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.

抽象的

河岸带对维持水生生态系统功能的完整性很重要，但被认为特别容易受到植物入侵的影响。然而，对陆地河岸植物入侵在损害水生生态系统过程中的作用仍知之甚少。这个问题对于临时河流尤为重要，尽管它们对生物地球化学过程无处不在且有广泛的贡献，但与永久河流系统相比，这些河流的研究还比较少。在这里，我们通过实验评估了南部非洲博茨瓦纳东南干旱的一条临时河流中的凋落物分解动力学。我们比较了水浸，微生物和无脊椎动物凋落物分解对原生铅木Combretum imberbe和入侵河红树胶的贡献。桉树camaldulensis在洛萨讷河。细网眼（有害杂物排除）和粗网眼（有害杂物包含）袋子分别装满了每种物种的凋落物，并在水期（湿相）期间分布在河中，并在6周的时间内进行了分解。E. camaldulensis的沥出液比本地的C. imberbe明显多。然而，在自然环境中比在侵害性凋落物中观察到明显更多的微生物和有害微生物分解。总体而言，与微生物分解贡献相比，无脊椎动物对生物凋落物分解过程的贡献很小。尽管在天然叶子中的无脊椎动物数量明显较高，但在该研究中发现其凋落物的无脊椎动物数量较低。这项研究强调了微生物对临时干旱区河流碎屑侵蚀的作用，而无脊椎动物的贡献相对较小。该研究进一步有助于我们了解侵入性河岸植物物种如何改变被入侵的临时湿地生态系统中的水生碎屑池动态。