Data from: Earthworms increase plant biomass more in soil with no earthworm legacy than in earthworm mediated soil, and favor late successional species in competition

As ecosystem engineers, earthworms greatly affect plant communities. They create persistent soil structures enriched by nutrients that improve the conditions for plant growth and modify competition between plant species. We therefore hypothesized that earthworm activity would be more important in early stages of the primary succession, when the soil is not modified by earthworms, than in the late stages of the succession, when the soil is already improved by earthworms. On the other hand, earthworms also affect plants via many other effects such as seed predation or excreting hormone-like compounds, which could make earthworm presence important in late successional soil. To explore earthworm effects on plant community succession, we performed a laboratory microcosm experiment without and with earthworms (Lumbricus rubellus and Aporrectodea caliginosa), with early successional plants (Poa compressa, Medicago lupulina, and Daucus carota) and late successional plants (Arrhenatherum elatius, Lotus corniculatus, and Plantago lanceolata), and with soil previously unaffected by earthworms (young soil) and soil substantially affected by earthworms (developed soil). These soils were taken from the early and late successional post-mining sites of the Sokolov coal mining district (northwest Czech Republic). When both early and late successional plants were grown separately, earthworms increased plant biomass proportionally more in the young soil than in the developed soil, indicating that earthworm activity is more important in undeveloped than in developed soil. When early and late successional plants were competing each other, the biomass of the early successional plants was reduced. In the young soil the reduction was independent of earthworm presence. In the developed soil the reduction was promoted by the earthworms. Late successional plants profited from the reduction of early successional plants and increased their biomass. This increase was promoted by the earthworm presence. Our results indicate that the direct effects of earthworm presence on plants decrease during succession because of the cumulative effects of earthworm activity on soil conditions. Such ecosystem engineering effects favor late successional competitors and therefore promote the replacement of species during succession.作为生态系统工程师（ecosystem engineers），蚯蚓对植物群落具有显著影响。它们可构建持久的养分富集土壤结构，以此改善植物生长条件，并调节植物物种间的种间竞争关系。据此我们提出假说：在原生演替（primary succession）的早期阶段（此时土壤尚未经蚯蚓活动改造），蚯蚓的活动重要性将高于演替晚期阶段——此时土壤已因蚯蚓的长期活动得到改良。另一方面，蚯蚓还可通过多种其他途径影响植物，例如取食种子或分泌类激素化合物，这使得即便在演替晚期的土壤中，蚯蚓的存在依然具有重要生态意义。 为探究蚯蚓对植物群落演替的调控效应，我们开展了实验室微宇宙实验（microcosm experiment）。实验设置了有无蚯蚓（赤子爱胜蚓（Lumbricus rubellus）和暗色爱胜蚓（Aporrectodea caliginosa））两个处理组，分别使用演替早期植物（early successional plants）（扁秆早熟禾（Poa compressa）、天蓝苜蓿（Medicago lupulina）和野胡萝卜（Daucus carota））与演替晚期植物（late successional plants）（高燕麦草（Arrhenatherum elatius）、百脉根（Lotus corniculatus）和长叶车前（Plantago lanceolata）），并采用此前未受蚯蚓影响的幼龄土壤（young soil）与经蚯蚓显著改造的成熟土壤（developed soil）。上述土壤采自捷克共和国西北部索科洛夫煤田的采矿后早期与晚期演替样地。 当单独培养演替早期植物与晚期植物时，蚯蚓对幼龄土壤中植物生物量的提升幅度显著高于成熟土壤，这表明蚯蚓活动在未改造土壤中的重要性高于已改造土壤。 当演替早期植物与晚期植物共同种植以开展种间竞争实验时，早期植物的生物量会出现下降。在幼龄土壤中，该下降幅度不受蚯蚓存在与否的影响；而在成熟土壤中，蚯蚓的存在会加剧这一生物量下降过程。演替晚期植物可通过早期植物的生物量降低获益，自身生物量得以提升，而这一增益效应同样会因蚯蚓的存在而得到促进。 本研究结果表明，蚯蚓对植物的直接影响会随演替进程逐渐减弱，这源于蚯蚓活动对土壤条件的累积改造效应。这类生态系统工程效应会优先利于演替晚期的竞争物种，进而推动演替过程中的物种更替。