Abstract
AbstractNitrogen fertilizer is the most used nutrient source in modern agriculture and represents significant environmental and production costs. In the meantime, the demand for grain increases and production per area has to increase as new cultivated areas are scarce. In this context, breeding for an efficient use of nitrogen became a major objective. In wheat, nitrogen is required to maintain a photosynthetically active canopy ensuring grain yield and to produce grain storage proteins that are generally needed to maintain a high end‐use quality. This review presents current knowledge of physiological, metabolic and genetic factors influencing nitrogen uptake and utilization in the context of different nitrogen management systems. This includes the role of root system and its interactions with microorganisms, nitrate assimilation and its relationship with photosynthesis as postanthesis remobilization and nitrogen partitioning. Regarding nitrogen‐use efficiency complexity, several physiological avenues for increasing it were discussed and their phenotyping methods were reviewed. Phenotypic and molecular breeding strategies were also reviewed and discussed regarding nitrogen regimes and genetic diversity.
Highlights
Nitrogen-use efficiency (NUE) has been the subject of a wealth of literature and underpinning projects for its improvement
Supposing an average French grain yield of 7 t/ha and assuming a reference NUE value between 37.8 kg DM/kg N (Cormier et al 2013) and 33.3 kg DM/kg N, this equates to a saving of approximately 6–8 kg N/ha after 10 years of genetic improvement
Over the same 10-year period, Sylvester-Bradley and Kindred (2009) showed that this price ratio has varied from 3 to 9 (Sylvester-Bradley and Kindred 2009), leading to a necessity to increase NUE from 23.8 to 28.6 kg DM/kg N requiring almost 40 years of breeding progress. This leads us to conclude that breeding programmes need to tackle NUE more efficiently than it has been doing at the current rate
Summary
The concept of nitrogen-use efficiency (NUE) has been widely used to characterize plant responses to different levels of nitrogen (N) availability. Moll et al (1982) defined the most use of NUE, at least among breeders, which computes the grain dry mass divided by the total N available to a plant. The approach could be taken further by targeting nitrogen use (NU) as kg N absorbed by the plant instead of NUpE; in much the same way that WU is seen as (arguably) the most important target in improving water response (Blum 2009). This would avoid dividing an already rather imprecise variable (NU) by an even more imprecise one (available N). The expression of length and density of root hairs may be synergistic (Ma et al 2001), and there may be antagonistic interactions between biomass allocation to different root classes due to competition for assimilates (Walk et al 2006)
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