Academia Sinica's Tsay Yi-Fang Identifies the Key Gene for Plant Nitrate Uptake, Unlocking the Secret of Nitrogen Fertilizer

Nitrogen, phosphorus and potassium are the three essential elements of fertilizer, with nitrogen fertilizer being the most important. Do you know how the nitrogen fertilizer farmers apply is actually absorbed by plants? If plants are deficient in nitrogen they become sickly, so why is it that applying too much nitrogen fertilizer makes it ineffective instead? What exactly is the most efficient and most precise way to fertilize?

The ultimate answers to these questions must be sought in the field of molecular biology, and the leading authority in Taiwan, China on the molecular mechanisms of plant nitrogen fertilizer uptake is Tsay Yi-Fang, Distinguished Research Fellow at the Institute of Molecular Biology, Academia Sinica.

Warm, modest and clear-thinking, Professor Tsay Yi-Fang has devoted nearly thirty years to research in this field and knows well the "beauty and sorrow" of nitrogen fertilizer. The beauty is that nitrogen is absolutely essential for healthy plant growth, and only crops with ample nutrition taste good; the sorrow is that farmers often over-fertilize, causing large amounts of nitrogen fertilizer to remain in the soil and be washed away, resulting in serious environmental pollution and energy depletion.

Over-fertilizing is wasting energy; nitrogen fertilizer production accounts for 1% of global energy consumption

"Only 30-50% of the nitrogen fertilizer we apply is actually taken up by plants - what a waste!" Tsay Yi-Fang said bluntly. "Some estimate that one yuan of fertilizer requires four yuan to clean up the environmental problems."

Tsay Yi-Fang explained that the earliest source of nitrogen fertilizer was guano, from the Chincha Islands of Peru. Next came the mining of natural saltpeter, mainly from Chile. Finally, German scientist Fritz Haber and engineer Carl Bosch combined nitrogen gas and hydrogen gas, using high temperature and high pressure with iron as a catalyst to synthesize ammonia, and from that to manufacture nitrogen fertilizer - this is the famous "Haber process." After the Green Revolution, demand for fertilizer soared, and saltpeter was quickly mined out. Fortunately, the Haber process could synthesize it artificially, solving the major problem of nitrogen fertilizer shortage, and the two men were awarded the Nobel Prize in Chemistry for it.

Nitrogen gas makes up 78% of the air, so the raw material for nitrogen fertilizer seems inexhaustible and never in short supply. However, the high-pressure, high-temperature production process consumes enormous amounts of energy. Tsay Yi-Fang said, "1% of the world's energy is spent on making nitrogen fertilizer!" Yet when farmers apply fertilizer, few realize they are "consuming energy."

Tsay Yi-Fang pointed out the crisis: "Energy is becoming more and more precious, but demand for nitrogen fertilizer keeps rising, exceeding 100 million tonnes per year, and it is predicted to rise further in the future." As energy becomes more expensive in the future, the price of nitrogen fertilizer will also rise year by year, and fertilizer's share of agricultural expenditure may grow steadily.

Nitrogen fertilizer waste causes water eutrophication and increases greenhouse gases

"The money problem and the energy problem can still be solved; the hardest to solve is the environmental problem," Tsay Yi-Fang emphasized. Most nitrogen fertilizer cannot be used by plants, and it also produces nitrous oxide, a greenhouse gas 300 times more potent than carbon dioxide.

Moreover, the nitrogen fertilizer remaining in the soil is quickly washed away by rain, flowing through groundwater and rivers into the ocean, causing coastal eutrophication - that is, excessive nutrients and massive algae blooms, which deprive the water of oxygen and kill all the fish and shrimp. The "dead zones" along many coasts around the world arise precisely from this.

The Council of Agriculture has long promoted "rational fertilization," but the vast majority of farmers still feel that "with nitrogen there is blessing," developing a fertilizing habit of "better too much than too little." However, the "diminishing returns" effect of nitrogen fertilizer application is often overlooked.

"At first, adding nitrogen really does increase yield, but beyond a certain point, adding more nitrogen does not continue to increase yield. This is what the Council of Agriculture keeps trying to tell farmers, but farmers are unwilling to accept even a slight drop in yield, so they always apply it to the maximum."

Tsay Yi-Fang's deep study of the molecular biological mechanisms of plant nitrogen fertilizer uptake is precisely aimed at exploring: how can plants' utilization efficiency be maximized? And can this thereby reduce the waste of nitrogen fertilizer?

How exactly do plants absorb nitrate? Unraveling the mystery: the amazing transporter protein

Apart from a few plants that can live symbiotically with nitrogen-fixing bacteria, most plants use nitrogen in the form of nitrate and ammonium salts, the two main forms of nitrogen fertilizer. Ammonium salts in the soil are mostly converted by bacteria into nitrate, so nitrate is the main nitrogen source for plants.

But nitrate carries a negative charge, and soil particles also carry a negative charge, so they repel each other. As a result, nitrate is actually very hard to retain in the soil, and before plants can absorb it, a rain will wash it away.

How exactly do plants absorb nitrate? Tsay Yi-Fang's research team discovered that the key lies in the epidermal cells and root hairs of plant roots, whose cell membranes carry a transporter protein called CHL1.

"The cell membrane is a super material, like a thin layer of oil wrapping the cell, but the cell cannot be too much of a homebody - it has to exchange materials with the outside world, so there are holes in the membrane, which are proteins." The one responsible for carrying nitrate from outside the cell to inside the cell is this CHL1 transporter protein.

Tsay Yi-Fang explained that plants have two uptake systems for nitrogen fertilizer: low-affinity and high-affinity. When the nitrate concentration outside is high, the "low-affinity" system is activated, absorbing large amounts of nitrate to store, and when needed