SPAD in "dry" leaves

Project Guidance

Hi. I measured chlorophyll content (protocol SPAD) in leaves catalpa in 1, 2 and 5 days after cut. After 2 - 5 days - –§II, LEF - negative values (this is understandable). Indicators of SPAD in the "dry" leaves grow (40, 58, 59.6). Why?

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Greg Austic

Oct 2015

Hey Andriy - yeah, I see it, that's unusual but it I could understand on 2 levels:

  1. The SPAD calculation also takes into account the thickness of the leaf - so if the leaf is losing water, it will become thinner. In theory that shouldn't matter, but that thickness measurement is probably not perfect so it may be affecting the final output.

  2. The leaf itself is shrinking, which would concentrate the chlorophyll into a smaller area.

I can see PhiNPQ go up and Phi2 go down, as expected, so the measurements themselves look very good actually.

Do you have any images of the leaves themselves to compare before and after? Do they look less green? These chlorophyll measurements are just measures of relative greenness.

Hi. I got value the "SPAD" - "NA" Plants is Yucca filamentosa. Is there a maximum value for the device - 90-100 units? Does it depend on the thickness of the leafe plants? Thanks.

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Greg Austic

Jan 2016

Hey guys - so the way the macro is written, it ignores any raw detector values if they are <500 because they can produce distorted SPAD values. Because these leaves as so thick, the absorbance for all 3 intensities (SPAD 1 - 3) were below 500 for the red light, so the program logic then prevented any of them from being used to produce the final SPAD value.

So in short, yes, you exceeded the maximum thickness. Yucca is quite thick, and I'm not too surprised. It's very hard to get around this, especially when performing the wide variety of measurements we do on a single device with a single detector. When I re-develop the new SPAD for the v1.0 I'll try to expand the range as much as possible.