Nitrogen recycling in coupled green and brown food webs: Weak effects of herbivory and detritivory when nitrogen passes through soil
Nitrogen recycling in coupled green and brown food webs: Weak effects of herbivory and detritivory when nitrogen passes through soil
复制标题
绿色和棕色食物网耦合中的氮循环：氮穿过土壤时草食性和碎食性的微弱影响
作者：
Robert W. Buchkowski;O. Schmitz;M. Bradford
对绿色和棕色食物网的耦合研究提高了我们理解营养循环和植物群落如何对扰动作出反应的能力。然而，仍然很难预测一个食物网的变化如何快速和持续地传播到另一个食物网。一个特别不确定的领域是植物对草食动物和营养动物引起的凋落叶氮释放变化的反应。采用田间试验和理论分析相结合的方法，研究了草食、施肥和营养对凋落叶氮素释放和植株生长的影响。我们在温室网箱中使用蝗虫草食和附加氮肥的因子组合生产凋落叶。我们的实验使用15N标记的凋落叶来测量田间等足类凋落叶消耗、凋落叶氮释放和植物氮吸收。然后，我们使用一个动态系统模型来区分植物生长是否直接依赖于(a)凋落物氮释放或(b)其他氮途径，因此凋落物氮释放的变化几乎没有直接影响。结果表明，氮肥处理对凋落叶等足类动物加工的影响强于草食处理。土壤速效氮和植物生长不受凋落物氮释放量的影响。我们的动态模型将这种独立性归因于其他氮源和氮汇，它们缓冲了植物可利用氮库。当我们考虑到最初的田间环境条件时，具有草食历史的等足类和凋落物会降低地上植物的生长，尤其是竞争优势的黄花的丰度。因此，等足类和凋落物性状的影响确实会传播到植物生长中，但没有足够大的影响来克服一年内植物生物量和群落组成的初始差异。合成。结果表明，绿色和棕色食物网中的动物可以改变植物凋落物氮的释放，但对植物生长没有明显的养分循环作用。考虑外部氮源和土壤氮源的可用性，以及当前的植物群落和微生物生物量，可能对确定植物生长何时响应动物介导的凋落物分解变化至关重要。
The study of coupled green and brown food webs has improved our ability to understand how nutrient cycling and plant communities respond to perturbations. Yet, it is still difficult to predict how rapidly and consistently changes in one food web propagate to the other. An area of particular uncertainty is the response of plants to the changes in leaf litter nitrogen release caused by herbivores and detritivores. We combined a field experiment and theoretical analysis to assess how herbivory, fertilization, and detritivory changed leaf litter nitrogen release and plant growth. We produced leaf litter in greenhouse cages with a factorial combination of grasshopper herbivory and additional nitrogen fertilizer. Our experiment used the resulting 15N‐labelled leaf litter to measure isopod litter consumption, litter nitrogen release, and plant nitrogen uptake in the field. We then used a dynamical systems model to distinguish whether plant growth relied (a) directly on litter nitrogen release or (b) on other nitrogen pathways so that changes in litter nitrogen release have little immediate impact. Our empirical results show that the effect of nitrogen fertilization on isopod processing of leaf litter was stronger than the effect of herbivory. Regardless, the available soil nitrogen and plant growth were independent of litter nitrogen release. Our dynamical model attributes the independence to other nitrogen sources and sinks, which buffer the plant‐available nitrogen pool. Isopods and litter with a history of herbivory reduced above‐ground plant growth when we accounted for initial field mesocosm conditions, especially the abundance of the competitively dominant goldenrods. Consequently, the impact of isopods and litter traits do propagate to influence plant growth, but do not have a large enough effect to overcome initial differences in plant biomass and community composition in one year. Synthesis. Our results indicate animals in green and brown food webs can alter plant litter nitrogen release without any significant nutrient recycling effect on plant growth. Considering the availability of external and soil‐based nitrogen sources, as well as the current plant community and microbial biomass, may be critical to determining when plant growth will respond to animal‐mediated changes in litter decomposition.