In a world in which atmospheric concentrations of carbon dioxide are rising, what will happen to the extra carbon after being taken up by plants during photosynthesis? Experiments in northern California have been carried out to address this question. They involve grassland growing under conditions of ambient and twice-ambient levels of carbon dioxide, and show that the additional carbon is not sequestered in organic matter but cycles through the system more rapidly. This is a highly complicated issue, however, and the situation in forests may well be different.
