17 Dec 2009


One of the hottest news now is the United Nations Climate Change Conference in Copenhagen. Although the countries still dispute much with each other in terms of financial input and policy enforcement, let’s wish that Hopenhagen does deliver hope. Having lived under the gray sky of Beijing for six months, I support campaigns to reduce pollution.

On the other hand, as I read more about the topic, I must say that we really know little about each environmental factor and its effects. For example, increasing nitrogen deposition and atmospheric carbon dioxide concentration has occurred over the last few decades. Each factor alone is known to reduce biodiversity through promoting the growth of above ground plants. As a result, above ground resources such as light become less available to plants below, resulting in a decrease in species. Biodiversity is important for community stability and resistance to diseases and invasive species.

With this background, the logical prediction is that when both nitrogen and carbon dioxide increase, there should be an additive or synergistic effect, resulting in further reduction in biodiversity. However, in a recent report by Peter Reich, the effect of both factors on biodiversity appears to cancel out each other.[Reich P. Science 2009;326:1399-402] In a 10-year project, 16 plant species were grown under different combinations of carbon dioxide and nitrogen levels. Although elevated carbon dioxide and nitrogen reduced biodiversity by 2% and 16%, respectively, both factors in combination only reduced biodiversity by 8%. Though the cause of the observation is unclear, it is possible that nitrogen and carbon dioxide may affect plant growth and changes in resources in different layers and thus have differential effects.

This is just a simple example to remind me to be humble and not to draw quick conclusions. Readers of this blog, however, may laugh and point out that the article caught my eyes mostly because of the amazing study duration.

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