Topography and canopy cover influence soil organic carbon composition and distribution across a forested hillslope in the discontinuous permafrost zone
Topography and canopy cover influence soil organic carbon composition and distribution across a forested hillslope in the discontinuous permafrost zone
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DOI：
10.1002/ppp.2200
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发表时间：
2023-07
影响因子：
5
通讯作者：
Erin C. Rooney;V. Bailey;Kaizad F. Patel;A. Kholodov;H. Golightly;R. Lybrand
中科院分区：
文献类型：
--
作者：
Erin C. Rooney;V. Bailey;Kaizad F. Patel;A. Kholodov;H. Golightly;R. Lybrand
地形和冠层覆盖的影响地面温度变暖的冻土景观，但土壤温度的异质性介观地形坡度的位置，植被覆盖的微地形差异，以及随后的影响对比温度条件下对土壤有机碳（SOC）动态的研究不足。在北方森林中，受永久冻土影响的土壤对气温升高的缓冲作用可以反映表层土壤的特征（例如，有机材料的厚度）以及冠层覆盖的程度和类型（例如，开盖与闭盖）。景观和土壤性质相互作用，以确定地面变暖的中尺度和微尺度异质性。我们在阿拉斯加州费尔班克斯附近的一个不连续多年冻土区采集了一个山坡连锁样带，以测试小尺度（1至3 m）的斜坡位置和覆盖类型对土壤有机质组成的影响。从后坡、低后坡和坡脚位置采集了深度为19至60厘米的矿物活性层样本。我们研究了土壤矿物组成，土壤水分，总碳和氮含量，以及有机垫厚度，并使用傅里叶变换离子回旋共振质谱（FT-ICR-MS）评估SOC组成。坡脚位置的土壤中木质素类化合物的相对贡献较高，而背坡土壤中脂肪族和缩合芳香族化合物较多，如使用FT-ICR-MS所测定。开放式和封闭式树冠覆盖的效果随坡位而变化。在后坡，我们发现更高的分子氧化下开盖比封闭的覆盖，表明土壤温度对分解的影响。在坡脚位置的土壤中几乎没有观察到冠层的影响，我们将其部分归因于土壤水分含量对集水坡脚位置SOC动态的强烈影响。薄的有机垫下开盖的后坡位置可能有助于土壤温度的差异，从而SOC氧化下开放和封闭的冠层。在这里，较薄的有机垫没有出现缓冲底层土壤对温暖的季节空气温度，从而增加SOC分解的SOC分子的氧化程度较高，并在开放的覆盖下比封闭的树冠网站的简单分子的贡献较低。我们的研究结果表明，冠层覆盖SOC动态的作用不同的景观位置和土壤性质，即，有机垫厚度和土壤水分的函数。开放和封闭的冠层覆盖下的SOC组成的条件特异性异质性突出了冠层覆盖对后坡位置土壤的保护作用。
Topography and canopy cover influence ground temperature in warming permafrost landscapes, yet soil temperature heterogeneity introduced by mesotopographic slope positions, microtopographic differences in vegetation cover, and the subsequent impact of contrasting temperature conditions on soil organic carbon (SOC) dynamics are understudied. Buffering of permafrost‐affected soils against warming air temperatures in boreal forests can reflect surface soil characteristics (e.g., thickness of organic material) as well as the degree and type of canopy cover (e.g., open cover vs. closed cover). Both landscape and soil properties interact to determine meso‐ and microscale heterogeneity of ground warming. We sampled a hillslope catena transect in a discontinuous permafrost zone near Fairbanks, Alaska, to test the small‐scale (1 to 3 m) impacts of slope position and cover type on soil organic matter composition. Mineral active layer samples were collected from backslope, low backslope, and footslope positions at depths spanning 19 to 60 cm. We examined soil mineralogical composition, soil moisture, total carbon and nitrogen content, and organic mat thickness in conjunction with an assessment of SOC composition using Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). Soils in the footslope position had a higher relative contribution of lignin‐like compounds, whereas backslope soils had more aliphatic and condensed aromatic compounds as determined using FT‐ICR‐MS. The effect of open versus closed tree canopy cover varied with the slope position. On the backslope, we found higher oxidation of molecules under open cover than closed cover, indicating an effect of warmer soil temperature on decomposition. Little to no effect of the canopy was observed in soils at the footslope position, which we attributed, in part, to the strong impact of soil moisture content in SOC dynamics in the water‐gathering footslope position. The thin organic mat under open cover on the backslope position may have contributed to differences in soil temperature and thus SOC oxidation under open and closed canopies. Here, the thinner organic mat did not appear to buffer the underlying soil against warm season air temperatures and thus increased SOC decomposition as indicated by the higher oxidation of SOC molecules and a lower contribution of simple molecules under open cover than the closed canopy sites. Our findings suggest that the role of canopy cover in SOC dynamics varies as a function of landscape position and soil properties, namely, organic mat thickness and soil moisture. Condition‐specific heterogeneity of SOC composition under open and closed canopy cover highlights the protective effect of canopy cover for soils on backslope positions.