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

ABSTRACT

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 leadwood Combretum imberbe and invasive river red gum Eucalyptus camaldulensis in 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. camaldulensis shed significantly more leachate than the native C. 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.

KEYWORDS:

• biological invasions
• cross-ecosystem connectivity
• detritivore decomposition
• leaf litter decomposition
• microbial decomposition
• riparian zones

Acknowledgements

We thank the Botswana International University of Science and Technology (BIUST) for providing infrastructure and funding to SS and RJW. RC acknowledges funding from the Alexander von Humboldt Foundation. TD acknowledges funding from University of Venda. Gratitude is extended to the Department of Meteorological Services of Botswana for rainfall data, and to Murphy Tladi for assistance in laboratory and field. The Ministry of Environment, Natural Resources Conservation and Tourism (Botswana) is thanked for the issuing of a research permit (ENT 8/36/4XXXXII [14]).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Alexander von Humboldt-Stiftung [grant number N/A]; Botswana International University of Science and Technology [grant number DVC/2/1/13 XI]; University of Venda [grant number SES/18/ERM/10].