Plant Cuttings

Spotlight on macronutrients: Hydrogen (and oxygen…)

No matter how well we think we understand water, there are always more surprises to uncover.
Image: Marvin Smith/Wikimedia Commons.
Image: Marvin Smith/Wikimedia Commons.

We are often reminded that water is a ‘most interesting/odd/peculiar/amazing/incredible compound’ with many fascinating properties – both physical and chemical, and biological. And its roles within plant biology are many and varied. But no matter how well we think we understand water, there are always more surprises to uncover. Take, for example, Juergen Burkhardt and Mauricio Hunsche’s intriguingly entitled Hypothesis and Theory article, ‘“Breath figures” on leaf surfaces – formation and effects of microscopic leaf wetness’. ‘Breath figures’ is a term used in material science to describe the condensation, as well as the linked wetting and de-wetting processes, on different kinds of surfaces, which the article’s authors extend to the surfaces of leaves. The water is mainly maintained by transpired vapour that condenses onto the phylloplane and onto attached leaf surface particles. However, with an estimated thickness of less than 1 μm, this microscopic layer is approximately two orders of magnitude thinner than morning dewfall (the more widely known form of condensation upon leaves); it is therefore easily overlooked(!) and consequently un(der)appreciated. The authors hypothesise that microscopic leaf wetness occurs on almost any plant worldwide, often permanently. Since it can constitute a continuous thin layer even on otherwise hydrophobic leaf surfaces, and can enhance dissolution, emission and reaction of specific atmospheric trace gases such as ammonia, SO2 or ozone (which compounds can be injurious to plant health),  it is a topic fully deserving of an airing. As the authors conclude, ‘The omission of microscopic water in general leaf wetness concepts has caused far-reaching, misleading conclusions in the past…’.
[I don’t know if breath figures have any connection with ‘frost flowers’, but as a nod in the direction of ‘winterval’ and those almost-forgotten frosty days of December in the northern hemisphere, and in an attempt to gladden the heart – and lighten the spirit and maybe lift the soul at this dark time of the year – I’m happy to illustrate this item with an example of this other, intriguing water-based phenomenon. For more on that topic, do visit Illinois State University’s Emeritus Professor James Carter’s ‘My World of Ice’ site – Ed.]