Chlorophyll Meter Quick Overview-MC-100 Explained

I’m Bruce Bugbee, president of Apogee
instruments. Today I’d like to talk about chlorophyll meters especially the
non-destructive chlorophyll meters that are vary widely used by a number of
people. We’ll go through a little bit of the history of it how they work and then
the advances that have been made over the years. So in the 1980s Minolta came out with this meter it was made by the scientific
products analysis division at Minolta a they use their acronym, they
call it a SPAD meter. Sometime people begun to think S.P.A.D. is synonymous with
chlorophyll and it is not it’s an acronym for a company. That was the first
meter. Then some years later Optisciences came out with this meter. It has some advantages over the
Minolta meter, little bigger area to average leaves and then recently Apogee
instruments came out with this meter which has some fundamental advances over
the other types of research-grade meters for chlorophyll. So let’s take a look at
what those differences are. The first thing is if we draw a leaf it’s full of
cells and these cells are full of chlorophyll. If we shine a light on this
leaf and we put a detector down here we can get the transmitted light through
the leaf. This is pretty easy to do and it gets us the amount of cellulose in
the leaf and the amount of chlorophyll in the leaf, both together. The
chlorophyll is in here in little packets inside these cells so to really be able
to measure this we take another wavelength of light and another
detector down here and this is red light and this is near
infrared light (NIR). These are all on the apogee website, the details of these. And now by
subtraction we can get at the amount of chlorophyll in this leaf. And it’s the
electrical output of these two detectors. When we make a graph of this difference
and we put transmission down here, the ratio of these wavelengths and we put
chlorophyll up here. And I’m going to abbreviate that just CHL for chlorophyll.
This would be lovely if we got a nice straight line and the transmission was
directly related to chlorophyll we would have a meter that told us chlorophyll.
Unfortunately the distribution of chlorophyll in a leaf is so clumped
up that the light goes in many directions. It doesn’t come straight through
the leaf and when we make this graph it’s highly nonlinear. That’s a
fundamental characteristic of all of these optical meters to get this non-linear relationship between transmission and chlorophyll. So here, let
me show you what happens with this, if we put tick marks in this graph now and we
have 12345, we make a measurement here and we have that much chlorophyll, let’s
call that about one. now we make another measurement out here at five, and you would think the chlorophyll went
up by a factor of two and a half and in fact it doesn’t. This only doubles
so the transmission is not a direct indicator of the chlorophyll in the
leaf. This has led to lots of problems. People write papers and they say
“the SPAD number went from two to four therefore my chlorophyll doubled.” And
that is wrong, the chlorophyll did not double. This index doubled, so the SPAD
Minolta meter that reads in SPAD units only gives an index that’s non-linearly
related to chlorophyll. The Optisciences meter also gives an index that’s non-linearly related to chlorophyll. And because of these problems and because of
the need to really measure chlorophyll Apogee instruments built on the research
that developed characteristic lines like this for each species of plant. There’s
one line for wheat, there’s another line for corn, there’s a line for rice, they
all take the same basic shape they just have slightly different curvatures. With
this equation you can convert transmission into actual chlorophyll in the
leaf and the result is a graph where we have chlorophyll here, actual chlorophyll measured by
extracting the chlorophyll, and this unit down here is now optical chlorophyll, or optical CHL, and the relationship is a
straight line. So we can very accurately measure chlorophyll in the
leaf with the appropriate software in the meter to convert this
family of curved lines into straight lines. That’s the beauty of the apogee
meter in terms of what it does to get chlorophyll. This took a lot of work, a
lot of measurements of chlorophyll and non-destructive chlorophyll. We have a
video that shows the techniques to do that. There’s a family of curves in there
for twenty two species and it’s growing. We’re getting a curve in there for
potatoes and other species now so we can establish this linear relationship
between what the optical meter measures and the true chlorophyll in the leaf. So in
a nutshell that’s the advance in this, and it’s a sufficiently big advance
that Apogee patented this meter, it has a patent pending on this meter. It now
allows researchers to get measurements of chlorophyll without having to kill
the leaf, without having to extract a leaf and measure it in a
spectrophotometer. So thanks for listening. That’s a nutshell of the
advances in these measurements over the last thirty years.

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