Evans-White Michelle A, Halvorson Halvor M
Department of Biological Sciences, University of Arkansas, FayettevilleAR, United States.
Department of Biological Sciences, University of Southern Mississippi, HattiesburgMS, United States.
Front Microbiol. 2017 Jun 29;8:1184. doi: 10.3389/fmicb.2017.01184. eCollection 2017.
The framework of ecological stoichiometry was developed primarily within the context of "green" autotroph-based food webs. While stoichiometric principles also apply in "brown" detritus-based systems, these systems have been historically understudied and differ from green ones in several important aspects including carbon (C) quality and the nutrient [nitrogen (N) and phosphorus (P)] contents of food resources for consumers. In this paper, we review work over the last decade that has advanced the application of ecological stoichiometry from green to brown food webs, focusing on freshwater ecosystems. We first review three focal areas where green and brown food webs differ: (1) bottom-up controls by light and nutrient availability, (2) stoichiometric constraints on consumer growth and nutritional regulation, and (3) patterns in consumer-driven nutrient dynamics. Our review highlights the need for further study of how light and nutrient availability affect autotroph-heterotroph interactions on detritus and the subsequent effects on consumer feeding and growth. To complement this conceptual review, we formally quantified differences in stoichiometric principles between green and brown food webs using a meta-analysis across feeding studies of freshwater benthic invertebrates. From 257 datasets collated across 46 publications and several unpublished studies, we compared effect sizes (Pearson's r) of resource N:C and P:C on growth, consumption, excretion, and egestion between herbivorous and detritivorous consumers. The meta-analysis revealed that both herbivore and detritivore growth are limited by resource N:C and P:C contents, but effect sizes only among detritivores were significantly above zero. Consumption effect sizes were negative among herbivores but positive for detritivores in the case of both N:C and P:C, indicating distinct compensatory feeding responses across resource stoichiometry gradients. Herbivore P excretion rates responded significantly positively to resource P:C, whereas detritivore N and P excretion did not respond; detritivore N and P egestion responded positively to resource N:C and P:C, respectively. Our meta-analysis highlights resource N and P contents as broadly limiting in brown and green benthic food webs, but indicates contrasting mechanisms of limitation owing to differing consumer regulation. We suggest that green and brown food webs share fundamental stoichiometric principles, while identifying specific differences toward applying ecological stoichiometry across ecosystems.
生态化学计量学框架主要是在以“绿色”自养生物为基础的食物网背景下发展起来的。虽然化学计量学原理也适用于以“棕色”碎屑为基础的系统，但这些系统在历史上一直未得到充分研究，并且在几个重要方面与绿色系统不同，包括碳（C）质量以及消费者食物资源中的养分[氮（N）和磷（P）]含量。在本文中，我们回顾了过去十年中推动生态化学计量学从绿色食物网应用到棕色食物网的研究工作，重点关注淡水生态系统。我们首先回顾绿色和棕色食物网不同的三个重点领域：（1）光照和养分可利用性的自下而上控制，（2）消费者生长和营养调节的化学计量限制，以及（3）消费者驱动的养分动态模式。我们的综述强调了需要进一步研究光照和养分可利用性如何影响碎屑上的自养生物 - 异养生物相互作用以及对消费者摄食和生长的后续影响。为补充这一概念性综述，我们通过对淡水底栖无脊椎动物摄食研究的荟萃分析，正式量化了绿色和棕色食物网之间化学计量学原理的差异。从46篇出版物和几项未发表研究中整理出的257个数据集中，我们比较了资源N:C和P:C对草食性和碎屑食性消费者生长、摄食、排泄和排遗的效应大小（皮尔逊r）。荟萃分析表明，草食动物和碎屑食性动物的生长都受到资源N:C和P:C含量的限制，但仅碎屑食性动物的效应大小显著高于零。对于N:C和P:C，草食动物的摄食效应大小为负，而碎屑食性动物的为正，表明在资源化学计量梯度上有明显的补偿性摄食反应。草食动物的P排泄率对资源P:C有显著的正响应，而碎屑食性动物的N和P排泄没有响应；碎屑食性动物的N和P排遗分别对资源N:C和P:C有正响应。我们的荟萃分析强调了资源N和P含量在棕色和绿色底栖食物网中普遍具有限制作用，但表明由于消费者调节不同而存在对比鲜明的限制机制。我们认为绿色和棕色食物网共享基本的化学计量学原理，同时确定了在跨生态系统应用生态化学计量学时的具体差异。
