Above- and belowground responses of arctic tundra ecosystems to altered soil nutrients and mammalian herbivory
Above- and belowground responses of arctic tundra ecosystems to altered soil nutrients and mammalian herbivory
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DOI：
10.1890/11-1631.1
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发表时间：
2012-07-01
期刊：
影响因子：
4.8
通讯作者：
Johnson, David R.
中科院分区：
文献类型：
--
作者：
Gough, Laura;Moore, John C.;Johnson, David R.
理论和观察表明，初级生产力的变化可以改变植物和资源自下而上的影响与食草动物和捕食者对生态系统结构和功能的自上而下的调节之间的平衡。开发生态系统假说（EEH）认为，随着地上净初级生产力（ANPP）的增加，额外的生物量应该支持更高的营养水平。我们开发了 EEH 的扩展，以与地上类似的方式包括 ANPP 增加对地下消费者的影响，但间接通过光合产物分配给根的变化。我们在两个常见的北极苔原植物群落中测试了对地上植物和地下植食性线虫及其捕食者的预测，这些植物群落经历了 11 年土壤养分可用性增加和/或排除哺乳动物食草动物。生产力较低的干石南 (DH) 群落符合地上 EEH 的预测，施肥地块中的 ANPP 和植物生物量最大，免受草食性侵害。施肥地块中可口的草类增多，而矮化常绿灌木和地衣则减少。在地下，植食性线虫也如预测的那样做出反应，在较高 ANPP 的地块中获得更大的生物量，而在这些相同的地块中捕食者生物量往往较低（尽管不显着）。在生产力较高的潮湿酸性草丛（MAT）群落中，地上反应有很大不同。食草动物刺激了环境和富土壤养分地块中的 ANPP 和生物量；最大 ANPP 出现在暴露于食草动物的受精地块中。施肥的土地开始以矮桦（一种落叶灌木）和云莓（一种多年生草本植物）为主；在环境条件下，这两个物种与莎草、常绿矮灌木和泥炭藓共存。尽管对照地块中捕食者生物量最大，但植食性线虫对 ANPP 的变化没有显着反应。这两个北极苔原植物群落的对比结果表明，EEH 的预测可能适用于非常低的 ANPP 群落，但其他因素，包括竞争和植被组成向不太适口的物种的转变，可能会混淆对较高 ANPP 群落（例如本文研究的 MAT）生产力变化的预测响应。
Theory and observation indicate that changes in the rate of primary production can alter the balance between the bottom-up influences of plants and resources and the top-down regulation of herbivores and predators on ecosystem structure and function. The Exploitation Ecosystem Hypothesis (EEH) posited that as aboveground net primary productivity (ANPP) increases, the additional biomass should support higher trophic levels. We developed an extension of EEH to include the impacts of increases in ANPP on belowground consumers in a similar manner as aboveground, but indirectly through changes in the allocation of photosynthate to roots. We tested our predictions for plants aboveground and for phytophagous nematodes and their predators belowground in two common arctic tundra plant communities subjected to 11 years of increased soil nutrient availability and/or exclusion of mammalian herbivores. The less productive dry heath (DH) community met the predictions of EEH aboveground, with the greatest ANPP and plant biomass in the fertilized plots protected from herbivory. A palatable grass increased in fertilized plots while dwarf evergreen shrubs and lichens declined. Belowground, phytophagous nematodes also responded as predicted, achieving greater biomass in the higher ANPP plots, whereas predator biomass tended to be lower in those same plots (although not significantly). In the higher productivity moist acidic tussock (MAT) community, aboveground responses were quite different. Herbivores stimulated ANPP and biomass in both ambient and enriched soil nutrient plots; maximum ANPP occurred in fertilized plots exposed to herbivory. Fertilized plots became dominated by dwarf birch (a deciduous shrub) and cloudberry (a perennial forb); under ambient conditions these two species coexist with sedges, evergreen dwarf shrubs, and Sphagnum mosses. Phytophagous nematodes did not respond significantly to changes in ANPP, although predator biomass was greatest in control plots. The contrasting results of these two arctic tundra plant communities suggest that the predictions of EEH may hold for very low ANPP communities, but that other factors, including competition and shifts in vegetation composition toward less palatable species, may confound predicted responses to changes in productivity in higher ANPP communities such as the MAT studied here.