Photosynthesis and Microbes

Sunlight, Carbon Dioxide, and Microbes Clean Our Air and Produce Food

We learn in school that plants carry out photosynthesis. Plants convert carbon dioxide (CO2), water, and sunlight (energy) into sugar, oxygen (O2), and water (H2O). The following is the formula:

Light + 6CO₂ + 12H₂O -> C6H₁₂O6 + 6O₂ + 6H₂O

The process occurs in the leaves of plants. The leaves act like solar panels. The light that hits the leaves is absorbed into the chlorophyll. Carbon dioxide is taken in during the day through microscopic openings in the leaves, known as stomata, and oxygen is released throughout the night. Water is pulled up from the roots into the leaves, and sugars are pulled down from the leaves into the roots. In the rhizosphere—the region immediately around the roots—bacteria feed on the sugars to run their metabolism, in which they use the energy to form their cell walls that contain nutrients for the plants. (See The Rhizophagy Cycle.)

Numerous factors, particularly for those that live close to plants, can affect how bacteria perform photosynthesis. They include quorum sensing, chelation, and microbial metabolites (covered in Chapter 6). Let's take a broad look at this:

Rhizosphere microbes, bacteria, and fungi that reside close to plant roots can improve the nutritional intake of nitrogen, phosphate, iron, and other elements necessary for photosynthetic processes, enhancing photosynthesis.

Endophytic microbes: Fungi and bacteria that live inside plant tissues can change photosynthesis directly or indirectly by making plants more resistant to stress, killing pathogens, and making phytohormones. Certain fungi from the genus Trichoderma live on the roots of crop plants and cause genes and pigments to be turned on that help the plants make more food through photosynthesis. Higher rates of photosynthesis will draw more CO₂ from the atmosphere, and stronger plant roots will allow for the transfer of more sequestered carbon to the roots and subsequent soil storage. (Harman et al., 2021).

Plants can receive nutrients like phosphate and water through mycorrhizal or fungal networks attached to their roots, which enhances the plants' capacity for photosynthetic processes. However, a close look at physiological gene expression and gas-exchange measurements showed that mycorrhizal tomato plants sped up photosynthesis and moved carbon from shoots to roots, even though they did not add any nutrition. In the same way, phosphate levels did not affect at least half of the changes in leaf metabolism and better carbon uptake in mycorrhizal Plantago major. (Gavito et al., 2019)

Biofertilizers: Microbial inoculants introduced to soils can enhance photosynthetic efficiency and plant development through phosphorus solubilization or nitrogen fixation.

Detoxification: Microorganisms may mitigate the harmful effects of toxins and heavy metals on plant photosynthesis by degrading, storing, or altering their chemical structure.

Quorum sensing: Some bacteria attached to plants release compounds that prompt plants to shut their stomata to maximize photosynthesis and water uptake.

Apart from plants, algae and certain microorganisms can also carry out photosynthesis, transforming light and carbon dioxide into sugar and oxygen. Together, cyanobacteria and purple non-sulfur bacteria are called photosynthetic bacteria because they can fix carbon dioxide, release oxygen, and use sunlight as a source of energy. In a symbiotic relationship, plants and cyanobacteria allow the former to fix nitrogen and the latter to obtain additional nutrients for photosynthetic processes. Two examples are cyanobacteria associated with hornwort and cycads. Later in this series, we shall go into more detail on cyanobacteria. 

In summary, diverse microbial communities work with plants to provide essential nutrients, hormones, and signals, enabling plants to conduct photosynthesis and stimulate growth efficiently.

References:

Gavito, M. E., Jakobsen, I., Mikkelsen, T. N., & Mora, F. (2019). Direct evidence for modulation of photosynthesis by an arbuscular mycorrhiza-induced carbon sink strength. New Phytologist, 223(2), 896-907. https://doi.org/10.1111/nph.15806

Harman, G. E., Doni, F., Khadka, R. B., & Uphoff, N. (2021). Endophytic strains of Trichoderma increase plants’ photosynthetic capability. Journal of Applied Microbiology, 130(2), 529-546. https://doi.org/10.1111/jam.14368