Colonization by foliar endophytic fungi can affect the expression of host plant defenses and other ecologically important traits. However, whether endophyte colonization affects the uptake or redistribution of resources within and among host plant tissues remains unstudied. We inoculated leaves of Theobroma cacao with four common colonizers that range in their effect from protective to pathogenic (Colletotrichum tropicale, Pestalotiopsis sp., C. theobromicola, or Phytophthora palmivora, respectively). We pulsed the soil with 15N and then traced 15N uptake and its subsequent distribution to whole plants and individual leaves. At a whole-plant level, C. tropicale-inoculated plants showed significantly greater 15N uptake compared to endophyte-free plants in the same pot. Among leaves within plants, younger leaves were particularly enriched in 15N, but endophyte inoculation at the individual leaf level did not alter 15N distribution within plants. However, leaves co-inoculated with pathogenic Phytophthora and protective C. tropicale experienced significantly elevated 15N content as pathogen damage increased, compared to leaves inoculated only with the pathogen. Further, endophyte-pathogen co-infection also increased total plant biomass. Our results indicate that colonization by foliar endophytes significantly affects nitrogen uptake and distribution among and within host plants in ways that appear to be context-dependent on other microbiome components. This article is protected by copyright. All rights reserved.
