Department of Forest Resources, University of Minnesota, St. Paul, Minnesota, United States of America.
PLoS One. 2011;6(9):e24087. doi: 10.1371/journal.pone.0024087. Epub 2011 Sep 1.
Changes in plant diversity may induce distinct changes in soil food web structure and accompanying soil feedbacks to plants. However, knowledge of the long-term consequences of plant community simplification for soil animal food webs and functioning is scarce. Nematodes, the most abundant and diverse soil Metazoa, represent the complexity of soil food webs as they comprise all major trophic groups and allow calculation of a number of functional indices.
METHODOLOGY/PRINCIPAL FINDINGS: We studied the functional composition of nematode communities three and five years after establishment of a grassland plant diversity experiment (Jena Experiment). In response to plant community simplification common nematode species disappeared and pronounced functional shifts in community structure occurred. The relevance of the fungal energy channel was higher in spring 2007 than in autumn 2005, particularly in species-rich plant assemblages. This resulted in a significant positive relationship between plant species richness and the ratio of fungal-to-bacterial feeders. Moreover, the density of predators increased significantly with plant diversity after five years, pointing to increased soil food web complexity in species-rich plant assemblages. Remarkably, in complex plant communities the nematode community shifted in favour of microbivores and predators, thereby reducing the relative abundance of plant feeders after five years.
CONCLUSIONS/SIGNIFICANCE: The results suggest that species-poor plant assemblages may suffer from nematode communities detrimental to plants, whereas species-rich plant assemblages support a higher proportion of microbivorous nematodes stimulating nutrient cycling and hence plant performance; i.e. effects of nematodes on plants may switch from negative to positive. Overall, food web complexity is likely to decrease in response to plant community simplification and results of this study suggest that this results mainly from the loss of common species which likely alter plant-nematode interactions.
植物多样性的变化可能会引起土壤食物网结构的明显变化，并伴随土壤对植物的反馈。然而，关于植物群落简化对土壤动物食物网和功能的长期后果的知识还很缺乏。线虫作为最丰富和多样的土壤后生动物，代表了土壤食物网的复杂性，因为它们包含了所有主要的营养群，并允许计算许多功能指数。
方法/主要发现：我们研究了草原植物多样性实验（耶拿实验）建立三年和五年后线虫群落的功能组成。由于植物群落的简化，常见的线虫物种消失了，群落结构发生了明显的功能转变。真菌能流在 2007 年春季比 2005 年秋季更为重要，特别是在物种丰富的植物组合中。这导致植物物种丰富度与真菌食者与细菌食者的比例之间存在显著的正相关关系。此外，五年来，随着植物多样性的增加，捕食者的密度显著增加，表明在物种丰富的植物组合中土壤食物网的复杂性增加。值得注意的是，在复杂的植物群落中，线虫群落有利于微生物食者和捕食者，从而减少了五年来植物食者的相对丰度。
结论/意义：研究结果表明，物种贫乏的植物组合可能受到不利于植物的线虫群落的影响，而物种丰富的植物组合则支持更多的微生物食性线虫，从而刺激养分循环，进而促进植物表现；也就是说，线虫对植物的影响可能从负面转变为正面。总的来说，食物网的复杂性可能会随着植物群落的简化而降低，而本研究的结果表明，这主要是由于常见物种的丧失，这可能改变植物-线虫相互作用。
