The decomposition of dead organic matter is a key process for the metabolism and functioning of lotic ecosystems. Particulate organic matter from fallen leaves is the main source of energy input also in forested springs. However, detritus processing in spring habitats has been rarely investigated. The present paper is aimed to assess, for the first time, the influence of detritus origin on leaf litter breakdown in a hydrologically, thermally and chemically stable cold spring and to evaluate the relative contribution of microorganisms and invertebrate detritivores to the decomposition process. For this purpose, we used leaves of the native black poplar (Populus nigra) and the invasive common reed (Phragmites australis) enclosed in leaf-bags of different mesh sizes. We demonstrated that leaf detritus of native black poplar decomposed twofold faster than the invasive common reed. We also found that the percentage of dry mass loss was significantly higher in medium/coarse litter bags compared to fine ones. However, microorganisms alone in fine mesh bags were able to decompose about 80% (poplar) and 60% (common reed) of the initial dry mass. No substantial differences were detected in structure, composition and functional organization of assemblages colonizing poplar and common reed leaf-bags. Therefore, differences in microbial activity and microbial/detritivore interactions rather than composition, diversity and abundance of the detritivore guild could better explain the faster breakdown of native leaves. Our results suggest that the substitution of natural riparian vegetation with invasive low-quality leaf plant species will have severe impacts on spring ecosystems. Alterations of structural and functional attributes of springs will be strictly related to the specific characteristics of plant invaders and to local conditions which may influence the detritivore/microbial contribution to leaf litter decomposition/breakdown.

中文翻译：

---

植物碎屑的起源和微生物与有害微生物的相互作用影响中亚冷宁（意大利）冷泉中凋落物的分解

死有机物的分解是许多生态系统代谢和功能的关键过程。落叶森林中的颗粒状有机物也是输入能量的主要来源。但是，很少研究春季生境中的碎屑处理。本文旨在首次评估碎屑来源对水文，热学和化学稳定的冷泉中凋落物分解的影响，并评估微生物和无脊椎动物碎屑对分解过程的相对贡献。为此，我们使用了天然黑杨（Populus nigra）和侵入性芦苇（Phragmites australis）的叶子。）装入不同网眼尺寸的叶袋中。我们证明了天然黑杨杨的叶片碎屑比入侵的普通芦苇分解的速度快两倍。我们还发现，中型/粗垃圾袋的干重损失百分比明显高于细垃圾袋。然而，细网眼袋中的单独微生物能够分解初始干燥质量的约80％（杨树）和60％（常见芦苇）。没有发现在定植于杨树和普通芦苇叶袋中的组合的结构，组成和功能组织方面的实质性差异。因此，微生物活性和微生物/有害生物相互作用的差异，而不是有害生物行业协会的组成，多样性和丰度的差异，可以更好地解释天然叶片的快速分解。我们的研究结果表明，用侵入性低质量叶片植物替代天然河岸植被将对春季生态系统产生严重影响。弹簧的结构和功能属性的变化将与侵略者的特定特征以及可能影响有害因素/微生物对凋落物分解/分解的局部条件密切相关。