Reducing nitrogen demand while maintaining yields

10 May 2022
Fertiliser spreading

A recent paper from NIAB Scientists focuses on a potential way to reduce the nitrogen demand in wheat, reducing the carbon footprint of crop production and making agriculture more sustainable. NIAB’s Dr Matt Milner, the paper’s lead author, explains more:

With ever increasing expenditure on both fertiliser inputs and production costs, a better understanding of how to make cereal crops more fertiliser efficient is paramount to maintaining food security, the profitability of food production and the drive towards net zero.

Recent advancements in our understanding of how plants perceive and deal with nutrient limitation at the gene level points to a hormone called brassinosteroids (BR) as being important for maintaining yields under a range of abiotic stresses.

Brassinosteroids were first is identified as an unknown growth-promoting compound from brassica pollen, hence the “brass” in brassinosteroids. Controversy soon followed as a pure compound had not been identified when their existence was first hypothesised. This eventually led to the active compound being isolated and purified by a research team at the US Department of Agriculture in the 1970s. To isolate the active compound scientists had to collect 500 pounds of bee-collected Brassica napus pollen to purify and obtain a mere 4mg of brassins (now called brassinolide), the active form of BR from the pollen.

While many genes are involved in the synthesis and regulation of BRs in plants, a major gene conserved in all higher plants is DWARF4, (DWF4), which is believed to be the rate-limiting enzyme in BR production.

Many reports have shown that increasing DWF4 expression in plants leads to increased yields, but growth was always studied under high nutrient conditions. To understand if these same increased yields could be seen in plants grown under low nutrient input conditions wheat plants overexpressing the wheat form of DWF4 were created at NIAB. Researchers from NIAB and the University of Cambridge worked to understand if plants overexpressing TaDWF4 could also help promote better fertiliser use efficiency under less-than-ideal conditions.

What the results showed

What the team uncovered, and published in Communications Biology, was that higher expression of the wheat gene DWF4 led to plants having altered nitrogen (N) perception. Plants overexpressing DWF4 did not recognise N as limiting and kept growing and photosynthesising as if N was available for growth. This altered reality helps wheat plants maintain growth and increase yields on 33% less N compared to “normal” wheat plants. The effect of overexpressing DWF4 led to greater comparative yield gains on low N levels than under current higher N levels (approx. 210 kg/ha). Although at high N levels increased yields were still observed in plants overexpressing TaDWF4. However, there was a trade off as grain protein content was also lower in plants overexpressing DWF4 regardless of amount of N supplied.

Wheat plants in nitrogen overexpression experiment

The differences in growth under low N in hydroponics, with the overexpression lines on the left.

Based on these results simply increasing TaDWF4 expression could allow farmers to reduce the application of N fertiliser by up to 70 kg/ha whilst still producing the same amount of yield per plant as currently grown at standard 210 kg/ha N input level. When this 70 kg/ha saving is multiplied by the estimated land in which wheat is grown in the UK (1.69 million ha in 2019) there is the potential to reduce CO2 released into the atmosphere from fertiliser production by over 100,000 t. This is equivalent to the energy needed to power and heat more than 15,000 UK homes for one year.

While these results are fascinating, our understanding is still in the early stages. We still want to understand if increased DWF4 expression effects only N fertilisation or if other fertiliser inputs could also be overcome by increased DWF4 expression and if we can do this in a non-GM way. So stay tuned!

Read the full, open access paper: ‘TaDWF4 overexpression in wheat overrides normal nutrient sensing and allows for increased biomass under limiting nutrient conditions

Lead author: Dr Matt Milner