Arctic vegetation represents a significant portion of the world’s global carbon stocks and is particularly sensitive to global climate change. Net plant carbon exchange depends on both photosynthesis and respiration, the latter of which is poorly understood in arctic ecosystems and yet is highly sensitive to global environmental change.
Mitochondrial respiration can confound measurements of photosynthesis and thus is often isolated by measuring it in the dark. We also know, however, that respiration can be inhibited by light, which complicates extrapolations from measurements in darkness. Furthermore, the extent of this inhibition may be unique in arctic ecosystems as a result of the constant daylight they receive during growing seasons.
We applied the Kok method to a survey of forty of the most common tundra plants found in communities surrounding the Toolik Lake Long Term Ecological Research Site in Alaska’s North Slope. The Kok method segregates rates of respiration in the dark and those in the light by applying incrementally decreasing light levels to leaves. Using this approach, we were able to compare these different rates and determine the extent of light inhibition across a variety of species, functional groups and habitat types.
Results/Conclusions:
Respiration is less inhibited by light in the Arctic than it is expected to be based on observations from lower latitudes. We measured several functional traits in order to identify the mechanisms plants have used to acclimatize to constant daylight. Carbohydrate content, photosynthetic capacity (Amax) and specific leaf area (SLA) were significant predictors of levels of inhibition. There did not appear to be a significant effect of functional group membership on inhibition. We detected considerable intraspecific variation in trait values and levels of inhibition and thus species identity did not explain variation in inhibition. Preliminary tests for effects of evolutionary history on levels of inhibition indicate that inhibition may be lower in plants that have diversified at higher latitudes.
These results underline the importance of accounting for respiration in the light in arctic carbon models. Arctic carbon stocks may be significantly lower than previously thought since current estimates don’t include respiration in the light.