Warming accelerates the production of nitrogen by trees. This will make further global greening easier

(ORDO NEWS) — Nitrogen fixation is important for maintaining accelerated plant growth—and it has now been found to work best at very high temperatures. This explains the nitrogen deficiency in the soil of the northern lands.

Today, global greening is underway on Earth: the area of ​​\u200b\u200bleaves is rapidly increasing, which is why the planet looks greener than before in satellite images from space every decade.

At the same time, the green biomass of plants grows faster than the area of ​​leaves, since an increase in the concentration of CO 2 in the air reduces the need for individual plants in excess leaf area (they serve to absorb carbon dioxide, and often a smaller leaf area is sufficient for photosynthesis).

However, all these processes, caused by anthropogenic carbon emissions, have raised concerns among a number of scientists about the future deficiency of soil nitrogen.

All living beings need nitrogen to build important components of cells; without it, even a high amount of CO 2 in the air will not allow further growth of green biomass. Many have argued that increased plant growth will deplete the nitrogen reserves in the soil, after which global greening may come to a halt.

To clarify this issue, a group of researchers from the United States studied how the processes of biological nitrogen fixation proceed with increasing temperatures.

Nitrogen fixation is the process of assimilation of nitrogen from atmospheric air by living organisms. The genes needed for this are found only in bacteria and archaea, but not in plants. However, many plant species traditionally exist in symbiosis with soil bacteria located at their roots.

Plants provide symbiont bacteria with sugar (it takes 500 grams of sucrose to fix a gram of nitrogen), and they give them nitrogen. The production of sugars by plants is theoretically related to temperature, but it is difficult to reliably determine at what temperature it is the highest.

Warming accelerates the production of nitrogen by trees This will make further global greening easier 2

For example, although it is believed that plant photosynthesis is optimal at plus 25-30 degrees, in fact, experiments show that the optimal photosynthesis temperature for leaves of plants of the same species depends on the temperature at which these leaves were formed.

For winter wheat leaves, formed at plus 35, the optimal temperature for photosynthesis will be the same plus 35 degrees. But in the wild, outside of laboratory experiments, winter wheat practically does not encounter such a temperature.

For Antarctic plants, the optimal rate of photosynthesis is achieved at plus 8-15, and for heat-loving Tidestromia oblongifolia – at plus 45.

Therefore, it is extremely difficult to estimate how the rate of nitrogen fixation will change in symbionts of real plants. Observations or experiments would be optimal to find out empirically.

The authors of the new work took seedlings of red alder ( Alnus rubra ), one of the species of waxwort ( Myrica cerifera ), false acacia locust ( Robinia pseudoacacia ) and the tropical tree Gliricidia sepium.

These species were chosen as representatives of genera that play a large role in nitrogen fixation around the world. In experiments (in closed ground), scientists gradually raised temperatures and measured the rate of nitrogen fixation for symbiont bacteria in each case.

It turned out that this speed was highest at plus 29.0-36.9 degrees – temperatures that even tropical trees do not encounter everywhere, but where they collide – not too often. Temperate trees encounter something like this rarely at all.

From this, the authors conclude that in ecosystems with a cool climate, the efficiency of nitrogen fixation, at least for trees, is limited by temperature, and this may explain the typical nitrogen deficiency in northern soils, which is especially severe in the northern taiga.

Warming accelerates the production of nitrogen by trees This will make further global greening easier 1

The researchers also note that plus 29.0–36.9 degrees, on the contrary, was the norm in the Mesozoic and early Cenozoic. In their opinion, it was precisely such high temperatures that contributed to the evolution of the symbiosis of nitrogen-fixing bacteria and plants.

The subsequent cooling of the climate lasting tens of millions of years, on the contrary, could make some plant genera lose their ability to fix nitrogen: it became too cold for it to remain quite effective.

In addition, the authors measured the rate of photosynthesis for each plant at an air CO2 concentration of 275 parts per million (this was before the industrial revolution) and at 400 parts per million (this was in the 2010s).

It turned out that at pre-industrial levels of CO 2 , the optimal temperatures for photosynthesis were much lower than at present-day CO 2 levels .


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