Changes in soil organic matter stability with depth in two alpine ecosystems on the Tibetan Plateau
Changes in soil organic matter stability with depth in two alpine ecosystems on the Tibetan Plateau
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DOI：
10.1016/j.geoderma.2019.05.034
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发表时间：
2019-10-01
期刊：
影响因子：
6.1
通讯作者：
Zhu, Biao
中科院分区：
文献类型：
--
作者：
Hou, Yanhui;Chen, Ying;Zhu, Biao
土壤有机碳（SOC）分解对气候变化具有潜在的反馈作用。然而，控制土壤碳稳定性的生物、非生物和内在因素，以及这些因素随土壤深度的变化，仍然知之甚少。在这项研究中，我们结合了一些互补的方法来量化的生物，热，化学，分子和同位素指标的土壤有机质（SOM）的稳定性沿着土壤剖面（0-70厘米）在两个对比高寒生态系统（草甸和灌丛）在青藏高原。首先，我们进行了有氧实验室培养试验无根，筛分土壤。土壤有机质稳定性的生物学指标，即呼吸初始有机碳5%的天数，随土壤深度的增加而减少。土壤有机质半质量损失温度（TG-T50）随土壤深度的增加而升高。此外，每克SOC的热水可提取有机碳（HWEOC），有机质稳定性的化学指标，表现出弱（草甸）和小（灌丛）随深度的下降趋势。此外，我们使用傅里叶变换红外光谱（FTIR）和核磁共振（NMR）光谱表征SOM的分子组成。FTIR谱的非线性指数和NMR谱的非线性度和芳香度的综合指数均随深度的增加而增加，表明有机质的分子组成随深度的增加而变得更加复杂。最后，有机质（C-13和N-15）的同位素值和基于C-14的SOC周转时间都随深度增加，表明有机质稳定性的同位素指标也随深度增加。总的来说，我们的研究结果表明，热，化学，分子和同位素指标的SOM稳定性是相互关联的，并都表现出增加的趋势，随着土壤深度的增加，在两个高山生态系统，虽然生物指标（无根筛分土壤有氧培养测量）显示相反的结果。
Soil organic carbon (SOC) decomposition can potentially feedback to climate change. However, the biotic, abiotic and inherent factors controlling the stability of soil carbon, and changes in these factors with soil depth, remain poorly understood. In this study, we combined a number of complementary methods to quantify the biological, thermal, chemical, molecular and isotopic indices of soil organic matter (SOM) stability along the soil profile (0-70 cm) in two contrasting alpine ecosystems (meadow and shrubland) on the Tibetan Plateau. Firstly, we conducted an aerobic lab-incubation experiment on root-free, sieved soils. The number of days to respire 5% of initial SOC, a biological index of SOM stability, decreased with soil depth. Moreover, the temperature at which half of SOM mass loss (TG-T50), a thermal index of SOM stability, increased with soil depth. Additionally, hot-water extractable organic carbon (HWEOC) per gram SOC, a chemical index of SOM stability, showed weak (meadow) and little (shrubland) declining trend with depth. Further, we used Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy to characterize the molecular composition of SOM. The index of recalcitrance of FTIR spectra and the combined index of aliphaticity and aromaticity of NMR spectra both increased with depth, suggesting that the molecular composition of SOM was more complex with increasing depth. Finally, the isotopic values of SOM (C-13 and N-15) and the C-14-based SOC turnover time both increased with depth, indicating that the isotopic indices of SOM stability also increased with depth. Overall, our results suggest that the thermal, chemical, molecular and isotopic indices of SOM stability were mutually correlated and all showed increasing trend with increasing soil depth in the two alpine ecosystems, although the biological index (as measured by aerobic incubation of root-free sieved soils) showed the opposite results.