Abstract Decomposing litter is regarded as the most important source of allelochemicals released into soil. In this study, a greenhouse experiment was designed to assess the net effect of differently aged leaf litter from exotic (Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila) and native riverine trees (Populus alba, Populus nigra and Ulmus minor) on the germination and growth of three herb species (Trifolium repens, Dactylis glomerata and Chenopodium album). We also characterized the chemical composition of litter samples at different litter ages (0, 1, 2 and 3 months) based on phenolic compounds, fibers and ergosterol (as a measure of fungal biomass) contents. Overall, litter from both native and exotic species had a negative effect on shoot and root growth of target species, indicating that phytotoxic effects of litter predominate over positive effects. The inhibition effect of the exotic species was similar or even lower than that of the natives, which does not support the Novel Weapons Hypothesis. Among exotic trees, U. pumila showed the highest inhibition effect on the growth of the target species. T. repens was the most sensitive target species. The importance of litter age varied with both target and donor species. In general, D. glomerata was more inhibited by fresh litter, C. album by half-decomposed litter of U. pumila and R. pseudoacacia and by fresh litter of A. altissima and T. repens was more inhibited by fresh litter of A. altissima and P. alba and by highly decomposed litter of U. minor. The concentration of total phenolics and flavonoids decreased while acid detergent fiber, lignin and ergosterol increased with increasing litter age. Hydroxybenzoic and protocatechuic acids and the flavonoid quercetin were detected in all litter species and at most of the litter ages, while gallic, chlorogenic, vanillic, coumaric and rosmarinic acids were species-specific and they were only detected in fresh litter. Ergosterol concentration appeared as the strongest constrictor of inhibitory effects of litter on understory species. The results of this study contribute to the understanding of the net effect of fresh and decomposed litter from exotic and native trees on the growth of understory species.

中文翻译：

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落叶龄调节本地和外来树种对河岸林林下草本植被的影响

摘要 腐烂的凋落物被认为是释放到土壤中的化感物质的最重要来源。在这项研究中，设计了一个温室实验来评估来自外来植物（臭椿、刺槐和榆树）和当地河流树木（白杨、黑杨和小榆树）的不同龄期落叶对发芽和生长的净影响三种草本植物（三叶草、Dactylis glomerata 和藜属植物）。我们还根据酚类化合物、纤维和麦角甾醇（作为真菌生物量的量度）含量表征了不同窝龄（0、1、2 和 3 个月）的窝料样品的化学成分。总体而言，来自本地和外来物种的凋落物对目标物种的枝条和根系生长都有负面影响，表明凋落物的植物毒性作用优于积极作用。外来物种的抑制效果与本土物种相似甚至更低，不支持新武器假说。在外来树种中，U. pumila 对目标树种的生长抑制作用最大。T. repens 是最敏感的目标物种。窝龄的重要性因目标物种和供体物种而异。总的来说，新鲜凋落物对D. glomerata 的抑制作用更强，U. pumila 和R. pseudoacacia 的半分解凋落物对C. album 的抑制作用更大，A. altissima 和T. repens 的新鲜凋落物对新鲜凋落物的抑制作用更大。 altissima 和 P. alba 以及高度分解的 U. minor 垃圾。总酚和黄酮的浓度降低，而酸性洗涤纤维，木质素和麦角甾醇随着窝龄的增加而增加。羟基苯甲酸和原儿茶酸以及类黄酮槲皮素在所有垫料物种和大多数垫料年龄中均被检测到，而没食子酸、绿原酸、香草酸、香豆酸和迷迭香酸具有物种特异性，仅在新鲜垫料中检测到。麦角甾醇浓度似乎是凋落物对林下物种抑制作用的最强限制因素。这项研究的结果有助于了解来自外来和本地树木的新鲜和腐烂的枯枝落叶对林下物种生长的净影响。香豆酸和迷迭香酸具有物种特异性，仅在新鲜垫料中检测到。麦角甾醇浓度似乎是凋落物对林下物种抑制作用的最强限制因素。这项研究的结果有助于了解来自外来和本地树木的新鲜和腐烂的枯枝落叶对林下物种生长的净影响。香豆酸和迷迭香酸具有物种特异性，仅在新鲜垫料中检测到。麦角甾醇浓度似乎是凋落物对林下物种抑制作用的最强限制因素。这项研究的结果有助于了解来自外来和本地树木的新鲜和腐烂的枯枝落叶对林下物种生长的净影响。