrogen accumulation and transport, Protein content

1 Introduction

As one of the important grain crops in China, wheat is the main source of calories and protein for the Chinese people and its yield and quality directly concern China’s food security and people’s nutritional health[1].With the improvement in living standards and the rapid development of the food industry, the requirements of people for the quality of wheat are becoming higher and higher.Therefore, at the same time of focusing on improving wheat yield, it is also required to pay attention to improving wheat grain quality[2].Protein content is an important quality indicator of wheat and is directly related to the nutritional quality and processing quality of wheat[3].Zhang Yufengetal.[4]found that the protein content of wheat grains is affected by both genotype and environmental conditions, and high-protein wheat varieties can maintain high protein content under most environmental conditions; however, some studies show that the environment has a greater impact on the protein content of wheat grains compared with the differences in genotypes[5-6].The formation of wheat grain protein is the result of the comprehensive effect of nitrogen absorption, accumulation, transport and distribution.Studying the characteristics of nitrogen accumulation and transport in wheat is favorable for increasing the protein content of wheat grains and accordingly improving wheat quality[2].Different wheat varieties have large differences in nitrogen uptake and utilization and protein formation, which can be optimized by changing the growing environment of wheat[7-8].Findings of Wang Demeietal.[9]showed that changing the water supply in environmental factors can regulate the nitrogen accumulation, transport and distribution in wheat, and ultimately affect the formation of grain protein.However, there are few studies on the differences in protein content of different nitrogen-efficient wheat varieties and their responses to irrigation.In view of these, using nitrogen physiologically inefficient(referred to as nitrogen inefficient)varieties Luohan 17 and Xinhua 818 and nitrogen physiologically efficient(referred to as nitrogen efficient)varieties Bainong 418 and Bainong 419 as materials, under rainfed and irrigated conditions, we studied the differences in nitrogen accumulation and transport characteristics, protein content and protein yield of wheat varieties with different nitrogen efficiencies and their responses to irrigation, to provide a theoretical basis and technical support for the efficient and high-quality production of wheat.

2 Materials and methods

2.1 Overview of experimental materials and test materialsThe experiment was carried out in Qianli Village, Zhaojing Town, Huojia County, Xinxiang City, Henan Province from 2016 to 2017.The soil of the experimental field was clay, the groundwater level was 4-5 m, the soil pH of the 0-20 cm soil layer was 8.1, the organic matter content was 12.1 g/kg, the content of alkaline hydrolyzable nitrogen was 55.2 mg/kg, the content of available phosphorus was 8.3 mg/kg, and the content of available potassium was 125.6 mg/kg.The test wheat varieties were Luohan 17, Xinhua 818, Bainong 418, and Bainong 419, of which Luohan 17 and Xinhua 818 were nitrogen-inefficient varieties, and Bainong 418 and Bainong 419 were nitrogen-efficient varieties.

2.2 Experimental designWe adopted a two-factor split-plot design, the main plot was water treatment, with the rainfed(no irrigation during the whole growth period)and irrigated(irrigation during jointing and booting stages), and the subplots were wheat varieties, namely Luohan 17, Xinhua 818, Bainong 418, and Bainong 419.The plot area was 9 m2and repeated 3 times.Wheat was sown on October 16-17, 2016, and the four-leaf stage seedlings were fixed to 2.4 million seedlings/ha.The dosages of base fertilizer N, P2O5, and K2O were 120, 120, and 120 kg/ha, respectively, which were applied at one time before soil preparation, and topdressed with nitrogen fertilizer 120 kg/ha during the jointing period.Nitrogen, phosphorus, and potassium fertilizers adopted urea, superphosphate, and potassium chloride, respectively.The total rainfall during the wheat growing period was 196 mm, which was equivalent to the average annual rainfall(201 mm), so it was a normal year.Other management measures were the same as the conventional field.

2.3 Measurement items and methods

2.3.1Nitrogen accumulation and transport characteristics in wheat plants.We surveyed the number of tillers per unit area at the flowering and mature stages of wheat.At the same time, we selected 20 representative wheat plant samples in each plot, and counted the number of tillers.After that, the tillers were fixed at 105 ℃ for 30 min, and then the plant samples at the flowering stage were divided into two parts: stem leaf sheath(referred to as stem leaf)and ear.The mature plant samples were divided into three parts: stem leaf sheath, ear axle + grain husk(referred to as husk), and grain.The fixed plant samples were dried at 65 ℃ to a constant mass, and the dry mass was measured and the dry matter accumulation was calculated.After crushing, the samples were digested by H2SO4-H2O2method-Kjeldahl method to determine the total nitrogen content.The nitrogen accumulation of an organ is the product of the dry matter accumulation of the organ and the total nitrogen content, and the nitrogen accumulation in a certain period is the sum of the nitrogen accumulation of each organ in that period[10].With reference to the method of Huo Zhongyangetal.[10], we calculated the nitrogen accumulation and transport indicator of wheat:

Nitrogen transport in stem leaves(ears)before flowering=Nitrogen accumulation in stem leaves(ears)at flowering stage-Nitrogen accumulation in stem leaves(husks)at mature stage;

Total nitrogen transport before flowering=Nitrogen accumulation at flowering stage-Nitrogen accumulation in stem leaves at mature stage-Nitrogen accumulation in husks at mature stage;

Contribution of nitrogen transport to grain before flowering=Nitrogen transport before flowering/Grain nitrogen accumulation at mature stage×100%;

Nitrogen accumulation after flowering=Nitrogen accumulation at mature stage-Nitrogen accumulation at flowering stage.

2.3.2Grain protein content and protein yield.Grain protein content(%)=Grain total nitrogen content×5.7; Grain protein yield(kg/ha)=Grain nitrogen accumulation×5.7.

3 Results and analysis

3.1 Nitrogen accumulation and transport characteristics of wheat varieties with different nitrogen efficiencies and their responses to irrigationAs shown in Table 1, under rain-fed conditions, the nitrogen transport in the stem leaves of the nitrogen-inefficient wheat varieties before flowering was higher than that of the nitrogen-efficient varieties, with an average increase of 20.43%; the nitrogen transport amount of ears before flowering varied greatly among different wheat varieties of the same nitrogen efficiency type, but had little difference among different nitrogen efficiency types of wheat varieties.The contribution rate of nitrogen transport to the grain before flowering of the nitrogen-inefficient and nitrogen-efficient wheat varieties was not significantly different, and both exceeded 85.00%, indicating that the nitrogen accumulation in wheat mainly came from before flowering; the nitrogen accumulation after flowering of the nitrogen-inefficient varieties was 37.01% higher than that of the nitrogen-efficient varieties.

Table 1 Nitrogen accumulation and transport characteristics of wheat varieties with different nitrogen efficiencies and their responses to irrigation

Compared with rain-fed conditions, irrigation could increase nitrogen transport in stem leaves and ears of nitrogen-inefficient wheat varieties before flowering, but the effect on nitrogen-efficient wheat varieties was different between different varieties.Irrigation of nitrogen-inefficient wheat varieties increased the contribution of nitrogen transport to grains before flowering and reduced nitrogen accumulation after flowering by 51.15%.By comparison, irrigation of nitrogen-efficient wheat varieties significantly reduced the contribution rate of nitrogen transport to grains before flowering, and increased nitrogen accumulation after flowering by 274.80%.

The nitrogen transport of nitrogen-efficient wheat varieties before flowering was separately reduced by 15.08% and 10.71% under rainfed and irrigated conditions compared with those of nitrogen-inefficient wheat varieties; the contribution rate of nitrogen transport to grain before flowering was increased by 2.2% under rain-fed conditions compared with nitrogen inefficient wheat varieties, and decreased by 22.56% compared with nitrogen inefficient wheat varieties under irrigated conditions; the nitrogen accumulation after flowering was 27.01% lower than that of nitrogen-inefficient wheat varieties under rainfed conditions, and increased by 460.00% under irrigated conditions.

3.2 Nitrogen accumulation at mature stage of wheat varieties with different nitrogen efficiencies and their responses to irrigationAs indicated in Table 2, under rainfed conditions, the nitrogen accumulation in the ground parts of nitrogen-inefficient and nitrogen-efficient wheat varieties was 199.5-213.3 and 141.1-155.1 kg/ha, respectively.The Mean nitrogen accumulation in the ground parts of nitrogen-efficient wheat varieties was 28.25% lower than that of nitrogen-inefficient wheat varieties.Specifically, nitrogen accumulation in stem leaves and husks decreased by 61.98% and 48.90%, respectively.The nitrogen accumulation in the grains of the nitrogen-inefficient and nitrogen-efficient wheat varieties was 148.3-150.4 and 117.9-131.5 kg/ha, respectively.The average nitrogen accumulation in grains of nitrogen-inefficient wheat varieties increased by 19.81% compared with nitrogen-efficient wheat varieties.

Table 2 Nitrogen accumulation at mature stage of wheat varieties with different nitrogen efficiencies and their responses to irrigation(kg/ha)

Compared with rainfed conditions, the nitrogen accumulation in stem leaves of Luohan 17, Xinhua 818, Bainong 418 and Bainong 419 after irrigation increased by 47.06%,-4.26%, 273.05% and 137.04%, respectively; the nitrogen accumulation in husks increased by 52.99%, 11.54%, 276.92% and 163.51%, respectively; the nitrogen accumulation in grains increased by-2.73%, 5.26%, 36.30% and 44.03%, respectively.Compared with the rain-fed conditions, the nitrogen accumulation at the mature stage of the nitrogen-inefficient wheat varieties and nitrogen-efficient wheat varieties after irrigation increased by 6.59% and 67.05%, respectively.Compared with the nitrogen-inefficient wheat varieties, the nitrogen accumulation in the ground parts and various organs at the mature stage of the nitrogen-efficient wheat varieties under rainfed conditions was lower, but the increase in nitrogen accumulation of nitrogen-efficient wheat varieties after irrigation was significantly greater than that of nitrogen-inefficient wheat varieties.

3.3 Grain protein content and protein yield of wheat varieties with different nitrogen efficiencies and their responses to irrigationAs shown in Table 3, under rainfed conditions, the grain protein contents of the nitrogen-inefficient wheat varieties Luohan 17 and Xinhua 818 were 17.3% and 15.2%, respectively, the grain protein contents of nitrogen-efficient wheat varieties Bainong 418 and Bainong 419 were 14.4% and 14.3%, respectively; the average grain protein content of nitrogen-efficient wheat varieties was 11.66% lower than that of nitrogen-inefficient wheat varieties.Under rainfed conditions, the grain protein yields of Luohan 17, Xinhua 818, Bainong 418 and Bainong 419 were 857.0, 845.3, 672.0, and 749.4 kg/ha, respectively; the mean grain protein yield of nitrogen-inefficient wheat varieties was 19.77% higher than that of nitrogen-efficient wheat varieties.

Table 3 Grain protein content and protein yield of wheat varieties with different nitrogen efficiencies and their responses to irrigation

Compared with rain-fed conditions, the grain protein content of nitrogen-inefficient and nitrogen-efficient wheat varieties under irrigated conditions decreased by 13.50% and 3.47%, respectively; the decrease rate of nitrogen-efficient wheat varieties was smaller than that of nitrogen-inefficient wheat varieties.After irrigation, the grain protein yield of nitrogen-inefficient wheat varieties did not change much from that under rain-fed conditions, while the grain protein yield of nitrogen-efficient wheat varieties increased by 40.37% compared with rain-fed conditions.

4 Conclusions and discussion

Now, it is a hot spot and focus of scientific and technological workers to find how to improve the nitrogen accumulation and transport characteristics of wheat, and how to promote the distribution of nitrogen in the grain, thereby improving the quality of wheat.Liu Pengpengetal.[6]found that genotype, environment and their interaction had significant effects on protein content of winter wheat, and the effect was environment > interaction > genotype.According to findings of Zhang Minetal.[11], reducing irrigation could promote the transport of nitrogen from the vegetative organs of strong gluten wheat to the grain and increase the grain protein content.The research of Sun Minetal.[12]showed that the protein content and its components at grain filling stage of high nitrogen absorption wheat variety Qinmai 11 was higher than that of low nitrogen absorption wheat variety Yang 9817.The results of this study indicated that for nitrogen-inefficient wheat cultivars, irrigation is beneficial to increase the amount of nitrogen transport and the contribution of nitrogen transport to the grain before flowering, but it would reduce the grain protein content; for nitrogen-efficient wheat cultivars, irrigation reduces the contribution rate of nitrogen transport to grains before flowering and increases nitrogen accumulation after flowering.The protein content of grain is mainly affected by the genetics of the variety, and is relatively less affected by irrigation, while the protein yield is mainly controlled by irrigation conditions.In production, it is necessary to take different irrigation measures in accordance with the nitrogen physiological efficiency of wheat to ensure or improve the protein content of wheat.