Tardigrades, also known as ‘water bear’ or ‘moss piglet’, inhabit diverse environments ranging from marine to freshwater and terrestrial habitats. They occupy various trophic levels in the micro-food web attributed to their different feeding preferences and different predators, which also heralds the complexity of their ecological functions. Therefore, understanding the ecological preference of tardigrades and their interactions with other organisms is crucial for uncovering the changes in ecosystem functions performed by these organisms under future scenarios of climate change. Here, we investigated the diversity and community composition of tardigrades, and their driving factors from 194 soil samples across south and eastern Australia, based on amplicon sequencing of 18S rRNA gene. We further validated the presence or absence of tardigrades in selected soil samples using morphological detection. Eleven tardigrade genera were observed in 53 samples, predominantly from coastal soils, with as the most dominant genus. Notably, mean annual temperature (MAT) was the most important factor influencing the presence of tardigrades, revealing a decreased relative abundance of tardigrades as MAT increased. Other abiotic factors, including soil pH, total nitrogen, and mean annual precipitation, as well as biotic factors, including bacteria, fungi, protists, algae and nematodes, were also critical to the distribution of tardigrades, as revealed by structural equation modelling. Morphological identification broadly aligned with our molecular findings; it also illustrated the sporadic distribution pattern of tardigrades. Taken together, our findings provide the first empirical evidence for the relationships between soil tardigrades and the environmental factors using environmental DNA and demonstrated the importance of both biotic and abiotic factors in shaping the large-scale distribution patterns of soil tardigrades. Additionally, our findings imply a certain degree of feasibility for soil tardigrade researches using environmental DNA, and highlight the potential risk of a decline in tardigrade communities in the face of increasing global temperatures.

中文翻译：

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通过分子鉴定揭示澳大利亚大范围土壤缓步动物的分布


缓步动物，也被称为“水熊”或“苔藓小猪”，栖息在从海洋到淡水和陆地栖息地的多种环境中。由于不同的摄食偏好和不同的捕食者，它们在微食物网中占据不同的营养级，这也预示着它们生态功能的复杂性。因此，了解缓步动物的生态偏好及其与其他生物的相互作用对于揭示这些生物在未来气候变化情景下所执行的生态系统功能的变化至关重要。在这里，我们基于 18S rRNA 基因的扩增子测序，研究了澳大利亚南部和东部 194 个土壤样本中缓步动物的多样性和群落组成及其驱动因素。我们使用形态学检测进一步验证了所选土壤样本中是否存在缓步动物。在 53 个样本中观察到 11 个缓步动物属，主要来自沿海土壤，其中最主要的属。值得注意的是，年平均温度（MAT）是影响缓步动物存在的最重要因素，表明随着 MAT 的增加，缓步动物的相对丰度减少。结构方程模型揭示，其他非生物因素，包括土壤 pH 值、总氮和年平均降水量，以及生物因素，包括细菌、真菌、原生生物、藻类和线虫，对缓步动物的分布也至关重要。形态学鉴定与我们的分子发现大致一致；它还说明了缓步动物的零星分布模式。 总而言之，我们的研究结果利用环境 DNA 为土壤缓步动物与环境因素之间的关系提供了第一个经验证据，并证明了生物和非生物因素在塑造土壤缓步动物大规模分布模式中的重要性。此外，我们的研究结果表明利用环境DNA进行土壤缓步动物研究具有一定程度的可行性，并强调了在全球气温升高的情况下缓步动物群落减少的潜在风险。