Overlooked biocrust impacts on surface soil thermal properties: Evidence from heat-pulse sensing on large volume samples

IF 4 2区 农林科学 Q2 SOIL SCIENCE European Journal of Soil Science Pub Date : 2024-11-03 DOI:10.1111/ejss.70004
Junru Chen, Bo Xiao, Joshua Heitman
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Abstract

Biocrusts are a critical surface cover in global drylands, but knowledge about their influences on surface soil thermal properties are still lacking because it is quite challenging to make accurate thermal property measurements for biocrust layers, which are only millimetres thick. In this study, we repacked biocrust layers (moss- and cyanobacteria-dominated, respectively) that had the same material as the original intact biocrusts but was more homogeneous and thicker. The thermal conductivity (λ), heat capacity (C) and thermal diffusivity (k) of the repacked and intact biocrusts were measured by the heat pulse (HP) technique at different mass water contents (θm) and mass ratios (Wt), and the differences between repacked and intact biocrusts were analysed. Our results show that biocrusts substantially alter the thermal properties of the soil surface. The average λ of moss (0.37 W m−1 K−1) and cyanobacteria biocrusts (0.90 W m−1 K−1) were reduced by 63.0% and 10.3% compared with bare soil (1.00 W m−1 K−1), respectively. Edge effects including heat loss and water evaporation caused the λ and k of the biocrusts to be underestimated, but the C to be overestimated. The differences in thermal properties were significant (p <0.001), except for the differences in thermal conductivity between repacked and intact cyanobacteria biocrusts, which were not significant (p = 0.379). Specifically, in the volumetric water content (θv) range of 0 to 20%, the λ and k of the repacked moss biocrusts were underestimated by 59.1% and 61.8%, respectively, and the C was overestimated by 23.9% compared with the intact moss biocrusts. The λ and k of the repacked cyanobacteria biocrusts were underestimated by 15.8% and 79.2%, respectively, and the C was overestimated by 34.8% compared with the intact cyanobacteria biocrusts at the θv range of 0 to 30%. Typically, this difference increased as the θv rises between repacked and intact biocrusts. Our new measurements provide evidence that the thermal properties of biocrusts were previously misjudged due to the measurement limitations imposed by their limited thickness when measured in situ. Biocrusts are likely more significant in regulating soil heat and temperature in drylands than was previously assumed.

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被忽视的生物群落对表层土壤热特性的影响:大体积样本热脉冲感应的证据
生物簇是全球旱地的重要表层覆盖物,但由于生物簇层只有几毫米厚,要对其进行精确的热属性测量非常困难,因此有关生物簇对表层土壤热属性影响的知识仍然缺乏。在本研究中,我们对生物簇层(分别以苔藓和蓝藻为主)进行了重新包装,其材料与原始完整生物簇层相同,但更均匀、更厚。通过热脉冲(HP)技术测量了不同质量含水量(θm)和质量比(Wt)下重新包装的生物簇和完整生物簇的导热系数(λ)、热容量(C)和热扩散率(k),并分析了重新包装的生物簇和完整生物簇之间的差异。结果表明,生物簇极大地改变了土壤表面的热特性。与裸土(1.00 W m-1 K-1)相比,苔藓(0.37 W m-1 K-1)和蓝藻生物簇(0.90 W m-1 K-1)的平均λ分别降低了 63.0% 和 10.3%。热量损失和水分蒸发等边缘效应导致生物簇的λ和k被低估,但C被高估。除了重新包装的蓝藻生物簇与完整蓝藻生物簇之间的导热系数差异不显著(p = 0.379)外,其他热特性差异均显著(p <0.001)。具体而言,在体积含水量(θv)为0-20%的范围内,与完整的苔藓生物簇相比,重新包装的苔藓生物簇的λ和k分别被低估了59.1%和61.8%,C被高估了23.9%。与完整的蓝藻生物簇相比,在 θv 为 0 至 30% 的范围内,重新组合的蓝藻生物簇的λ 和 k 分别被低估了 15.8% 和 79.2%,C 被高估了 34.8%。通常情况下,随着重新包装的生物簇与完整生物簇之间 θv 值的增加,这一差异也会增大。我们的新测量结果提供了证据,证明生物簇的热特性以前曾被误判,这是因为在原位测量时,生物簇的厚度有限,测量受到限制。生物簇在调节旱地土壤热量和温度方面的作用可能比以前认为的更大。
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来源期刊
European Journal of Soil Science
European Journal of Soil Science 农林科学-土壤科学
CiteScore
8.20
自引率
4.80%
发文量
117
审稿时长
5 months
期刊介绍: The EJSS is an international journal that publishes outstanding papers in soil science that advance the theoretical and mechanistic understanding of physical, chemical and biological processes and their interactions in soils acting from molecular to continental scales in natural and managed environments.
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