Why doesn’t the oxygen we breathe run out?

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To the question: “Where does the oxygen we breathe come from?”, most of us would answer only plants, keeping in mind the image of the Amazon rainforest or our mountains and mountains, associated the importance of their conservation. . However, the correct answer includes, alongside plants, tiny marine organisms that float by the thousands in every drop of water: cyanobacteria.

Marine cyanobacteria are responsible for more than 50% of the oxygen produced on Earth. They provide oxygen to the sea, allowing marine beings to breathe. If cyanobacteria ceased to fulfill their function, the sea would be a cemetery. They gave us the primitive oxygen bag from which we still breathe.

How the oxygen we breathe was created

During the first half of our planet’s history, there was no oxygen in the atmosphere. It was primitive cyanobacteria that evolved through oxygenated photosynthesis: a method of harnessing energy from sunlight to produce sugars from water and CO2, ultimately leading to the release of oxygen.

This spectacular event known as the Great Oxidation Event or the Oxygen Revolution was pivotal in our evolutionary history. The increase in oxygen concentration has allowed the appearance of multicellular life forms, which have become more complex until reaching the current biodiversity.

Today we continue to live on this reserve created over millions of years, which is maintained thanks to the fact that the balance with the other processes where oxygen is consumed is almost zero. Only one thousandth of the world’s photosynthetic activity escapes biological processes and adds to atmospheric oxygen.

The lack of oxygen that devastates marine life

At the surface of the oceans, marine cyanobacteria produce enormous quantities of oxygen. Enough for marine life. However, sometimes the system becomes out of balance and the waters become uninhabitable for most aerobic organisms.

In them, the solubility of oxygen is lower, water is less dense, and there are no currents for ventilation. These areas have multiplied in recent years, mainly due to the warming of the oceans, which decreases the solubility of gases, and due to the excess of nutrients, due to anthropogenic activity. This is what happens, for example, in the Mar Menor which, due to the release of large quantities of nutrients from agricultural activity (nitrates and phosphates), causes eutrophication and decreases the oxygen which fish need to live.

The consequences of these hypoxic zones on marine life are obvious. Only individuals capable of migrating to other regions survive, and organisms unable to move on their own or moving very slowly (algae, invertebrates, molluscs, corals, seagrasses, certain echinoderms, etc.) die or will die. If we were to run out of oxygen in the oceans, there would be a huge loss of habitat and biodiversity.

The importance of marine cyanobacteria

Marine cyanobacteria are part, with unicellular algae, of phytoplankton. These micro-organisms float by the thousands in every drop of water in the upper layers of the ocean and constitute the first link in the food chain of these ecosystems. Without them, the seas and oceans would be lifeless deserts. In addition, they contribute substantially to the maintenance of carbon, oxygen and nitrogen cycles in the biosphere.

These microorganisms complete their cycle of renewal and death in just a few days. They are the source that produces most of the world’s oxygen and in addition to absorbing light and releasing oxygen, they remove dissolved CO2 to attach it, in the form of carbohydrates, to their biological structures. When the phytoplankton die, some of the sequestered carbon falls into the deep ocean.

Marine cyanobacteria: Synechococcus Yes Prochlorococcus

Marine cyanobacteria are mainly composed of two large genera: Synechococcus Yes Prochlorococcus. Until about 45 years ago, these microorganisms were completely unknown. Synechococcus was only discovered in the late 1970s and its closest relative, Prochlorococcusuntil 1986.

The ocean distribution of these groups depends, among other factors, on nutrient availability and temperature. While Prochlorococcus abounds in nutrient-poor waters of subtropical and tropical areas, Synechococcus it thrives in waters with intermediate and moderately low nutrient levels, colonizing a large number of ecological niches. Recent studies have shown that interactions with predators are also an important factor in the distribution of these microorganisms.

Although cyanobacteria require nitrogen as an essential nutrient for their growth, its availability is a limiting factor in the oceans. This element can be found in the form of ammonium, urea, nitrite, nitrate or amino acids, the first being the preferred source of these microorganisms.

Are the two sexes able to coexist?

Both organisms inhabit areas where nutrients are very scarce, and it is debatable whether they can co-exist, or the presence of one excludes the other as they compete for the same nutrients. The answer is yes, they coexist. Even though Prochlorococcus is more abundant Synechococcus marine is able to successfully coexist even in oligotrophic areas of the oceans. So how do you get it? This answer is not yet known with certainty, but one hypothesis is that Synechococcus prefer to use nitrate in the medium and not compete for ammonium.

Therefore, the assimilation of nitrate is of particular interest, since it is an abundant form of nitrogen in marine environments, although at the same time it is an expensive source for the cell, since it is completely oxidized and the cell must carry out two reduction reactions to be able to use it: it must pass from nitrate to nitrite and from nitrite to ammonium. Moreover, almost all marine lineages of Synechococcus have the genes that code for the machinery to assimilate nitrate, unlike most Prochlorococcuswho lack it.

Our laboratory work with Synechococcus It consists of measuring different parameters that indicate the state of crops depending on the availability of nitrogen. Some preliminary results from our group suggest the existence of a system that allows Synechococcus detect nanomolar concentrations of nitrate. Is it a specific system in its response to very low nitrate concentrations? We continue to work to answer this question which allows us to deepen our knowledge of the greatest producers of oxygen on Earth.

Character font: Yesica María Melero Rubio / THE CONVERSATION

Reference article: https://theconversation.com/why-the-oxygen-we-breathe-is-not-depleted-180434

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