Extreme flood events at higher temperatures exacerbate the loss of soil functionality and trace gas emissions in grassland
Extreme flood events at higher temperatures exacerbate the loss of soil functionality and trace gas emissions in grassland
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DOI：
10.1016/j.soilbio.2018.12.021
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发表时间：
2019-03
影响因子：
9.7
通讯作者：
A. R. Sánchez–Rodríguez;C. Nie;P. Hill;D. Chadwick;Davey L. Jones
中科院分区：
文献类型：
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作者：
A. R. Sánchez–Rodríguez;C. Nie;P. Hill;D. Chadwick;Davey L. Jones
预计在可预见的未来，极端天气事件（例如洪水、干旱）的频率和强度将会增加，预计这些将对农业生态系统的功能产生负面影响。然而，我们对草原生态系统如何应对一年中不同时间发生的极端天气事件的了解还很缺乏。为了更好地了解草原对洪水的季节性响应，我们将一个农业草原在三种不同温度（5°C-冬季、15°C-春/秋季和25°C-夏季）下经历了为期8周的极端洪水事件，然后在洪水清除后跟踪其随后的恢复9周。我们重点关注生态系统功能的关键指标，包括初级生产、养分循环、温室气体 (GHG) 排放、氨 (NH3) 挥发和土壤微生物群落。该实验使用了完整的土壤中生态系统（1公斤），其中含有从以前没有洪水历史的草原上收集的本土植被。洪水使生物量产量在 5°C 时减少 18%，在 15°C 时减少 50%，在 25°C 时减少 95%。洪水还显着扰乱了元素循环（氮、磷和碳），这一点可以从 P、Fe 和 NH4+ 释放到土壤和上覆洪水中的增加以及大量 CH4 和 NH3 释放到大气中（主要是在洪水期间）来证明。这些效应在较高温度下更为明显（例如，在 15°C 和 25°C 下分别为 45–700kg CH4 单键 C ha−1 和 1–5kg NH3 单键 N ha−1）。此外，洪水去除后，NH4+迅速硝化，导致N2O大量损失（5-25°C时分别为1.0-14.2kg N2O单键N ha−1）。特别是在较高温度下，淹水会导致土壤微生物生物量减少（25°C 时相当于未淹水处理的 58% 以上），并导致微生物群落结构发生变化（通过 PLFA 评估）。此外，其中一些变化在洪水消除后仍然存在，包括放线菌、丛枝菌根真菌和真菌的损失。总体而言，我们得出的结论是，生态系统对极端天气事件的反应很大程度上取决于温度，在较高温度下发生的事件比在最低温度（5°C）下发生的事件具有更大的负面影响。 CH4和N2O的大量潜在排放也表明，在比较自上而下和自下而上的国家清单计算时，应将洪水事件视为温室气体的潜在来源，并且需要进一步开展工作以更好地完善这些事件的温室气体排放估算。
The frequency and intensity of extreme weather events (e.g. flood, drought) are predicted to increase for the foreseeable future and it is expected that these will negatively impact upon agroecosystem functioning. Our understanding of how grassland ecosystems respond to extreme weather events occurring at different times of the year, however, is lacking. To better understand the seasonal response of grassland to flooding, we subjected an agricultural grassland to an 8-week extreme flood event at three different temperatures (5 °C-winter, 15 °C-spring/autumn and 25°C-summer) and then followed its subsequent recovery for 9 weeks after floodwater removal. We focused on key indicators of ecosystem functioning including primary production, nutrient cycling, greenhouse gas (GHG) emissions, ammonia (NH3) volatilization, and soil microbial communities. The experiment used intact soil mesocosms (1 kg) with indigenous vegetation collected from a grassland with no previous history of flooding. Flooding reduced biomass production by 18% at 5 °C, 50% at 15 °C and 95% at 25 °C. Flooding also significantly disrupted elemental cycling (nitrogen, phosphorus and carbon) as evidenced by an increased release of P, Fe and NH4+into the soil and overlying floodwater and large amounts of CH4and NH3released to the atmosphere (mainly during the flooding). These effects were more pronounced at higher temperatures (e.g. 45–700 kg CH4single bondC ha−1and 1–5 kg NH3single bondN ha−1at 15 and 25 °C, respectively). In addition, after floodwater removal this NH4+was rapidly nitrified leading to large losses of N2O (1.0–14.2 kg N2Osingle bondN ha−1at 5–25 °C, respectively). Especially at higher temperatures, flooding resulted in a reduction in soil microbial biomass (more than 58% of the equivalent unflooded treatment at 25 °C) and changes in microbial community structure (assessed by PLFAs). Further, some of these changes persisted after flood removal including a loss of actinomycetes, arbuscular mycorrhizal fungi and fungi. Overall, we conclude that ecosystem responses to extreme weather events are critically dependent on temperature with those occurring at higher temperatures having a greater negative impact than those at the lowest temperature (5 °C). The large potential release of CH4and N2O also suggests that flood events should be considered as a potential source of GHGs when comparing top-down and bottom-up calculations of national inventories, and that further work is needed to better refine GHG emission estimates for these events.