Every day is Dewsday in the forest…

Image: Fir0002/Flagstaffotos/Wikimedia Commons.

Image: Fir0002/Flagstaffotos/Wikimedia Commons.

The dew point is ‘the tem­per­at­ure to which a volume of humid air must be cooled… for water vapor to con­dense into liquid water’, and is usu­ally an early-morning or early-evening phe­nomenon in nature. OK, but, ‘what is the point of dew’? That is a dif­fer­ent ques­tion, but one which might have been answered by Michael Latakos et al. – at least in a botan­ical con­text. In their intriguing study they demon­strate that dew – ‘con­densed water that forms on a solid sur­face’ – is gen­er­ated on the bark of under­storey trees in a low­land forest in French Guiana until early after­noon, because of the thermal prop­er­ties of the trunks. This extens­ive win­dow of hydra­tion – up to 0.69 mm of dew­fall a day – is instru­mental in pro­long­ing pho­to­syn­thesis, of epi­phytic crustose lichens in par­tic­u­lar. The team pro­pose that this phe­nomenon may be a more gen­eral fea­ture of forest hab­it­ats world­wide, and that this hitherto unre­cog­nised mech­an­ism of mid­day dew form­a­tion con­trib­utes to the water sup­ply of most cor­ti­col­ous (bark-dwelling) organ­isms. Nice work!

In addi­tion to the art­icle, I also recom­mend Michael Proctor’s thought­ful com­ment­ary thereon. Coincidentally, though, sim­ilar con­clu­sions about the import­ance of dew were reached by Khumbudzo Maphangwa et al., who examined an alto­gether drier envir­on­ment where ‘dif­fer­en­tial inter­cep­tion and evap­or­a­tion of fog, dew and water vapour and ele­mental accu­mu­la­tion by lichens explain their rel­at­ive abund­ance in a coastal desert’. Just as new hydro­botan­ical dis­cov­er­ies are made above ground, news of another, down below. Using neut­ron tomo­graphy, Ahmad Moradi and co-workers have quan­ti­fied and 3-D visu­al­ized the water con­tent in situ in the rhizo­spheres of chick­pea (Cicer ariet­inum), white lupin (Lupinus albus) and maize (Zea mays). Finding that – counter-intuitively – soil water con­tent increased towards the root sur­face for all three spe­cies, the team pro­pose that plants modify the hydraulic prop­er­ties of the rhizosphere’s soil in a way that improves water uptake under dry con­di­tions. This ‘reser­voir’ of water can be viewed as a reserve that helps the plants over­come short peri­ods of drought. Hydraulic lift (sorry, redis­tri­bu­tion – ; Rebecca Neumann and Zoe Cardon), any­one?

Nigel Chaffey. ORCID 0000-0002-4231-9082

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an educational, and entertaining way...) about plants and plant-people interactions.

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