Institute of Zoology, Department of Integrative Biology and Biodiversity Research, University of Natural Resources and Life Sciences Vienna, Gregor Mendel Straße 33, Vienna, A-1180, Austria.
BMC Ecol. 2013 May 13;13:20. doi: 10.1186/1472-6785-13-20.
Biodiversity loss and species invasions are among the most important human-induced global changes. Moreover, these two processes are interlinked as ecosystem invasibility is considered to increase with decreasing biodiversity. In temperate grasslands, earthworms serve as important ecosystem engineers making up the majority of soil faunal biomass. Herbivore behaviour has been shown to be affected by earthworms, however it is unclear whether these effects differ with the composition of plant communities. To test this we conducted a mesocosm experiment where we added earthworms (Annelida: Lumbricidae) to planted grassland communities with different plant species composition (3 vs. 12 plant spp.). Plant communities had equal plant densities and ratios of the functional groups grasses, non-leguminous forbs and legumes. Later, Arion vulgaris slugs (formerly known as A. lusitanicus; Gastropoda: Arionidae) were added and allowed to freely choose among the available plant species. This slug species is listed among the 100 worst alien species in Europe. We hypothesized that (i) the food choice of slugs would be altered by earthworms' specific effects on the growth and nutrient content of plant species, (ii) slug herbivory will be less affected by earthworms in plant communities containing more plant species than in those with fewer plant species because of a more readily utilization of plant resources making the impacts of earthworms less pronounced.
Slug herbivory was significantly affected by both earthworms and plant species composition. Slugs damaged 60% less leaves when earthworms were present, regardless of the species composition of the plant communities. Percent leaf area consumed by slugs was 40% lower in communities containing 12 plant species; in communities containing only three species earthworms increased slug leaf area consumption. Grasses were generally avoided by slugs. Leaf length and number of tillers was increased in mesocosms containing more plant species but little influenced by earthworms. Overall shoot biomass was decreased, root biomass increased in plant communities with more plant species. Earthworms decreased total shoot biomass in mesocosms with more plant species but did not affect biomass production of individual functional groups. Plant nitrogen concentrations across three focus species were 18% higher when earthworms were present; composition of plant communities did not affect plant quality.
Given the important role that both herbivores and earthworms play in structuring plant communities the implications of belowground-aboveground linkages should more broadly be considered when investigating global change effects on ecosystems.
生物多样性丧失和物种入侵是人类引起的最重要的全球变化之一。此外，这两个过程是相互关联的，因为生态系统的可入侵性被认为随着生物多样性的降低而增加。在温带草原中，蚯蚓作为重要的生态系统工程师，构成了土壤动物区系生物量的大部分。食草动物的行为已被证明受到蚯蚓的影响，但尚不清楚这些影响是否因植物群落的组成而有所不同。为了检验这一点，我们进行了一个中观实验，在这个实验中，我们向具有不同植物物种组成（3 种与 12 种植物 spp.）的种植草原群落中添加了蚯蚓（环节动物门：Lumbricidae）。植物群落具有相同的植物密度和禾本科、非豆科草本植物和豆科植物的功能群比例。后来，我们添加了 Arion vulgaris 蛞蝓（以前称为 A. lusitanicus；腹足纲：Arionidae），并允许它们在可用的植物物种中自由选择。这种蛞蝓物种被列为欧洲 100 种最具入侵性的外来物种之一。我们假设：（i）蚯蚓对植物物种生长和养分含量的特定影响会改变蛞蝓的食物选择，（ii）蚯蚓在含有更多植物物种的植物群落中对蛞蝓的草食性的影响较小，因为植物资源更容易利用，蚯蚓的影响不太明显。
蛞蝓的草食性受到蚯蚓和植物物种组成的共同影响。无论植物群落的物种组成如何，有蚯蚓存在时，蛞蝓对叶片的损害减少了 60%。蛞蝓消耗的叶片面积百分比在含有 12 种植物的群落中降低了 40%；在只含有三种物种的群落中，蚯蚓增加了蛞蝓对叶片面积的消耗。蛞蝓通常会避开禾本科植物。在含有更多植物物种的中观实验中，叶片长度和分蘖数增加，但受蚯蚓影响较小。总的地上生物量减少，根生物量增加，在含有更多植物物种的植物群落中。蚯蚓减少了含有更多植物物种的中观实验中的总地上生物量，但对各功能群的生物量生产没有影响。在三个重点物种中，当有蚯蚓存在时，植物的氮浓度增加了 18%；植物群落的组成没有影响植物的质量。
鉴于食草动物和蚯蚓在植物群落结构中的重要作用，在调查全球变化对生态系统的影响时，应该更广泛地考虑地下-地上联系的影响。
