Abstract
Nitrogen (N) plays a vital role in photosynthesis and crop productivity. Maize plants may be able to increase physiological N utilization efficiency (NUtE) under low-N stress by increasing photosynthetic rate (Pn) per unit leaf N, that is, photosynthetic N-use efficiency (PNUE). In this study, we analyzed the relationship between PNUE and N allocation in maize ear-leaves during the grain-filling stage under low N (no N application) and high N (180 kg N ha-1) in a 2-year field experiment. Under low N, grain yield decreased while NUtE increased. Low-N treatment reduced the specific N content of ear leaves by 38% without significant influencing Pn, thereby increasing PNUE by 54%. Under low-N stress, maize plants tended to invest relatively more N into bioenergetics to sustain electron transport. In contrast, N allocated to chlorophyll and light-harvesting proteins was reduced to control excess electron production. Soluble proteins were reduced to shrink the N storage reservoir. We conclude that optimization of N allocation within leaves is a key adaptive mechanism to maximize Pn and crop productivity when N is limited during the grain-filling stage in maize under low-N conditions.
Highlights
In modern crop production systems, nitrogen (N) plays a vital role in yield formation; it is the mineral element required in the greatest amounts by plants, and is often the growth-limiting nutrient
Thylakoid N is distributed between two types of proteins: (1) proteins related to bioenergetics, including Cyt b/f and CF1/CF0 involved in electron transport and photophosphorylation, and (2) light-harvesting proteins, such as photosystem I (PSI), photosystem II (PSII), and light-harvesting complex II (LHCII) proteins, that are associated with the light reactions of photosynthesis (Makino et al, 1997; Takashima et al, 2004; Tazoe et al, 2005; Uribelarrea et al, 2009)
The current results suggest that sufficient N allocation into bioenergetics is essential to maintain leaf photosynthesis with reducing Specific leaf N (SLN)
Summary
In modern crop production systems, nitrogen (N) plays a vital role in yield formation; it is the mineral element required in the greatest amounts by plants, and is often the growth-limiting nutrient. Forms of N include soluble components such as nitrates, amino acids and proteins, and insoluble components in cell walls, membranes and other structures. Thylakoid N is distributed between two types of proteins: (1) proteins related to bioenergetics, including Cyt b/f and CF1/CF0 involved in electron transport and photophosphorylation, and (2) light-harvesting proteins, such as photosystem I (PSI), photosystem II (PSII), and light-harvesting complex II (LHCII) proteins, that are associated with the light reactions of photosynthesis (Makino et al, 1997; Takashima et al, 2004; Tazoe et al, 2005; Uribelarrea et al, 2009). When grown under high light, C3 leaves typically invested 58% of leaf N to soluble protein
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