Predator Contributions to Belowground Responses to Climate Warming at Harvard Forest 2014

Identifying the factors that control soil CO2 emissions will improve our ability to predict the magnitude of climate change-soil ecosystem feedbacks. Despite the integral role of invertebrates in belowground systems, they are excluded from climate change models. Soil invertebrates have consumptive and non-consumptive effects on microbes, whose respiration accounts for nearly half of soil CO2 emissions. By altering the behavior and abundance of invertebrates that interact with microbes, invertebrate predators may have indirect effects on soil respiration. We examined the effects of a generalist arthropod predator on belowground respiration under different warming scenarios. Based on research suggesting invertebrates may mediate soil CO2 emission responses to warming, we predicted that predator presence would result in increased emissions by negatively affecting these invertebrates. We altered the presence of wolf spiders (Pardosa spp.) in mesocosms containing a forest floor community. To simulate warming, we placed mesocosms of each treatment in ten open-top warming chambers ranging from 1.5 to 5.5° C above ambient at Harvard Forest, MA. As expected, CO2 emissions increased under warming and we found an interactive effect of predator presence and warming, though the effect was not consistent through time. The interaction between predator presence and warming was the inverse of our predictions: mesocosms with predators had lower respiration at higher levels of warming than those without predators. Carbon dioxide emissions were not significantly associated with microbial biomass. We did not find evidence of consumptive effects of predators on the invertebrate community, suggesting that predator presence mediates response of microbial respiration to warming through non-consumptive means. In our system we found a significant interaction between warming and predator presence that warrants further research into mechanism and generality of this pattern to other systems.探明调控土壤二氧化碳（soil CO2）排放的关键因子，可提升我们预测气候变化-土壤生态系统反馈强度的能力。尽管无脊椎动物在地下生态系统中发挥着不可或缺的作用，但当前气候变化模型并未将其纳入考量。土壤无脊椎动物对微生物兼具消耗性与非消耗性效应，而微生物呼吸作用几乎贡献了一半的土壤二氧化碳排放。通过改变与微生物互作的无脊椎动物的行为与种群丰度，无脊椎动物捕食者可对土壤呼吸产生间接影响。我们针对不同增温情景下，一种广食性节肢动物捕食者对地下呼吸的影响展开了研究。基于“无脊椎动物可介导土壤二氧化碳排放对增温的响应”这一前期研究结论，我们提出假设：捕食者的存在会通过对无脊椎动物产生负面影响，进而提升土壤碳排放。我们在包含森林地表群落的中宇宙（mesocosms）实验系统中设置了狼蛛（豹蛛属（Pardosa spp.））有无两个处理组。为模拟增温效应，我们将各处理组的中宇宙系统放置于10个开顶式增温箱中，这些增温箱可使箱内温度较马萨诸塞州哈佛森林的环境背景水平高出1.5至5.5℃。正如预期，增温条件下二氧化碳排放量显著升高；同时我们观测到捕食者存在与增温之间存在交互效应，但该效应随时间推移并不稳定。捕食者存在与增温的交互效应与我们的预测恰好相反：在较高增温水平下，放置有狼蛛的中宇宙系统的呼吸速率显著低于无捕食者组。此外，二氧化碳排放量与微生物生物量并无显著关联。我们未发现捕食者对无脊椎动物群落产生消耗性效应的证据，这表明捕食者的存在是通过非消耗性途径，介导了微生物呼吸对增温的响应。在本实验系统中，我们观测到增温与捕食者存在之间存在显著交互效应，这一发现值得针对其作用机制以及该模式在其他生态系统中的普适性展开进一步研究。