Ecosystem Properties and the Continued Operation of the Terrestrial Carbon Sink
Four ecosystem properties are particularly important in determining the magnitude and continued operation of the terrestrial carbon sink as CO2 levels rise, anthropogenic N-deposition continues and the climate changes. First, the time lag between the responses of NPP (net primary productivity) and soil respiration make it inevitable that a transient carbon sink is created in response to continuously increasing CO2 levels. The magnitude of this effect depends on the responses of photosynthesis and plant growth to elevated CO2 and the residence time of carbon in ecosystem pools. Secondly, the temperature sensitivities of NPP and soil respiration are critical in determining the responses of ecosystems to warming. The temperature responses of the component processes need to be better known, and feedbacks involving nutrients, water and CO2 can be overriding. Thirdly, the extent to which ecosystems respond to elevated CO2 by increasing nutrient acquisition and/or use efficiency is critical in determining the amount of carbon that can be sequestered. The extent and consequences of increased carbon allocation to roots in nutrient-limited ecosystems, and shifts of nutrients between ecosystem components are particularly important. Fourthly, the extent of water-stress-induced decreases in NPP and vegetation (especially forest) dieback depend on stomatal responses to elevated CO2 and changes in leaf area, which in turn depend on nutrient supplies. It is concluded that there is no short-cut to modelling all the main processes and couplings within the carbon, nutrient and water cycles if the current and future behaviour of the terrestrial carbon sink is to be predicted.
KeywordsBiomass Migration Dioxide Respiration Photosynthesis
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