UV-treatment of the digestive fluid of Nepenthes hemsleyana pitcher plants affects their digestive process, possibly via reducing microbial inquilines

Interactions with microbes are ubiquitous, and many of them are essential
for the survival and success of plants. In Nepenthes pitcher plants, they
occur as part of a diverse community of organisms, so-called inquilines,
that live inside the digestive fluid of the pitcher traps. However,
evidence is ambiguous regarding the role of microbial inquilines: they may
complement the plants’ prey digestion, fix atmospheric N, act as
competitors that reduce plant-available nutrients, or affect the plants in
other ways unrelated to the breakdown of prey. In a field experiment on
Borneo, we investigated the effect of a UV-disinfection of the digestive
fluid on prey digestion of N. hemsleyana that captures and
digests insects as well as bat faeces in its pitchers. We show that in the
short term photosynthetic performance of plants with UV-treated digestive
fluids decreases compared to untreated plants, likely due to lower
abundances of microbial inquilines. However, at the end of two months,
responses of pitcher plants with UV-treated and untreated digestive fluids
tend to equalise. Nutrient source, whether from insects or bat faeces,
does not influence prey digestion. We expect our findings to be a starting
point for unveiling the ecological role of microbial inquilines in pitcher
plants and how they interact with other inquiline groups of higher trophic
levels. Ultimately, this will also help to improve understanding of the
functioning and evolution of convergent interactions in other carnivorous
plants.