The secret of nitrogen fertilizer has been uncovered for the first time in the world! Cai Yifang, a specially appointed researcher at the Academia Sinica, identified the key genes for plant nitrate uptake.

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Nitrogen, phosphorus and potassium are the three elements of fertilizer, of which nitrogen fertilizer is the first. Do you know how the nitrogen fertilizer applied by farmers is absorbed by plants? If plants suffer from nitrogen deficiency, why is it that too much nitrogen fertilizer is not effective? What is the most efficient and accurate method of fertilizing?

The ultimate answer to these questions must be answered in the field of molecular biology, and the first place in domestic research on the molecular mechanism of plant nitrogen uptake is Cai Yifang, a specially appointed researcher at the Institute of Molecular Biology of Academia Sinica.

Teacher Tsai Yifang, who is gentle and clear-minded, has been engaged in research in this field for nearly 30 years, and is well aware of the "beauty and sadness" of nitrogen fertilizer. The beauty is that nitrogen sources are absolutely necessary for the healthy growth of plants, and nutritious crops can only be delicious. Sadly, farmers often apply too much fertilizer, resulting in a large amount of nitrogen fertilizer being washed away in the soil, resulting in serious environmental pollution and energy depletion.

Cai Yifang (Photo / Cai Jiashan) excessive fertilization is a waste of energy, and nitrogen fertilizer production accounts for 1% of the world's energy consumption.

"the nitrogen fertilizer we apply is really absorbed by plants by only 30-50%. What a waste!" Tsai Yifang said bluntly, "some people estimate that for one yuan of fertilizer, it will cost four yuan to clean up (clean up) the environment."

Tsai Yifang explained that the earliest source of nitrogen fertilizer was bird dung, which came from the Qincha Islands in Peru. Then there is the mining of natural saltpeter, mainly from Chile. Finally, Fritz Haber, a German scientist, and Carl Bosch, an engineer, mix nitrogen and hydrogen and synthesize ammonia through high temperature and high pressure with iron as a catalyst to produce nitrogen fertilizer. This is the well-known "Harper method". After the Green Revolution, the demand for fertilizer soared, and saltpeter was quickly mined out. Fortunately, Harper's method could be synthesized to solve the big problem of nitrogen shortage, and the two men won the Nobel Prize in chemistry.

Nitrogen accounts for 78% of the air, and the raw materials of nitrogen fertilizer seem to be in an endless supply, but the high-pressure and high-temperature process requires a lot of energy. "1% of the world's energy is spent on making nitrogen fertilizer," Cai Yifang said. But when farmers fertilize, few people think that they are "consuming energy".

Cai Yifang pointed out the crisis. "Energy is becoming more and more precious, but the demand for nitrogen fertilizer has been increasing, exceeding 100 million tons a year, and it is expected to rise in the future." In the future, as energy becomes more expensive, the price of nitrogen fertilizer will rise year by year, and the proportion of fertilizer in agricultural expenditure is likely to increase day by day.

Waste of nitrogen fertilizer, leading to the optimization of water areas and the increase of greenhouse gases

"the problems of money and energy can still be solved, but the last thing that can't be solved is the environment," stresses Tsai Yifang. Most of the nitrogen fertilizer cannot be used by plants, and it also produces nitrous oxide, a greenhouse gas 300 times stronger than carbon dioxide.

Moreover, the nitrogen fertilizer left in the soil was quickly washed away by Rain Water and flowed to the sea through groundwater and rivers, resulting in coastal optimization, that is, excessive nutrients and the proliferation of algae, resulting in lack of oxygen in the waters and the death of all fish and shrimp. The "dead zone" (Dead Zone) of many coasts around the world is born from this.

Global anoxic Coast Map (Photo Source / WRI)

The Council of Agriculture has been promoting "rational fertilization" for many years, but the vast majority of farmers still feel that they have "nitrogen protection" and have formed the habit of fertilizing "it is better to use too much fertilizer than to lack it." However, the effect of "diminishing returns" caused by the application of nitrogen fertilizer is often ignored.

"it is true that the output has increased when nitrogen is added at the beginning, but to a certain extent, if you add nitrogen, the yield will not continue to increase. This is what the Council of Agriculture has been trying to tell the farmers, but the farmers do not want the output to be so low, so they must increase it to the full. "

Cai Yifang delves into the molecular biological mechanism of nitrogen absorption by plants in order to explore: how to maximize the utilization efficiency of plants? Is it possible to reduce the waste of nitrogen fertilizer?

How on earth do plants absorb nitrate? Unravel the Mystery: magical Transporter

Except for a few plants that can symbiosis with nitrogen-fixing bacteria, most plants use nitrogen through nitrates and ammonium salts, the two main forms of nitrogen fertilizer. Ammonium salts are mostly converted into nitrates by bacteria in soil, so nitrate is the most important nitrogen source for plants.

However, nitrate is negatively charged, and soil particles are also negatively charged and mutually exclusive, so nitrate is actually very difficult to preserve in the soil. When plants don't have time to absorb it, it will be washed away as soon as it rains.

How on earth do plants absorb nitrate? Cai Yifang's team found that the key lies in the epidermal cells and root hairs of plant roots, where there is a transporter called CHL1 on the cell membrane.

"the cell membrane is a super material, like a thin layer of oil that wraps up the cell, but the cell can't be too homesick, and it has to exchange material with the outside world, so there are holes in the membrane, which is protein," and this CHL1 transporter is responsible for sending nitrate from outside to inside the cell.

Cai Yifang explained that plants have two sets of absorption systems for nitrogen fertilizer: low compatibility and high compatibility. When the concentration of nitrate outside is high, the "low affinity" system is activated to absorb a large amount of nitrate and store it.