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Cruz, C., Lips, S. and Martins-Loucao, M.  1997.  Changes in the Morphology of Roots and Leaves of Carob Seedlings Induced by Nitrogen Source and Atmospheric Carbon Dioxide.  Annals of Botany 80: 817-823.

Cruz, C., Lips, H. and Martins-Loucao, M.A.  2003.  Nitrogen use efficiency by a slow-growing species as affected by CO2 levels, root temperature, N source and availability.  Journal of Plant Physiology 160: 1421-1428.