Leaf litter can be retained in floodplains for several months before it enters rivers as lateral inputs. During this period, the environmental conditions on the floodplain can alter leaf litter chemistry and, consequently, affect its subsequent processing in the river. We analysed the effect of contrasting floodplain conditions on the chemical composition of leaf litter and its leachates, and how this affected their biodegradability and processing in rivers. To do so, we placed reed leaf litter (Phragmites australis) in open- and closed-canopy habitats of three floodplain sites with contrasting climates (semiarid Mediterranean, humid Mediterranean and continental) for 105 days. We then used litterbags in a river to examine the decomposition of preconditioned leaf litter in comparison with a control (non-preconditioned litter), and laboratory assays to examine the biodegradation of their leachates. Contrasting conditions on the floodplain prompted differences in the nutrient content of leaf litter among floodplain sites. Preconditioning caused a generalized decline in the C content and an increase in the lignin content of leaf litter. Even so, preconditioning did not affect litter decomposition rates in the river, although it did reduce decomposition efficiency and biodegradability of leachates. Shredder colonization of litter was variable and generally higher on preconditioned litter, but not significantly so. Different floodplain conditions had no influence on the aquatic processing of preconditioned litter. Our results demonstrate that the retention of leaf litter in terrestrial environments can affect C budgets of fluvial ecosystems and the recipient food web by reducing the input and the biodegradability of C and nutrients.

叶子凋落物在进入河流之前作为横向输入物可以在洪泛区中保留数月。在此期间，洪泛区的环境条件可能会改变枯枝落叶的化学性质，从而影响其在河流中的后续加工。我们分析了对比洪泛区条件对枯枝落叶及其渗滤液化学成分的影响，以及这如何影响其在河流中的生物降解能力和加工过程。为此，我们放置了芦苇枯枝落叶（Phragmites australis）位于三个洪泛区地点的开放式和封闭式顶棚栖息地中，气候相反（半干旱，地中海湿润和大陆性），持续105天。然后，我们在河中使用垃圾袋与对照（非预处理垃圾）相比，检查预处理叶子垃圾的分解情况，并通过实验室分析来检查垃圾渗滤液的生物降解能力。洪泛区的不同条件促使洪泛区之间的凋落物养分含量不同。预处理导致叶片凋落物中碳含量普遍下降，木质素含量增加。即使这样，预处理也不会影响河流中的垃圾分解速率，尽管它确实会降低分解效率和渗滤液的生物降解性。垃圾的切碎机定植是可变的，通常在预处理垃圾上更高，但变化不大。漫滩条件不同对预处理垃圾的水生加工没有影响。我们的结果表明，在地面环境中保留叶子凋落物可以通过减少C和养分的投入以及其生物降解性来影响河流生态系统和受主食物网的C收支。