The mushroom Amanita thiersii dots American lawns from Texas to Illinois, a small white button on the grass’s emerald expanse. Unlike similar mushrooms, A. thiersii does not live in a symbiotic relationship with nearby trees; instead, it gets its energy by feasting on the corpses of its neighbors—that is, dead grasses. That predilection means that the mushroom is uniquely suited to report on what those grasses were like before they perished, according to a new paper in Journal of Geophysical Research: Biogeosciences. In fact, an analysis of 40-odd A. thiersii samples taken from lawns across the Midwest over 27 years suggests that the mushrooms, as a result of the grasses they eat, may be able reflect the changing climate of the last few decades in their chemistry.
The reason it might be possible to trace climate change in grass at all is because plants can be distinguished by the different ways they handle photosynthesis. The new paper looks at two methods of photosynthesis in particular: C3 and C4, named after the structure of the molecules the methods produce. The majority of plant species perform C3, which produces energy at higher concentrations of CO2 and at lower temperatures. C4 plants, meanwhile—most of which evolved in hotter and drier climates—are more efficient in higher temperatures, but too much CO2 is hard for them to deal with.