CO2 fertilization effect
2 fertilization effect or carbon fertilization effect is the increased rate of photosynthesis in plants that results from increased levels of carbon dioxide (CO
2) in the atmosphere. The effect varies depending on the plant species, the temperature, and the availability of water and nutrients. However, enhanced rates of photosynthesis in plants due to CO
2 fertilization are only partially transferred to enhanced plant growth and any hypothesized CO2 fertilization response is unlikely to significantly reduce the human-made increases in atmospheric CO2 concentration over the next century.
Studies led by Trevor Keenan from the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) show that, from 2002 to 2014, plants appear to have gone into overdrive, starting to pull more carbon dioxide out of the air than they have done before. The result was that the rate at which carbon dioxide accumulates in the atmosphere did not increase during this time period, although previously, it had grown considerably in concert with growing greenhouse gas emissions. Keenan concluded “Unfortunately, this increase is nowhere near enough to stop climate change.”
Theory predicts the tropics to have the largest uptake due to the CO
2 fertilization effect, but this has not been observed. The amount of CO
2 uptake from CO
2 fertilization also depends on how forests respond to climate change, and if they are protected from deforestation.
Free-Air CO2 Enrichment (FACE) experiments
- Increased root production stimulated by increased CO
2, resulting in more soil carbon.
- An initial increase of net primary productivity, which was not sustained.
- Faster decline in nitrogen availability in increased CO
2 forest plots.
- Change in plant community structure, with minimal change in microbial community structure.
- Enhanced CO
2 cannot significantly increase the leaf carrying capacity or leaf area index of an area.
FACE experiments have been criticized as not being representative of the entire globe. These experiments were not meant to be extrapolated globally. Similar experiments are being conducted in other regions such as in the Amazon rainforest in Brazil.
Decreases in minerals and impacts on human nutrition
Empirical evidence shows that increasing levels of CO
2 result in lower concentrations of many minerals in plants tissues. Doubling CO
2 levels results in an 8% decline, on average, in the concentration of minerals. Declines in magnesium, calcium, potassium, iron, zinc and other minerals in crops can worsen the quality of human nutrition. Researchers report that the CO
2 levels expected in the second half of this century will likely reduce the levels of zinc, iron, and protein in wheat, rice, peas, and soybeans. Some two billion people live in countries where citizens receive more than 60 percent of their zinc or iron from these types of crops. Deficiencies of these nutrients already cause an estimated loss of 63 million life-years annually.
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