Part of my undergraduate thesis on leaf longevity involves studying how leaf age affects the chlorophyll content of evergreen leaves. We have measured chlorophyll content for broadleaved evergreen species, such as Rhododendrons and hollies, using an AtLeaf+ chlorophyll meter.
Unfortunately, this instrument typically does not work for most conifers, such as firs, spruces, and yews, because the needles are too narrow to cover the width of the measuring window and the results are variable and unreliable. However, with just the tools shown below, we have been able modify the usual procedure for use with narrow conifer needles.
We cut an insert (middle left) out of a sheet of thin plastic; this allows the needles to be precisely placed over the measuring window. We arrange a few needles next to each other to cover the hole in the insert, with no gaps and minimal overlap between leaves, and then tape the leaves down with clear tape.
We then carefully place the insert in the chlorophyll meter so that leaves are over the measuring window, and we’re set to measure chlorophyll content! In effect, this simple procedure is a way to increase the width of the leaf surface area being measured.