Mesquite trees, the research team discovered, benefit not only from a changing landscape, but also from a climate shifting toward higher temperatures and greater variability in rainfall.
This was surprising, given that, evolutionarily speaking, grasses are better adapted to hot and dry conditions because they use a modified biochemical pathway for photosynthesis, the process by which plants take in carbon dioxide from the atmosphere and convert it into sugars.
"Plants have to open pores in their leaves to breathe in carbon dioxide, and while their pores are open, water diffuses out," Barron-Gafford explained. "Compared to grasses, mesquite trees have to keep their pores open longer for the same amount of sugars they make, meaning they lose more water in the process."
But mesquites overcome their physiological disadvantage with roots that reach down to 160 feet or more; they can tap into groundwater not accessible to plants with shallow root systems.
"Mesquites waste more water, but they can access it much better," Barron-Gafford said. "Their roots are always out there and they find it, allowing them to bypass the grasses' evolutionary advantage. These deep-rooting shrubs and trees are accessing deeper water that was previously unavailable to drive plant biology in this area."
"It levels the playing field," he said. "In the pre-monsoon season in April and May, when the land is very dry and grasses are browning, the mesquites are leafing out. You could say they have their toes dangling in the groundwater pool. In an athletic analogy, it's like some sprinters are already running, while the competition is still getting their shoes on. "
"All of the benefits we associate with these shrubs, such as potentially greater carbon capture from our atmosphere, increased shade, attraction of wild life
|Contact: Daniel Stolte|
University of Arizona