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Juniperus flaccida Schltdl. is a very important forest species which is severely affected by Phoradendron juniperinum Engelm. at El Cardonal, Hidalgo, Mexico. The objective of this research was to evaluate the response, in terms of tree twig biomass and nutrient status of both the tree and its parasitic species, to fertilization with nitrogen (N), phosphorus (P), and potassium (K), in a natural forest of J. flaccida. The fertilizer rates and sources were 0, 1000; 0, 300 and 0, 450, 900 g tree'1 of urea, phosphoric acid and potassium sulphate, respectively. The experimental design was a completely randomized factorial (2X2X3) with six replicates, Soil analysis showed low levels of N and P, and adequate levels of K in the site. Nitrogen or phosphorus alone did not significantly affect twig biomass, despite of being deficient nutrients in the study site. J. flaccida displayed higher concentrations of N, Mg, Cu, Mn, and B than P. juniperinum and the latter, showed higher concentrations of P, K, Ca, Fe, and Zn than its host species. Application of nitrogen significantly decreased the concentration of K in P. juniperinum and influenced the partition of foliar P between J. flaccida and P. juniperinum, in favor of the host tree and to the detriment of the parasitic species. Application of K increased foliar N in J. flaccida. Vector analysis showed that the combination of phosphorus with the highest dose of potassium led to an increase in twig biomass of J. flaccida. [ABSTRACT FROM AUTHOR]