Does invasive river red gum (Eucalyptus camaldulensis) alter leaf litter decomposition dynamics in arid zone temporary rivers?

Riparian zones are important for the maintenance of aquatic ecosystem functional integrity, yet are considered to be particularly vulnerable to plant invasions. The role of terrestrial riparian plant invasions in compromising aquatic ecosystem processes is, however, still poorly understood. This issue is particularly relevant for temporary rivers, which are understudied compared to permanent river systems, despite their ubiquity and largescale contributions to biogeochemical processes. Here we experimentally assessed leaf litter breakdown dynamics in situ in a temporary river in arid southeastern Botswana, Southern Africa. We contrasted aquatic leaching and microbial and invertebrate litter breakdown contributions to the native leadwoodCombretum imberbeand invasive river red gumEucalyptus camaldulensisin the Lotsane River. Fine-mesh (detritivore exclusion) and coarse-mesh (detritivore inclusion) bags were separately filled with leaf litter from each species and deployed in the river during a hydroperiod (wet phase), with decomposition measured over a 6-week period.E. camaldulensisshed significantly more leachate than the nativeC. imberbe.Significantly more microbial and detritivore breakdown was, however, observed in native than in invasive leaf litter. Overall, invertebrates contributed little to biological leaf litter breakdown processes compared to microbial breakdown contributions. Although significantly higher in native leaves, low invertebrate numbers were found in leaf litter in the study. This study highlights the role of microbial contributions to detrital decay in temporary arid zone rivers, whereas invertebrate contributions were relatively minor. The study further contributes to our understanding of how invasive riparian plant species alter aquatic detrital pool dynamics in invaded temporary wetland ecosystems.

Automated summary

This study assessed the dynamics of leaf litter breakdown in a temporary river in arid southeastern Botswana and found that invasive riparian plant species have significant impacts on aquatic ecosystem processes. Microbial contributions to leaf litter breakdown were higher than invertebrate contributions, highlighting the role of microbes in detrital decay in temporary arid zone rivers. The study contributes to our understanding of how invasive species alter detrital pool dynamics in temporary wetland ecosystems.