Grasses get their carbon from the air, transforming it into carbohydrates via photosynthesis. But grasses need other elements too, including nitrogen. Unfortunately, the nitrogen in the air is in a form that is too tightly bonded to be harvested directly, and so grasses get this element from nitrogen compounds that are the by-products of decomposition in the soil, or via nitrogen fixing bacteria (such as those in legumes). But what happens if you live in nitrogen poor soils?
Carnivorous plants are not the norm in plants, and have mostly been restricted to species that live in nitrogen poor environments and cannot get their N requirements the old fashioned (and less energy intensive) way, by absorption of N compounds through the soil or N-fixing bacteria. Instead, such plants kill and eat animals to get this essential element from their victims.
The fascination with such carnivorous plants as Nepenthes and Dionaea made me wonder whether some grasses have made the leap to carnivory, at least to supplement their normal nitrogen intake.
Incredibly enough, there is some evidence that some grasses have made the leap to utilizing N from animal sources, albeit indirectly, through partnerships with endophytic fungi. The way they do this is simple and quite interesting, and involves fungi that kill insects in the soil. Such fungi bore thorough the insect cuticle, proliferate within, and ultimately kill it.
|Roach killed by Metarhizium fungi. By Chengshu Wang and Yuxian Xia - PLoS Genetics, January 2011|
Sasan RK, Bidochka MJ. The insect-pathogenic fungus Metarhizium robertsii (Clavicipitaceae) is also an endophyte that stimulates plant root development. Am J Bot. 2012 Jan;99(1):101-7. doi: 10.3732/ajb.1100136. Epub 2011 Dec 14.