3 ms·

plants only use part of the spectrum. Likely they have hit some local or maybe even global maximum that would be hard to evolve past. See https://en.wikipedia

by dekhn 2y ago

plants only use part of the spectrum. Likely they have hit some local or maybe even global maximum that would be hard to evolve past. See https://en.wikipedia.org/wiki/Photosynthetic_efficiency https://en.wikipedia.org/wiki/Photosynthetic_efficiency

adrian_b 2y ago
The terrestrial plants use only a small part of the spectrum, because the available light is frequently too abundant for them, which was even more true at the beginning of their evolution, when there were no forests providing shadows. For terrestrial plants, it is usually a more important problem to not be overwhelmed by too much energy captured from light, than to capture more. This is why the green plants dominate on continents, because they reflect a good part of the light, instead of absorbing it, so they are not destroyed by excessive light. On the other hand, in the oceans the green algae are a minority in comparison with diatoms, brown algae and other kinds of algae that absorb much larger fractions of the solar light, because they can use only the less intense light that remains after passing through water. On the bottoms of waters there are many places where there are combined algal and bacterial mats that act like a multijunction photovoltaic cell, i.e. there are multiple layers of different algae and bacteria, e.g. diatoms, blue-green algae (cyanobacteria), purple non-oxygenic phototrophic bacteria and green non-oxygenic phototrophic bacteria, so that each layer absorbs a different part of the solar light spectrum, resulting in almost complete absorption through all layers.
- card_zero 2y ago
  You might clarify "too abundant", "overwhelmed", and "destroyed". Elsewhere, somebody told me: > one must know that chemical reactions with gases are very dependent on the pressure of the gases. Even the direction, that is if it's exothermic or endothermic, depends highly on the pressure. If RuBisCo would be faster the carbon dioxide could not come fast enough onto the site of enzymatic activity and would therefore drop in pressure there. And > Generally plants have too much energy for the amount of water and, most important, carbon dioxide, to synthesize sugar. So the idea I come away with is that CO2 is not abundant enough for the energy (that a differently-made plant could extract from the light) to be useful.
  - gus_massa 2y ago
    Can a plant near a volcano get a boost? How fast can plants (or gree algae) evolve to absorb the increased CO2 in the air?
    - card_zero 2y ago
      That is a fun question. Like life around hydrothermal vents, but on land. I can't search for answers easily because of course volcanic soil is really fertile anyway, so people have plenty to say about plants that grow around volcanos already, without reference to carbon dioxide.
  - adrian_b 2y ago
    That is correct. By overwhelmed, I have meant exactly this, i.e. if the terrestrial plants had captured more solar energy, the only effect would have been the accumulation in their cells of free oxygen and of intermediate reduced chemical compounds that could not be used fast enough to synthesize useful substances like carbohydrates, for various reasons, of which the lack of enough captured carbon dioxide is a major reason. The capture of carbon dioxide can be hampered by the free oxygen produced by capturing solar light, even if the plant cells attempt to separate the cell parts where these incompatible processes occur. It might be possible to improve the productivity of the plants by improving their ability to capture carbon dioxide, more than by improving their ability to capture light. However I believe that such research directions are misguided. We are already able to capture light very efficiently with non-biological devices and the same is likely to become true for carbon dioxide capture and electrolytic reduction. What is unlikely to happen any time soon is to find any way for synthesizing complex organic molecules like those needed for food as efficiently as by using living cells. So the non-biological capture of solar energy and capture and reduction of carbon dioxide and dinitrogen should be combined with biological syntheses in cultivated organisms.

by dekhn 2y ago

adrian_b 2y ago

The terrestrial plants use only a small part of the spectrum, because the available light is frequently too abundant for them, which was even more true at the beginning of their evolution, when there were no forests providing shadows. For terrestrial plants, it is usually a more important problem to not be overwhelmed by too much energy captured from light, than to capture more. This is why the green plants dominate on continents, because they reflect a good part of the light, instead of absorbing it, so they are not destroyed by excessive light. On the other hand, in the oceans the green algae are a minority in comparison with diatoms, brown algae and other kinds of algae that absorb much larger fractions of the solar light, because they can use only the less intense light that remains after passing through water. On the bottoms of waters there are many places where there are combined algal and bacterial mats that act like a multijunction photovoltaic cell, i.e. there are multiple layers of different algae and bacteria, e.g. diatoms, blue-green algae (cyanobacteria), purple non-oxygenic phototrophic bacteria and green non-oxygenic phototrophic bacteria, so that each layer absorbs a different part of the solar light spectrum, resulting in almost complete absorption through all layers.

card_zero 2y ago
You might clarify "too abundant", "overwhelmed", and "destroyed". Elsewhere, somebody told me: > one must know that chemical reactions with gases are very dependent on the pressure of the gases. Even the direction, that is if it's exothermic or endothermic, depends highly on the pressure. If RuBisCo would be faster the carbon dioxide could not come fast enough onto the site of enzymatic activity and would therefore drop in pressure there. And > Generally plants have too much energy for the amount of water and, most important, carbon dioxide, to synthesize sugar. So the idea I come away with is that CO2 is not abundant enough for the energy (that a differently-made plant could extract from the light) to be useful.
- gus_massa 2y ago
  Can a plant near a volcano get a boost? How fast can plants (or gree algae) evolve to absorb the increased CO2 in the air?
  - card_zero 2y ago
    That is a fun question. Like life around hydrothermal vents, but on land. I can't search for answers easily because of course volcanic soil is really fertile anyway, so people have plenty to say about plants that grow around volcanos already, without reference to carbon dioxide.
- adrian_b 2y ago
  That is correct. By overwhelmed, I have meant exactly this, i.e. if the terrestrial plants had captured more solar energy, the only effect would have been the accumulation in their cells of free oxygen and of intermediate reduced chemical compounds that could not be used fast enough to synthesize useful substances like carbohydrates, for various reasons, of which the lack of enough captured carbon dioxide is a major reason. The capture of carbon dioxide can be hampered by the free oxygen produced by capturing solar light, even if the plant cells attempt to separate the cell parts where these incompatible processes occur. It might be possible to improve the productivity of the plants by improving their ability to capture carbon dioxide, more than by improving their ability to capture light. However I believe that such research directions are misguided. We are already able to capture light very efficiently with non-biological devices and the same is likely to become true for carbon dioxide capture and electrolytic reduction. What is unlikely to happen any time soon is to find any way for synthesizing complex organic molecules like those needed for food as efficiently as by using living cells. So the non-biological capture of solar energy and capture and reduction of carbon dioxide and dinitrogen should be combined with biological syntheses in cultivated organisms.