Hubei Key Laboratory of Regional Development and Environmental Response, Faculty of Resource and Environment, Hubei University, Wuhan 430062, China.
Department of Biology/Aquatic Ecology, Ecology Building, Lund University, S-223 62 Lund, Sweden.
Environ Sci Technol. 2021 Apr 20;55(8):5272-5281. doi: 10.1021/acs.est.1c00884. Epub 2021 Mar 25.
In addition to a rise in global air and water mean temperatures, extreme climate events such as heat waves are increasing in frequency, intensity, and duration in many regions of the globe. Developing a mechanistic understanding of the impacts of heat waves on key ecosystem processes and how they differ from just an increase in mean temperatures is therefore of utmost importance for adaptive management against effects of global change. However, little is known about the impact of extreme events on freshwater ecosystem processes, particularly the decomposition of macrophyte detritus. We performed a mesocosm experiment to evaluate the impact of warming and heat waves on macrophyte detrital decomposition, applied as a fixed increment (+4 °C) above ambient and a fluctuating treatment with similar energy input, ranging from 0 to 6 °C above ambient (i.e., simulating heat waves). We showed that both warming and heat waves significantly accelerate dry mass loss of the detritus and carbon (C) release but found no significant differences between the two heated treatments on the effects on detritus dry mass loss and C release amount. This suggests that moderate warming indirectly enhanced macrophyte detritus dry mass loss and C release mainly by the amount of energy input rather than by the way in which warming was provided (i.e., by a fixed increment or in heat waves). However, we found significantly different amounts of nitrogen (N) and phosphorus (P) released between the two warming treatments, and there was an asymmetric response of N and P release patterns to the two warming treatments, possibly due to species-specific responses of decomposers to short-term temperature fluctuations and litter quality. Our results conclude that future climate scenarios can significantly accelerate organic matter decomposition and C, N, and P release from decaying macrophytes, and more importantly, there are asymmetric alterations in macrophyte-derived detrital N and P release dynamic. Therefore, future climate change scenarios could lead to alterations in N/P ratios in the water column via macrophyte decomposition processes and ultimately affect the structure and function of aquatic ecosystems, especially in the plankton community.
除了全球空气和水的平均温度上升外，极端气候事件（如热浪）在全球许多地区的频率、强度和持续时间都在增加。因此，了解热浪对关键生态系统过程的影响及其与平均温度升高的区别，对于采取适应性管理应对全球变化的影响至关重要。然而，人们对极端事件对淡水生态系统过程的影响，特别是大型植物残体分解的影响知之甚少。我们进行了一个中观实验，以评估升温以及热浪对大型植物残体分解的影响，实验施加的升温幅度为环境温度之上的 4°C（固定增量），并施加一个波动处理，其能量输入与环境温度之上 0-6°C （即模拟热浪）的情况相似。结果表明，升温以及热浪均显著加速了残体的干物质损失和碳（C）释放，但在两种加热处理方式对残体干物质损失和 C 释放量的影响方面，我们没有发现显著差异。这表明适度升温主要通过能量输入量间接增强了大型植物残体的干物质损失和 C 释放，而不是通过升温的方式（即通过固定增量或热浪）。然而，我们发现两种升温处理方式下氮（N）和磷（P）的释放量存在显著差异，并且 N 和 P 释放模式对两种升温处理方式的响应存在不对称性，这可能是由于分解者对短期温度波动和凋落物质量的特定物种响应所致。我们的研究结果表明，未来的气候情景可能会显著加速有机物质分解以及 C、N 和 P 从腐烂的大型植物中的释放，更重要的是，大型植物残体衍生的 N 和 P 释放动态会发生不对称变化。因此，未来的气候变化情景可能会通过大型植物分解过程改变水柱中的 N/P 比值，并最终影响水生生态系统的结构和功能，特别是浮游生物群落。
