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Litter mixing plays an important role in enhancing carbon and nutrient cycling, but little is known about the effects of nutrient-rich mistletoe litter on the decomposition of slow-decaying litter in nutrient-poor environments. We investigated the effects of mistletoe litter on the decomposition and nutrient release of host Vachellia karroo litter in semi-arid savanna, southwest Zimbabwe. Mass loss and nutrient release was quantified in litter of each single species, two-species, three-species and four-species mixtures of mistletoe, Erianthemum ngamicum, Plicosepalus kalachariensis and Viscum verrucosum, and the host V. karroo in 30 × 30 cm nylon-mesh litterbags under field conditions at 2-month intervals for one year. Repeated-measures analysis of variance was used to test the effects of litter type, incubation time and their interaction on mass loss and nutrient release. The effects of initial litter quality, incubation time and litter mixture on decomposition rate were also tested. Litter mixtures of mistletoes and V. karroo decomposed three times faster than V. karroo decomposing alone, and decomposition of litter mixtures was influenced by initial litter quality and incubation time. Further, non-additive effects are reported, with synergistic interactions being greater after 12 months and common regarding mass loss, phosphorus and carbon, whereas antagonistic interactions were common in nitrogen release. These effects varied both in magnitude and direction between litter-mixing treatments and with incubation time (P < 0.05). Our findings show that mistletoe litter enhance the decomposition of recalcitrant host litter consistent with findings in other ecosystems that contain hemiparasites, suggesting that hemiparasite litter plays an important role in carbon and nutrient flux in this system. Further, by enhancing the decomposition and nutrient release rate of recalcitrant host litter, mistletoes increase nutrient availability to other organisms within the ecosystem lending support to the premise that parasitic plants function as keystone species in environments where they occur.

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