Imbalance of water potential and photosynthetic efficiency in the parasitic relationship between Struthanthus flexicaulis and Baccharis dracunculifolia

Hemiparasitic plants can reduce photosynthesis and alter the host plant’s foliar traits. This relationship may be more intense in ecosystems with nutritionally poor soil, such as the campo rupestre, known for its high endemism. This work evaluated the impact of a generalist hemiparasitic species (Struthanthus flexicaulis) on the physiology as well as physical and chemical traits of a native species (Baccharis dracunculifolia) frequently found in the campo rupestre. We planted twenty 60-day-old B. dracunculifolia individuals in a campo rupestre area. Two year after planting, during the 2019 dry season, we evaluated the water potential (Ψw), photosynthetic efficiency (PE), specific leaf area (SLA) and succulence (SU) of parasitized and non-parasitized host plants. These parameters were measured again in the dry season of 2020, when we also measured chlorophyll, nitrogen balance index (NBI) and phenolic content of leaves of the same individuals. Parasitized individuals had a higher Ψw and PE compared to non-parasitized individuals during the most critical period of the day (12:00 pm to 3:00 pm). However, towards the end of the day, parasitized individuals had lower Ψw and PE than non-parasitized ones. There was no effect of parasitism on SLA and SU. Parasitized plants had higher NBI and lower phenolic content than non-parasitized plants. We concluded that S. flexicaulis parasitism interfered in the physiology and chemical leaf traits of B. dracunculifolia. Parasitism, while momentarily increasing the PE and Ψw of parasitized individuals, can cause physiological imbalances, which could negatively affect the development and lead to the death of the host plant over time.