New model revises estimates of terrestrial carbon diox...(the global scale said Atul Jain a U. of ...)

Nitrogen is vital to carbon dioxide uptake in plants, and if the available nitrogen runs out, the plants wont be able to make use of the added CO2, Jain said. In an agricultural landscape, nitrogen may be added as needed, he said, but forests have limited amounts of nitrogen in their soils.

The integrated science assessment model, originally developed by Jain, now has been expanded to take into account the net carbon impact of human activities and the role of rising atmospheric temperatures on the process of carbon uptake.

Everything is integrated, not only the nitrogen, carbon and climate, but also we looked at land cover and land use changes, Jain said. A lot of deforestation and also aforestation and reforestation are going on, and that has a direct effect on the carbon dioxide release or absorption.

The model accounts for different soil and vegetation types, the impact of climate and the inadvertent nitrogen deposition that results from fossil fuel and biomass burning.

Interestingly, warming temperatures in response to rising carbon dioxide levels could make more nitrogen available, said Xiaojuan Yang, a doctoral student in Jains lab. This factor must also be weighed in any calculation of net carbon dioxide load, she said.

Previous modeling studies show that due to warming, the soil releases more carbon dioxide through increased decomposition, she said. But they are not considering the nitrogen effect. When the soil is releasing more CO2, at the same time more nitrogen is mineralized. This means that more nitrogen becomes available for plants to use.

Increased nitrogen availability allows plants to uptake more carbon dioxide, a factor that mitigates, somewhat, the added burden of carbon dioxide in the atmosphere.

Even so, Jain said, the failure to lo
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