Variation In Soil Temperature Research Articles

Nighttime warming enhances ecosystem carbon‐use efficiency in a temperate steppe

Abstract Reductions in the diurnal temperature range (DTR), for example, greater increases in daily minimum than maximum temperatures, have occurred for several decades and are projected to continue over this century, which could affect terrestrial carbon (C) cycling. Carbon‐use efficiency of plants (CUEp) and ecosystems (CUEe) represents the capacity of plants to capture C and ecosystems to store C fixed from the atmosphere, respectively. Few studies have examined how grassland CUE responds to asymmetric warming. As part of a long‐term (2006–2016) field experiment that simulated daytime and nighttime warming in a semi‐arid temperate steppe on the Mongolian Plateau, this study was conducted to examine the effects of daytime and nighttime warming on CUEp and CUEe. Nighttime warming, unlike daytime warming, increased CUEe by 54.2%, whereas neither nighttime nor daytime warming affected CUEp. Ecosystem‐level CUE linearly increased with soil moisture but declined with soil temperature variation (CVST). The suppressed ER, which might have been driven by the reduced CVST, primarily contributed to the higher CUEe under nighttime warming. These observations indicate that a reduced DTR, associated with a warmer night under asymmetric diurnal climate warming, could increase the capacity of the temperate steppe transferring C into ecosystems by elevating CUEe, resulting more C sequestration. A free Plain Language Summary can be found within the Supporting Information of this article.

Response of shallow soil temperature to climate change on the Qinghai–Tibetan Plateau

AbstractUnder climate change, soil temperature change remarkably influences regional landscapes, ecosystems, hydrological processes, and other parameters. Based on daily soil temperature data from 56 stations from 1965 to 2014, the spatiotemporal variations in shallow soil temperature (0, 5, 10, 15, and 20 cm) on the Qinghai–Tibetan Plateau (QTP) were investigated. The mean shallow soil temperature decreased obviously with altitude both annually and seasonally, except in winter. Primarily dependent on station latitude, the spatial distribution of winter soil temperature was significantly affected by the snow cover conditions. As the soil depth increased, the soil temperature showed a cooling trend in spring and summer but a warming trend in autumn and winter. In the past 50 years, the shallow soil temperature increased considerably on the QTP both annually and seasonally. The warming rate of soil temperature was greatly dependent on station altitude in winter and dependent on latitude in summer and longitude in autumn. Unlike the increasing air temperature that was contributed mainly by winter, the warming rate of soil temperature in winter at depths of 5, 10, 15, and 20 cm was obviously lower than that in other seasons and air temperature in winter. This occurrence may be caused by relatively less snow cover in winter, which produces a weak insulation effect and further makes the soils more vulnerable to cooling from cold air. For the entire region, the soil temperature variability was strongly correlated with the change in air temperature but weakly correlated with precipitation. Although the warming rate in shallow soil tended to be low (high) at stations with a high amount of precipitation (snow cover), the influence of precipitation (including snow) on shallow soil temperature was limited on the QTP in the past few decades.

The effects of the soil environment on soil organic carbon in tea plantations in Xishuangbanna, southwestern China

Increasing soil organic carbon (SOC) reserves in agricultural land is important for mitigating global climate change. The soil environmental factors that affect SOC storage in agricultural cultivation are relatively easy to manage, but the effects of these factors on SOC have not been studied systematically, especially the relative weight of each factor is still unclear. In this study, more than 30 soil environmental factors including SOC, soil physical and chemical properties, mineral types, and microorganisms present in the 0–140 cm soil layer were determined hierarchically within tea plantations. The main and secondary factors affecting SOC storage were then analyzed quantitatively using a structural equation model. The most important factors affecting SOC storage in tea plantations included water content (18.9 %), total nitrogen (N, 18.8 %), oxalate-extractable iron (active iron, poorly crystalline iron, Feox, 16.3 %), sulfur (S, 13.1 %), total phosphorus (P, 8.6 %), calcium (6.1 %), oxidation reduction potential (5.4 %), clay (4.5 %), bromine (4.3 %), and manganese (4.0 %). Variations in soil temperature and pH on this small scale were small and thus these factors had negligible effects on SOC storage in this study. Organic fertilizer application increased C, N, S, and P concentrations, which can contribute to SOC storage. Appropriate irrigation can also improve SOC storage. We identified a set of Fe-N-S-P coupling mechanisms that promoted SOC storage. Soils with high Fe, N, and S concentrations, high water content, and high oxidation reduction potential relate to an increased Feox concentration, which is important for enhancing SOC stability. Therefore, the application of magnetic (iron oxide) fertilizer to increase Feox in soil promotes SOC storage.

Soil greenhouse gas emissions under different land-use types in savanna ecosystems of Kenya

Abstract. Field measurement data on greenhouse gas (GHG) emissions are still scarce for many land-use types in Africa, causing a high level of uncertainty in GHG budgets. To address this gap, we present in situ measurements of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions from the lowlands of southern Kenya. We conducted eight chamber measurement campaigns on gas exchange from four dominant land-use types (LUTs) comprising (1) cropland, (2) bushland, (3) grazing land, and (4) conservation land between 29 November 2017 and 3 November 2018, accounting for regional seasonality (wet and dry seasons and transitions periods). Mean CO2 emissions for the whole observation period were the highest by a significant margin (p value < 0.05) in the conservation land (75±6 mg CO2-C m−2 h−1) compared to the three other sites, which ranged from 45±4 mg CO2-C m−2 h−1 (bushland) to 50±5 mg CO2-C m−2 h−1 (grazing land). Furthermore, CO2 emissions varied between seasons, with significantly higher emissions in the wet season than the dry season. Mean N2O emissions were highest in cropland (2.7±0.6 µg N2O-N m−2 h−1) and lowest in bushland (1.2±0.4 µg N2O-N m−2 h−1) but did not vary with season. In fact, N2O emissions were very low both in the wet and dry seasons, with slightly elevated values during the early days of the wet seasons in all LUTs. On the other hand, CH4 emissions did not show any significant differences across LUTs and seasons. Most CH4 fluxes were below the limit of detection (LOD, ±0.03 mg CH4-C m−2 h−1). We attributed the difference in soil CO2 emissions between the four sites to soil C content, which differed between the sites and was highest in the conservation land. In addition, CO2 and N2O emissions positively correlated with soil moisture, thus an increase in soil moisture led to an increase in emissions. Furthermore, vegetation cover explained the seasonal variation in soil CO2 emissions as depicted by a strong positive correlation between the normalized difference vegetation index (NDVI) and CO2 emissions, most likely because, with more green (active) vegetation cover, higher CO2 emissions occur due to enhanced root respiration compared to drier periods. Soil temperature did not show a clear correlation with either CO2 or N2O emissions, which is likely due to the low variability in soil temperature between seasons and sites. Based on our results, soil C, active vegetation cover, and soil moisture are key drivers of soil GHG emissions in all the tested LUTs in southern Kenya. Our results are within the range of previous GHG flux measurements from soils from various LUTs in other parts of Kenya and contribute to more accurate baseline GHG emission estimates from Africa, which are key to reducing uncertainties in global GHG budgets as well as for informing policymakers when discussing low-emission development strategies.

Alpine Hummocks Drive Plant Diversity and Soil Fertile Islands on the Tibetan Plateau

Earth hummocks are widely distributed in arctic, sub-Arctic and alpine regions and have important roles in determining plant diversity and the nutrient content of soils. We investigated the impact of the spatial heterogeneity on soil properties and plant communities caused by the hummocks on the Tibetan Plateau. The results indicated alpine hummocks created higher plant diversity and soil fertile island patterns under Kobresia Genus communities. Vegetation height, cover, above-ground and underground biomass, species richness and diversity at the top of well-developed hummocks were the significantly higher than those in the inter-hummocks and surrounding flat ground. The soil organic carbon content in surface soil layer (0-50 cm) at the hummock top was 154.6% and 172.3% higher than those in inter-hummock area and the flat ground, respectively. From the developing to well-developed stage, K. littledalei became the dominant population at hummock top instead of K. humilis, and fertile islands gradually formed with higher soil organic carbon and total nitrogen, lower soil moisture and wider soil temperature variation. RDA analysis further indicated the interactions of plant community succession and soil fertile island could create positive feedbacks to nutrient-rich patches.

Response of Soil CO2 Efflux to Shelterwood Harvesting in a Mature Temperate Pine Forest

In forest ecosystems, soil CO2 efflux is an important component of ecosystem respiration (RE), which is generally driven by variability in soil temperature and soil moisture. Tree harvesting in forests can alter the soil variables and, consequently, impact soil CO2 efflux. This study investigated the response of total soil CO2 efflux, and its components, to a shelterwood harvesting event of a mature temperate white pine (Pinus strobus L.) forest located in Southern Ontario, Canada. The objective was to explore the response of soil CO2 effluxes to changes in the forest microclimate, such as soil temperature and soil moisture, after shelterwood harvesting removed approximately one-third of the overstory canopy. No significant differences were found in both soil temperature and soil moisture between the pre-harvesting (2008–2011) and post-harvesting (2012–2014) periods. Despite similar soil microclimates, total soil CO2 effluxes were significantly reduced by up to 37%. Soil CO2 effluxes from heterotrophic sources were significantly reduced post-harvesting by approximately 27%, while no significant difference in the mineral-soil horizon sources were measured. An analysis of RE, measured with an eddy covariance tower over the study area, showed an increase post-harvesting. However, the overall net ecosystem carbon exchange showed no significant difference between pre- and post-harvesting. This was due to an increase in the gross ecosystem productivity post-harvesting, compensating for the increased losses (i.e., increased RE). This study highlights the complexities of soil CO2 efflux after a disturbance, such as a harvest. The knowledge gained from this study adds to our understanding of how shelterwood harvesting may influence ecosystem carbon exchange and will be useful for forest managers focused on carbon sequestration and forest conservation.

Landscape-scale variability of air and soil temperature related to tree growth in the treeline ecotone

Treeline isotherms are used in comparative and modelling studies to predict treeline positions. However, how representative local short-term temperature records are for a given region remains poorly understood. Furthermore, the predictive value of on-site temperatures for explaining tree growth requires further validation. Here we present temperature records and tree growth datasets from treeline ecotone sites differing in elevation and slope direction in the High Sudetes (Czechia and Poland). The goal was to determine the spatial and temporal variability of soil and air temperatures and to describe the relationship of various temperature metrics with tree growth. Our results demonstrate that, because of spatial and temporal variability, major temperature metrics used in comparative studies should be provided with an uncertainty range between 0.6 and 0.8 K for seasonal mean soil and air temperature. While soil temperatures exhibit high spatial variability, air temperatures vary more with time. Elevation is the most important driver of temperature patterns in treeline ecotones. Differences related to slope direction were important mainly for soil temperatures in lower parts of treeline ecotones. Tree growth is tightly related to June–September air temperature, with a modulating role of the onset date of soil temperature-defined growing season. In this study, we describe patterns of temperature variation in the treeline ecotones of two mountain ranges and demonstrate the extremely strong dependence of tree stem growth on air temperature, with very limited remaining space for other potentially limiting factors.

Coupled variations of soil temperature and moisture in reclaimed fields filled with coal gangue of different grain size distributions

This study was aimed at investigating the effects of different reclamation modes on coupled variations of soil temperature and moisture. An experimental field was established, which consists of three plots (plots I, II, and III) filled with coal gangue of different grain size distributions (coarse grain, middle-coarse grain, and fine grain) and covered with the same thickness (50 cm) of soil. Temperature and moisture at four depths (10, 25, 50, and 65 cm) in three plots were monitored and analyzed. The study reveals that both in winter and summer soil temperature at each depth was highest in plot III and lowest in plot I. Although plot III performed better in heat preservation in winter, soil temperature of which was too high in summer for crop growth. The results also indicate that annual average of soil moisture at the depth of 10 cm and 25 cm was highest in plot II, namely plot II performed best in water holding in the tillage layer for the whole year. Soil temperature and moisture in plot II were more conducive to crop growth on the whole, and it is recommended to adopt the reclamation mode of plot II for land reclamation in coal mining subsidence areas with high ground water table.

Soil Temperature Dynamics at Hillslope Scale—Field Observation and Machine Learning-Based Approach

Soil temperature plays an important role in understanding hydrological, ecological, meteorological, and land surface processes. However, studies related to soil temperature variability are very scarce in various parts of the world, especially in the Indian Himalayan Region (IHR). Thus, this study aims to analyze the spatio-temporal variability of soil temperature in two nested hillslopes of the lesser Himalaya and to check the efficiency of different machine learning algorithms to estimate soil temperature in the data-scarce region. To accomplish this goal, grassed (GA) and agro-forested (AgF) hillslopes were instrumented with Odyssey water level and decagon soil moisture and temperature sensors. The average soil temperature of the south aspect hillslope (i.e., GA hillslope) was higher than the north aspect hillslope (i.e., AgF hillslope). After analyzing 40 rainfall events from both hillslopes, it was observed that a rainfall duration of greater than 7.5 h or an event with an average rainfall intensity greater than 7.5 mm/h results in more than 2 °C soil temperature drop. Further, a drop in soil temperature less than 1 °C was also observed during very high-intensity rainfall which has a very short event duration. During the rainy season, the soil temperature drop of the GA hillslope is higher than the AgF hillslope as the former one infiltrates more water. This observation indicates the significant correlation between soil moisture rise and soil temperature drop. The potential of four machine learning algorithms was also explored in predicting soil temperature under data-scarce conditions. Among the four machine learning algorithms, an extreme gradient boosting system (XGBoost) performed better for both the hillslopes followed by random forests (RF), multilayer perceptron (MLP), and support vector machine (SVMs). The addition of rainfall to meteorological and meteorological + soil moisture datasets did not improve the models considerably. However, the addition of soil moisture to meteorological parameters improved the model significantly.

Straw and plastic management regulate air-soil temperature amplitude and wetting-drying alternation in soil to promote intercrop productivity in arid regions

Soil coverage with straw and plastic mulch is a valuable and useful strategy for enhancing crop production in arid regions. However, a better understanding of the mechanism by which this innovative practice drives spatial and temporal variation in soil temperature and water content and improves crop production could guide cropping system optimization. A three-year field experiment was performed with four wheat-maize strip-intercropping treatments: 1) no-tillage with 25−30 cm tall wheat straw standing in wheat strips and residual plastic mulching in maize strips (NTS), 2) no-tillage with 25−30 cm tall wheat straw mulching in wheat strips and residual plastic mulching in maize strips (NTM), 3) conventional tillage with 25−30 cm tall wheat straw incorporation in wheat strips and annual new plastic mulching in maize strips (CTS), and 4) conventional tillage without wheat straw retention in wheat strips and annual new plastic mulching in maize strips (CT). The temporal and spatial variation in soil temperature and soil water content was assessed. NTM had the greatest soil water retention, and increased soil water content in the 0−120 cm soil depth by 6.4, 5.2, and 5.4 % at the wheat independent growing period, intercrops co-growing period, and maize independent growing period, respectively, compared with CT. In the 0−15 cm soil depth, compared with CT, NTS decreased soil temperature by 0.73, 1.18, and 0.85 °C, NTM decreased it by 1.35, 1.95, and 1.38 °C, during the three aforementioned crop growing periods. With the intercropping treatment, soil temperature in the 0−15 cm soil depth of maize strips was higher than that of wheat strips with NTS by 1.13, 3.67, and 1.44 °C, and with NTM higher by 1.32, 2.97, and 1.75 °C, especially higher as 1.38, 4.00,and 1.68 °C with CT, during the three aforementioned crop growing periods. According to the value of difference between air and soil temperatures, NTM maintained soil heat in the low temperature season and reduced soil temperature in the high temperature season. These allowed the intercrops to grow in a collaborative state with the NTM treatment during their growing period, it is an important regulation mechanism for growth and development of intercropped wheat and maize. NTM improved total grain yield of wheat plus maize by 14.9 % in comparison to CT. The optimized soil temperature and increased soil moisture for the intercrops’ strips with NTM indicates that the integrated set of practices in this treatment can be used as a superior technique to overcome simultaneous water shortage and heat stress in arid irrigated areas of northwestern China.

Spatial and temporal variations in soil temperatures over the Qinghai–Tibet Plateau from 1980 to 2017 based on reanalysis products

A change in soil temperature (ST) is a significant indicator of climate change, so understanding the variations in ST is required for studying the changes of the Qinghai–Tibet Plateau (QTP) permafrost. We investigated the performance of three reanalysis ST products at three soil depths (0–10 cm, 10–40 cm, and 40–100 cm) on the permafrost regions of the QTP: the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim), the second version of the National Centers for Environmental Prediction Climate Forecast System (CFSv2), and the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). Our results indicate that all three reanalysis ST products underestimate observations with negative mean bias error values at all three soil layers. The MERRA-2 product performed best in the first and second soil layers, and the ERA-Interim product performed best in the third soil layer. The spatiotemporal changes of annual and seasonal STs on the QTP from 1980 to 2017 were investigated using Sen’s slope estimator and the Mann–Kendall test. There was an increasing trend of ST in the deeper soil layer, which was less than that of the shallow soil layers in the spring and summer as well as annually. In contrast, the first-layer ST warming rate was significantly lower than that of the deeper soil layers in the autumn and winter. The significantly (P < 0.01) increasing trend of the annual ST indicates that the QTP has experienced climate warming during the past 38 years, which is one of the factors promoting permafrost degradation of the QTP.

Microbial dynamics and soil physicochemical properties explain large-scale variations in soil organic carbon.

First-order organic matter decomposition models are used within most Earth System Models (ESMs) to project future global carbon cycling; these models have been criticized for not accurately representing mechanisms of soil organic carbon (SOC) stabilization and SOC response to climate change. New soil biogeochemical models have been developed, but their evaluation is limited to observations from laboratory incubations or few field experiments. Given the global scope of ESMs, a comprehensive evaluation of such models is essential using in situ observations of a wide range of SOC stocks over large spatial scales before their introduction to ESMs. In this study, we collected a set of in situ observations of SOC, litterfall and soil properties from 206 sites covering different forest and soil types in Europe and China. These data were used to calibrate the model MIMICS (The MIcrobial-MIneral Carbon Stabilization model), which we compared to the widely used first-order model CENTURY. We show that, compared to CENTURY, MIMICS more accurately estimates forest SOC concentrations and the sensitivities of SOC to variation in soil temperature, clay content and litter input. The ratios of microbial biomass to total SOC predicted by MIMICS agree well with independent observations from globally distributed forest sites. By testing different hypotheses regarding (using alternative process representations) the physicochemical constraints on SOC deprotection and microbial turnover in MIMICS, the errors of simulated SOC concentrations across sites were further decreased. We show that MIMICS can resolve the dominant mechanisms of SOC decomposition and stabilization and that it can be a reliable tool for predictions of terrestrial SOC dynamics under future climate change. It also allows us to evaluate at large scale the rapidly evolving understanding of SOC formation and stabilization based on laboratory and limited filed observation.

A Method for Reconstructing the Past Soil Temperature Based on Tree-Ring Widths

Abstract Soil temperature can affect tree growth and is one of the most important types of basic data for forest cultivation and management. To obtain a long-term time series of soil temperatures, we explored the utility of dendroclimatology in a subtropical area of China. In this study, the relations between tree-ring-width chronologies and climate factors were explored by correlation analysis. The results indicated that the limiting climatic factors for the radial growth of Huangshan pine were elevation-specific. Further investigation found that chronology at high elevations was significantly correlated with soil temperature. Then, we described a reconstruction of the soil temperatures of the Dabie Mountains area using the tree-ring width chronology from 1869 to 2015 and showed that the reconstruction explained 42.9 percent of the instrumental soil temperature variation in the common years. We found that the 1970s and 2000s were the coldest and warmest decades since 1884, respectively. The results of the reconstruction method for describing past soil temperatures can provide a reference for other subtropical forests. Furthermore, the results of our research also have a certain significance for guiding policymaking related to forest cultivation and management.

The effect on soil nitrogen mineralization resulting from biochar and straw regulation in seasonally frozen agricultural ecosystem

To thoroughly explore the effects of different regulation measures on soil nitrogen cycling in seasonally frozen areas, four treatments, natural control (BL), biochar addition (BA), straw addition (SA) and combined of biochar and straw (CBS), were established on the Songnen Plain of Northeast China. Variations in soil moisture, temperature and urease activity were analyzed. In addition, the mineralization rate was calculated based on the changes of soil inorganic nitrogen content. Furthermore, the response functions of the soil nitrogen mineralization rate were constructed, and the response mechanism for the effect of different regulation patterns on soil nitrogen was determined. It showed that during the freezing period, straw mulch effectively inhibited the loss of soil water and heat, and hindered the reduction in soil urease activity; the average soil urease activity under the SA treatment increased by 0.390, 0.272, and 0.157 mg⋅(g−1·d−1) relative to those under the BL, BA, and CBS treatments, respectively. During the thawing period, the combined of bio char and straw had better heat preservation and water conservation, which greatly enhanced the activity of soil urease. The regulation of biochar and straw significantly affected the soil nitrogen mineralization rate its relationship with influencing factors. During the freezing period, the inorganic nitrogen content was the highest under the SA treatment. During the thawing period, the combined of biochar and straw enhanced the accumulation of soil nitrogen, and the response of the nitrogen mineralization rate to soil water, heat, and urease activity was strongest. In addition, the regulation abilities of biochar and straw decreased with increasing soil depth. These research results have important significance for understanding nitrogen transformations and efficiently guiding agricultural cleaner production.

Microclimatic effects on alpine plant communities and flower-visitor interactions

High-alpine ecosystems are commonly assumed to be particularly endangered by climate warming. Recent research, however, suggests that the heterogeneous topography of alpine landscapes provide microclimatic niches for alpine plants (i.e. soil temperatures that support the establishment and reproduction of species). Whether the microclimatic heterogeneity also affects diversity or species interactions on higher trophic levels remains unknown. Here we show that variation in mean seasonal soil temperature within an alpine pasture is within the same range as in plots differing in nearly 500 m in elevation. This pronounced heterogeneity of soil temperature among plots affected the spatial distribution of flowering plant species in our study area with a higher plant richness and cover in warmer plots. This increased plant productivity in warmer plots positively affected richness of flower visitor taxa as well as interaction frequency. Additionally, flower-visitor networks were more generalized in plots with higher plant cover. These results suggest that soil temperature directly affects plant diversity and productivity and indirectly affects network stability. The strong effect of heterogeneous soil temperature on plant communities and their interaction partners may also mitigate climate warming impacts by enabling plants to track their suitable temperature niches within a confined area.

Non-rainfall water contributions to dryland jujube plantation evapotranspiration in the Hilly Loess Region of China

Non-rainfall water inputs (NRWIs) provide crucial water resources for dryland ecosystems in arid and semi-arid regions. However, little is known about the quantitative characteristics and formation of NRWIs, and the relative importance of NRWIs as water sources in a dryland jujube (Ziziphus jujuba Mill.) plantation in the Hilly Loess Region of China. The objectives of this study were to determine the characteristics of NRWIs during the jujube growing season with regard to amount, duration, and contributions to transpiration, evaporation, and evapotranspiration. Dew intensity and duration were monitored using dielectric leaf wetness sensors, Also sap flow, soil water content, soil temperature, and meteorological variables were measured during the 2017 and 2018 growing seasons. NRWIs were found to be composed of canopy dew (CD) and water vapor adsorption (WVAS) in the 0–5 cm soil layer, amounting to 75.218 mm in 2017 and 75.309 mm in 2018 (CD accounted for about 81% of NRWI). Daily average CD was significantly greater than WVAS (P < 0.05), and CD duration was 2.09–9.14 h more than WVAS duration (P < 0.05). The CD rate and frequency generally exceeded that of WVAS. CD occurred from 19:00 to 9:00. WVAS mainly occurred from 6:30 to 9:00. CD reduced nocturnal sap flow by 7.36–55.64%, but increased soil water storage (in the 5–100 cm root zone) by 0.274–0.717 mm. WVAS had no effect on soil water evaporation. Over the entire growing season, the ratio of CD to total transpiration was 0.218 in 2017 and 0.258 in 2018, and the ratio of WVAS to soil water evaporation was 0.082 in both years. NRWIs occurred more frequently and were quantitatively more stable than rainfall events. Their contributions to evapotranspiration reached a maximum value of 0.184 in 2018. NRWIs are important components of the hydrological cycle in this region, and probably have potential positive ecological effects on dryland jujube plantations in the Hilly Loess Region of China.

The spatiotemporal variations of soil water content and soil temperature and the influences of precipitation and air temperature at the daily, monthly, and annual timescales in China

Soil water content (SWC) and soil temperature (ST) are important properties in water-energy balance processes. Our objective was to analyze the SWC and ST variations at different soil depths (0–10, 10–40, 40–100, and 100–200 cm) and different timescales (daily, monthly, and annual) affected by precipitation and air temperature at seven sub-regions and entire mainland China. The sine function was used to fit the variations of daily and monthly ST. The results showed that the monthly and annual SWC and ST values were relatively low in northwest China and the alpine region of Qinghai-Tibetan plateau; however, higher values were shown in east China. SWC and ST fluctuated both randomly and periodically, especially at the 0–10 cm depth. The daily and monthly ST had regular time-lags and typical periodical changes, which could be fitted by a sine function for both the grids and sub-regions in China with a coefficient of determination (R2) of 0.855. Further, the correlations between SWC and precipitation were good in southern and northeastern China, but poor in northwestern China and Qinghai-Tibet Plateau at the depths 0.76). In conclusion, the spatiotemporal distribution of SWC and ST was greatly affected by precipitation and air temperature. The fitted sine functions for daily and monthly ST are very useful for elementary determination of the long-term mean ST values for a location.

Unfolding the effects of different forestry treatments on microclimate in oak forests: results of a 4-yr experiment.

A stable below‐canopy microclimate of forests is essential for their biodiversity and ecosystem functionality. Forest management necessarily modifies the buffering capacity of woodlands. However, the specific effects of different forestry treatments on site conditions, the temporal recovery after the harvests, and the reason for the contrasts between treatments are still poorly understood. The effects of four different forestry treatments (clear‐cutting, retention tree group, preparation cutting, and gap‐cutting) on microclimatic variables were studied within a field experiment in a managed oak‐dominated stand in Hungary, before (2014) and after (2015–2017) the interventions by complete block design with six replicates. From the first post‐treatment year, clear‐cuts differed the most from the uncut control due to the increased irradiance and heat load. Means and variability of air and soil temperature increased, air became dryer along with higher soil moisture levels. Retention tree groups could effectively ameliorate the extreme temperatures but not the mean values. Preparation cutting induced slight changes from the original buffered and humid forest microclimate. Despite the substantially more incoming light, gap‐cutting could retain the cool and humid air conditions and showed the highest increase in soil moisture after the interventions. For most microclimate variables, we could not observe any obvious trend within 3 yr. However, soil temperature variability decreased with time in clear‐cuts, while soil moisture difference continuously increased in gap‐ and clear‐cuts. Based on multivariate analyses, the treatments separated significantly based mainly on the temperature maxima and variability. We found that (1) the effect sizes among treatment levels were consistent throughout the years, (2) the climatic recovery time for variables appears to be far more than 3 yr, and (3) the applied silvicultural methods diverged mainly among the temperature maxima. Based on our study, the spatially heterogeneous and fine‐scaled treatments of continuous cover forestry (gap‐cutting, selection systems) are recommended. By applying these practices, the essential structural elements creating buffered microclimate could be more successfully maintained. Thus, forestry interventions could induce less pronounced alterations in environmental conditions for forest‐dwelling organism groups.

Investigating green infrastructure as potential medium for ground heat exchangers

Space heating and cooling comprises a significant portion of the overall energy consumption. Ground heat exchangers (GHE), are a sustainable alternative to conventional, non-renewably powered heating and cooling systems. Space is a scarce resource in densely urbanised areas, allocating dedicated locations to build GHE systems can result in high initial capital costs and an inflexibility in retrofitting. An alternative solution is to utilise existing, multi-benefit and resilient Sustainable Drainage Systems (SuDS) in cities. An investigation into the feasibility of utilising SuDS as sites for potential GHEs requires an understanding of their thermal and hydrological behaviour and boundary conditions. This study utilises a heavily-instrumented, vegetated lysimeter setup, exposed to atmospheric conditions, to test a pilot-scale SuDS heat exchanger. Heat rejection into the substrate of a SuDS has been simulated with the application of heat via voltage-controlled heating cables at a depth of 850 mm for 72-hour durations (at three different power inputs) with 96-hours between each power input. These heat dissipation periods are reflected in measured soil temperature profiles. Volumetric water content, matric suction, soil temperature and heat flux are monitored at various locations in the lysimeter. A finite difference modelling scheme has been developed to simulate the variation in soil temperature due to heat rejection.

Research on Spatiotemporal Variation of Soil Temperature in China from 1948 to 2018

The change of soil temperature can affect the regional climate, so it is of great significance to research the spatial and temporal evolution characteristics of regional soil temperature over a long period of time for the research of the land-air interaction, climate change and ecological agricultural construction. We use the v2.0 and v2.1 data set combined with GLDAS and Noah models to analyze the spatiotemporal variation of temperature in soil layers of 0 - 200 cm in China during the period of 71 years from 1948 to 2018. Firstly, the Mann-Kendall test method is used to research the variation trend of soil temperature over the past 71 years in China and the spatial variation of these trends. Secondly, by calculating the spatiotemporal coefficient of variation (CV) of soil temperature, the spatial-temporal fluctuation of soil temperature in China is further studied and analyzed. Finally, the Hurst index is used to analyze the possible future trend of soil temperature in China. Based on these methods, we have drawn the following conclusions: 1) The soil temperature in most areas of northern China had an increasing trend, especially in the northeast China. The soil temperature in most of the south China had a decreasing trend. The temperature trends of the four soil layers had little difference, and it remained stable on the whole. 2) The regional difference of soil temperature in China remained stable before 1999, and decreased suddenly in 2000. After 2008, the regional difference increased. Compared with the previous period, the temperature in some areas increased or decreased abnormally. 3) The soil temperature in eastern, southeast China and Xinjiang had a relatively significant variation in the 71 years. From 0 - 10 cm soil surface to 100 - 200 cm soil bottom, the spatial difference of temperature gradually decreased, which was due to the fact that the soil temperature was more affected by the surface atmospheric temperature. 4) The soil temperature in the north and northwest of China will continue to grow, and in the southern—most will continue to decrease. The soil temperature in the north of central China will become a decreasing trend, while the temperature in the south of central China will become an increasing trend.