Marine RuBisCo runs something like 8 times as fast because there’s oodles of carbonate and bicarbonate ions in the water which marine algae can enzymatically convert to CO2 in the cell for basically no cost
So if we could grow crops underwater we could get a lot more energy?
In a manner of speaking yes. That’s part of how kelp and seaweed (and to a lesser extent coral) manage to grow so fricking fast and part of how free-floating phytoplankton replicates fast enough to feed a biomass of zooplankton larger than itself at any given moment.
Only a fraction of the wattage of the biological energy available to plants that is converted from light can actually be captured by the carbon-fixation system as carbs and biomass-production, a lot more just can’t get stored long-term. In marine algae with all the extra carbon floating around, it’s rather a larger fraction that can be stored.
There’s other issues with marine agriculture, having to do with nutrient concentration and hervibory and the fact that the light only goes down through the water so far...
‘M.pyrifera is one of the fastest-growing organisms on Earth. They can grow at a rate of 0.6 meters a day to reach over 45 metres (148 ft) long in one growing season.’
Honestly not sure how these stack up in terms of energy capture per square meter.
EDIT 2: It should also be noted that despite the fact that the ocean coveres 70+% of earth’s surface and is full of carbon, it only represents something between 50 and 85% of the total photosynthesis that occurs on Earth depending on whose figures you listen to. Between low levels of many mineral nutrients, lack of a solid substrate near most of its surface, temperature variations, and dimming of sunlight with depth, it’s not as naturally productive compared to land as its carbon levels would indicate. The aforementioned superkelp grows in shallow water near nutrient-rich upwelling cold water.
EDIT 3: A little more research on my part shows that given the pigments and the chemical processes involved, the maximum theoretical energy yield of photosynthesis in sunlight is ~25% and maximum theoretical carb yield of a plant is ~10-11 % which will go down with light as bright a sunlight because the machinery has a maximum rate per square centimeter at which it can work which is actually partially why most plants arent simple planes but have lots of leaves pointing every whichaway, so the light intensity on any given leaf is less and it can be more efficient. Typical wild land plants are doing a lot of non-carbon-fixing energy-using activities and are hamstrung by low CO2 and manage less than 1% carb production, a bunch of crop plants that have been optimized for energy storage rather than other energy-using processes manage something like 2%, and sugarcane (a domesticated C4 plant) in tropical high light high humidity conditions can manage 7 or 8%. Typical wild algae apparently easily manages ~4-5% and in artificial conditions can be boosted much higher.
So if we could grow crops underwater we could get a lot more energy?
In a manner of speaking yes. That’s part of how kelp and seaweed (and to a lesser extent coral) manage to grow so fricking fast and part of how free-floating phytoplankton replicates fast enough to feed a biomass of zooplankton larger than itself at any given moment.
Only a fraction of the wattage of the biological energy available to plants that is converted from light can actually be captured by the carbon-fixation system as carbs and biomass-production, a lot more just can’t get stored long-term. In marine algae with all the extra carbon floating around, it’s rather a larger fraction that can be stored.
There’s other issues with marine agriculture, having to do with nutrient concentration and hervibory and the fact that the light only goes down through the water so far...
EDIT:
http://en.wikipedia.org/wiki/Aquaculture_of_giant_kelp
‘M.pyrifera is one of the fastest-growing organisms on Earth. They can grow at a rate of 0.6 meters a day to reach over 45 metres (148 ft) long in one growing season.’
http://en.wikipedia.org/wiki/Seaweed_farming
Honestly not sure how these stack up in terms of energy capture per square meter.
EDIT 2: It should also be noted that despite the fact that the ocean coveres 70+% of earth’s surface and is full of carbon, it only represents something between 50 and 85% of the total photosynthesis that occurs on Earth depending on whose figures you listen to. Between low levels of many mineral nutrients, lack of a solid substrate near most of its surface, temperature variations, and dimming of sunlight with depth, it’s not as naturally productive compared to land as its carbon levels would indicate. The aforementioned superkelp grows in shallow water near nutrient-rich upwelling cold water.
EDIT 3: A little more research on my part shows that given the pigments and the chemical processes involved, the maximum theoretical energy yield of photosynthesis in sunlight is ~25% and maximum theoretical carb yield of a plant is ~10-11 % which will go down with light as bright a sunlight because the machinery has a maximum rate per square centimeter at which it can work which is actually partially why most plants arent simple planes but have lots of leaves pointing every whichaway, so the light intensity on any given leaf is less and it can be more efficient. Typical wild land plants are doing a lot of non-carbon-fixing energy-using activities and are hamstrung by low CO2 and manage less than 1% carb production, a bunch of crop plants that have been optimized for energy storage rather than other energy-using processes manage something like 2%, and sugarcane (a domesticated C4 plant) in tropical high light high humidity conditions can manage 7 or 8%. Typical wild algae apparently easily manages ~4-5% and in artificial conditions can be boosted much higher.