What are stable isotopes and their role in ecological research? Is it possible to make a climate reconstruction using growth rates and stable isotopes in age ring wood or cellulose?
Almost every element has isotopes, atoms of the same element, but different in their masses. Carbon for example is made up of isotopes with masses of 12, 13 and 14 (neutrons and protons). A stable isotope could be a tool, to find out more about physiological and chemical processes in environmental biology. The atmospheric CO2 (carbon dioxide)(molecule) enters the leaf through the stomata, which then diffuses into the chloroplast, where it is converted into glucose by the process of photosynthesis and then incorporated into the tree. A study of tree growth rings on their 12C and 13C signature can be used to learn more about climate information .
In wet and cold years, the light 12C is preferably incorporated into the tree by reason of the enzyme RuBisCO , which discriminates the heavy isotope 13C because it needs more energy to incorporate the 13C into the plant. In a dry and hot summer the stomata will be often closed to protect the plant against desiccation, which leads to a limited gas (CO2) exchange with the atmosphere, so the heavy 13C is also incorporated into the tree. By using a mass spectrometer to determine the carbon isotope ratio, measuring the annual ring widths, I have been able to compare this data with the mean annual precipitation and the mean annual air temperature of the tree location. However, the results show us that the theory of isotope discrimination at this location is not as easy to confirm as I thought because of many unexpected side-factors that had to be considered for obtaining the data.