Comparative Ecosystem Ecology: Acclimation of ecosystem function to warmer temperatures and altered moisture

光合作用和植物生产力对支持我们生物圈的运作至关重要。目前的共识表明，未来气候变暖将导致生态系统光合作用减少和二氧化碳净损失，但涉及的机制、预期正反馈的大小以及对未来生态系统功能的影响存在很大的不确定性。尽管有这种共识，但最近在全球尺度上进行的几项测量表明，光合作用和生态系统净二氧化碳吸收量在过去几十年中一直在增加。对于更高全球尺度的光合作用，提出了两个重要的机制：(i)叶面积和光合活性的时间和持续时间的变化，以及（ii）水利用效率（WUE）的提高。需要进一步的研究来测试这些促进全球光合作用生态系统服务的机制是否会被环境条件的进一步变化所改变或限制。我建议研究控制植物和生态系统如何对温度升高和降水变化做出反应和适应的机制。一种比较方法，包括一个由四个地点组成的网络，配有涡动相关通量塔，将用于研究阿尔伯塔西南部两个地点由两种不同的植物功能类型（草地，落叶林）主导的生态系统。第一个目标是测试温度升高对光合作用时间和持续时间变化的影响，以及对生长季节净碳增益的相关后果。此外，我们将确定水分胁迫和光周期在限制潜在的变暖导致的生长季节延长和生态系统碳增益方面的作用。第二个目标是在生态系统尺度上测试光合作用和呼吸作用的温度适应，并确定这种潜在的适应如何与其他环境变化相互作用。光合作用和生态系统呼吸的温度驯化可以导致净二氧化碳交换的温度响应改变，尽管目前尚不清楚哪种驯化过程对生长季节净碳吸收的影响最大。第三个目标将测试植物和生态系统尺度WUE对环境条件变化的敏感性，并确定未来WUE的潜在增长是否会受到预估的更温暖和更干燥条件的限制。这些研究的数据将与定量模型的预测结果进行比较，以进一步了解所观察到的植物和生态系统对环境变化的反应的机制控制和原因。最后，从这些研究中产生的新信息将用于改进评估全球环境变化对光合作用和生态系统生产力的影响的模型。

Photosynthesis and plant productivity are essential for supporting the operation of our biosphere. A current consensus suggests that future climate warming will result in reduced photosynthesis and net loss of carbon dioxide from ecosystems, but there is large uncertainty about the mechanisms involved, the magnitude of the expected positive feedback, and the consequences for future ecosystem function. Despite this consensus, several recent measurements, made at the global-scale, indicate that photosynthesis and net ecosystem CO2 uptake have been increasing for the last several decades. Two important mechanisms proposed for higher global-scale photosynthesis are: (i) shifts in the timing and duration of leaf area and photosynthetic activity, and (ii) increases in water-use efficiency (WUE). Further studies are required to test if these mechanisms, which have contributed to the ecosystem service of enhanced global photosynthesis, could be altered or restricted by further changes in environmental conditions. I propose to investigate the mechanisms that control how plants and ecosystems respond and acclimate to warmer temperatures and altered precipitation. A comparative approach, involving a network of four sites instrumented with eddy covariance flux towers, will be used to study ecosystems dominated by two different plant functional types (grassland, deciduous forest) in two locations in southwestern Alberta. The first objective is to test the effect of warmer temperatures on shifts in the timing and duration of photosynthesis and the associated consequences for growing season net carbon gain. In addition, we will determine the role of water stress and photoperiod in limiting potential warming-induced extensions to the growing season and ecosystem carbon gain. The second objective will test for temperature acclimation of photosynthesis and respiration at the ecosystem-scale and determine how this potential acclimation interacts with other environmental changes. Temperature acclimation of either or both photosynthesis and ecosystem respiration can lead to an altered temperature response of net carbon dioxide exchange, although it is not yet clear which acclimation process would have the largest effect on growing season net carbon uptake. The third objective will test the sensitivity of plant- and ecosystem-scale WUE to changes in environmental conditions and determine whether potential future increases in WUE will be constrained by projected warmer and drier conditions. Data from these studies will be compared to the predictions of quantitative models to gain further understanding of the mechanistic controls and the reasons for the observed responses of plants and ecosystems to the environmental changes. Finally, the new information generated from these studies will be used to improve models that evaluate the consequences of global environmental changes for photosynthesis and ecosystem productivity.