Scientists have discovered that certain plants can survive stressful, dry conditions by controlling water loss through their leaves without relying on their usual mechanism: tiny pores known as ‘stomata’.
Non-stomatal control of transpiration in maize, sorghum and proso millet – all C4 crops critical to global food security – gives these plants an advantage in maintaining a favorable microclimate for photosynthesis in their leaves.
This allows the plants to absorb carbon dioxide as part of the photosynthesis and growth process, despite higher temperatures and increased atmospheric demand for water, without increasing water consumption.
Publish their findings in PNASResearchers from the University of Birmingham, the Australian National University, Canberra, and James Cook University, Cairns, are challenging the traditional understanding of plant transpiration and photosynthesis under stressful and dry growing conditions, namely that stomata only control leaf water loss.
Co-author Dr. Diego Márquez, from the University of Birmingham, commented: “This revolutionized our understanding of plant-water relationships by demonstrating that non-stomatal control of transpiration limits water loss without compromising carbon gain – a challenge for which is usually accepted as an inevitable trade-out.
“Our findings have significant implications for plant adaptation to climate change and for how crops can be grown in arid environments. Understanding this mechanism could open new avenues for improving water use efficiency in C4 crops , which are vital for global food security.”
The study confirms that C4 plants maintain lower relative humidity in the substomatal cavity, up to 80% under vapor pressure deficit (VPD) stress, reducing water loss and highlighting a crucial role of non-stomatal control in water use efficiency.
This mechanism helps plants maintain photosynthesis by reducing water loss without significantly reducing intercellular CO2 levels for photosynthesis. This is crucial for maintaining the growth and flowering of the crops.
The findings also suggest that non-stomatal control mechanisms may have evolved before the divergence of the C3 and C4 photosynthetic pathways, indicating a shared evolutionary feature.
“Our research reframes the understanding of water use efficiency in C4 plants and shows that this alternative mechanism helps plants continue to grow and sequester carbon dioxide even when atmospheric water demand is high, challenging traditional assumptions questions about how these plants survive droughts,” added Dr. Marquez.
Photosynthesis is the way plants use light and carbon dioxide to make sugars for growth, using an enzyme called Rubisco. Plants use the carbon dioxide that enters through open stomata to produce sugar, while open stomata also let water vapor out.
While C3 plants rely solely on CO2 diffusion through their stomata for carbon gain, C4 plants possess specialized leaf structures and enzymes that concentrate carbon dioxide around Rubisco, improving their photosynthetic performance and water use efficiency. However, this benefit comes with a trade-off, as these plants are vulnerable to significant reductions in photosynthesis when stomata close. Therefore, the non-stomatal mechanism is crucial in ensuring their success in controlling water loss while allowing stomata to remain open.
