Academia Sinica Academician Tsay Yi-Fang Is the First in the World to Identify the Key Gene for Plant Nitrate Uptake

Nitrogen, phosphorus and potassium are the three essential elements of fertilizer, and nitrogen fertilizer ranks first among them. Do you know how the nitrogen fertilizer that farmers apply is actually taken up by plants? If plants lack nitrogen they become sickly, so why is it that when too much nitrogen fertilizer is applied, it instead has no effect? What exactly is the most efficient and most precise method of fertilization?

The ultimate answers to these questions must be sought back 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, a Distinguished Research Fellow at the Institute of Molecular Biology, Academia Sinica.

The gentle, modest and clear-minded Teacher Tsay Yi-Fang has devoted herself to research in this field for nearly thirty years, and knows well the "beauty and sorrow" of nitrogen fertilizer. The beauty is that nitrogen is absolutely essential for the healthy growth of plants, and only crops with sufficient 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.

Excessive fertilization is a waste of 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, and that is such a waste!" Tsay Yi-Fang said bluntly. "Some people 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, the German scientist Fritz Haber and the engineer Carl Bosch combined nitrogen and hydrogen, using high temperature and high pressure with iron as a catalyst to synthesize ammonia and thereby produce 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 made artificial synthesis possible, solving the major problem of nitrogen fertilizer shortage, and the two men were thereby awarded the Nobel Prize in Chemistry.

Nitrogen gas makes up 78% of the air, and the raw material for nitrogen fertilizer seems to be inexhaustible and never lacking from then on. 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 producing nitrogen fertilizer!" But when farmers apply fertilizer, few people think about the fact that they are "consuming energy."

Tsay Yi-Fang pointed out the crisis: "Energy is becoming more and more precious, but demand for nitrogen fertilizer keeps increasing, exceeding 100 million tons each 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 the proportion of agricultural expenditure accounted for by fertilizer may well grow day by day.

Wasted nitrogen fertilizer causes water eutrophication and also increases greenhouse gases

"The problems of money and energy can still be solved; what cannot be solved is the environmental problem," Tsay Yi-Fang emphasized. Most nitrogen fertilizer cannot be used by plants, and it also produces nitrous oxide (N2O), 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 to the ocean, causing coastal eutrophication, that is, excessive nutrients and massive algal blooms, which deprive the water of oxygen and kill all the fish and shrimp. The "dead zones" found along many coasts around the world arise from this.

The Council of Agriculture has long been promoting "rational fertilization," but the vast majority of farmers still feel that "with nitrogen there is blessing," and have developed a fertilization 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 after a certain point, adding more nitrogen will not continue to increase yield. This is what the Council of Agriculture has been trying to tell farmers, but farmers are unwilling to accept even that little bit less yield and insist on applying the maximum."

Tsay Yi-Fang delved into the molecular biological mechanisms of plant nitrogen fertilizer uptake precisely in order to investigate: how can plants achieve the highest utilization efficiency? And can nitrogen fertilizer waste thereby be reduced?

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

Aside from a few plants that can live symbiotically with nitrogen-fixing bacteria, most plants use nitrogen through nitrate (NO3-) and ammonium salts (NH4+), which are the two main forms of nitrogen fertilizer. In the soil, ammonium salts 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 difficult to retain in the soil, and when plants do not have time to absorb it, it is washed away as soon as it rains.

How exactly do plants take up 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 have 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 and must exchange substances with the outside world, so there are holes in the membrane, which are proteins," and the one responsible for transporting nitrate from outside the cell to inside the cell is this CHL1 transporter