Where can we find water? The most obvious sources are bulk water (e.g. rivers, lakes, tap and bottled water), foods (e.g. fruits and vegetables), but then there are more obscure sources. Many minerals, such as gypsum, can hold water in their chemical structure. But can living organisms extract this water?
Palacio et al. (Palacio et al., 2014, Nat. Comm. 5:4660) set out to determine whether a plant that grows in and around gypsum can use water contained in the mineral. Helianthemum squamatum is a plant with shallow roots that remains active even during drought. How do you determine if a plant is using water from the soil or from gypsum? Well gypsum water has a different composition of hydrogen and oxygen isotope. An isotope is a different form of an atomic element – all atoms are made up of protons, neutrons and electrons. Elements differ based on the number of protons – hydrogen for example has 1 proton, while carbon has 6 protons – while isotopes vary in the number of neutrons. Special machines can determine which isotopes of different elements are present in things such as water.
Palacio et al. looked at the isotopes of hydrogen and oxygen present in soil water, gypsum water, and water contained in the plant tissue. They found that the plants used gypsum and soil water in about equal proportions during the relatively wet spring, however during the dry summer, the isotope composition of the water was extremely close to that found in gypsum. This tells us that H. squamatum can ‘drink’ water from gypsum so-to-speak. Furthermore, the authors speculate that the dehydrated gypsum could be rehydrated simply by moisture in the air, which means that water could be available for the plant even through long droughts.
What are the implications? Exobiology: Mars contains gypsum on its surface, which means that some plants may be able to survive Martian soils (but maybe not the atmosphere). Furthermore, our search for habitable planets outside our solar system might miss some candidates that might lack bulk water, but are covered in water-containing minerals such as gypsum. More down-to-Earth implications include understanding how life can survive very dry habitats and how we might be able to reclaim such land according to Palacio et al.
Stay safe and stay informed,