The enemy within: the effects of mistletoe parasitism on infected and uninfected host branches

To comprehend how mistletoes affect their host functioning is a key matter in plant ecology. As yet, it is not clear whether the impact of mistletoes is confined to infected branches or the entire host is compromised as well. Here, we compared leaf functional traits between branches infected by mistletoes (infected), uninfected branches yet close to mistletoe attachment (neighbour), and branches of trees without any mistletoe (control). Our model species pairs were Phoradendron crassifolium infecting Eremanthus erythropappus tree and Psittacanthus robustus infecting Vochysia thyrsoidea tree. The study was carried out in the Brazilian savannah, Cerrado. We found that neighbour branches of E. erythropappus suffered a greater reduction in specific leaf area compared to infected branches. Control branches occupied an intermediary position between infected and neighbour branches. On the other hand, both infected and neighbouring branches of V. thyrsoidea suffered a reduction in carbon assimilation rate compared to control trees. As far as we know, our study is the first to describe the presence of mistletoe affecting the healthy branches neighbouring the mistletoe attachment. This finding sheds light on the need to consider both infected and neighbouring branches when evaluating the effects of parasitism on tropical trees. (AU)