The secret of nitrogen fertilizer has been uncovered for the first time in the world! Cai Yifang, an academician of the Chinese Academy of Sciences, identified the key genes for nitrate uptake by plants.

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Nitrogen, phosphorus and potassium are three elements of fertilizer, among which nitrogen fertilizer is the first. Do you know how the nitrogen fertilizer that farmers apply is absorbed by plants? If nitrogen deficiency can make plants sick, why is it that too much nitrogen fertilizer has no effect? What exactly is the most efficient and accurate fertilization method?

The ultimate answer to these questions must be found in molecular biology, and one of the first researchers in Taiwan to study the molecular mechanism of nitrogen uptake by plants is Cai Yifang, a special researcher at the Institute of Molecular Biology of the Academia Sinica.

Cai Yifang, a warm and modest teacher with clear thinking, has been engaged in research in this field for nearly 30 years and knows well the "beauty and sadness" of nitrogen fertilizer. The beauty is that nitrogen source is absolutely necessary for the healthy growth of plants, and crops with sufficient nutrients will taste good; while the sorrow is that farmers often over-fertilize, resulting in a large amount of nitrogen left in the soil being washed away, causing serious environmental pollution and energy depletion.

Cai Yifang (Photo/Cai Jiashan) Excessive fertilization is a waste of energy. Nitrogen fertilizer production consumes 1% of the world's energy.

"Only 30-50% of the nitrogen fertilizer we applied was absorbed by the plants. What a waste!" Cai Yifang cut to the chase."Some people estimate that one yuan of fertilizer costs four yuan to clean up the environment."

Tsai explains that the earliest source of nitrogen fertilizer was bird droppings from Peru's Kipcha Islands. Then there is the mining of natural saltpeter, mainly from Chile. Finally, German scientist Fritz Haber and engineer Carl Bosch mixed nitrogen and hydrogen, and through high temperature and high pressure plus iron as a catalyst, ammonia was synthesized to make nitrogen fertilizer. This is the famous "Haber method". After the Green Revolution, the demand for fertilizer exploded, and saltpeter was quickly mined out. Fortunately, Haber's method could be synthesized artificially, solving the big problem of nitrogen shortage. The two men won the Nobel Prize in Chemistry.

Nitrogen accounts for 78% of the air, nitrogen fertilizer raw materials seem endless, from now on, but high pressure and high temperature process, but need a lot of energy. "One percent of the world's energy is spent on nitrogen fertilizer," Cai said. But when farmers apply fertilizer, few people think 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 every year. It is estimated that it will rise in the future." As energy becomes more expensive in the future, the price of nitrogen fertilizer will rise year by year, and the proportion of fertilizer in agricultural expenditure will probably increase day by day.

Nitrogen waste, eutrophication and greenhouse gas emissions

"The money problem and the energy problem can still be solved, but the most unresolved problem is the environment," Tsai stresses. Most nitrogen fertilizer cannot be used by plants, and it also produces nitrous oxide (N2O), a greenhouse gas 300 times stronger than carbon dioxide.

Moreover, the nitrogen fertilizer remaining in the soil is quickly washed away by rainwater and flows to the ocean through groundwater and rivers, resulting in eutrophication of the coast, that is, excessive nutrients and algae proliferation, resulting in oxygen deficiency in the water area and the death of all fish and shrimp. Many of the world's coastal "dead zones"(Dead Zone), that is, from this.

Global map of anoxic coasts (Photo courtesy/Cai Yifang)

The Council of Agriculture has been pushing for "rational fertilization" for many years, but most farmers still feel that "there is protection when nitrogen is available" and have developed the habit of "rather excessive than insufficient" fertilization. However, nitrogen fertilizer application has a "diminishing return" effect, which is often ignored.

"At the beginning, nitrogen is added, and the yield does increase, but to a certain extent, if nitrogen is added, the yield will not continue to increase. That's what the Council of Agriculture has been telling farmers, but farmers don't want to lose that much. They have to make it full."

tsai yi fang delves into the molecular biology of nitrogen uptake by plants in order to explore: how do plants maximize their efficiency? Could this reduce the waste of nitrogen fertilizer?

How exactly do plants absorb nitrates? Uncovering the Mystery: The Magical Transporter

Except for a few plants that can coexist with nitrogen-fixing bacteria, most plants use nitrogen through nitrate (NO3-) and ammonium (NH4 +), the two main forms of nitrogen fertilizer. Ammonium salts are mostly converted into nitrates by bacteria in the soil, so nitrates are the most important nitrogen source for plants.

However, nitrates are negatively charged, and soil particles are also negatively charged and repel each other. Therefore, nitrates are actually not well preserved in soil. When plants have no time to absorb them, they will be washed away by rain.

How exactly do plants absorb nitrates? Cai's team found that the key lies in the epidermal cells and root hairs of plant roots, which have a transporter protein called CHL1 on their cell membranes.

"The cell membrane is a super material, like a thin layer of oil to wrap the cell, but the cell can not be too homey, to do material exchange with the outside world, so there are holes in the membrane, that is, protein," and responsible for transporting nitrate from the outside of the cell to the inside of the cell, is CHL1 transport.