Hydrobiologia, 2025 (SCI-Expanded)
While numerous studies have investigated the effects of climate-induced increase of allochthonous matter (AM), the differential impacts of multiple AM sources on plankton dynamics are poorly understood. Here, we investigated the effects of two different sources of AM on zooplankton biomass, composition, taxonomic and functional indices (richness and evenness) and functional stability in a six-week outdoor mesocosm experiment. The treatments included a single pulse of alder tree leaf leachate (L, the nutrient effect), HuminFeed® (HF, the brownification effect) and the two combined (HFL) relative to control (no AM addition). HF did not give enough brownification to change zooplankton biomass. L and HFL enhanced zooplankton and Daphnia biomass. The biomass increase was more pronounced in HFL than L. The taxonomic richness and functional evenness were higher in HFL, no significant change for HF and L. The zooplankton functional stability, measured as biomass, in HF was resistant to disturbance. The communities in L and HFL showed low resistance, and only HFL community recovered. Our results highlight the stronger effect of the higher quality of L (i.e. nutrient content) and suggest that its combination with HF may have had synergistic effects, emphasising the importance of considering AM source quality in studies on planktonic communities.