This week’s group meeting featured a special joint production with Molecular Physiology to welcome Prof Graham Farquhar from the Australian National University. Graham was in the UK to receive a Rank Prize Fund award for his contributions to food security by helping to guide the breeding of wheat varieties that use water more efficiently.
His talk, “Water user efficiency and water use effectiveness, a stomatal perspective using stable isotopes” was a far-reaching overview of his amazing research career, dating back to his time as a PhD student. But he started his talk with a very provocative and timely consideration of global changes in rainfall and human population growth.
Rainfall is inherently random. Sometimes there is too much, sometimes there is too little. Australia is a country that experiences both these extremes. For example, there are often heavy floods in the monsoon region while other areas, particularly where agriculture is concentrated in the southern part of the country, is drying up. The desire to expand cultivated land inevitably means there is more pressure on more marginal rainfall. An astounding statistic that Graham rolled off was that 1 ha of cultivated land was needed to feed 20 people. 20 people are added to the world’s population about every second! Clearly, that’s a problem.
Graham’s talk then focused on how plants can use the least amount of water for a fixed amount of carbon. He began by introducing his classic work on stomatal regulation of transpiration relative to carbon assimilation, which shows the two processes are fundamentally linked. Changing evaporation will always change assimilation. He then considered how plants could arrange the temporal expenditure of water to maximize assimilation of CO2. Carbon isotopes are particularly useful here for discriminating among transpiration efficiencies associated with different genotypes and can help identify future crop varieties that use water more efficiently. In dry conditions, greater transpiration efficiency improves crop yield and selects for low C isotope discrimination in leaf dry mater.
As we ran out of time, we were left with questions about how the process of balancing carbon and water demands might be influenced by life history strategy (perennial versus annual) and competition for water in soil.