Department of Plant Biology and Ecology, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain.
Basque Foundation for Science, IKERBASQUE, Bilbao, Spain.
Microb Ecol. 2024 Jan 16;87(1):32. doi: 10.1007/s00248-024-02343-w.
Alders are nitrogen (N)-fixing riparian trees that promote leaf litter decomposition in streams through their high-nutrient leaf litter inputs. While alders are widespread across Europe, their populations are at risk due to infection by the oomycete Phytophthora ×alni, which causes alder dieback. Moreover, alder death opens a space for the establishment of an aggressive N-fixing invasive species, the black locust (Robinia pseudoacacia). Shifts from riparian vegetation containing healthy to infected alder and, eventually, alder loss and replacement with black locust may alter the key process of leaf litter decomposition and associated microbial decomposer assemblages. We examined this question in a microcosm experiment comparing three types of leaf litter mixtures: one representing an original riparian forest composed of healthy alder (Alnus lusitanica), ash (Fraxinus angustifolia), and poplar (Populus nigra); one with the same species composition where alder had been infected by P. ×alni; and one where alder had been replaced with black locust. The experiment lasted six weeks, and every two weeks, microbially driven decomposition, fungal biomass, reproduction, and assemblage structure were measured. Decomposition was highest in mixtures with infected alder and lowest in mixtures with black locust, reflecting differences in leaf nutrient concentrations. Mixtures with alder showed distinct fungal assemblages and higher sporulation rates than mixtures with black locust. Our results indicate that alder loss and its replacement with black locust may alter key stream ecosystem processes and assemblages, with important changes already occurring during alder infection. This highlights the importance of maintaining heathy riparian forests to preserve proper stream ecosystem functioning.
桤木是一种具有固氮能力的河岸树种，通过其高营养的落叶输入促进溪流中的落叶分解。虽然桤木在欧洲广泛分布，但由于受到卵菌 Phytophthora ×alni 的感染，它们的种群面临威胁，这种卵菌会导致桤木枯萎。此外，桤木的死亡为具有侵略性的固氮入侵物种——刺槐（Robinia pseudoacacia）的建立开辟了空间。从含有健康桤木的河岸植被到受感染的桤木，最终到桤木的死亡和被刺槐取代，可能会改变落叶分解和相关微生物分解者组合这一关键过程。我们通过一个微宇宙实验来研究这个问题，该实验比较了三种类型的落叶混合物：一种代表由健康的桤木（Alnus lusitanica）、白蜡（Fraxinus angustifolia）和黑杨（Populus nigra）组成的原始河岸森林；一种是与相同物种组成的混合物，其中桤木已被 P. ×alni 感染；另一种是用刺槐取代桤木的混合物。实验持续了六周，每两周测量一次微生物驱动的分解、真菌生物量、繁殖和组合结构。受感染的桤木混合物中的分解率最高，而含有刺槐的混合物中的分解率最低，这反映了落叶中营养物质浓度的差异。与含有刺槐的混合物相比，含有桤木的混合物表现出独特的真菌组合和更高的孢子形成率。我们的结果表明，桤木的丧失及其被刺槐取代可能会改变关键的溪流生态系统过程和组合，而且在桤木感染期间已经发生了重要的变化。这凸显了保持健康的河岸森林以维持适当的溪流生态系统功能的重要性。
