Copper-bottomed deficiency detection

Plants need copper in order to grow and reproduce properly, as copper is an essential component of the enzyme that synthesises the structural compound lignin. The first outward sign of copper deficiency, which is a common problem for plants grown in soil with low copper levels such as sandy soil, is white leaf tips, caused by the reduced lignin synthesis. Unfortunately, the detrimental effects of copper deficiency on plant growth and reproduction occur long before these visible signs appear, and so growers could really do with a method for diagnosing copper deficiency as early as possible.

What makes things even more difficult is that there is not a direct relationship between copper concentrations in plants and copper deficiency, as whether a plant is deficient in copper or not also depends on the species, growth stage and level of other nutrients. Two plants may have the same copper concentration, but only one may have its growth affected by copper deficiency.

Now, though, Søren Husted and his colleagues at the University of Copenhagen in Denmark have shown that NIR spectroscopy can accurately diagnose copper deficiency in plants. They tested its ability on leaves from barley plants grown in both normal and copper-deficient soil. As they report in the Journal of Agricultural and Food Chemistry, NIR spectroscopy wasn’t able to determine the copper concentration in the leaves, but it could distinguish leaves from copper deficient barley plants from those from normal plants with an accuracy of 92%.

NIR spectroscopy was able to detect copper deficient barley plants after just 13 days of growth. If additional copper was added to the soil at this point then the plants quickly started growing normally, showing that NIR spectroscopy can detect copper deficiency early enough to provide effective remedial treatment. In addition, NIR spectroscopy could distinguish barley plants deficient in copper from those deficient in other micronutrients such as manganese.

Interestingly, although copper deficiency primarily affects the synthesis of lignin, Husted and his team found that NIR spectroscopy could distinguish copper deficient plants from normal plants before there was any detectable difference in their lignin concentrations. This indicates that copper deficiency alters the composition of lignin before starting to reduce its concentration.