%&LaTeX
\documentclass{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{textcomp}

\begin{document}

\begin{thebibliography}{1}

\bibitem{Sierra_etal2007} Sierra, J., Daudin, D., Domenach, A. M., Nygren, P., \& Desfontaines, L. (2007). Nitrogen transfer from a legume tree to the associated grass estimated by the isotopic signature of tree root exudates: A comparison of the N-15 leaf feeding and natural N-15 abundance methods. \textit{Eur. J. Agron.}, \textit{27}(2-4), 178--186.

\end{thebibliography}

\end{document}

