Data from: Recognizing cross-ecosystem responses to changing temperatures: soil warming impacts pelagic food webs

The energy and materials that move across ecosystem boundaries influence food web structure and key ecosystem functions. Despite the acknowledged importance of such ecological subsidies, surprisingly little information is available regarding the role of environmental temperature in influencing subsidy quality and the response of the recipient ecosystem. We evaluated the impacts of temperature-mediated changes in leaves from deciduous trees, an important subsidy from terrestrial to freshwater ecosystems, on both the producer-based and detritivore-based components of a pelagic pond food web in a field mesocosm experiment. We hypothesized that variation in leaf chemistry driven by increased soil temperature would alter both the quality of leaf subsidies and the pond response. We collected red maple Acer rubrum leaves from heated and ambient temperature plots from the long-term soil warming experiment at the Harvard Experimental Forest and added them to 167-l field mesocosms containing established plankton communities, creating ‘no leaf’, ‘ambient leaf’ and ‘heated leaf’ treatments during autumn 2012. We then monitored physical, chemical, and biological responses to treatments until the mesocosms froze six weeks later. Experimental soil warming altered the chemical composition of deciduous leaves, the physical and chemical environment of the aquatic ecosystems to which leaves were added, and the pelagic pond food webs as measured by community composition. Compared to leaves from ambient-temperature soils, leaves from warmed soils initially resulted in lower water column phosphorus and dissolved organic carbon, reducing bacterial densities. However, the diminished carbon and phosphorus resulting from soil warming also increased light availability that ultimately stimulated cladoceran zooplankton relative to ambient-temperature leaves. Our results suggest that changes in temperature can alter ecological subsidies in unanticipated ways, and suggest that accurately predicting the potential consequences of climate change will require conducting research across ecosystem boundaries.

跨生态系统边界流动的能量与物质，会对食物网结构及关键生态系统功能产生显著影响。尽管学界已公认这类生态补给（ecological subsidy）的重要性，但关于环境温度如何调控补给质量以及受体生态系统响应的相关研究却极为匮乏。本研究依托野外中宇宙实验（field mesocosm experiment），评估了落叶乔木叶片的温度介导变化——这是一类重要的陆地-淡水跨界生态补给——对浮游型池塘食物网中生产者基型与腐食者基型两个组成部分的影响。我们提出假说：土壤升温驱动的叶片化学组成变异，会同时改变叶片生态补给的质量与池塘生态系统的响应。我们从哈佛大学实验林（Harvard Experimental Forest）的长期土壤增温实验样地中，采集了增温与对照温度样地的红花槭（Acer rubrum）叶片，并于2012年秋季将其添加至167升的野外中型受控生态箱中，这些生态箱内已建立稳定的浮游生物群落，由此设置了“无叶片”“对照温度叶片”与“增温叶片”三个处理组。随后我们监测各处理组的物理、化学及生物学响应，直至六周后中型生态箱内水体完全封冻。实验性土壤增温改变了落叶乔木叶片的化学组成、叶片输入的水生生态系统的物理与化学环境，以及基于群落组成表征的浮游型池塘食物网结构。与对照温度土壤来源的叶片相比，增温土壤来源的叶片初始会降低水柱中的磷与溶解性有机碳（dissolved organic carbon）含量，进而抑制细菌密度。但土壤增温导致的碳、磷含量降低，同时提升了光照可获得性，最终较对照叶片处理组更能促进枝角类浮游动物（cladoceran zooplankton）的生长。本研究结果表明，温度变化可通过未被预见的途径改变生态补给，同时也提示，若要精准预测气候变化的潜在影响，需开展跨生态系统边界的相关研究。