| 英文摘要: | Inland water sediments receive large quantities of terrestrial organic matter1, 2, 3, 4, 5 and are globally important sites for organic carbon preservation5, 6. Sediment organic matter mineralization is positively related to temperature across a wide range of high-latitude ecosystems6, 7, 8, 9, 10, but the situation in the tropics remains unclear. Here we assessed temperature effects on the biological production of CO2 and CH4 in anaerobic sediments of tropical lakes in the Amazon and boreal lakes in Sweden. On the basis of conservative regional warming projections until 2100 (ref. 11), we estimate that sediment CO2 and CH4 production will increase 9–61% above present rates. Combining the CO2 and CH4 as CO2 equivalents (CO2eq; ref. 11), the predicted increase is 2.4–4.5 times higher in tropical than boreal sediments. Although the estimated lake area in low latitudes is 3.2 times smaller than that of the boreal zone, we estimate that the increase in gas production from tropical lake sediments would be on average 2.4 times higher for CO2 and 2.8 times higher for CH4. The exponential temperature response of organic matter mineralization, coupled with higher increases in the proportion of CH4 relative to CO2 on warming, suggests that the production of greenhouse gases in tropical sediments will increase substantially. This represents a potential large-scale positive feedback to climate change. Tropical and boreal biomes harbour approximately 50% of the lakes on Earth12. These inland waters emit substantial amounts of carbon dioxide (CO2; on the order of 0.5 Pg yr−1; refs 1, 4, 13, 14) and methane (CH4; 70 Tg yr−1; ref. 15). Organic matter escapes mineralization through burial in lake sediments, representing a global carbon (C) sink13, 14, 15. Cold conditions are favouring organic carbon preservation in lakes at northern latitudes8, 9, 10, 16, whereas warm inland waters show intense organic degradation supporting high C emissions to the atmosphere4, 5, 17, 18. Temperature and organic carbon mineralization were recently shown to be strongly positively related in boreal lake sediments overlain by oxic water9. However, most freshwater sediments below the uppermost layer (typically a few millimetres) are anoxic19, where the anaerobic biological degradation of organic carbon releases not only CO2 but also significant amounts of CH4 (ref. 15). Although higher temperatures are also expected to increase metabolic responses20, the effects of changing temperatures on organic carbon mineralization can depend on several factors including organic matter characteristics (for example, the carbon–quality–temperature hypothesis)21. Thus, the temperature sensitivity of organic carbon stocks at high latitudes previously reported6, 7, 8, 16 may not be valid in the tropics where temperature sensitivity data are much more scarce22. We compared the anaerobic organic carbon mineralization to CO2 and CH4 in tropical and boreal lake sediments along a temperature gradient. We simultaneously sampled a wide range of lake sediments from both tropical and boreal zones (Supplementary Information and Supplementary Table 1). We assessed the temperature response of organic carbon mineralization to CO2 and CH4 in the different sediments in one integrated experiment to ensure that all sediments were treated similarly. The temperature range used for all sediments in the experiment was 4–40 °C, and the results were compared with expected temperature increases according to the conservative B1 Intergovernmental Panel on Climate Change (IPCC) scenario11 (see Supplementary Information for details). Anaerobic organic carbon mineralization increased exponentially with temperature (Fig. 1; that is, linear regressions of log10 C gas production versus temperature; see Supplementary Information and Table 1 for further details). The temperature sensitivity of the anaerobic organic carbon mineralization was not significantly different between boreal and tropical lakes on the basis of the Wilcoxon rank-sum test for CH4 (W = 30, P = 0.61), CO2 (W = 37, P = 0.96) and CO2eq (W = 41, P = 0.67). This was confirmed using alternative statistical approaches including a t-test and one-way analysis of variance (P values were always >0.3 for both slopes and intercepts in the tropical and boreal equations given in Table 1). The temperature sensitivity varied among lakes (Supplementary Figs 1 and 2), but was on average not different between biomes.
| http://www.nature.com/nclimate/journal/v4/n6/full/nclimate2222.html
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