How Bornean figs use sophisticated optical systems to harvest solar power efficiently.
Cystoliths are tiny optical constructions (less then a tenth of a millimeter wide) distributed in the surface layers of the leaves of many Bornean figs.
Worldwide Cystoliths are commonly found in the leaves of many plant families including the Acanthacea, Urticaceae and Moraceae (Ficus and Artocarpus).
For example the leaves of the Common nettle Urtica dioeca (Urticaceae) of Europe contain cystoliths.
The evolutionary function of cystoliths is to increase the light gathering surface of the green chlorophyll cells near the surface of the leaf to enhance the rate of photosynthesis.
Most Bornean ficus species in Section Conosycea (stranglers) have cystoliths on both the upper and under layers of the leaf. This ensures a highly efficient harvesting of light both from direct sunlight above and from reflected light below the leaf.
The illustration above adapted from Pg.19, Berg and Corner (2005) shows a section through the upper surface of a leaf of Ficus elastica.
A rod of silica (similar to a fiber optic cable) leads from the sunlit upper surface of the leaf down to a light scattering transparent conglomerate of calcite (calcium carbonate Ca CO3 ) which is surrounded by plant cells containing chlorophyll. The chlorophyll via photosynthesis converts atmospheric carbon dioxide into sugars (food) for the plant with a waste product of oxygen.
For an excellent overview of bio-mineralization of in fig leaves see Pierantoni et al (2018) Mineral Deposits in Ficus Leaves Morphologies and Function
Three ficus species in Africa are recently reported to be able to sequester and store calcium compounds apparently both to deter herbivores and enhance the the productivity of the local acid soils by reducing the PH in Samburu, Kenya. Mike Rowley’s research on wild Kenyan fig trees shows they can turn atmospheric carbon dioxide CO2 into calcium carbonate CaCO3. This happens when microorganisms in the soil and within the wood transform calcium oxalate, a compound the trees produce, into the mineral form, effectively sequestering the carbon long after the tree dies. This discovery has potential implications for climate change mitigation throughout the world distribution of figs.
