College of JunCao Science and Ecology, Fujian Agriculture and Forestry University, Fuzhou, China.
State Key Laboratory of Efficient Utilization of Arid and Semi-arid Arable Land in Northern China, National Hulunber Grassland Ecosystem Observation and Research Station, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China; School of Life Science, Shanxi University, Taiyuan, China.
Sci Total Environ. 2024 Sep 20;944:173742. doi: 10.1016/j.scitotenv.2024.173742. Epub 2024 Jun 3.
Climate change is causing more frequent and intense heatwaves. Therefore, it is important to understand how heatwaves affect the terrestrial carbon cycle, especially in grasslands, which are especially susceptible to climate extremes. This study assessed the impact of naturally occurring, simultaneous short-term heatwaves on CO fluxes in three ecosystems on the Mongolia Plateau: meadow steppe (MDW), typical steppe (TPL), and shrub-grassland (SHB). During three heatwaves, net ecosystem productivity (NEP) was reduced by 86 %, 178 %, and 172 % at MDW, TPL, and SHB, respectively. The changes in ecosystem respiration, gross primary production, evapotranspiration, and water use efficiency were divergent, indicating the mechanisms underlying the observed NEP decreases among the sites. The impact of the heatwave in MDW was mitigated by the high soil water content, which enhanced evapotranspiration and subsequent cooling effects. However, at TPL, insufficient soil water led to combined thermal and drought stress and low resilience. At SHB, the ecosystem's low tolerance to an August heatwave was heavily influenced by species phenology, as it coincided with the key phenological growing phase of plants. The potential key mechanism of divergent NEP response to heatwaves lies in the divergent stability and varying importance of environmental factors, combined with the specific sensitivity of NEP to each factor in ecosystems. Furthermore, our findings suggest that anomalies in soil environment, rather than atmospheric anomalies, are the primary determinants of NEP anomalies during heatwaves. This challenges the conventional understanding of heatwaves as a discrete and ephemeral periods of high air temperatures. Instead, heatwaves should be viewed as chronologically variable, compound, and time-sensitive environmental stressors. The ultimate impact of heatwaves on ecosystems is co-determined by a complex interplay of environmental, biological, and heatwave features.
气候变化导致热浪更加频繁和剧烈。因此，了解热浪如何影响陆地碳循环非常重要，特别是在草原地区，它们尤其容易受到气候极端事件的影响。本研究评估了自然发生的、同时发生的短期热浪对蒙古高原三个生态系统中 CO 通量的影响：草甸草原（MDW）、典型草原（TPL）和灌丛草原（SHB）。在三次热浪期间，MDW、TPL 和 SHB 的净生态系统生产力（NEP）分别减少了 86%、178%和 172%。生态系统呼吸、总初级生产力、蒸散和水分利用效率的变化是发散的，表明了观察到的 NEP 在这些地点减少的机制。MDW 中热浪的影响因高土壤含水量而得到缓解，这增强了蒸散作用和随后的冷却效应。然而，在 TPL，土壤水分不足导致热胁迫和干旱胁迫的综合作用以及低弹性。在 SHB，生态系统对 8 月热浪的低耐受性受到物种物候的严重影响，因为它与植物的关键物候生长阶段相吻合。对热浪 NEP 响应的潜在关键机制在于环境因素的不同稳定性和重要性，以及生态系统中每个因素对 NEP 的特定敏感性。此外，我们的研究结果表明，在热浪期间，土壤环境异常而不是大气异常是 NEP 异常的主要决定因素。这挑战了将热浪视为离散和短暂的高空气温度时期的传统理解。相反，热浪应被视为具有时间变化、复合和对时间敏感的环境胁迫源。热浪对生态系统的最终影响是由环境、生物和热浪特征的复杂相互作用共同决定的。
