Figure 2. Fitted Michaelis-Menten curves of incorporation of ¹⁵N-labelled ammonium (circles), glycine (triangles) or nitrate (squares) by excised roots from plants grown in fertilized (solid symbols) or unfertilized (hollow symbols) soils.

Roots were incubated in an equimolar solution of the three N sources with one N source ¹⁵N-labelled and two N sources unlabeled. Data represents averages ¹⁵N incorporation for each N source across eight replicate plants at four time points. Error bars are standard error of the mean. Estimated V_max values for each curve are inset.