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.

Is there a way to show that a chlorophyll measurement is authentic?