Range Of Soil Temperatures Research Articles

Effects of planting density on diurnal variation of microenvironment in Huangguogan orchards

In this experiment, Huangguogan was used as the material. The effects of different planting densities on the diurnal variation of microenvironment in citrus orchard was studied, and thekey research findingsare as below. The orchard environmental factors, including light, daily average temperature and soil moisture, increased with the decrease of planting density. Compared with the density of 2×3m, thephotosynthetically active radiation(PAR in short), air temperature, soil temperature and soil moisture of density 4×5m on average increased by 423.7%, 5.5%, 2.18% and 4.9%. Air CO2 concentration and air humidity on average decreased by 1.8% and 4%. The daily range of PAR, air temperature, air humidity, soil temperature and soil humidity increased, and the daily range of air CO2 concentration decreased.

Calibrating bacterial tetraether distributions towards in situ soil temperature and application to a loess-paleosol sequence

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) produced by soil-dwelling bacteria offer a promising tool for reconstructing terrestrial temperatures. However, in most previous studies, due to lack of soil temperature data, brGDGTs are calibrated to the air rather than the soil temperature. This may impede our understanding of the accurate response of brGDGTs to temperature, and thus affect the quantitative paleotemperature reconstruction using these lipids. Here, we investigated modern soil brGDGTs and the corresponding soil temperature across a large climatic gradient in China (mean annual soil temperature (MAST) range: −2.7 to 26.2 °C). The results show that the MAST is higher than the mean annual air temperature (MAAT) by 0–6 °C, and the difference is related to vegetation coverage. This supports the idea that vegetation can modulate MAST and points to the necessity of exploring the direct response of brGDGTs to soil temperature. Employing stepwise regression (sr), we developed MASTsr and MAATsr calibrations, which improve accuracy and reduce the error compared with previous global MAAT calibrations. In Lantian loess-paleosols, the MASTsr calibration resulted in ∼4 °C lower glacial temperatures and a ∼10 °C deglacial warming comparable with other terrestrial records and climate models. However, the global MATmr and MBT’/CBT calibrations produced abnormally higher glacial temperatures, while the empirical MAATsr calibration overestimated MAAT during the deglacial period with low vegetation coverage. This demonstrates that the calibration with soil temperature is preferred for quantitative paleotemperature reconstruction. Nevertheless, soil brGDGTs might be useful for inferring MAAT if underlying surface conditions are sufficiently constrained.

SENSOR EFFECTIVENESS FOR SOIL WATER CONTENT MEASUREMENTS UNDER NORMAL AND EXTREME CONDITIONS

AbstractAn environmental sensor (the Decagon 5TE sensor with an EM50 data logger) is a soil salinity, temperature and water content (SWC) sensor that can be used by researchers and farmers around the world. Herein, 22 sensors were tested under different conditions of soil salinity, temperature, organic matter, texture, clay content, bulk density and water content, ranging from normal to extreme. The results indicated that the main issue with this device is that its SWC determinations are only accurate within a limited soil salinity and temperature range. Conversely, the organic matter, texture, clay content and bulk density have no direct impact on the sensors' accuracy. The sensors work best when the soil salinity and temperature are 2.5 dS m−1 and 25 °C, respectively. This sensor can be used appropriately after calibration when the soil salinity and temperatures are within the 1.9–4.0 dS m−1 and 16–30 °C ranges, respectively. When the soil salinity and temperature values are higher or lower than these ranges, the sensors do not work accurately. More investigation is needed to study the effectiveness of the sensors under high values of soil salinity and temperature. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.

Effects of soil temperature and moisture on biological nitrogen fixation in soybean crop

Soil temperature and humidity are the chief determinants for good nodule formation at the time of sowing and emergence. The aim of this study was to estimate the soil temperature and humidity range, at which the Bradyrhizobium spp., and Azospirillum brasilense may have the highest effect on root enhancement and development of nodulation in soybean. Two experiments were conducted, the first of which was done in the seed laboratory performing the treatments listed as non-inoculated; inoculation with Bradyrhizobium; root enhancers; inoculation with Bradyrhizobium + root enhancers; co-inoculation with Bradyrhizobium + Azospirillum brasilense; co-inoculation with Bradyrhizobium + Azospirillum brasilense + root enhancers, and assessed at temperatures of 15, 20, 25, 30 and 35ºC. The experimental design was completely randomized with distribution in a factorial. The second experiment was executed in a greenhouse, employing the same treatments affected in the seed laboratory experiment, but with the addition of non-inoculated control with mineral nitrogen. Tests were done at the soil moisture levels of 25, 50, 75 and 100% water retention capacity, forming a factorial 7 x 4 (only second experiment). All co-inoculated treatments induced the soybean root system to improve, in terms of length, volume, surface area and root diameter, exhibiting superiority to the uninoculated control in the 20 to 30ºC temperature range. The co-inoculation raised nodulation in the soybean crop, when soil water retention capacity was at the range of 56 - 96%, achieving higher means compared to the standard inoculation. The root planter added no improvement to either the root system or nodulation in soybean.

Effect of Woodchips Biochar on Sensitivity to Temperature of Soil Greenhouse Gases Emissions

Research Highlights: Biochar is the carbonaceous product of pyrolysis or the gasification of biomass that is used as soil amendment to improve soil fertility and increase soil carbon stock. Biochar has been shown to increase, decrease, or have no effect on the emissions of greenhouse gases (GHG) from soil, depending on the specific soil and biochar characteristics. However, the temperature sensitivity of these gas emissions in biochar-amended soils is still poorly investigated. Background and Objectives: A pot experiment was set up to investigate the impact of woodchips biochar on the temperature sensitivity of the main GHG (CO2, CH4, and N2O) emissions from soil. Materials and Methods: Nine pots (14 L volume) were filled with soil mixed with biochar at two application rates (0.021 kg of biochar/kg of soil and 0.042 kg of biochar/kg of soil) or with soil alone as the control (three pots per treatment). Pots were incubated in a growth chamber and the emissions of CO2, CH4, and N2O were monitored for two weeks with a cavity ring-down gas analyzer connected to three closed dynamic chambers. The temperature in the chamber increased from 10 °C to 30 °C during the first week and decreased back to 10 °C during the second week, with a daily change of 5 °C. Soil water content was kept at 20% (w/w). Results: Biochar application did not significantly affect the temperature sensitivity of CO2 and N2O emissions. However, the sensitivity of CH4 uptake from soil significantly decreased by the application of biochar, reducing the CH4 soil consumption compared to the un-amended soil, especially at high soil temperatures. Basal CO2 respiration at 10 °C was significantly higher in the highest biochar application rate compared to the control soil. Conclusions: These results confirmed that the magnitude and direction of the influence of biochar on temperature sensitivity of GHG emissions depend on the specific GHG considered. The biochar tested in this study did not affect soil N2O emission and only marginally affected CO2 emission in a wide range of soil temperatures. However, it showed a negative impact on soil CH4 uptake, particularly at a high temperature, having important implications in a future warmer climate scenario and at higher application rates.

Moss biocrusts regulate surface soil thermal properties and generate buffering effects on soil temperature dynamics in dryland ecosystem

Biocrusts are promising ecosystem engineers in dryland ecosystems, but their effects on soil temperature, which is the most important environmental factor of soil biological and biochemical processes, have not yet been well understood. In a semiarid ecosystem on the Chinese Loess Plateau, the thermal properties of moss-dominated biocrust layer and bare soil (upper 2 cm) were measured, and their correlations with the biocrust characteristics as well as soil properties (especially soil water content, θ) were analyzed. Afterwards, the soil temperature dynamics of the biocrust covered soil and bare soil were continuously recorded at 2, 6, and 10 cm depths during a year. From in-situ measurements in wet season, we found that the biocrusts increased surface soil heat capacity (C) by 10.3% (1.42 vs. 1.28 MJ m−3 K−1), thermal conductivity (λ) by 27.7% (0.69 vs. 0.54 W m−1 K−1), and thermal diffusivity (α) by 27.9% (5.01 vs. 3.92 × 10−7 m2 s−1) as compared with the bare soil, through holding more soil water (θ of the biocrusts vs. bare soil = 0.06 vs. 0.03 cm3 cm−3). However, in dry season (θ < 0.05 cm3 cm−3) they decreased 33.4% of surface soil C (0.78 vs. 1.17 MJ m−3 K−1), 54.9% of λ (0.17 vs. 0.37 W m−1 K−1), and 22.9% of α (2.32 vs. 3.01 × 10−7 m2 s−1) mostly by decreasing surface soil bulk density. Accordingly, the biocrusts decreased soil temperature by as much as 6.3–11.1 °C at 0–10 cm depth in wet season (summer), and they increased soil temperature by up to 1.3–3.7 °C in dry season (winter). More importantly, the diurnal range of soil temperature of the biocrust covered soil was sometimes as much as 6.8–9.4 °C lower than that of the bare soil at 0–10 cm depth. The decreasing or increasing effects of the biocrusts on soil temperature were exactly explained by the increased thermal properties of the biocrust layer in wet season or reduced thermal properties of the biocrust layer in dry season. We concluded that the biocrusts regulated surface soil thermal properties through increasing soil water holding capacity and decreasing soil bulk density; thus, they generated considerable buffering effects on soil temperature dynamics. In dryland ecosystem, such buffering effects of the biocrusts on soil temperature should be highly considered in various soil biological and biochemical processes.

Annual Variation in Soil Enzyme Activity in a Paddy Field: Soil Temperature and Nutrient Availability Are Important for Controlling Enzyme Activities

Annual variations in enzyme activities involved in carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling and soil physicochemical properties were examined in a Japanese paddy field. All the enzyme activities determined at the field soil temperature (range, 2.2°C–28.3°C) increased exponentially with soil temperature (p&lt;0.001). Significant negative correlations were found between Bray-2P concentration and the ratio of acid phosphatase to β-D-glucosidase activity (Spearman r = −0.631, p = 0.005) and between total N and the ratio of L-asparaginase to β-D-glucosidase activity (r = −0.612, p=0.007), suggesting that in accordance with the resource allocation model, acid phosphatase and L-asparaginase were synthesized by microorganisms depending on the temporal changes in soil P and N availability. These results suggest the significance of soil temperature in controlling in situ enzyme activities in paddy soil and also that the stoichiometry of enzyme activities associated with C, N, and P acquisition reflects the soil nutrient availability.

N2O flux measurements over an irrigated maize crop: A comparison of three methods

This paper presents the NitroCOSMES campaign, aimed at testing and evaluating the performance of three methods for monitoring N2O fluxes over an agricultural field. The experiment was conducted from May to August 2012 at a site located in the south-west of France. N2O fluxes from a 24 ha irrigated maize field were measured using eddy covariance (EC), automated chamber (AC) and static chamber (SC) methodologies. Uncertainties were calculated according to the specificities of each set-up. Measurements were performed over a large range of water-filled pore spaces (WFPS), soil temperatures, and mineral nitrogen availability, and offered the opportunity to compare methodologies over a wide range of N2O emission intensities. The average N2O fluxes were compared among the three methodologies during the same periods of measurement and for different intensities of emissions (low, moderate and high). Periods of comparison were determined according to the AC results. On average, the three methods gave comparable results for the low (SC: 14.7 ± 2.2, EC: 15.7 ± 10.1, AC: 17.5 ± 1.6 ng N2O-N m−² s−1) and the high (SC: 131.7 ± 22.1, EC: 125.3 ± 8, AC: 125.1 ± 8.9 ng N2O-N m−² s−1) N2O emission ranges. For the moderate N2O emission range, AC measurements gave higher emissions (57.2 ± 3.9 ng N2O-N m−² s−1) on average than both the SC (41.6 ± 6.6 ng N2O-N m−² s−1) and EC (33.8 ± 3.9 ng N2O-N m−² s−1) methods, which agreed better with each other. The relative standard deviation coefficient (RSD) indicated that EC methodology gave highly variable values during periods of low N2O emissions, from -52.2 ± 88.1 to 62.2 ± 50.7 ng N2O-N m−² s−1, with a mean RSD of 151%. Water vapour effects (dilution and spectroscopic cross-sensitivity) were discussed in an attempt to explain the high variability in low N2O emission measurements. Even after applying the Webb term correction, there could still be a spectroscopic cross-sensitivity effect of water vapour on the N2O trace gas signal because of the layout of the analysers, which was not determined during the experiment. This study underlined that EC methodology is a promising way to estimate and refine N2O budgets at the field scale and to analyse the effects of different agricultural practices more finely with continuous flux monitoring. It also highlighted the need to continue the effort to assess and develop chambers and EC methodologies, especially for the low N2O emission measurement range, for which values and systematic uncertainties remain high and highly variable.

Resilience of bacteria, archaea, fungi and N-cycling microbial guilds under plough and conservation tillage, to agricultural drought

Climate change causes droughts, which in turn cause significant physiological stress for soil microorganisms. In this study, we investigated how the abundance of total bacterial, crenarchaeal and fungal communities and the abundance of N-cycling microbial guilds responded to a severe agricultural drought event in a long-term experiment of minimum tillage (MT) and conventional ploughing (CT) at two soil depths. Drought, defined as a reduction of soil water content and increased soil temperature, significantly decreased the abundance of all the studied microbial communities. The data showed linear relationships between all dependent variables and soil water content and soil temperature for the examined range of soil water content (WHC 13–76%) and examined range of average daily soil temperature at 5 cm depth (17–30 °C). Thus, we found that the abundance of most studied microbial communities decreased by about 2% when water content decreased by 1 mass % and by about 10% when temperature increases by 1 °C. When comparing communities at average soil water content and average soil temperature, MT had higher average abundances of total bacterial and crenarchaeal 16S rRNA and fungal ITS genes in the 0–10 cm soil layer than did CT (1.9, 2.9 and 2.5 times, respectively), as well as AOA and AOB amoA (3.9 and 1.7 times, respectively), nirK, nirS, nosZI and nosZII genes (2.0, 1.8, 1.8 and 2.3 times, respectively); while significant differences between MT and CT in the 10–20 cm soil layer were found only in the average abundance of crenarchaeal 16S rRNA and crenarchaeal amoA genes (3.5 and 2.7 times greater under MT than CT). Regardless of the weather conditions during our study, the abundances of all communities were greater under MT 0–10 than under CT 0–10. After three weeks of severe drought, the greatest decrease in the abundance of all communities, bacterial and archaeal N-cycling guilds as well as total prokaryotes and fungi, was observed under MT 0–10. However, after only a few rainfall events, all communities under both tillage systems reached their initial abundance, demonstrating a high resilience.

Microclimate response of soil to plateau pika's disturbance in the northeast Qinghai‐Tibet Plateau

SummaryThe plateau pika (Ochotona curzoniae) is one of the main native soil faunas on the Qinghai‐Tibet Plateau and plays a key role in the terrestrial ecosystem there. To understand how and why the soil microclimate changes after the plateau pika's disturbance, this study measured soil, vegetation, hydrologic and thermal properties and investigated soil moisture and soil temperature dynamics from 2014 to 2015 at the plot scale of four types of land surface: original grassland, new mound, old mound and bald patch. Our results showed that the average coefficients of surface runoff of original grassland, new mound, old mound and bald patch were 0.6, 3.0, 4.3 and 10.0%, respectively (P &lt; 0.05). Evapotranspiration was largest for original grassland, especially under wet conditions, and was similar among the other three types of land surface during the growing season (P &lt; 0.01). During varying precipitation events, the soil moisture content of new mound increased first, followed by old mound, original grassland and bald patch. Meanwhile, the increasing magnitude of soil moisture content had the same order. At the seasonal timescale, soil moisture content at 5‐cm depth was largest for old mound and smallest for bald patch (P &lt; 0.01). The mean daily soil temperature at 5‐cm depth of new mound was approximately 0.8°C higher than that of old mound (P &lt; 0.01) because of the smaller land surface reflectance of the former. The daily range of soil temperature at 5‐cm depth of original grassland and bald patch was about 2.7 and 4.7°C higher than the average value of new and old mounds, respectively, because of the larger soil thermal conductivity of the former two. A conceptual framework is suggested in this study to synthesize the evolution of soil microclimate under disturbance by the plateau pika. Overall, results indicated that new and old mounds accelerate soil hydrologic processes and have a better soil temperature buffer.Highlights Change in soil microclimate of different types of land surface under disturbance by the plateau pika. New and old mounds accelerate soil hydrologic processes and have a better soil temperature buffer. New and old mounds provide advantageous environments for plateau pika. Bald patch had the smallest soil moisture content and largest daily range of soil temperature.

Effect of snow cover on soil frost penetration

AbstractSnow cover occurrence affects wintering and lives of organisms because it has a significant effect on soil frost penetration. An analysis of the dependence of soil frost penetration and snow depth between November and March was performed using data from 12 automated climatological stations located in Southern Moravia, with a minimum period of measurement of 5 years since 2001, which belong to the Czech Hydrometeorological institute. The soil temperatures at 5 cm depth fluctuate much less in the presence of snow cover. In contrast, the effect of snow cover on the air temperature at 2 m height is only very small. During clear sky conditions and no snow cover, soil can warm up substantially and the soil temperature range can be even higher than the range of air temperature at 2 m height. The actual height of snow is also important – increased snow depth means lower soil temperature range. However, even just 1 cm snow depth substantially lowers the soil temperature range and it can therefore be clearly seen that snow acts as an insulator and has a major effect on soil frost penetration and soil temperature range.

Weather thresholds for clubroot development on canola and brassica vegetables

Clubroot, caused by Plasmodiaphora brassicae, is an important soil-borne disease of canola (Brassica napus) and other brassica crops worldwide. Temperature and soil moisture are known to affect clubroot development. To understand the influence of weather on development of clubroot, replicated small-plot seeding date trials were conducted from 2011 to 2014 at the Muck Crops Research Station in southern Ontario. Each year, canola cultivar ‘InVigor 5030ʹ was seeded at 2-week intervals, and plants were sampled and assessed weekly for clubroot incidence and severity using a 0–3 scale. A base temperature of 14°C provided the best fit for degree day assessments, based on the assessments in 2011 and 2012. For modelling, data from previous trials on Chinese flowering cabbage (B. rapa subsp. chinensis var. utilis) from the same site were included in the data set, following assessment to ensure that both host species responded similarly across a range of environments. Temperature and rainfall affected clubroot initiation and development, but the results indicated that when conditions exceeded a threshold of temperature and soil moisture, clubroot quickly developed to high levels, irrespective of additional heat units or moisture. This indicated that clubroot initiation and development at sites where resting spores occur at high levels occurred rapidly across a wide range of soil temperature and moisture conditions above a low threshold around 14°C.

Grafting as a Method to Increase the Tolerance Response of Bell Pepper to Extreme Temperatures

Core Ideas Shoot and root interactions under extreme temperatures contributed to tolerance. Impact of root dynamics on soil pore water EC and Cl uptake increased under extreme temperatures. Tolerance of extreme temperatures increased assimilation and allocation of C and N to organ growth. Fluctuations of winter and summer and day and night temperatures strongly influence shoot and root growth, as well as the whole plant tolerance to extreme soil temperatures. We compared the response of a commercial pepper (Capsicum annuum L.) hybrid (Romance, Rijk Zwaan) to a range of soil temperatures when grafted to a new rootstock hybrid (S101, Syngenta), self‐grafted, or ungrafted. The new rootstock hybrid was bred for enhancing abiotic stress tolerance. Plants were grown during winter and summer seasons in a plastic greenhouse with natural ventilation. Minirhizotron cameras and in‐growth cores were used to investigate grafted bell pepper root dynamics and root and shoot interactions in response to extreme (low and high air and soil) temperatures. Soil and air temperatures were measured throughout the experiment. The variations of the grafted peppers and the ungrafted aboveground biomass exposed to low and high temperatures during winter and summer were higher in the Romance grafted on the S101 rootstock than in the self‐grafted and ungrafted Romance. The plot of rootstock S101 accumulated Cl, and the rootstock efficiently allocated C into the leaves, stems, and roots and N into the leaves, stems, and fruits. These traits of rootstock S101 can be used to improve the tolerance of other pepper cultivars to low and high soil temperatures, which could lengthen the pepper growing season, as well as provide highly interesting information to plant breeders.

Temperature Effects on Biomass and Regeneration of Vegetation in a Geothermal Area.

Understanding the effects of increasing temperature is central in explaining the effects of climate change on vegetation. Here, we investigate how warming affects vegetation regeneration and root biomass and if there is an interactive effect of warming with other environmental variables. We also examine if geothermal warming effects on vegetation regeneration and root biomass can be used in climate change experiments. Monitoring plots were arranged in a grid across the study area to cover a range of soil temperatures. The plots were cleared of vegetation and root-free ingrowth cores were installed to assess above and below-ground regeneration rates. Temperature sensors were buried in the plots for continued soil temperature monitoring. Soil moisture, pH, and soil chemistry of the plots were also recorded. Data were analyzed using least absolute shrinkage and selection operator and linear regression to identify the environmental variable with the greatest influence on vegetation regeneration and root biomass. There was lower root biomass and slower vegetation regeneration in high temperature plots. Soil temperature was positively correlated with soil moisture and negatively correlated with soil pH. Iron and sulfate were present in the soil in the highest quantities compared to other measured soil chemicals and had a strong positive relationship with soil temperature. Our findings suggest that soil temperature had a major impact on root biomass and vegetation regeneration. In geothermal fields, vegetation establishment and growth can be restricted by low soil moisture, low soil pH, and an imbalance in soil chemistry. The correlation between soil moisture, pH, chemistry, and plant regeneration was chiefly driven by soil temperature. Soil temperature was negatively correlated to the distance from the geothermal features. Apart from characterizing plant regeneration on geothermal soils, this study further demonstrates a novel approach to global warming experiments, which could be particularly useful in low heat flow geothermal systems that more realistically mimic soil warming.

Study on the local climatic effects of large photovoltaic solar farms in desert areas

Large-scale solar power plants are rapidly increasing in size and number across the world. However, the surface heat balance is altered when a photovoltaic (PV) power plant is operating. Modifications to the surface albedo through the deployment of photovoltaic arrays have the potential to change radiative forcing, surface temperatures and local weather patterns. In this work, the field observation data from a large solar farm and a region without PV array in Golmud are used to study the impact of large solar farms in desert areas on the local meteorology. The results show that the total daily values of upward shortwave radiation and net radiation in the two sites are significantly different. The mean daily albedo in the solar farm is 0.19, while it is 0.26 in the region without PV. The annual mean net radiation in the solar farm is evidently higher than that of the region without PV. The daily range of soil temperatures at a depth of 5–10cm in the solar farm is lower than that in the region without a PV farm. The annual range of soil temperatures at a depth of 5–180cm in the solar farm is higher than that in the region without PV. The soil temperatures at different depths in winter in the solar farm are clearly lower than those in the region without PV. The daily mean of soil temperatures at a depth of 5–80cm from October 2012 to March 2013 is clearly lower than that in the region without a PV array. The 2-m daytime air temperature in the two sites is essentially the same during winter, while during the other seasons, the daytime air temperature in the PV farm is higher than that in the region without PV, with the maximum difference appearing during the summer. The nighttime air temperatures at a height of 2m during the four seasons in the solar farm are higher than those in the region without PV. The monthly average 2-m air temperature in the solar farm is higher than that in the region without PV.

Presence of snow coverage and its thickness affected the mortality of overwintering pupae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae).

Helicoverpa armigera causes serious damage to most crops around the world. However, the impacts of snow thickness on the H. armigera overwintering pupae are little known. A field experiment was employed in 2012-2015 at Urumqi, China. At soil depths of 5, 10, and 15cm, overwintering pupae were embedded with four treatments: no snow cover (NSC), snow cover (SC), increasing snow thickness to 1.5 times the thickness of SC (ISSC-1), and to two times the thickness of SC (ISSC-2). Results suggested that snow cover and increasing snow thickness both significantly increased soil temperatures, which helped to decrease the mortality of overwintering pupae (MOP) of H. armigera. However, the MOP did not always decrease with increases in snow thickness. The MOPs in NSC and ISSC-1 were the highest and the lowest, respectively, though ISSC-2 had much thicker snow thickness than ISSC-1. A maximum snow thickness of 60cm might lead to the lowest MOP. The longer the snow cover duration (SCD) at a soil depth of 10cm in March and April was, the higher the MOP was. A thicker snow cover layer led to a higher soil moisture content (SMC) and a lower diurnal soil temperature range (DSTR). The highest and the lowest MOP were at a depth of 15 and 10cm, respectively. The SMC at the depths of 10 and 15cm had significant effects on MOP. A lower accumulated temperature (≤0°C) led to a higher MOP. The DSTR in March of approximately 4.5°C might cause the lowest MOP. The largest influence factor for the MOPs at depths of 5 and 10cm and the combined data were the SCDs during the whole experimental period, and for the MOPs at a depth of 15cm was the soil temperature in November.

Sensible Heat Balance Estimates of Transient Soil Ice Contents

Core Ideas Soil ice content is difficult to quantify. A sensible heat balance with heat pulse probes may indicate soil ice contents. A sensible heat balance can determine transient soil ice content from −5 to 0°C. Soil ice contents below −5°C can be determined with heat capacity changes. Heat pulse probes can monitor soil ice contents at and below 0°C. Soil ice content is an important component for winter soil hydrology. The sensible heat balance (SHB) method using measurements from heat pulse probes (HPPs) is a possible way to determine transient soil ice content. In a previous study, in situ soil ice content estimates with the SHB method were inaccurate, due to thermal conductivity errors and the use of relatively long time steps for calculations. The objective of this study is to reexamine the SHB method for soil ice content determination. A soil freezing and thawing laboratory experiment was performed with soil columns and heat exchangers. Transient soil ice contents in the soil columns during soil freezing and thawing were determined with the SHB method. The SHB method was able to determine dynamic changes in soil ice contents during initial freezing and final thawing for soil temperatures between −5 and 0°C when latent heat values associated with ice formation or with thawing were relatively large. During an extended freezing period, when soil temperatures were below −5°C, the small associated latent heat fluxes were below the sensitivity of the SHB method, and the SHB method did not provide accurate estimates of ice contents with time. However, the soil ice contents during the extended freezing period could be estimated well from changes in volumetric heat capacity (C) determined with HPP. Thus, combining the SHB method for initial freezing and final thawing, with a change in C method for extended freezing periods, allowed determination of dynamic soil ice contents for the entire range of freezing and thawing soil temperatures investigated. HPPs were able to measure soil ice contents.

Temperature selects for static soil enzyme systems to maintain high catalytic efficiency

Knowledge on enzymatic mechanisms of acclimation to temperature is required to predict the effects of warming on decomposition of soil organic matter – the largest C stock in terrestrial ecosystems. Based on Michaelis–Menten kinetics we tested the hypothesis that enzyme affinity to substrate (Km) is more sensitive to warming at cold than at warm temperatures. We also predicted a gradual increase in Km values with increasing temperature. The kinetic parameters of six enzymes involved in cycles of C, (cellobiohydrolase, β-glucosidase and xylanase), P (phosphatase), and N (leucine-aminopeptidase, tyrosine-aminopeptidase) were determined after one month of soil incubation at a temperature range 0–40 °C (with 5° increment).Contrary to our hypothesis, the increase in Km with temperature was not gradual for most tested enzymes. Within large range of temperatures from 0 to 15 °C (phosphatase), 0–20 °C (enzymes involved in C cycle) and 0–40 °C (proteases) the hydrolytic activity was governed by enzymes with nearly constant substrate affinity. Temperature, therefore, mainly selected for soil enzyme systems maintaining static Km. The catalytic efficiency of the enzymes (Vmax/Km) increased from low to intermediate temperatures (0–20 °C) as a result of linear increase of Vmax at constant Km. Static Km values were explained either by low flexibility (high structural stability) of a single enzyme type, which catalyzed the reaction over a broad temperature range, or by production of multiple isoenzymes each with different temperature optima but with similar affinity to substrate. Thus, maintaining static Km with temperature increase ensured high enzyme efficiency within a low and intermediate soil temperature range.

Microclimate buffering and fertility island formation during Juniperus communis ontogenesis modulate competition–facilitation balance

AbstractAimsFacilitation has been reported in a wide range of plant communities, with evidence of positive interactions between beneficiary and nurse plants shifting during their ontogenetic development. This study explored the hypothesis that shrubs of Juniperus communis subsp. nana (thereafter Juniperus) play a crucial role in the successional sequence of plant communities acting as nurse for different species, but only after reaching a certain size. In addition, we examined whether plant–plant interaction changes during ontogenesis of these shrubs in the presence of contrasting disturbance regimes in terms of substrate stability.LocationSibillini National Park, central Italy. The vegetation is semi‐natural dry grasslands (92/43/EEC Habitats Directive: Habitat 6210 ‐ Festuco‐Brometalia).MethodsField measurements were carried out to assess the effects of Juniperus on (1) the distribution of co‐existing vascular species, (2) the above‐ and below‐ground microclimate, and (3) changes in soil fertility and hydrology.ResultsThe capacity of Juniperus shrubs to facilitate heterospecific plants considerably increases during its ontogenetic development, i.e. small shrubs mainly compete for resources with local vegetation, whereas large shrubs act as nurse plants for herbaceous and especially for woody species. The facilitation effect was slight, albeit significantly higher in the disturbed area than in the more stable one. Juniperus was able to promote the formation of an island of fertility under its canopy by accumulating a considerable amount of organic matter, N, P, Ca2+, Mg2+ and K+ in a few decades. Juniperus shrubs improve soil hydrological properties and mitigate the daily range of soil temperature, reducing the exposure of co‐existing plants to high temperatures and water loss through soil evaporation, particularly during the growing periods in spring and summer.ConclusionsThis study demonstrates that biogenic amelioration of soil quality, coupled with the mitigation of below‐canopy microclimatic conditions, control the establishment and growth of co‐existing plants during Juniperus shrub development.

Effects of soil temperature and snow cover on the mortality of overwintering pupae of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae).

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is one of the most damaging insect pests in the world. However, little is known about the effects of snow cover and soil temperature on the overwintering pupae of H. armigera. A field experiment was conducted from November 2, 2012 to April 24, 2013 at the agrometeorological experimental station in Wulanwusu, China. Overwintering pupae were embedded into the soil at depths of 5, 10, and 15cm in the following four treatments: without snow cover, snow cover, and increased temperatures from 600 and 1200W infrared lights. The results showed that snow cover and rising temperatures could all markedly increase soil temperatures, which was helpful in improving the survival of the overwintering pupae of H. armigera. The mortality of overwintering pupae (MOP) at a depth of 15cm was the highest, and the MOP at a depth of 5cm followed. The lower accumulated temperature (≤0°C) (AT ≤ °C) led to the higher MOP, and the lower diurnal soil temperature range (DSTR) likely led to the lower MOP. After snowmelt, the MOPs at the depths of 5 and 10cm increased as the soil temperature increased, especially in April. The AT of the soil (≤0°C) was the factor with the strongest effect on MOP. The soil moisture content was not a major factor affecting the MOP in this semiarid region because precipitation was 45mm over the entire experimental period. With climate warming, the MOP will likely decrease, and the overwintering boundary air temperatures of H. armigera should be expanded due to higher soil temperatures and increased snow cover.