Does More Carbon Dioxide Mean Increased Crop Water Productivity? (arstechnica.com)

An anonymous reader points us to an Ars Technica report: For the most part, we think of rising levels of carbon dioxide as an environmental problem. But atmospheric CO2 can also boost agricultural productivity by helping plants grow. How do these potential issues balance out? In an investigation recently published in Nature Climate Change, scientists have looked into the global implications of carbon dioxide's ability to enhance agricultural productivity. Increased levels of CO2 can enhance photosynthesis and reduce leaf-level transpiration, the process by which some of the water that plants draw from the ground gets released back into the atmosphere. These changes can reduce growing seasons and water loss. The result could be an increase in what's called "crop water productivity," i.e. the amount of food produced for each unit of water expended. If elevated CO2 levels increase crop yield and reduce water consumption at large scales, this could help ensure water and food security despite the climate disruptions. By combining data from a massive network of field experiments and global crop models, the scientists claimed that depending on the crop type, global crop water productivity will increase by 10 to 27 percent by the 2080s. Arid regions exhibited large increases that were based on crop type.

Comments

Aquariums Add CO2 for plant benefits.

[AdamThor]

I've got a planted freshwater aquarium. In addition to good lighting and appropriate fertilization, people who like to keep this kind of aquarium tend to inject carbon dioxide to keep the plants growing well. The difference in plant performance in the aquarium with and without CO2 injection is substantial.

Re:Aquariums Add CO2 for plant benefits.

[Aighearach]

Carbon is a main limiting nutrient for most types of fungus, or at least for the basidiocarps.

It is a lot easier to just mix a carbon source into the food. They don't breath the carbon in; the microbes in the feed have to capture it for them, since your shrooms were not mycorrhizal. If they were mycorrhizal then the plant could capture the carbon for them, but that doesn't include anything in the Psilocybe genus.

Mountain pine beetle bad example

[SuperKendall]

Most of the pine beetles were killed off in a heavy freeze a few years ago.

The reason why your example is bad is that even a rise of a few degrees C in temperature ON AVERAGE, does not mean you will not continue to have heavy cold snaps in areas like the mountains - and it only takes one such to kill back a large number of beetles.

Also trees getting more CO2 and warmer temperatures grow better and thus resist insects better also.

It's absurd to claim the offset in the ability to grow ANYTHING is offset entirely by a possibly increase in weeds and insects... come on.

I notice you post AC when spreading your warming alarmism, it speaks heavily to how much stock we should put in your claims.

Re:Mountain pine beetle bad example

[CanadianMacFan]

Of course there is the fact that some crops are not as nutritious when grown in an environment with an elevated CO2 level. This study tested certain crops with the expected CO2 level at the middle of the century and found:

"Wheat grown in high CO2 levels had 9% less zinc and 5% less iron, as well as 6% less protein, while rice had 3% less iron, 5% less iron and 8% less protein. Maize saw similar falls while soybeans lost similar levels of zinc and iron but, being a legume not a grass, did not see lower protein."

http://www.theguardian.com/env...

Probably not

[aepervius]

There are diminishing return at some point, and other elements begins to be a limiting factor : nitrogen fixation and phosphorus for example. So it *may* produce some better plant growth some places, but for our agriculture it sounds doubtful.

Re:uhmm...

[RatherBeAnonymous]

The difference this time around is that Carboniferous period fungi were unable to break down lignin. Lignin adds rigidity to plant cell walls and was what plants needed to grow into tall trees with the capacity to bind trillions of tonnes of carbon into wood. For about 50 millions years, all the tree trunks that fell over from storms, disease, old age, insects, earthquakes, dinosours knocking them over, what have you, did not rot completely. Much of their carbon was sequestered underground and compressed into coal. The Caboniferous period ended as Fungi evolved the means to digest lignin and ended the massive carbon sequestration.

http://www.mining.com/coal-sto...

So yeah, plant growth will spike, but don't expect that to mean much for reducing global C02 levels.

Re:There are adverse effects from this

[Anonymous Coward]

Exactly, the whole system interactions are the real question. Rubisco, the carbon capture enzyme in photosynthesis, isn't too efficient of an enzyme. It tends to grab O2 more than it should when it wants CO2. This is why C4 plants like corn, which have a mechanism to improve the carbon capture, tend to have better yields than C3 plants like wheat, and also why there have been efforts to use genetic engineering to re-create the C4 pathway in C3 crops to increase their yields, like the C4 rice project (which is less radical than one would think given the number of times C4 photosynthesis has independently evolved in different plant linage). It is likely that increased CO2 relative to O2 will be of some benefit to some crops. That's not really the question though; the bigger issue is if that boost will be enough to counter the increased stresses from pests, pathogens, weeds (all of which are likely to benefit more than crop plants), and various potential abiotic environmental stresses.

I'm not saying this research is flawed; I haven't read the paper yet but the concept is understood and this is one aspect to consider when discussing the impacts of climate change on agriculture, but I do expect this to be misrepresented as 'climate change isn't that bad.' Possibly right after 'climate change isn't happening.'

soyFACE experimental results

[estitabarnak]

Free-Air Concentration Enrichment studies such as soyFACE artificially raise CO2 (among other variables) and monitor plant response. SoyFACE, as the name implies, is focused on soy, an important food crop. Imagine a crop field surrounded by CO2 sprayers and heaters to simulate elevated CO2 and its effects.

Findings from the experiment include that increased temperatures will likely reduce yields of soy, even at elevated CO2. Higher average temperatures also increased susceptibility to herbivory by the Japanese beetle.

A related meta including 228 experimental observations found that barley, rice, wheat, soybean, and potato all have lower protein content at elevated CO2.doi: 10.1111/j.1365-2486.2007.01511.x

14 years of publications can be found here: http://www.igb.illinois.edu/so...

In short: even if water use efficiency were to increase, that does not result in increased yield, or crop quality.