Nitrogen-15 tracing

Nitrogen-15 tracing, also known as 15N tracing or the δ15N method, is a technique used to follow how nitrogen enters an ecosystem or organism. There are two common isotopes of nitrogen: 14N (also called Nitrogen-14), which makes up 99.6% of naturally occurring nitrogen, and the heavier 15N (Nitrogen-15), which makes up the rest. Since 15N is so much more rare in nature, scientists can introduce 15N into an ecosystem in order to follow how nitrogen is absorbed by organisms. For example, if a fertilizer containing a very high amount of 15N is used to grow a plant, then a high level of 15N in that plant most likely means that it absorbed nitrogen from the fertilizer.

 Overview 
To measure whether an ecosystem or organism contains a high level of the rare 15N (Nitrogen-15), scientists need to establish a normal level of 15N. Often, this is the amount of 15N found in the atmosphere, or how much is commonly found in whatever organism is being studied. Scientists measure δ15N, which is similar to how much more 15N is measured than is normal. If scientists introduce 15N to an ecosystem, a high δ15N in an organism probably means that the organism absorbed this introduced 15N.

 Applications 
Nitrogen is necessary to life, so nitrogen flows through an ecosystem in a process called the nitrogen cycle. Scientists can follow this flow of nitrogen in an ecosystem or follow how nitrogen moves in a single organism with 15N tracing. For example, if insects containing a high amount of 15N come into contact with a plant, scientists can measure whether the plant absorbed nutrients from those insects by measuring δ15N in the plant, or how much the plant's 15N is higher than normal. In 2020, scientists used this method to test whether Triantha occidentalis is a carnivorous plant, meaning it absorbs nutrients from organisms it traps. They tested whether T. occidentalis is carnivorous by answering the question, "does T. occidentalis absorb nitrogen from insects it traps?" Scientists taped flies containing large amounts of 15N to three plants: Erigeron peregrinus, a control plant which is not carnivorous, Drosera rotundifolia, a plant which is known to be carnivorous, and T. occidentalis. After two weeks, they measured the δ15N in each. The δ15N of E. peregrinus was about 0, meaning it absorbed no nitrogen from the flies, but the δ15N of D. rotundifolia and T. occidentalis were very high, meaning they both absorbed nitrogen from the flies. By tracing Nitrogen-15, the scientists had verified that T. occidentalis absorbed nitrogen from flies, meaning that they discovered a new carnivorous plant.

References

Category:Nitrogen
Category:Ecology