When tundra ecosystems in northern Alaska were exposed to increased C02 at nearly 600 ppm (about double the pre-industrial background) in a FACE experiment, there was an initial increase in growth which disappeared after 2-3 years. This particularly short-lived response is thought to occur because tundra ecosystems are strongly limited by nutrients: they cannot respond well to the extra carbon supply by increasing plant tissues because the nutrients they also need to build their tissues are in such short supply.
0ther FACE studies have included salt marshes, and tallgrass prairies in the Midwestern USA. These too have tended to show an initial burst of growth, followed by a decline in the advantage of C02-fertilized plots.
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