Variation In Soil Temperature Research Articles

Experimental study on the hydro-thermal-deformation characteristics of cement-stabilized soil exposed to freeze–thaw cycles

The exploration of the hydro-thermal characteristics and deformation behaviors of cement-stabilized soils is important for the prevention and control of freeze–thaw damage in cold region engineering. This study used six groups of cement-stabilized soil samples with different cement contents (i.e., 3%, 6%, 9%, 12%, 15%, and 18%) to investigate the variations in soil temperature, volumetric unfrozen water content, deformation, freezing temperature, and dry density. The results showed that the temperatures of the cement-stabilized soil samples during the freezing and thawing processes can be categorized into three stages and that the freezing temperature decreased with increasing cement content. Moreover, the cement content and ambient temperature significantly affected the volumetric unfrozen water content of the cement-stabilized soil samples during the freeze–thaw cycles, and the soil temperatures corresponding to the peak hysteresis degree were relatively consistent with the freezing temperature. The residual volumetric unfrozen water content primarily depended not only on the cement content but also on the freezing condition. Although the variations in volumetric unfrozen water contents during the freezing and thawing processes were similar, the ranges in temperature change differed significantly, particularly in the drastic phase transition zone. Additionally, adding cement into soils effectively inhibited deformation, mainly due to the dual positive effects of the liquid water reduction owing to hydration reaction and structure compaction owing to the filling of hydration products.

Climatic control of high-resolution stem radius changes in a drought-limited southern boreal forest

Key messageStem radius changes measured at high temporal resolution in a drought-limited southern boreal forest were primarily related to soil temperature and partly soil moisture variation, but only weakly to VPD.Forest productivity at the southern fringe of the boreal forest biome in Inner Asia is strongly drought-limited, as is evident from dendrochronological analyses. Using electronic point dendrometers, we studied the climate response of stem radius changes at high temporal resolution (10-min intervals) in a mixed larch–birch forest in northern Mongolia in a drought year and two subsequent moist years. Larch trees showed stronger stem radius fluctuations than birches, and this difference was more pronounced in dry than in moist years. Stem radius changes were most tightly related to soil temperature variation, while soil moisture was the dominant controlling factor only in birch in the dry year. Correlations with the atmospheric vapor pressure deficit (VPD), and even more so with air temperature, were much weaker. While the linkage between radius change and VPD might primarily reflect diurnal transpiration-driven stem shrinkage and expansion, soil temperature is thought to directly affect cambial cell division and elongation during wood formation. We conclude that the phenology of stemwood increment is strongly controlled by soil temperature even in drought-limited southern boreal forests under continental climate due to the combination of cold and dry climate.

Spatiotemporal Variations of Soil Temperature at 10 and 50 cm Depths in Permafrost Regions along the Qinghai-Tibet Engineering Corridor

Soil temperature plays an essential role in the permafrost thermal state and degradation process. Especially the soil temperatures at 10 cm and 50 cm depths in the active layer, which are much easier to be observed in situ, have great effects on the surface water cycles and vegetation, and could be used as the upper boundary for permafrost models to simulate the thermal state of the permafrost and active layer thicknesses. However, due to the limitations of the observation data, there are still large uncertainties in the soil temperature data, including at these two depths, in the permafrost region of Qinghai–Tibet Plateau (QTP). In this study, we evaluated and calibrated the applicability of four daily shallow soil temperature datasets (i.e., MERRA-2, GLDAS-Noah, ERA5-Land, and CFSR) by using the in situ soil temperature data from eight observation sites from 2004 to 2018 in the permafrost region along the Qinghai–Tibet Engineering Corridor. The results revealed that there were different uncertainties for all four sets of reanalysis data, which were the largest (Bias = −2.44 °C) in CFSR and smallest (Bias= −0.43 °C) in GLDAS-Noah at depths of 10 cm and 50 cm. Overall, the reanalysis datasets reflect the trends of soil temperature, and the applicability of reanalysis data at 50 cm depth is better than at 10 cm depth. Furthermore, the GLDAS-Noah soil temperatures were recalibrated based on our observations using multiple linear regression and random forest models. The accuracy of the corrected daily soil temperature was significantly improved, and the RMSE was reduced by 1.49 °C and 1.28 °C at the depth of 10 cm and 50 cm, respectively. The random forest model performed better in the calibration of soil temperature data from GLDAS-Noah. Finally, the warming rates of soil temperature were analyzed, which were 0.0994 °C/a and 0.1005 °C/a at 10 cm and 50 cm depth from 2004 to 2018, respectively.

Integrating pH into the metabolic theory of ecology to predict bacterial diversity in soil.

Microorganisms play essential roles in soil ecosystem functioning and maintenance, but methods are currently lacking for quantitative assessments of the mechanisms underlying microbial diversity patterns observed across disparate systems and scales. Here we established a quantitative model to incorporate pH into metabolic theory to capture and explain some of the unexplained variation in the relationship between temperature and soil bacterial diversity. We then tested and validated our newly developed models across multiple scales of ecological organization. At the species level, we modeled the diversification rate of the model bacterium Pseudomonas fluorescens evolving under laboratory media gradients varying in temperature and pH. At the community level, we modeled patterns of bacterial communities in paddy soils across a continental scale, which included natural gradients of pH and temperature. Last, we further extended our model at a global scale by integrating a meta-analysis comprising 870 soils collected worldwide from a wide range of ecosystems. Our results were robust in consistently predicting the distributional patterns of bacterial diversity across soil temperature and pH gradients-with model variation explaining from 7 to 66% of the variation in bacterial diversity, depending on the scale and system complexity. Together, our study represents a nexus point for the integration of soil bacterial diversity and quantitative models with the potential to be used at distinct spatiotemporal scales. By mechanistically representing pH into metabolic theory, our study enhances our capacity to explain and predict the patterns of bacterial diversity and functioning under current or future climate change scenarios.

Compositional variation of endangered spring fen biota reflects within-site variation in soil temperature

Compositional variation of endangered spring fen biota reflects within-site variation in soil temperature

Spatiotemporal Database Schema for Data Driven Applications in Smart Agriculture

Background: Data driven sustainable agriculture involves the collection, storage, processing, and analysis of enormous spatiotemporal data related to crop production processes, systems, infrastructure, and environment. Literature survey on smart agriculture research projects indicates that there is a need for improving handling of spatiotemporal data. There are gaps in handling spatial and temporal variability of parameters, division of crop field into management zones to reduce the variability for optimizing application of inputs such as fertilizers, water or pesticides. These gaps are to be addressed at design level of spatiotemporal database for smart agriculture. Objective: To engineer a spatiotemporal database schema that can be used for data driven sustainable agriculture. Methods: The methodology involves spatiotemporal data representation and modeling, Object oriented analysis and design of the database and Verification of the database using life cycle model and algorithmic steps. Findings: The resulting database is capable to store spatial and temporal variability of soil, plant and water parameters as well as handle spatial split, spatial merge, geometry and location changes of spatiotemporal objects. Novelty: Novel Use cases in smart agriculture along with spatiotemporal attributes are identified so that efficient applications can be realized. Adaption of the spatiotemporal database schema for Smart Irrigation System and its implementation methodology are presented. Keywords: Spatiotemporal Database Design; Data-Driven Agriculture; Agriculture Informatics; Database Verification; Spatiotemporal Data Analysis

Surface water-groundwater interaction affects soil temperature distributions and variations in salt marshes

Soil temperature is an important environmental factor affecting biogeochemical processes in salt marshes and further wetland ecological functions. This study conducted field investigation and numerical simulations to examine temperature distributions and variations in a creek-marsh section subjected to estuarine and meteorological forcing conditions. The results showed that periodic tidal inundation induced water and heat exchange across sediment-water interfaces and thus modified diurnal temperature variations in shallow soil layers caused by meteorological fluctuations. The combination of periodic tidal inundation and sediment-atmosphere heat exchange led to the formation of three characteristic soil temperature zones along the creek-marsh section: a high-elevation marsh zone with diurnal temperature variations influenced by meteorological fluctuations, a near-creek zone where tide-induced porewater circulations regulated soil temperatures, and a low-elevation and sloping zone where sediment-atmosphere heat exchange decreased with the reduced marsh elevation. Sensitivity analyses demonstrated that a larger hydraulic conductivity facilitated the porewater circulation and heat transport in the near-creek zone, enhancing temperature fluctuations. An increased soil thermal conductivity intensified vertical heat exchange across sediment-water-atmosphere interfaces and increased the effect of estuarine and meteorological conditions on soil temperature. This study highlights the importance of surface water-groundwater interaction on temperature variations and helps to understand thermodynamics-dependent biogeochemical processes in salt marshes.

Identification of Soil Features Suitable for Barley, Maize and Sugarcane Cultivation using Precision Agriculture

Agriculture plays a crucial role in a nation's economy by significantly contributing to its Gross Domestic Product (GDP). Improved methods of farming not only benefit farmers by lowering their workload but also boost crop yields. Identifying the optimal soil for each crop is essential for producing harvests of the highest quality and quantity. Precision farming in agriculture uses Internet of Things (IoT) technology to ensure the most efficient use of available resources to increase crop yields and reduce operational costs. It reduces instances of crop failure and aids in averting catastrophic losses. Variations in soil temperature and soil moisture have the most significant influence on crop yield. The Soil Moisture Sensors calculate the soil's total volumetric water content. Using the BMP280 absolute barometric pressure sensor, it is possible to get accurate temperature and air pressure measurements. In the paper, the primary purpose of precision agriculture usage is to determine the optimal soil characteristics for the production of Barely, Maize and Sugarcane crops.

Daily Variation on Soil Moisture and Temperature on Three Restinga Plant Formations

Restinga forests and open scrubby formations establish on sandy well-drained soils alongside the Brazilian coastline. Restinga plants are exposed to extreme conditions and vegetation types are mainly structured by species access to groundwater. But to date, no systematic evaluations have been done in order to characterize soil microclimatic conditions and understand how they are associated with variations in climatic drivers. We evaluated hourly soil moisture and temperature along 84 days at Restinga Seasonal Dry Forest (SDF), sparse (Open Clusia Scrubs—OCS), and dense (Open Ericacea Scrubs—OES) tickets at Restinga de Jurubatiba National Park, at Rio de Janeiro state (Brazil). Due to distinctions on physical structure and access to groundwater between plant formations, we expected higher daily soil moisture and lower daily moisture and temperature variations on forests than on open vegetated areas. Daily soil moisture was higher, respectively, on SDF, OES, and OCS, whereas soil moisture and temperature variability presented the opposite trend (SDF < OES < OCS), supporting our hypotheses. Daily soil temperature dynamics are quite well predicted by solar radiation incidence patterns, whereas daily soil moisture is mainly regulated by precipitation at OCS, an interaction of precipitation and temperature at OES and delayed effects of precipitation at SDF. Our results corroborate our expectations that forests are more effective in buffering both air temperature and precipitation effects on soil conditions than open vegetated areas. They also indicate that soil moisture and temperature conditions are important aspects differentiating Restinga vegetation types.

Changes in temperature regime of soil in cryolithozone considering climate warming

The current climate change in Russia is characterized as continuing warming. There is an increase of the deformity and accident rate for buildings located in the cryolithozone. It is necessary to identify regions that in the future will be most susceptible to the permafrost degradation and associated risks for existing buildings and structures, which require considering climate warming in the forecast estimates. The purpose of this study was to assess the impact of climate warming on the temperature regime of the soils of the Norilsk district. Numerical modeling of the temperature variation of soil considering air temperature increase according to the regional climate model of the Voeikov MGO on 60 years showed temperature rise of permafrost, lowering its top and increasing the thickness of the seasonally thawed layer. The warming of the climate in the area will have a significant impact on the temperature regime of the soil and will lead to a violation of the operational suitability of existing buildings and structures. In the Norilsk region climate warming should be regarded as a significant accident occurrence factor, which should be considered when calculating the bases in the cryolithozone for the entire period of construction and operation of facilities.

Soil Carbon Fluxes and Sensitivity Analysis – A Study in Pinus roxburghii Forest

The predicted increasing atmospheric carbon dioxide (CO2) level is responsive to altering the future climate, and a small change in the soil carbon may significantly affect the forest carbon cycle and climate system. Soil respiration (SR) and its influencing factors like soil temperature (ST), soil water content (SWC) and surface litter-fall were measured monthly over one year in a sub-tropical Pine (Pinus roxburghii) forest of Bhaktapur district located in central Nepal to determine the SR of the forest and, its variations and sensitivity. The results showed that SR varied to the changes in ST by an exponential significant positive correlation between them. The optimum SR was observed between 10 and 22ºC, and the highest SR were obtained above ST at 20ºC. The temperature sensitivity value of SR (Q10) was estimated at Q10 = 2.13. The significant exponential curve represented the effect of SWC on SR. The higher SR rate was mostly measured between 10 and 25% SWC. The monthly and seasonal variations of the SR rate were consistent with the ST, SWC and litter-fall variations. The study showed that the combined effect of temperature and precipitation might be the major cause of SR variations; however, ST is adequate for increasing SR. Hence, the warming further enhances carbon emission from the forest floor and inversely increases carbon to contribute to climatic change through this pine-dominated forest stand structure.

Spatiotemporal variation characteristics of hourly soil temperature in different layers in the low-latitude plateau of China

Soil temperature change has considerable impact on land surface energy and water balances, and hence on changes in weather/climate, surface/subsurface hydrology, and ecosystems. However, little is known regarding the spatiotemporal variations and influencing factors of changes in hourly soil temperature (depth: 5–320 cm) in low-latitude highland areas. This study analyzed the hourly soil temperature at each hour during 2004–2020 and at 08:00, 14:00, and 20:00 (Beijing Time) during 1961–2020. The results revealed the following. 1) As soil depth increased, average soil temperature increased in autumn and winter, and decreased annually and in spring and summer. It exhibited significant increase during 00:00–23:00 annually, seasonally, and monthly, especially at depths of 40–320 cm during 2004–2020. Average soil temperature increased at 08:00 and decreased at 14:00 and 20:00 with increasing soil depth, but the opposite trend was found annually, seasonally, and monthly at 08:00, 14:00, and 20:00 during 1961–2020. 2) With increasing elevation, average soil temperature decreased at 08:00, 14:00, and 20:00 at depths of 5–20 cm, and showed significant increase trend at 08:00 and 14:00 at depths of 10–20 cm (except at 14:00 at 10-cm depth). 3) At 5-cm depth, the critical accumulated soil temperature of ≥12°C and 14°C extended the potential growing season during 1961–2020. 5) Significant uptrend of hourly soil temperature annually, seasonally, and monthly potentially leads to additional release of carbon to the atmosphere and increased soil respiration, reinforcing climate warming. These findings contribute to better understanding of the variation of shallow soil temperatures and land–atmosphere interactions in low-latitude highland areas.

The hydrothermal changes of permafrost active layer and their impact on summer rainfall-runoff processes in an alpine meadow watershed, northwest China

The freezing-thawing variation of permafrost active layer increases the complexity of rainfall-runoff processes in alpine river basins, Northwest China. And alpine meadow is the prominent ecosystem in these basins. This study selected a small alpine meadow watershed in the upper reaches of the Shule River Basin, China. We investigated alpine rainfall-runoff processes, as well as impacts of summer thaw depth of active layer, soil temperature and moisture variation on streamflow based on in-situ observations from July 2015 to December 2020. Some hydrologic parameters or indices were calculated using statistical methods, and impacts of permafrost change on river runoff were assessed using the variable infiltration capacity model (VIC). In the alpine meadow, surface soil (0–10 cm depth) of the active layer starts to freeze in mid-October each year, and begins to thaw in early April. Also, the deeper soil (70–80 cm depth) of the active layer starts to freeze in late October, and begins to thaw in late June. Moisture content in shallow soils fluctuates regularly, whereas deeper soils are more stable, and their response to rainstorms is negligible. During active layer thawing, the moisture content increases with soil depth. In the alpine meadow, vertical infiltration only occurred in soils up to 40 cm deep, and lateral flow occurred in 0–20 and 60–80 cm deep soils at current rainfall intensity. Summer runoff ratios were 0.06–0.31, and runoff floods show lags of 9.5–23.0 h following the rainfall event in the study area. The freeze–thaw process also significantly impacts runoff regression coefficients, which were 0.0088–0.0654 per hour. Recession coefficient decrease negatively correlates with active layer thawing depth in summer and autumn. Alpine river basin permafrost can effectively increase peak discharge and reduce low flow. These findings are highly significant for rainfall–runoff conversion research in alpine areas of inland rivers.

No-tillage with straw mulching and re-using old film boost crop yields and mitigate soil N2O emissions in wheat-maize intercropping at arid irrigated regions

Water shortage and heavy greenhouse gas emissions are threatening agricultural sustainability with food security severely, and becoming a major issue in arid areas. It is unclear whether improved farming systems on strip-intercropping integrated with no-tillage with straw returning and re-using old film practices can be developed to reduce soil nitrous oxide (N 2 O) emissions and boost crop yields for tackling those issues. A four-year field experiment for wheat-maize intercropping was carried on straw residue and film management of northwestern China in 2014–2017 and aimed to comprehensively assess crop yields and soil N 2 O emissions. The results showed that NTSMF (no-tillage with straw mulching and re-using old film), NTSSF (no-tillage with straw standing and re-using old film), and CTSF (conventional tillage with straw incorporation and mulching new film every year) treatments increased grain yields by 15.1%, 13.7%, and 12.8% respectively, compared to CTF (conventional tillage with no straw returning and mulching new film every year, the control treatment). NTSMF, NTSSF, and CTSF treatments had greater water use efficiency by 15.7%, 13.1%, and 14.2% than CTF, respectively. On the contrary, NTSMF and NTSSF treatments had lower soil N 2 O emissions (NE) by 23.9% and 20.4% than CTF, and lower by 19.8% and 16.0% than CTSF, respectively. No-tillage practice used more soil moisture and produced more grain yields but emitted less N 2 O than conventional tillage, NTSMF and NTSSF treatments reduced soil N 2 O emission per volume of evapotranspiration (WUE NE ) by 23.6% and 20.9%, and reduced soil N 2 O emission intensity (NEI) by 33.9% and 30.0% in comparison to CTF. The better effect on the reduction of NE, WUE NE , and SEI was found in NTSMF, and the three indicators were successively decreased by 5.3%, 4.4%, and 6.9% over NTSSF in 2016–2017. NTSMF reduced NE and boosted GY was attributed to increased synchronicity of water demand and reduced adverse effects of soil temperature variations of both intercrops’ strips. Our study concluded that grain yields were enhanced and soil N 2 O emissions were reduced by NTSMF treatment, and NTSMF treatment is a practical cropping production system for environmentally clean in an arid irrigated region. • The improved treatment on NTSMF with straw mulching in wheat strips and re-using old film in maize strips. • The improved treatment reduced soil N 2 O emissions (NE) and boosted grain yields (GY). • NTSMF reduced NE and boosted GY was attributed to increased synchronicity of water demand and reduced adverse effects of soil temperature variations. • NTSMF treatment is a practical cropping system for environmentally clean in arid irrigated areas.

Soil Respiration Variations in Temperate Rhododendron (Rhododendron arboreum) Forest of Annapurna Conservation Area (ACA) in Nepal

Temperate forests are considered most fragile hence need to recognize their vulnerability owing to continuous climatic changes and anthropogenic activities. In this study, we assessed soil respiration (SR) by using the chamber method in a natural Rhododendron (Rhododendron arboreum) forest which is recognized as the world’s largest forest type located at Annapurna Conservation Area in the temperate region of Nepal. We evaluated the consequences of multiple ecological parameters mainly climatic and biotic factors on SR variations during the month of October in 2016 and 2017. Our results confirmed that SR well corresponded with soil temperature (ST) variables represented with the highly significant ( p < 0.05 ) exponential curve (y = 1.049e0.529x, 2016 and y = 26.34e0.284x, 2017). And the variation in SR was mediated by a short-range (2-3°C) of ST difference in the month of October during autumn season. However, the effect of soil water content (SWC) on SR was scattered and the photosynthetic photon flux density (PPFD) stood weak to represent the SR variation. The seasonal trend of SR was compatible with the PPFD and litter input with having accountable temporal, diurnal, and interannual variations of SR, ST, SWC, and litterfall. The SR over the entire measurement period were averaged at 269.9 mg CO2 m−2·h−1 in 2016 and 295.1 mg CO2 m−2·h−1 in 2017. Our study manifested that temperate forests could store maximum soil carbon with limited emission through SR and become a larger sink of atmospheric carbon dioxide even though SR is very sensitive to environmental changes and interactively affected by multiple ecological factors. Thus, our finding is an appreciable measure for the temperate forest to understand the regional carbon balance and suggested temperate forests are valued to incorporate them in evaluating global carbon budget.

An Analytical Solution for the Heat Conduction–Convection Equation in Non-homogeneous Soil

Heat transfer through the soil is important in shallow geothermal applications, in plant growth as well as in the surface energy balance. In this work, an analytical solution for a conduction–convection equation that models heat transfer is presented for non-homogeneous soil. The main assumption underlying the solution is that the thermal diffusivity of soil is piecewise-constant. A method to determine the depth-dependent thermal diffusivity and the water flux density through the porous medium based on temperature measurements is also developed and applied to field data from a site in Ioannina, Greece. The thermal diffusivity was found to increase in the layer below the surface and decrease for larger depths, while convection through the porous medium was found to be present in wet conditions and to account for about 10% of the heat flux in terms of the annual variability of temperature. Finally, the capability of the novel method in capturing the spatio-temporal variability of soil temperature is compared to three commonly used algorithms: the amplitude, the phase, and the conduction–convection algorithm. The novel method is able to reduce the root-mean-square error for the predicted variability of temperature at all depths by an order of magnitude compared to the other three algorithms.

Impact of tundra vegetation type on topsoil temperature in central Spitsbergen (Svalbard, High Arctic)

Current climatic models and projections forecast further increases in air temperature in the Arctic in the future. Therefore, new knowledge concerning the variability of air and soil temperature as well as its dependence on environmental factors is urgently needed to better understand and forecast the consequences of climate warming in the Arctic region. The main aims of this study were: 1) to determine the variability of the topsoil temperature for the one-year time scale under different types of tundra vegetation in the Adventdalen Valley in the central part of Spitsbergen (Svalbard, High Arctic), and 2) to determine the impact of different types of tundra vegetation on the topsoil temperature on a microscale in this area. The obtained results indicate that wet sites covered with marsh and moss tundra vegetation exhibited a significantly higher mean annual topsoil temperature (−0.7 °C and −1.2 °C, respectively) than sites featuring bare ground (−1.5 °C), Arctic meadow (−2.1 °C), and heath tundra vegetation (−2.4 °C). The mean topsoil temperature during the summer season was the lowest at sites covered with Arctic meadow and heath tundra vegetation (4.9 °C and 5.7 °C, respectively), and highest at the site with bare ground (6.9 °C). The topsoil temperature was highly and significantly correlated with the air temperature (correlation coefficient between 0.86 and 0.92); however, the correlation was clearly higher during the autumn and summer seasons (correlation coefficient between 0.76 and 0.89; p < 0.001) in comparison with the winter season (correlation coefficient between 0.67 and 0.89; p < 0.001) and especially the spring season (correlation coefficient between 0.62 and 0.71; p < 0.001). Freeze-thaw events were substantially less frequent in the topsoil (up to 16 events) compared to the atmosphere (at least 80 events), and their number was clearly different even at the microscale (from 4 to 16 events). Local microtopography, snow cover, tundra vegetation type, soil properties, and soil moisture were responsible for variances in topsoil temperature and number of freeze–thaw events. The obtained results indicated that the topsoil temperature is significantly different, even at the microscale, and further research is needed in other Arctic terrestrial environments to better understand and forecast the consequences of climate warming in this region of the world.

The Seasonal and Diurnal Variation Characteristics of Soil Moisture at Different Depths from Observational Sites over the Tibetan Plateau

Using observational data of soil moisture from the third Tibetan Plateau Experiment for atmospheric science (TIPEX III), the seasonal and diurnal variations characteristics of soil moisture at different depths of 5–160 cm from seven stations were analyzed, with emphasis on the comparative analysis of the differences of soil moisture between different sites and the differences of the synergistic relationship between soil moisture and temperature. The soil moisture was wet in the southeast and dry in the northwest. The studied sites were Lhari, Biru, Nyainrong, Amdo, Nagqu, Baingoin and Seng-ge Kambab in descending order, according to the soil moisture. The seasonal variation of soil moisture at the different sites showed a significant three-peak structure, which was more obvious in the shallow layer than in the deep layer. The first peak occurred from March to May, which was mainly due to the soil thawing in spring. The other two peaks corresponded to the two rainy seasons in the plateau. Soil moisture was the greatest during this rainy period. The diurnal variations of soil moisture and temperature in Amdo, Nagqu, Nyainrong and Baingoin showed a significant positive correlation in the four seasons. The soil moisture and temperature in Lhari and Biru were significantly positively correlated in winter and spring but negatively correlated in summer and autumn. The profiles of the soil moisture with depth varied greatly at different stations in different seasons. The distribution of soil water content at each observational site did not increase or decrease with depth but showed a certain high aquifer, which might be related to the types of the underlying surface and physical properties of soil. During the summer monsoon period, soil moisture in the shallow layer of 5–10 cm was higher at all observational sites. The spatial distribution of soil moisture in the plateau was more heterogeneous than that in the plain area, and only in the central part of the Tibetan Plateau, the soil moisture varied greatly from site to site. This also indicated that it was unreasonable to only use the soil moisture of several stations to represent the overall soil moisture of the region. The results provided a multi-angle observational basis for the validation of satellite data and parameterization of the numerical model of soil moisture over the Tibetan Plateau.

Variation characteristics of soil temperature, moisture, and heat flux in the understorey of evergreen broadleaf forest in South China

Based on observation data from the observation tower station in Zhuhai in South China from October 2015 to May 2018, the variations in soil temperature, moisture, and heat flux in the understorey of evergreen broadleaf forest are analyzed. The ground surface temperature is slightly greater than the canopy surface temperature; the soil temperature is the smallest. The seasonal variation in the soil moisture fluctuates around a relative equilibrium as the rain increases or decreases. Both ground and canopy surface temperatures have valley values before sunrise and peak values in the afternoon. The diurnal variations in soil temperature are characterized by a cosine function. With the deepening of the soil layer, the time of valley and peak lag and the amplitude of the variation in the soil temperature decrease. There is almost no diurnal variation in soil temperature at 40 cm depth or the soil heat flux at 30 cm depth. The heat fluxes at depths of 7.5 cm and 15 cm show an “S” pattern variation, with a peak at 17:30. The net radiation of the canopy surface shows a bell-shaped variation, with a peak at 12:30. The averaged soil thermal conductivities are 2.18 W·m−1·K−1, 1.22 W·m−1·K−1, and 1.26 W·m−1·K−1 for 5 ~ 10 cm, 10 ~ 20 cm, and 20 ~ 40 cm depths, respectively.

Plant recruitment in drylands varies by site, year, and seeding technique

Restoration in dryland ecosystems is hindered by low establishment of seeded species. As such, evaluations of current seeding methods are critical to understanding limitations and barriers to seeding success. Drill seeding is perceived as an optimal seeding strategy in many dryland ecosystems, but broadcast seeding is more commonly used as a seeding method due to physical and logistical constraints. For example, broadcast seeding may be conducted by aerial drops where other methods are limited by topography or obstructive features in the landscape. Few studies have quantified the differences between drill and broadcast seeding through space and time. We compare 2‐year recruitment of emergent Pseudoroegneria spicata (bluebunch wheatgrass) seedlings in the sagebrush steppe biome for drill versus broadcast seeding methods across three seeding years, three landscape aspects and two soil types using a 95% confidence interval approach to avoid the penalty of multiplicity. We found drill seeding had 2.7 times greater recruitment of seedlings after 2 years compared with broadcast seeding. However, differences were highly subject to seeding year, aspect and soil type, likely because of soil moisture and temperature variations. Drill seeding had an advantage on clay soils with flat and north aspects (10.1 and 4.6 times greater for drill than broadcast seeding, respectively). In most conditions, drill seeding had greater recruitment than broadcast seeding, though in 2014 on south aspects broadcast seeding had 2.7 times greater recruitment than drill seeding. The results of this study demonstrate a need for restoration plans that account for spatiotemporal variation in seeding success.