ARS | Publication request: VISIBLE FOLIAR INJURY CAUSED BY OZONE ALTERS THE RELATIONSHIP BETWEEN SPAD METER READINGS AND CHLOROPHYLL CONCENTRATIONS IN CUTLEAF CONEFLOWER

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2005
Publication Date: March 1, 2006
Citation: Neufeld, H.S., Chappelka, A.H., Somers, G.L., Burkey, K.O., Davison, A.W., Finkelstein, P.L. 2006. Visible foliar injury caused by ozone alters the relationship between spad meter readings and chlorophyll concentrations in cutleaf coneflower. Photosynthesis Research. 87 (3):281-287.

Interpretive Summary: Ground-level ozone is an air pollutant that has negative impacts on both crop plants and natural vegetation. Ozone effects include leaf injury in the form of purple or brown spots on the upper leaf surface accompanied by chlorophyll loss and necrotic lesions. In this study, a commercial instrument designed to rapidly and nondestructively measure leaf chlorophyll content was tested as a potential approach to assess ozone effects on plants. The results suggested that the instrument does not reliably measure leaf chlorophyll when a significant portion of the leaf surface exhibits ozone injury symptoms, possibly due to changes in leaf chemistry and/or leaf physical characteristics that are not compatible with underlying principles on which the instrument is based.

Technical Abstract: In this study the ability of the SPAD-502 chlorophyll meter to accurately quantify chlorophyll amounts in ozone-affected leaves of cutleaf coneflower (Rudbeckia laciniata var. digitata) was assessed. When relatively uninjured leaves were measured (percent leaf area affected by stipple less than 6%), SPAD meter readings were linearly related to total chlorophyll with an adjusted r2 of 0.85. However, when foliar injury (characterized as a purple to brownish stipple on the upper leaf surface) affected more than 6% of the leaf area, the SPAD meter no longer provided as accurate chlorophyll estimations, and the r2 for total chlorophyll decreased to only 0.57. We suspect that several factors are involved in reducing the accuracy of the SPAD meter when measuring chlorophyll amounts in visibly ozone-injured leaves, including production of oxidized phenolics and changes in light scattering due to tissue necrosis.