Why do the oceans have "low productivity" in terms of photosynthesis? How deep does the zone of photosynthesis extend in the oceans. Efficiency of photosynthesis in terrestrial and marine ecosystems In which zone of the ocean is photosynthesis impossible

Charles

Why do the oceans have "low productivity" in terms of photosynthesis?

80% of the world's photosynthesis takes place in the ocean. Despite this, the oceans also have low productivity - they cover 75% of the earth's surface, but from the annual 170 billion tons of dry weight recorded through photosynthesis, they provide only 55 billion tons. Do not these two facts, which I encountered separately, contradict? If the oceans fix 80% of the total C O X 2 "role="presentation" style="position: relative;"> CO X C O X 2 "role="presentation" style="position: relative;"> C O X 2 "role="presentation" style="position: relative;"> 2 C O X 2 "role="presentation" style="position: relative;"> C O X 2 "role="presentation" style="position: relative;">C C O X 2 "role="presentation" style="position: relative;">O C O X 2 " role="presentation" style="position: relative;">X C O X 2 "role="presentation" style="position: relative;">2 fixed by photosynthesis on earth and releases 80% of the total O X 2 "role="presentation" style="position: relative;"> O X O X 2 "role="presentation" style="position: relative;"> O X 2 "role="presentation" style="position: relative;"> 2 O X 2 "role="presentation" style="position: relative;"> O X 2 "role="presentation" style="position: relative;">O O X 2 " role="presentation" style="position: relative;">x O X 2 "role="presentation" style="position: relative;">2 Released by photosynthesis on Earth, they must also have been 80% of the dry weight. Is there a way to reconcile these facts? In any case, if 80% of photosynthesis takes place in the oceans, it hardly seems low productivity - then why are the oceans said to have low primary productivity (multiple reasons are also given for this - that light is not available at all depths in the oceans, etc.)? More photosynthesis should mean more productivity!

C_Z_

It would be helpful if you point out where you found these two statistics (80% of the world's productivity is in the ocean and the oceans produce 55/170 million tons of dry weight)

Answers

chocoly

First, we must know what are the most important criteria for photosynthesis; they are: light, CO2, water, nutrients. docenti.unicam.it/tmp/2619.ppt Secondly, the productivity you are talking about should be called "primary productivity" and is calculated by dividing the amount of carbon converted per unit area (m2) by the time. ww2.unime.it/snchimambiente/PrPriFattMag.doc

Thus, due to the fact that the oceans cover a large area of the world, marine microorganisms can convert a large amount of inorganic carbon into organic (the principle of photosynthesis). The big problem in the oceans is the availability of nutrients; they tend to deposit or react with water or other chemicals, even though marine photosynthetic organisms are mostly found on the surface, where of course light is present. This reduces as a consequence the potential for photosynthetic productivity of the oceans.

WYSIWYG ♦

M Gradwell

If the oceans fix 80% of the total CO2CO2 fixed from land photosynthesis and release 80% of the total O2O2 released from land photosynthesis, they should also account for 80% of the dry weight produced.

First, what is meant by "O 2 released"? Does this mean that "O 2 is released from the oceans into the atmosphere, where it contributes to the growth of surpluses"? This cannot be, since the amount of O 2 in the atmosphere is fairly constant, and there is evidence that it is much lower than during Jurassic times. In general, global O 2 sinks should balance O 2 sources, or if something should slightly exceed them, causing current atmospheric CO2 levels to gradually increase at the expense of O 2 levels.

Thus, by "released" we mean "released during photosynthesis at the time of its action."

The oceans fix 80% of the total photosynthesis-bound CO2, yes, but they also break it down at the same rate. For every algae cell that is photosynthetic, there is one that is dead or dying and consumed by bacteria (which consume O2), or it itself consumes oxygen to maintain its metabolic processes during the night. Thus, the net amount of O 2 emitted by the oceans is close to zero.

Now we have to ask what we mean by "performance" in this context. If a CO 2 molecule is fixed due to algae activity, but then almost immediately becomes unfixed again, is this considered "performance"? But blink and you'll miss it! Even if you don't blink, it's unlikely to be measurable. The dry weight of the algae at the end of the process is the same as at the beginning. so if we define "productivity" as "increase in dry weight of algae", then productivity will be zero.

For algae photosynthesis to have a sustainable impact on global CO 2 or O 2 levels, the fixed CO 2 must be incorporated into something less fast than algae. Something like cod or hake, which as a bonus can be collected and put on the tables. "Productivity" usually refers to the ability of the oceans to replenish these things after harvest, and it's really small compared to the land's ability to produce repeat crops.

It would be a different story if we viewed algae as potentially mass-harvesting, so that their ability to grow like wildfire in the presence of fertilizer runoff from the ground was seen as "productivity" rather than a profound inconvenience. But it's not.

In other words, we tend to define "productivity" in terms of what is beneficial to us as a species, and algae is generally useless.

Diatoms are predominantly autotrophic plants; in them, like in other autotrophic organisms, the process of formation of organic matter occurs in chloroplasts with the help of pigments during photosynthesis. Initially, it was found that pigments in diatoms consist of a mixture of chlorophylls with xanthophylls and fucoxanthin. Later, to clarify the composition of pigments in diatoms, a chromatographic method was used, which revealed the presence of eight pigments in diatom chloroplasts (Dutton and Manning, 1941; Strain and Manning, 1942, 1943; Strain a. oth., 1943, 1944; Wassink, Kersten, 1944, 1946; Cook, 1945; Hendey, 1964). These pigments are: chlorophyll α, chlorophyll c, β-carotene, fucoxanthin, diatoxanthin, diadinoxanthin, neofucoxanthin A, and neofucoxanthin B. The last four pigments are part of the previously discovered diatomine. Some authors also point to the minimal presence of xanthophyll and pheophytin (Strain a. oth., 1944).

The total amount of pigments in diatoms is on average about 16% of the lipid fraction, but their content is different in different species. There are very few data in the literature on the quantitative content of pigments in marine planktonic diatoms, and there are almost no data for benthic species, which are especially rich in yellow and brown pigments (Tables 1 and 2).

The above data show that the content of pigments varies even in the same species. There is evidence that the content of pigments is subject to fluctuations depending on the intensity of light, its quality, the content of nutrients in the medium, the state of the cell and its age. So, for example, an abundance of nutrients in the medium at a relatively low light intensity stimulates the productivity of pigments, and vice versa, a high light intensity with a lack of nutrients in the medium leads to a decrease in the concentration of pigments. With a lack of phosphorus and nitrogen, the content of chlorophyll a can decrease by 2.5-10 times (Finenko, Lanskaya, 1968). It has been established that the content of chlorophyll c decreases with cell age.

The functions of pigments other than chlorophylls in diatoms have not yet been sufficiently elucidated. Chlorophyll α is the main pigment that absorbs light energy of all rays of the spectrum, and it has two forms that differ in the assimilation of light: one of them is excited directly by red light, and the second, in addition, also by the energy transmitted by the auxiliary pigment fucoxanthin (Emerson, Rabinowitch, 1960). The remaining pigments are auxiliary to chlorophyll a, but they also play a relatively important role in photosynthesis. Chlorophyll c has a higher absorption maximum in the blue region than in the red region, and therefore it is able to utilize light rays of shorter wavelengths, its absorption maximum lies at 520-680 nm and drops to zero at a wavelength of 710 nm, therefore its absorption more intense in the blue light zone, i.e., at depths of 10-25 m from the water surface, where chlorophyll a is less effective. The role of β-carotene is not clear enough, its absorption spectrum abruptly breaks off at 500 nm, which indicates its ability to absorb in the rays of a wavelength of 500-560 nm, i.e. in the green-yellow light region (in water at depths of 20-30 m ). Thus, β-carotene transfers the absorbed energy to chlorophyll α (Dutton and Manning, 1941). This is known, for example, for Nitzschia dissipata, which absorbs energy in the green-yellow light region (Wassink and Kersten, 1944, 1946). Brown pigments from the fucoxanthin group have an absorption maximum at a wavelength of about 500 nm and, apparently, ensure the photosynthesis of diatoms at depths of 20–50 m by transferring the energy absorbed by them to chlorophyll. Dutton and Manning (Dutton and Manning, 1941), and later Wassink and Kersten (Wassink and Kersten, 1946) showed that fucoxanthin is the main accessory pigment in diatoms. The light absorbed by fucoxanthin is utilized for photosynthesis almost as efficiently as the light absorbed by chlorophyll. This is not observed in green and blue-green algae lacking fucoxanthin. Tanada (1951) also found that the freshwater diatom Navicula minima var. atomoides Fucoxanthin absorbs blue-blue light (450-520 nm) and utilizes it as efficiently as light absorbed by chlorophyll. Hendey (1964) indicates the wavelength of light at which the maximum absorption of light by various diatom pigments occurs. In acetone, they are as follows (in mcm): chlorophyll α - 430 and 663-665, chlorophyll c - 445 and 630, β-carotene - 452-456, fucoxanthin - 449, diatoxanthin - 450-452, diadinoxanthin - 444-446, neofucoxanthin A - 448 - 450 and neofucoxanthin B - 448.

The chemistry of photosynthesis in diatoms seems to be somewhat different from that in other plant organisms, in which carbohydrates are the end product of photosynthesis, while fats are in diatoms. Studies using an electron microscope did not reveal the presence of starch either in the stroma of chloroplasts or near pyrenoids. Fogg believes that carbohydrates are also the end product of assimilation in diatoms, but in further rapid metabolic processes they turn into fats (Collyer and Fogg, 1955; Fogg, 1956). The chemical composition of fats in diatoms is unknown either for assimilation products or for reserve nutrient oils and oil bodies (Goulon, 1956).

In the oceans, seas and freshwater bodies near the surface of the water, the conditions for photosynthesis are close to those in the air, but with immersion in depth they change due to changes in the intensity and quality of light. With regard to illumination, three zones are distinguished: euphotic - from the surface to 80 m depth, photosynthesis takes place in it; dysphotic - from 80 to 2000 m, here some algae are still found, and aphotic - below, in which there is no light (Das, 1954 and others). Photosynthesis of marine and freshwater phytoplankton in the surface water layer has been sufficiently studied both in natural and cultural conditions (Wassink and Kersten, 1944, 1946; Votintsev, 1952; Tailing, 1955, 1957a, 1966; Ryther, 1956; Edmondson, 1956; Ryther , Menzel, 1959; Steemann Nielsen and Hensen, 1959, 1961, etc.). In particular, year-round observations in the Black Sea have shown that the highest intensity of phytoplankton photosynthesis coincides with the highest solar radiation. In summer, the maximum photosynthesis of phytoplankton is observed in the period from 01:00 to 16:00. (Lanskaya and Sivkov, 1949; Bessemyanova, 1957). In different planktonic species, the maximum intensity of photosynthesis has limits of changes characteristic of a particular species. In this case, the latitudinal location of water areas is of great importance (Doty, 1959, etc.).

Among diatoms (both planktonic and benthic) there are light-loving and shade-loving species, which have different intensity of photosynthesis and utilization of solar energy at the same radiation. In light-loving species, like Cerataulina bergonii(planktonic) and Navicula pennata var. pontica(sublittoral), photosynthesis runs parallel to radiation and reaches a maximum at noon, and in shade-loving - Thalassionema nitzschioides (planktonic) and Nitzschia closterium(tychopelagic) - during the day there is a depression of photosynthesis, and the maximum intensity of this process falls on the morning and afternoon hours (Bessemyanova, 1959). The same course of photosynthesis is observed in cultures of northern pelagic species. Coscinosira polychorda and Coscinodiscus excentricus(Marshall and Ogg, 1928; Jenkin, 1937). In benthic forms, the intensity of photosynthesis per unit of biomass is much higher than in planktonic forms (Bessemyanova, 1959). This is quite natural "because benthic diatoms have large, intensely pigmented chloroplasts, i.e., their total number of photosynthetic pigments is much greater. Observations have shown that photosynthesis proceeds more actively in mobile forms than in immobile ones and is noticeably activated during the period of division of diatoms (Talling, 1955). Photosynthesis does not stop even in moonlight, but under these conditions, oxygen is released 10-15 times less than during the day. In the upper horizon of the water column, nighttime photosynthesis is only 7-8% of the daily one (Ivlev, Mukharevskaya, 1940; Subrahmanyan, 1960).

With depth, the intensity of light drops sharply. Measurement at various depths in the hall. Puget Sound (north-east Pacific Ocean) using a Kunz photoelectric camera showed that the illumination intensity (at the water surface taken as 100%) at a depth of 10 m drops to 9.6%, at a depth of 20 m it is 4%, and at 35 m - 2.4%, almost completely dark at this depth (Grein, in: Feldmann, 1938; Gessner, 1955-1959, I). Parallel to the fall of illumination, daylight hours are shortened. In the ocean at latitudes of 30-40 °, with the greatest transparency of water at a depth of 20 m, the length of a summer day is about 1 hour, at 30 m - 5 hours, at 40 m - only 5 minutes.

With depth, not only the intensity of illumination and the light period decrease, but the quality of light also changes due to the unequal absorption of the rays of the solar spectrum of different wavelengths. In table. Figure 3 shows changes in the absorption of light rays and the color of twilight illumination at different depths.

This table shows that the absorption of light in sea water is inversely proportional to the length of light waves, i.e., the longer the light waves of the rays of the spectrum, the faster they are absorbed by water. As light rays are absorbed at the corresponding depths, the color of twilight illumination changes. Both limit photosynthesis at depths. The decrease in the intensity of different rays of the spectrum at different depths in the sea is presented in Table. four.

The data in this table indicate that some marine brown and red algae can still vegetate at a depth of 75 m and probably deeper, provided that the water is very clear. As you know, the transparency of water varies greatly not only in different reservoirs, but also in the same reservoir. In the pelagic region of the seas and oceans, water is transparent to a depth of 40 to 160 m, while in the marine sublittoral, water transparency drops to 20 m or less. The lower limit of the distribution of algae is determined by the intensity of light at which assimilation and respiration are mutually balanced, i.e., when the so-called compensation point is reached (Marshall and Orr, 1928). Naturally, the compensation point in algae depends on the transparency of the water, the composition of the pigments, and a number of other factors. In this regard, there are some data for macrophyte algae with different pigment systems (Levring, 1966), but no such data for diatoms (Table 5).

Under equal lighting conditions, the compensation point in algae of different divisions depends on the function of their pigments. In blue-green algae (having pigments: chlorophylls a and b, β-carotene, ketocarotenoid, mixoxanthophyll), the compensation point is at a depth of about 8 m, for green algae (pigments: chlorophylls a and b, β-carotene, xanthophyll) - about 18 m, and in brown and red algae, which, in addition to chlorophyll, carotene and xanthophyll, have additional pigments (in brown phycoxanthin, in red algae - phycoerythrin and phycocyan), the compensation point drops significantly below 30 m.

In some diatom species of the Black Sea sublittoral, the compensation point, apparently, can drop to a depth of 35 m. The modern method of collecting sublittoral diatoms does not provide an accurate indicator of the habitat conditions of individual species. Based on the latest data, a general regularity in the distribution of sublittoral diatoms by depth has been established. In the sublittoral conditions of the Black Sea, they live to a depth of about 30 m (Proshkina-Lavrenko, 1963a), in the Mediterranean Sea - to a depth of 60 m (Aleem, 1951), which is quite natural with a water transparency in this sea of 60 m. There are indications of habitat diatoms up to 110 m (Smyth, 1955), up to 200 m (Bougis, 1946) and up to 7400 m (Wood, 1956), and Wood claims that living diatoms have been found at this depth (usually subtidal marine species along with freshwater ones!). The data of the last two authors are unreliable and require verification.

The compensation point for the same species of diatoms is not constant, it depends on the geographic latitude of the species, on the season of the year, water transparency and other factors. Marshall and Opp (Marshall and Orr, 1928) experimentally established by lowering the culture of diatoms to different depths in the bay (Loch Striven; Scotland) that Coscinosira polychorda in summer it has a compensation point at a depth of 20-30 m, and in winter near the water surface. Similar results were obtained by them for Chaetoceros sp.

Benthic diatoms undoubtedly have chromatic adaptation, which explains the ability of many of them to live at a certain range of depths under conditions of changing spectral light and its intensity; it is possible that they have different races (some species Amphora, Carrtpylodiscus, Diploneis, Navicula). It has been experimentally established that the process of adaptation to the intensity of illumination occurs rather quickly. So, for example, a freshwater immobile planktonic diatom Cyclotella meneghiniana adapts to illumination from 3 thousand to 30 thousand lux within 24 hours, it is able to endure much higher light intensity - up to 60 thousand lux and even up to 100 thousand lux (Jorgensen, 1964a, 1964b). Photosynthetic apparatus of mobile sublittoral species ( Tropidoneis, Nitzschia) adapts to light conditions at depths of 1-3 m, where the light intensity varies from 10 to 1% (Taylor, 1964). In general, a large literature is devoted to the issue of chromatic adaptation in diatoms (Talling, 1955, 1957a; Ryther, 1956; Ryther and Menzel, 1959; Steemann Nielsen and Hensen, 1959; Jørgensen, 1964a).

Planktonic diatoms can live much deeper than sublittoral ones, which is mainly due to the greater transparency of water in the pelagic zone. It is known that in the seas and oceans, diatom plankton spreads to a depth of 100 m or more. In the Black Sea, at a depth of 75-100 m, phytoplankton consists of Thalassionema nitzschioides and several types Nitzchia, and here they live in much greater numbers than in the water layer of 0-50 m (Morozova-Vodyanitskaya, 1948-1954). many kinds Nitzchia are known to easily switch from autotrophic nutrition to mixotrophic and heterotrophic. Apparently, planktonic species living in the dysphotic and aphotic zones of the seas have the same property; they create deep-water shadow plankton. However, Steemann Nielsen and Hensen (Steemann Nielsen and Hensen, 1959) consider surface phytoplankton as "light" under conditions of radiation intensity of 600-1200 lux and as "shadow" under conditions of low radiation: 200-450 lux. According to these researchers, the winter surface phytoplankton in the temperate zone is a typical "shadow". However, winter phytoplankton consists of late autumn and early spring species, which cannot be classified as "shadow" species. It should be recognized that the problem of phytosynthesis in diatoms is still at the initial stage of research, and on many topical issues of this problem there are only fragmentary and unverified data.

From the surface to the very bottom, the ocean is teeming with the life of a variety of animals and plants. Just like on land, almost all life here depends on plants. The main food is billions of microscopic plants called phytoplankton, which are carried by currents. Using the sun's rays, they create their own food from sea, carbon dioxide and minerals. During this process, called photosynthesis, phytoplankton produce 70% of atmospheric oxygen. Phytoplankton consists mainly of small plants called diatoms. There can be up to 50 thousand of them in a cup of sea water. Phytoplankton can only live near the surface, where there is enough light for photosynthesis. Another part of the plankton - zooplankton is not involved in photosynthesis and therefore can live deeper. Zooplankton are tiny animals. They feed on phytoplankton or eat each other. Zooplankton includes juveniles - larvae of crabs, shrimps, jellyfish and fish. Most of them do not look like adults at all. Both types of plankton serve as food for fish and other animals, from small jellyfish to huge whales and sharks. The amount of plankton varies from place to place and from season to season. Most of the plankton is found on the continental shelf and near the poles. Krill is a type of zooplankton. Most krill in the Southern Ocean. Plankton also lives in fresh water. If you can, examine under a microscope a drop of water from a pond or river, or a drop of sea water.

Food chains and pyramids

Animals eat plants or other animals and themselves serve as food for other species. More than 90% of the inhabitants of the sea end their lives in other people's stomachs. All life in the ocean is thus connected in a huge food chain, starting with phytoplankton. To feed one large animal, you need many small ones, so there are always fewer large animals than small ones. This can be depicted as a food pyramid. To increase its mass by 1 kg, tuna needs to eat 10 kg of mackerel. To obtain 10 kg of mackerel, you need 100 kg of young herring. For 100 kg of young herring, 1000 kg of zooplankton are needed. It takes 10,000 kg of phytoplankton to feed 1,000 kg of zooplankton.

Ocean floors

The thickness of the ocean can be divided into layers, or zones, according to the amount of light and heat that penetrate from the surface (see also the article ""). The deeper the zone, the colder and darker it is. All plants and most animals are found in the top two zones. The solar zone gives life to all plants and a wide variety of animals. Only a small amount of light from the surface penetrates into the twilight zone. The largest inhabitants here are fish, squids and octopuses. In the dark zone around 4 degrees Celsius. Animals here feed mainly on the “rain” of dead plankton that falls from the surface. In the abyssal zone, complete darkness and icy cold. The few animals that live there live under constant high pressure. Animals are also found in ocean trenches, at depths of more than 6 km from the surface. They feed on what comes down from above. About 60% of deep sea fish have their own glow to find food, detect enemies and signal relatives.

Coral reefs

Coral reefs are found in shallow waters in warm, clear tropical waters. They are made up of the skeletons of small animals called coral polyps. When old polyps die, new ones begin to grow on their skeletons. The oldest reefs began to grow many thousands of years ago. One type of coral reef is an atoll, which is shaped like a ring or a horseshoe. The formation of atolls is shown below. Coral reefs began to grow around the volcanic island. After the extinction of the volcano, the island began to sink to the bottom. The reef continues to grow as the island sinks. In the middle of the reef, a lagoon is formed (a shallow salt lake). When the island sank completely, the coral reef formed an atoll - a ring reef with a lagoon in the middle. Coral reefs are more diverse than other parts of the ocean. One third of all ocean fish species are found there. The largest is the Great Barrier Reef on the east coast of Australia. It stretches for 2027 km and shelters 3000 species

Charles