Plane and Fancy TH P Physiology? to Answer These Questions, Lange Et Al

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are watered by occasional showers or storms Daedalus rather than by fog and dew — do their crusts ICTURES have a different species composition and Plane and fancy TH P physiology? To answer these questions, Lange et al. have done their latest work1 in The synthesis of nylon is a well-known

ANET EAR southern Utah. demonstration. One component is One evident taxonomic feature of the dissolved in water, and a second one in an Utah desert is that, although there are many immiscible solvent. On mixing the two, a OMBER/PL lichens with green algae as their symbionts nylon film forms at the liquid interface, R. CO (as in the Negev and Namib deserts), the renewed as fast as it is pulled from the 8 most abundant crustal constituent is a gelati- mixture. nous lichen, Collema tenax, with a cyano- In principle, the interfacial film should bacterial symbiont. This lichen requires a be a perfect monolayer separating the two greater water supply (equivalent to over 1 reagents. Sadly, nylon with its chain- mm of precipitation) than do the green-algal molecules is very permeable. The reagents lichens to attain its maximum photosyn- can still get at each other; they react further Figure 1 Early morning in the Namib — the thetic rate. But, it then shows the highest to thicken the film. A polymer which cross- optimal time for crustal photosynthesis. photosynthetic capacity of any arid-zone soil linked into a true sheet molecule would be lichen yet studied. Moreover, C. tenax can a far better barrier. So Daedalus is devising superficial layers, derived from dew, fog and maintain photosynthetic activity over a wide two-solution syntheses of dense, cross- showers. The ecological value of the layer in range of temperatures, from near freezing to linked, water-repellent polymers with protecting the soils from wind erosion and as over 40 °C, with an optimum around 30 °C. It fluorocarbon or organometallic an absorptive organ for water is generally also requires a high light intensity for maxi- side-chains, excellent barriers to their appreciated, as is its role in providing germi- mal photosynthesis, and it has a high light- precursor reagents. At the solution nation sites for the seeds of flowering plants2. compensation point (the minimum light interface a true monolayer film will form, The presence of free-living, nitrogen- intensity at which it can break even in terms regenerated as fast as it can be hauled out of fixing cyanobacteria in the upper layer, of carbon balance). All of these are features the bath. together with lichens that contain cyano- that plant physiologists would associate with Monolayer film will be quite invisible. bacterial symbionts, suggests a pathway by a ‘sun plant’. Furthermore, being essentially all surface, which atmospheric nitrogen enters the Collema tenax has a distinctive physiolo- its two faces will absorb almost its own desert ecosystem. Moreover, the extensive gy that equips it well for the water regime weight of air. Unless it is chemically non- cover of even a thin layer of photosynthetic in Utah, where erratic showers bring larger inflammable, it will be highly explosive. So organisms is an important source of carbon quantities of rain at any given time than are it will be quite tricky to handle. On the fixation in an environment where primary experienced in the ‘fog’ deserts. The gelati- other hand, it will be immensely strong for production is low. In their studies of the nous nature of its thallus means that C. tenax its weight, the highest of high-tensile films. Namib Desert of southern Africa (Fig. 1), serves as a reservoir, maintaining its hydrat- It will also be the ultimate electrical Lange and colleagues have shown3 that the ed state long enough to provide for extended capacitor, holding a vast charge-density chlorophyll density of the microbial mat is photosynthesis even in the hot conditions, per unit weight. Monolayer film will make around 200–500 mg m–2 — of the same order when the light is high, in the middle of the amazing new electrometers, electrostatic as in the leaf of a higher plant. So the crust desert day. Lichens with cyanobacterial sym- speakers, balloon fabrics, and so on. has considerable photosynthetic potential, bionts are already known to need more water A wider range of products could be although this is limited by the need for to set photosynthesis in motion than lichens made by bringing many monolayers hydration before it can be exploited. with algal symbionts. So, perhaps the together into a loosely bonded multilayer. In the Negev Desert of Israel, Lange and features described for C. tenax will be of The resulting macroscopic film would be his team showed4 that they could induce wide taxonomic, physiological and biogeo- immensely tough. A crack could not maximal photosynthesis from the crust by graphical significance. propagate easily from layer to layer, so the moistening it with the equivalent of just Recognizing that such niche differentia- film should sum the tenacity of its 0.2–0.3 mm of precipitation. These photo- tion exists among the primary producers in individual monolayers. Even better, synthetic rates were around 20% of those desert crusts is an important step towards Daedalus plans to make multilayers of two achieved by local desert shrubs, such as Zygo- appreciating the complexity of crustal or more types of film, interleaved into a phyllum dumosum, illustrating the ability of micro-ecology. Because these soil features multiple laminate structure. If one of the the crust to act as a carbon sink. In the Negev, are so important in the water relations and layers were organometallic, the resulting as in the Namib, moisture mainly comes in nutrient cycling of desert soils, and because bulk ‘superlattice’ structure might give a the form of condensation — as dew and fog we know that they are sensitive to distur- transparent magnet, a high-temperature during the cold night. So, although these bance by the trampling pressures of humans, superconductor, an interference filter, a moisture levels are often achieved, the rising domestic animals and motor vehicles, specular X-ray mirror, a large-scale sun soon desiccates the productive crust into further understanding of crustal ecology quantum-tunnelling device or some other a dormant state, and crustal photosynthesis should soon provide a basis for conservation supermolecular marvel. is limited to an early-morning window when of desert crusts. A simpler sandwich structure could moisture and light briefly coincide. Peter D. Moore is in the Division of Life Sciences, have just three films: a central crumpled Now that general taxonomic surveys of King’s College, Campden Hill Road, London one bonded to two flat monolayer faces. It crust communities and their physiological W8 7AH, UK. would be a wonderful heat insulator. Being properties have been carried out, questions 1. Lange, O. L., Belnap, J. & Reichenberger, H. Funct. Ecol. 12, transparent, indeed invisible, it could not of geographical and ecological variations are 195–202 (1998). radiate. Applications to Emperors’ new 2. West, N. E. Adv. Ecol. Res. 20, 179–223 (1990). being tackled. For example, not all deserts 3. Lange, O. L., Meyer, A., Zellner, H. & Heber, U. Funct. Ecol. 8, winter clothing should follow. depend on condensation. The inter- 253–264 (1994). David Jones montane deserts of the western United States 4. Lange, O. L. et al. Funct. Ecol. 6, 519–527 (1992).