Wednesday, April 27, 2011

But, CO2 Is Plant Food !

And then there’s the "But CO2 Is Plant Food" meme.

Someone by the moniker of Dawei has posted a very informative collection of studies over at concerning different aspects of an increasingly CO2 enriched atmosphere. It seems that things aren't quite as simple as that. The true story is much more complicated and not near as reassuring.

It's a complicated image and Dawei has done a great job of reviewing the wide range of available literature, some of it quite recent. Of course, some of the following studies, specially the FACE work, is pioneering and as new data is received and processed today’s understanding will be refined. Such is the way of science.

I share the full list of author’s Dawei cites because I'm tired of folks implying that only a few scientists make up the consensus, when in fact the consensus is made of hundreds and thousands of fibers such as those listed below.

This is just a teaser, for the full narrative accompanying the studies visit

Climate control vs. climate change
The first and most obvious retort to this argument is that plants require more than just CO2 to live. Owners of industrial greenhouses who purchase excess CO2 also invest considerable effort in keeping their plants at optimum growing conditions, particularly with respect to temperature and moisture.

As CO2 continues to change the global climate, both of these variables are subject to change in an unfavorable way for a certain species in a certain region...
Lobell et al. 2008,
Luo 2009,
Zhao and Running 2010,
Challinor et al. 2010,
Lobell et al. 2011.
Only recently have researchers begun to pull away from these controlled settings and turn their attention to outdoor experiments. Known as Free-Air CO2 Enrichment or “FACE”, these studies observe natural or agricultural plants in a typical outdoor setting while exposing them to a controlled release of CO2...
Leaky et al. 2009,
Long et al. 2006,
Ainsworth 2005,
Morgan et al. 2005.

C3 & C4
Photosynthesis comes in a few different flavors, two of which are C3 and C4...
Cure and Acock 1986 (a greenhouse study)
Leaky et al. 2006 (a FACE study)
Crafts-Brandner & Salvucci, 2000,
Salvucci et al. 2001.

Chemical Responses & Nutrition
Even within a specific type of photosynthesis—indeed, even within a specific species—the positive responses to enhanced CO2 can vary widely. Nutrient availability in particular can greatly affect a plant’s response to excess CO2...
Stöcklin and Körner 2002,
Norby et al. 2010,
Larson et al. 2010.
The ability of plants to maintain sufficient nitrogen under excess CO2 conditions is also reduced for reasons not fully understood...
Bloom et al. 2010,
Taub and Wang 2008.

It has also been found that excess CO2 can make certain agricultural plants less nutritious for human and animal consumption...
Zhu 2005, a three-year FACE study,
Högy et al. 2009, also a FACE study

Increased CO2 has been shown to lead to lower production of certain chemical defense mechanisms in soybeans, making them more vulnerable to pest attack and diseases...
Zavala et al. 2008,
Eastburn et al. 2010.
Other studies have shown production of phenolics and tannins to increase under enhanced CO2 in some species, as well as many alkaloids...
Peñuelas and Estiarte 1999,
Ziska et al. 2005,
Stiling and Cornelissen 2007.
Furthermore, many “cyanogenic” species...
Gleadow et al., 2009a and Gleadow et al. 2009b.

Interactions with other species
Competing plant species have also been shown to drastically alter expected benefits from excess CO2...
Navas et al. 1999,
Poorter and Navas 2003
Ziska and George 2004,
Ziska et al. 2004,
Ziska and Teasdale 2000.
There is some evidence that interacting bacterial communities, particularly in the roots, will be affected through elevated CO2, leading to mixed results on overall plant health.
Treseder 2004,
Melloy et al. 2010.

... But there is another key piece to reduced stomatal conductance, considering that 90% of a plant’s water use is actually for cooling of the leaves and nothing more...
Ball et al. 1988,
Idso et al. 1993,
Long et al. 2006,
Roden et al. 1998.

CO2 is not the only atmospheric gas that is on the rise: concentrations of ground-level ozone (O3) are expected to rise 23% by 2050 due to continuing anthropogenic emissions of precursor gases like methane and nitrous oxides...
Monson et al. 1991,
Morgan et al. 2006,
Ainsworth 2008,
Feng et al. 2008,
Warrington 1988.

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