Hi Douglas, Interesting work. I have a couple questions. Does your research take into account depositions of particulates on leaf surfaces that might create a physical barrier to light or nutrients? Also, how do you decide if what you are seeing is due to air pollution or if it is due to some other stressor?
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Hi David, thanks for your interest. For your 1st question, if particulate deposition rate were significant enough to reduce the leaf’s ability to capture light and plant-level photosynthesis was reduced, this would be reflected in the isotopic composition. To my knowledge, there isn’t evidence that this has been the case, especially as a rain event washes off most of the deposition- which in my sites is very regular.
For your second question, assigning changes in growth rate to a particular stressor is challenging. That’s why I think a multi-variable approach is very useful. N isotopes and concentrations can provide a record of N deposition, sulfur concentrations provide a record of sulfur deposition, and base cation concentrations can provide a record of soil pH (which can impact plant nutrition). I’ll include precipitation and temperature records in my analysis (which are main drivers for short-term growth). A statistical model that includes at least a majority of the possible variables driving changes in plant growth should give pretty good confidence about what is most affecting the tree. -
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