As botanists – whether established, or ‘working-towards’ – we all recognise the importance of cellulose (an organic compound with the formula (C6H10O5)n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units) to the construction of plant cell walls. We probably also remember that it is very hard to digest, which is why such wood-eating organisms as termites need cellulose-digesting microbes in their guts to cope with it, and why we thank our lucky stars that God invented fungi so they could decompose woody plant debris and keep the cycle of life turning. But what we probably didn’t know – nor even suspect – was the role that cellulose (one of the planet’s most abundant carbon-based polymers) may have in a global, atmospheric/climate context. Well, thanks to a study by Naruki Hiranuma et al., we do now. Recognising the ubiquity of this plant cell wall polymer in the atmosphere, and the fact that some biological materials can act as ice-nucleation sites, the team investigated the role that cellulose might have in cloud formation. Although their studies were conducted on terra firma – albeit in ‘cloud simulation chambers’ – they found that cellulose-based ice nucleation becomes significant below about –21 °C, temperatures that are relevant to so-called mixed-phase clouds (which consist of supercooled cloud droplets and ice crystals). Since ice formation in such clouds can trigger the formation of precipitation (e.g. snow, hail, rain…), this discovery is important to both the hydrologic cycle (or ‘water cycle’) and to the radiative properties of clouds, with consequent global warming significance. It’s somewhat comforting to think that the influence of ground-based plants extends far beyond their terrestrial anchorage, and underlines (yet again…) the importance of plants – and their study, i.e. botany – to the planet.
[In the interests of balance, Mr P. Cuttings would like to add that cellulose is also an important polymer in the outer tunic of the marine invertebrate animals known as tunicates. But he doubts they have any role in cloud-formation… – Ed.]