School of Life Science, Henan University, Kaifeng, 475004, China.
PLoS One. 2023 Aug 18;18(8):e0290282. doi: 10.1371/journal.pone.0290282. eCollection 2023.
Numerous studies have shown that the function of earthworms may depend on their ecotype and density, which affects how they impact soil microbial and nematode communities. However, it is unclear how different earthworm species and densities alter the composition of soil microbial and nematode communities and how these modifications impact the soil micro-food web. The structural equation model (SEM) is a more accurate tool for identifying the intricate relationships between various trophic levels in the soil micro-food webs than the widely used bivariate data analysis. In order to ascertain the effects of earthworm species, including epigeic earthworm Eisenia fetida and anecic earthworm Metaphire guillelmi, as well as varying densities on the composition of main microbial groups, soil nematodes and their relationships, a microcosm experiment was conducted in a greenhouse. After nine weeks of observation, compared with the control treatments, Eisenia fetida increased the biomasses of total microorganism and bacteria, whereas Metaphire guillelmi decreased the biomasses of total microorganism, bacteria, and gram-positive bacteria, but showed an increase in AMF biomass. Additionally, both two earthworm species decreased the abundance of total soil nematode, bacterivores, and omnivore-predators, which is in contrast with the control treatments. The SEM results indicated that the addition of Eisenia fetida at different densities had indirect negative effects on the abundance of omnivore-predators, as it significantly increased the content of soil organic carbon, ammonium nitrogen, and nitrate nitrogen. The bottom-up effects were found to be the dominant forces, which promoted bacterial-dominated decomposition channels. The addition of Metaphire guillelmi with different density had direct negative impact on bacterivores and fungivores. Moreover, it had indirect negative effects on omnivore-predators by altering the soil properties. The dominant forces were still the bottom-up effects. Our study suggests that different earthworm species have distinct mechanisms that affect the soil micro-food web in different ways.
大量研究表明，蚯蚓的功能可能取决于其生态型和密度，这会影响它们对土壤微生物和线虫群落的影响。然而，不同蚯蚓物种和密度如何改变土壤微生物和线虫群落的组成，以及这些变化如何影响土壤微型食物网，目前尚不清楚。结构方程模型（SEM）是一种比广泛使用的二元数据分析更准确的工具，可以识别土壤微型食物网中不同营养水平之间的复杂关系。为了确定包括表栖蚯蚓赤子爱胜蚓和穴居蚯蚓威廉环毛蚓在内的不同蚯蚓物种以及不同密度对主要微生物群、土壤线虫及其关系组成的影响，在温室中进行了微宇宙实验。经过九周的观察，与对照处理相比，赤子爱胜蚓增加了总微生物和细菌的生物量，而威廉环毛蚓则降低了总微生物、细菌和革兰氏阳性菌的生物量，但增加了 AMF 的生物量。此外，两种蚯蚓物种都减少了总土壤线虫、细菌食性线虫和杂食性捕食线虫的丰度，与对照处理相反。SEM 结果表明，不同密度添加赤子爱胜蚓对杂食性捕食线虫的丰度有间接的负向影响，因为它显著增加了土壤有机碳、铵态氮和硝态氮的含量。发现底向上的作用是主要的驱动力，促进了以细菌为主的分解途径。不同密度添加威廉环毛蚓对细菌食性线虫和真菌食性线虫有直接的负面影响。此外，通过改变土壤性质，它对杂食性捕食线虫也有间接的负向影响。主要驱动力仍然是底向上的作用。我们的研究表明，不同的蚯蚓物种具有不同的机制，以不同的方式影响土壤微型食物网。
