Abstract
Soil temperature (ST) is an important property of soils and driver of below ground biogeochemical processes. Global change is responsible that besides variable meteorological conditions, climate-driven shifts in ST are observed throughout the world. In this study, we examined long-term records in ST by a trend decomposition procedure from eleven stations in western Germany starting from earliest in 1951 until 2018. Concomitantly to ST data from multiple depths (5, 10, 20, 50, and 100 cm), various meteorological variables were measured and included in the multivariate statistical analysis to explain spatiotemporal trends in soil warming. A significant positive increase in temperature was more pronounced for ST (1.76 ± 0.59 °C) compared with air temperature (AT; 1.35 ± 0.35 °C) among all study sites. Air temperature was the best explanatory variable to explain trends in soil warming by an average 0.29 ± 0.21 °C per decade and the trend peaked during the period from 1991–2000. Especially, the summer months (June to August) contributed most to the soil warming effect, whereby the increase in maximum ST (STmax) was nearby fivefold with 4.89 °C compared with an increase of minimum ST (STmin) of 1.02 °C. This widening between STmax and STmin fostered enhanced diurnal ST fluctuations at ten out of eleven stations. Subsoil warming up to + 2.3 °C in 100-cm depth is critical in many ways for ecosystem behavior, e.g., by enhanced mineral weathering or organic carbon decomposition rates. Thus, spatiotemporal patterns of soil warming need to be evaluated by trend decomposition procedures under a changing climate.Graphical abstract
Highlights
The spatiotemporal distribution of soil temperature (ST) is inevitable affected by increased air temperature (AT) but in contrast, its trend due to climate change has been less widely propagated
In order to assess the vulnerability of soil warming under the aspect of climate change, it is desirable to address three important aspects: (i) an altitude gradient should incorporate settings in lower terrain compared with mountainous terrain, (ii) long-term records (≥ 30 years) of ST must integrate a high vertical spatial distribution to differentiate between topsoil and subsoil layers, and (iii) the meteorological data set should include as many as possible parameters
The study sites were well distributed along the federal state North Rhine-Westphalia (Fig. 1) and the topography has a striking effect on the mean annual ST (Table 1, Fig. S1B and S1C)
Summary
The spatiotemporal distribution of soil temperature (ST) is inevitable affected by increased air temperature (AT) but in contrast, its trend due to climate change has been less widely propagated. Increased ST will enhance (i) metabolic activity of microorganisms, (ii) decomposition of soil organic matter and the supply of released nutrients for plant growth, and (iii) mineral weathering by enhanced feldspar dissolution, among other minerals (Schlesinger and Emily 2013; Williams et al 2010). All these processes are embedded within a changing climate with either a positive or negative feedback.
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