Departamento de Biología y Geología, Física y Química Inorgánica y Analítica, Escuela Superior de Ciencias Experimentales y Tecnología, Universidad Rey Juan Carlos, Móstoles, Spain.
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado.
Glob Chang Biol. 2018 Oct;24(10):4645-4656. doi: 10.1111/gcb.14399. Epub 2018 Aug 3.
A positive soil carbon (C)-climate feedback is embedded into the climatic models of the IPCC. However, recent global syntheses indicate that the temperature sensitivity of soil respiration (R ) in drylands, the largest biome on Earth, is actually lower in warmed than in control plots. Consequently, soil C losses with future warming are expected to be low compared with other biomes. Nevertheless, the empirical basis for these global extrapolations is still poor in drylands, due to the low number of field experiments testing the pathways behind the long-term responses of soil respiration (R ) to warming. Importantly, global drylands are covered with biocrusts (communities formed by bryophytes, lichens, cyanobacteria, fungi, and bacteria), and thus, R responses to warming may be driven by both autotrophic and heterotrophic pathways. Here, we evaluated the effects of 8-year experimental warming on R , and the different pathways involved, in a biocrust-dominated dryland in southern Spain. We also assessed the overall impacts on soil organic C (SOC) accumulation over time. Across the years and biocrust cover levels, warming reduced R by 0.30 μmol CO m s (95% CI = -0.24 to 0.84), although the negative warming effects were only significant after 3 years of elevated temperatures in areas with low initial biocrust cover. We found support for different pathways regulating the warming-induced reduction in R at areas with low (microbial thermal acclimation via reduced soil mass-specific respiration and β-glucosidase enzymatic activity) vs. high (microbial thermal acclimation jointly with a reduction in autotrophic respiration from decreased lichen cover) initial biocrust cover. Our 8-year experimental study shows a reduction in soil respiration with warming and highlights that biocrusts should be explicitly included in modeling efforts aimed to quantify the soil C-climate feedback in drylands.
积极的土壤碳（C）-气候反馈被纳入了 IPCC 的气候模型。然而，最近的全球综合研究表明，在地球上最大的生物群系——干旱地区，土壤呼吸（R）对温度的敏感性实际上在变暖的情况下比对照情况下更低。因此，与其他生物群系相比，未来变暖导致的土壤 C 损失预计会较低。然而，由于测试土壤呼吸（R）对变暖的长期响应背后途径的田间实验数量较少，因此干旱地区这些全球外推的经验基础仍然较差。重要的是，由于生物结皮（由苔藓、地衣、蓝藻、真菌和细菌组成的群落）覆盖了全球干旱地区，因此 R 对变暖的响应可能受到自养和异养途径的驱动。在这里，我们评估了 8 年的实验性增温对西班牙南部一个以生物结皮为主的干旱地区 R 和所涉及的不同途径的影响。我们还评估了随着时间的推移对土壤有机碳（SOC）积累的总体影响。在整个年份和生物结皮覆盖水平上，增温使 R 降低了 0.30 μmol CO 2 m 2 s （95% CI = -0.24 至 0.84），尽管仅在升温 3 年后，在初始生物结皮覆盖较低的地区，负向增温效应才具有统计学意义。我们发现，在初始生物结皮覆盖较低（通过降低土壤比呼吸和β-葡萄糖苷酶酶活性的微生物热驯化）和较高（微生物热驯化与减少地衣覆盖导致的自养呼吸减少相结合）的地区，有不同的途径调节着变暖导致的 R 减少。我们的 8 年实验研究表明，随着变暖土壤呼吸减少，并强调生物结皮应明确纳入旨在量化干旱地区土壤 C-气候反馈的建模工作中。
