Molecular Soil Biology 2025, Vol.16, No.5, 265-271 http://bioscipublisher.com/index.php/msb 267 3.2 Nitrogen effects on starch synthesis and kernel weight Nitrogen fertilizer also affects starch synthesis in wheat, which in turn affects grain weight. Starch is an important part of flour processing, and large grain weight can also affect total yield. If more nitrogen is applied, the amount of amylose in the grain may decrease, which will change the properties of the dough (Gu et al., 2023). In addition, grain size and weight are also related to nitrogen levels. Some QTLs that control these traits have been found, which are also related to resistance to nitrogen stress (Cui et al., 2015). However, it should be noted that protein content and thousand-grain weight are often negatively correlated, that is, more protein may reduce grain weight (Fan et al., 2020). 3.3 Combined effects on processing and nutritional quality The amount of nitrogen fertilizer will affect both the processing quality and nutritional value of wheat. For example, an appropriate amount of nitrogen fertilizer can make the dough form better and more stable, which is very important for making bread or noodles (Gu et al., 2023). Nitrogen fertilizer can also reduce phytic acid, so that trace elements such as iron and zinc are more easily absorbed by the human body. For colored wheat, applying less nitrogen may make anthocyanins more, which is good for health. However, if anthocyanins are increased, processing traits may be worse (Yan et al., 2024). All these indicate that different varieties, fertilizer amounts and growth environments must be well matched to take into account both processing quality and nutritional value (Iannucci et al., 2018; Fan et al., 2020). 4 Varietal Differences in Nitrogen Use Efficiency 4.1 Nitrogen absorption and utilization efficiency Different wheat varieties perform differently in terms of nitrogen absorption and utilization. Nitrogen absorption efficiency refers to the ability of plants to absorb nitrogen from the soil. Nitrogen use efficiency refers to the ability of plants to convert absorbed nitrogen into food. The combination of these two abilities determines the overall nitrogen use efficiency (NUE) of a variety. Some varieties absorb more nitrogen but convert less nitrogen, while others are good at both. For example, in soft red winter wheat, nitrogen use efficiency can contribute more than 50% to yield increases (Barraclough et al., 2010). Some of these differences come from genes, and some are also related to the environment such as climate and soil. But in general, the genetic characteristics of the variety play a key role (Ivić et al., 2021). 4.2 Genetic basis of nitrogen responsiveness Different wheat varieties also have great differences in their responses to nitrogen fertilizers. Some varieties grow faster and have higher yields when more fertilizer is applied; some varieties perform well even if less nitrogen fertilizer is applied. This response to nitrogen is related to the genetic genes of the variety itself. With the development of breeding technology, many new varieties have performed better and better in nitrogen utilization, especially in high yield (Ivić et al., 2021). The key factors that determine these abilities include the number of grains per ear, the nitrogen harvest index (that is, how much nitrogen is absorbed and converted into grain), and whether stable output can be achieved under different nitrogen fertilizer levels (Barraclough et al., 2010). These research results show that it is possible to adapt to different agricultural models, such as intensive planting or low-input farming, by breeding varieties specifically suitable for efficient nitrogen use. 4.3 Agronomic traits of efficient nitrogen-use genotypes Varieties with high nitrogen utilization rates generally have several characteristics: high yield, fast nitrogen absorption, and good adaptability. Regardless of whether more or less nitrogen fertilizer is used, these varieties tend to maintain stable performance. This also shows that when breeding new varieties, whether the target is high-fertilizer land or low-fertilizer land, improving nitrogen utilization efficiency is a worthwhile direction (Büchi et al., 2016; Ivić et al., 2021). In addition to efficient nitrogen uptake and use, these varieties often have other advantages, such as disease resistance, drought tolerance, and low weed pressure, which are conducive to use in organic farming or low-input systems. By combining these traits with nitrogen use efficiency in breeding, it is possible to breed wheat varieties that are both high-yielding and environmentally friendly.
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