Physiologists often use the expression Q10 to express the change in a metabolic
ID: 119432 • Letter: P
Question
Physiologists often use the expression Q10 to express the change in a metabolic process that occurs with a 10 degree celsius rise in temperature. In many areas, the Q10 for soil respiration is about 2.4. What will be the annual global increase in soil respiration with a 3 degree celsius rise in global temperature during the next century? How does this compare to fossil fuel emissions? Define the Q10 relationship. By definition, Q10 means that t=10. Cite your source for global soil respiration and what it would be in a world warmer by 3oC.
Explanation / Answer
If the Earth’s temperature rises due to the greenhouse effect, we can expect soils, globally, to be warmer, especially at high latitudes. Except in some deserts, soil respiration increases with increasing temperature – seen both in compilations of literature values and in studies with imposed soil warming. The increase in soil respiration per 100C rise in temperature – the Q10 of the relationship – is about 2.4. Root respiration is particularly responsive to increases in temperature, showing a Q10 as high as 4.6.
The soil respiration shows an exponential trend as thus a 30C rise will give a median value of 0.477 x 2.4 = 1.145
Therefore, the annual global increase in soil respiration with a 3 degree celsius rise in global temperature during the next century will be 1.145
Of course, the most important scenario to understand – and unfortunately the scenario we know least about – is one with simultaneous increases in CO2 and global temperature. Will soils be a net source or sink for carbon in these future conditions on our planet? Tropical rainforests have high NPP (as with higher CO2) and warm, wet conditions (as with most models of global warming), yet the carbon content of tropical soils is much smaller than that of the boreal region. Weak correlations between the pool of soil organic matter and NPP across world biomes. Apparently, large accumulations of soil organic matter do not derive from large inputs, but rather, soil organic matter accumulates where other factors (e.g., temperature) limit decomposers. As the planet warms, the area of temperature-limited decomposition should decline, and soils increasingly should become a source of CO2 to the atmosphere.