Experimental nutrient enrichment of forest streams increases energy flow to predators along greener food-web pathways
Experimental nutrient enrichment of forest streams increases energy flow to predators along greener food-web pathways
复制标题
DOI：
10.1111/fwb.12992
复制
发表时间：
2017-10-01
影响因子：
2.7
通讯作者：
Benstead, Jonathan P.
中科院分区：
文献类型：
--
作者：
Bumpers, Phillip M.;Rosemond, Amy D.;Benstead, Jonathan P.
营养盐富集是全球湖泊和溪流的一个关键压力源，影响着藻类和碎屑等重要基础资源的相对可用性。这些影响是由随后影响初级消费者和更高级别的捕食者的自养和异养微生物的反应控制的。尽管这些自下而上的影响传播的潜力，很少有研究探讨营养物质如何影响绿色（自养）与棕色（异养）的能量途径，捕食者通过数量或类型的变化被消耗。我们研究了营养富集影响两种捕食性蝾螈物种（Desmognathus quadramaculatus和Eurycea wilderae）的途径，使用详细的饮食分析之前和期间2年的营养添加到5个源头森林流。所述流连续地富含不同浓度的溶解氮（N）和磷（P），在每个流中产生相对更高的N或P浓度和不同的N：P比（2：1、8：1、16：1、32：1和128：1）。营养盐的添加导致更大的猎物数量，大小和生物量消耗的D.quadramaculatus，效果驱动更多的P比N添加。其中一些影响在富集的第二年更大，并且对于较大的个体更大。在猎物组成的D.quadramaculatus的变化包括增加的食藻动物和减少的食藻动物，跟踪观察到的处理对基础资源量的影响（例如，在肠道中的食藻动物丰度与藻类生物量，这增加了丰富，和肠道中的食藻动物丰度与碎屑常备股票，这减少了丰富）。对于E.wilderae饮食，有有限的证据增加猎物的大小和数量，或改变猎物的组成与丰富，尽管证据增加幼虫的生长。我们假设，两种蝾螈物种之间的体型差异部分解释了它们对富集的不同饮食反应。我们的研究结果表明，营养物质的添加，主要是P，影响的数量和组成的捕食者的饮食在我们的营养不良的流。这些对饮食的影响是一致的，与同期的研究表明，磷富集导致蝾螈的生长速度更快，发生部分通过影响藻类生物膜或绿色食物网途径，尽管在我们的重阴影森林流网站的碎屑或棕色资源的主导地位。因此，营养富集可以促进藻类与碎屑为基础的能量流途径在名义上光限制流生态系统，与相关的变化，食物网的特点和功能。
Nutrient enrichment is a key stressor of lakes and streams globally, affecting the relative availability of important basal resources such as algae and detritus. These effects are controlled by responses of autotrophic and heterotrophic microorganisms that subsequently affect primary consumers and higher level predators. Despite the potential for propagation of these bottom-up effects, few studies have examined how nutrients affect green (autotrophic) versus brown (heterotrophic) energy pathways to predators via changes in the quantity or type of prey consumed. We studied the pathways by which nutrient enrichment affected two predatory salamander species (Desmognathus quadramaculatus and Eurycea wilderae) using detailed diet analyses before and during 2-year nutrient additions to five headwater forest streams. The streams were continuously enriched with different concentrations of dissolved nitrogen (N) and phosphorus (P), creating relatively greater N or P concentrations and distinct N:P ratios (2:1, 8:1, 16:1, 32:1 and 128:1) in each stream. Nutrient addition resulted in greater prey number, size and biomass consumed by D.quadramaculatus, an effect driven more by P than by N additions. Some of these effects were greater in the second year of enrichment and were greater for larger individuals. Shifts in the prey composition of D.quadramaculatus included increases in algivores and decreases in detritivores, tracking observed treatment effects on basal resource quantity (e.g. algivore abundance in guts was related to algal biomass, which increased with enrichment, and detritivore abundance in guts was related to detrital standing stocks, which declined with enrichment). For E.wilderae diets, there was limited evidence for increased prey size and number, or for alteration of prey composition with enrichment despite evidence of increased larval growth. We hypothesise that body size differences between the two salamander species partially explain their different dietary responses to enrichment. Our results show that nutrient addition, primarily of P, affected the quantity and composition of predator diets in our nutrient-poor streams. These effects on diet were consistent with concurrent studies showing that P enrichment resulted in faster growth of salamanders and occurred partly via effects on algal biofilm or green food-web pathways, despite the dominance of detrital or brown resources in our heavily shaded forest stream sites. Thus, nutrient enrichment can promote algae- versus detritus-based energy-flow pathways in nominally light-limited stream ecosystems, with associated changes in food-web characteristics and function.