What is Nitrogen-15 tracing?
'''Nitrogen-15 tracing''', also known as '''<sup>15</sup>N tracing''' or the '''δ<sup>15</sup>N method''', is a technique used to follow how [[nitrogen]] enters an [[ecosystem]] or [[organism]]. There are two common [[isotope]]s of nitrogen: <sup>14</sup>N (also called Nitrogen-14), which makes up 99.6% of naturally occurring nitrogen, and the heavier <sup>15</sup>N (Nitrogen-15), which makes up the rest.<ref>{{cite book |page= 44 |title= Chalcogen-nitrogen Chemistry: From Fundamentals To Applications In Biological, Physical And Materials Sciences |last1= Chivers, |first1= T. |last2= Laitinen |first2= R.S. |isbn= 9789811241352 |url= https://books.google.com/books?id=iNlMEAAAQBAJ |year= 2021 |publisher= World Scientific Publishing Company}}</ref> Since <sup>15</sup>N is so much more rare in nature, scientists can introduce <sup>15</sup>N into an ecosystem in order to follow how nitrogen is absorbed by organisms. For example, if a [[fertilizer]] containing a very high amount of <sup>15</sup>N is used to grow a plant, then a high level of <sup>15</sup>N in that plant most likely means that it absorbed nitrogen from the fertilizer. == Overview == [[File:Δ15N diagram.svg|thumb|δ<sup>15</sup>N is related to how much more <sup>15</sup>N something contains than is normal]] To measure whether an ecosystem or organism contains a high level of the rare <sup>15</sup>N (Nitrogen-15), scientists need to establish a normal level of <sup>15</sup>N. Often, this is the amount of <sup>15</sup>N found in the [[atmosphere]], or how much is commonly found in whatever organism is being studied. Scientists measure δ<sup>15</sup>N, which is similar to how much more <sup>15</sup>N is measured than is normal. If scientists introduce <sup>15</sup>N to an ecosystem, a high δ<sup>15</sup>N in an organism probably means that the organism absorbed this introduced <sup>15</sup>N. == Applications == Nitrogen is necessary to life, so nitrogen flows through an ecosystem in a process called the [[nitrogen cycle]]. Scientists can follow this flow o