Last updated May 3, 2018 at 9:53 am
It’s taken 20 years to find this out, but it seems that as plants get older, their sensitivity to CO2 changes.
Past research has suggested that plants in what we know as the C3 group, which includes rice, wheat and trees, are more sensitive and thus grow more vigorously when CO2 levels are high than those in the C4 group, which includes most grasses, including corn and sugarcane.
However researchers from the University of Minnesota and the University of Wisconsin have discovered that this applies only for the first 12 years. After that, the situation reverses.
They monitored 88 separate plots and found that during the first 12 years C3 plots averaged a 20 per cent increase in total biomass in response to elevated carbon dioxide levels, compared to ambient conditions, while C4 plots averaged just a 1 per cent increase – changes that were in line with expectations.
Planning for climate change
However, during the next eight years C3 plots averaged 2 per cent less than their ambient counterparts and C4 plots averaged 24 per cent more biomass. Variables such as rainfall and net photosynthesis of the plants had little correlation with this reversal while, mysteriously, the mineralisation of nitrogen did.
The findings obviously have wide implications in a world planning for significant further climate change.
In a linked article, Associate Professor Mark Hovenden, from the University of Tasmania, and Dr Paul Newton, from AgResearch NZ, note that because C4 plant species contribute 25 per cent of land biomass globally, provide an important forage source for grazing animals, and are overrepresented among weeds, it is especially important to correctly estimate the future distribution of these plants.
Scientists categorise plants based on the way in which they process carbon. C3 and C4 are the most common classes.