Effects Of Soil Temperature Research Articles

Free Span Analysis for Submarine Pipelines

Pipelines are one of the most important and key elements that align with transferring hydrocarbon products in coastal and offshore industries which are exposed at various risks during their servicing. In this project, we are studding and describing free spanning of marine pipeline based on DNVGL-RP-F-105 regulation applying the finite element method by Abaqus software. For modeling, case studies of Gorze to Kish oil pipeline have been used. In order to provide and study the integrity of the structure against fatigue, the exact place as well as the free span length using software under environmental loading based on DNVGL-RP-F205 has been determined. Since based on DNVGL-TS-F101 free span causes local buckling, fatigue, and pipe burst then given to the servicing as well as environmental conditions, pipe condition has been monitored. Finally, using sensitivity analysis, the effect of different soil classes, elasticity module, and temperature on the pipe condition has been studied. At the end, the question if it is allowed to use a cross model for bed has been answered in previous studies.

Anaerobic Soil Disinfestation Efficacy Against Fusarium oxysporum Is Affected by Soil Temperature, Amendment Type, Rate, and C:N Ratio.

A meta-analysis of anaerobic soil disinfestation (ASD) efficacy against Fusarium oxysporum and F. oxysporum f. sp. lycopersici was conducted emphasizing effects of environment and organic amendment characteristics and pot and field studies conducted on ASD amendment C:N ratio and soil temperature effects on F. oxysporum f. sp. lycopersici inoculum survival. In a pot study, two organic amendments, dry molasses-based or wheat bran-based, applied at 4 mg of C/g of soil, with 40:1, 30:1, 20:1, and 10:1 C:N ratios, were evaluated against F. oxysporum f. sp. lycopersici at 15 to 25°C. This study was followed by a pot study with temperature regimes of 15 to 25°C and 25 to 35°C and two C:N ratios (20:1 and 40:1), and a field study at 40:1, 30:1, 20:1, and 10:1 C:N ratios, a 30:1 C:N ratio at a lower C rate (2 mg of C/g of soil), and an anaerobic control. Soil temperature >25°C and more labile amendments increased ASD suppression of F. oxysporum/F. oxysporum f. sp. lycopersici in the meta-analysis. In pot studies, F. oxysporum f. sp. lycopersici survival was reduced for molasses-based mixtures at 20:1 and 30:1 C:N ratios compared with wheat bran-based mixtures but not compared with the anaerobic control. At 25 to 35°C, all ASD treatments suppressed F. oxysporum f. sp. lycopersici relative to controls. In the field, all ASD treatments reduced F. oxysporum f. sp. lycopersici survival compared with the anaerobic control, and 4 mg of C/g of soil amendment rates induced higher anaerobic conditions and higher F. oxysporum f. sp. lycopersici mortality compared with the 2 mg of C/g of soil rate. Although amendment C:N ratios from 10 to 40:1 were similarly suppressive of F. oxysporum, lower temperatures reduced ASD effectiveness against F. oxysporum/F. oxysporum f. sp. lycopersici and further work is warranted to enhance suppression at soil temperatures <25°C.

Impact of soil temperature on fruit species within climate change scenarios

Climate change, with its consequent increase in temperatures and precipitation, has significant impacts on soil surface horizons, affecting the establishment, development, and production of crops and food security and safety. Solar radiation influences the thermals of Earth's surface. Apart from radiation, the effects of soil temperature (STe) are specific to fruit species and are mainly modified by humidity, soil cover and air temperature. Increasing the STe within an optimal range promotes the growth of roots and plants and increases the absorption of water and nutrients, photosynthesis, transpiration, efficient use of water and microbial processes. These effects have been demonstrated in several studies on fruit trees and on grape vines, citrus, cape gooseberries, Annonaceae, avocados, olives and prickly pears. However, apart from these positive results, an increased STe as the result of global warming can generate water stress and in turn affect the yield and quality of fruit trees. In terms of effects from cultural practices, mulching with black or blue plastic can increase the soil temperature, and white or silver plastic decreases it. When compared to air temperature, increases in STe in the plants physiology and climate impact studies have been little studied. Therefore, this review aimed to make significant contributions to facilitate decision-making with the goal of reducing the effects of global warming, especially on fruit trees.

Interannual Variability of Atmospheric CH4 and Its Driver Over South Korea Captured by Integrated Data in 2019

Understanding the temporal variability of atmospheric methane (CH4) and its potential drivers can advance the progress toward mitigating changes to the climate. To comprehend interannual variability and spatial characteristics of anomalous CH4 mole fractions and its drivers, we used integrated data from different platforms such as in situ measurements and satellites (TROPOspheric Monitoring Instrument (TROPOMI) and Greenhouse Gases Observing SATellite (GOSAT)) retrievals. A pronounced change of annual growth rate was detected at Anmyeondo (AMY), Republic of Korea, ranging from −16.8 to 31.3 ppb yr−1 as captured in situ through 2015–2020 and 3.9 to 16.4 ppb yr−1 detected by GOSAT through 2014–2019, respectively. High growth rates were discerned in 2016 (31.3 ppb yr−1 and 13.4 ppb yr−1 from in situ and GOSAT, respectively) and 2019 (27.4 ppb yr−1 and 16.4 ppb yr−1 from in situ and GOSAT, respectively). The high growth in 2016 was essentially explained by the strong El Niño event in 2015–2016, whereas the large growth rate in 2019 was not related to ENSO. We suggest that the growth rate that appeared in 2019 was related to soil temperature according to the Noah Land Surface Model. The stable isotopic composition of 13C/12C in CH4 (δ13-CH4) collected by flask-air sampling at AMY during 2014–2019 supported the soil methane hypothesis. The intercept of the Keeling plot for summer and autumn were found to be −53.3‰ and −52.9‰, respectively, which suggested isotopic signature of biogenic emissions. The isotopic values in 2019 exhibited the strongest depletion compared to other periods, which suggests even a stronger biogenic signal. Such changes in the biogenic signal were affected by the variations of soil temperature and soil moisture. We looked more closely at the variability of XCH4 and the relationship with soil properties. The result indicated a spatial distribution of interannual variability, as well as the captured elevated anomaly over the southwest of the domain in autumn 2019, up to 70 ppb, which was largely explained by the combined effect of soil temperature and soil moisture changes, indicating a pixel-wise correlation of XCH4 anomaly with those parameters in the range of 0.5–0.8 with a statistical significance (p &lt; 0.05). This implies that the soil-associated drivers are able to exert a large-scale influence on the regional distribution of CH4 in Korea.

Studies into Fungal Decay of Wood in Ground Contact—Part 2: Development of a Dose–Response Model to Predict Decay Rate

In this article a dose–response model was developed to describe the effect of soil temperature, soil moisture content, and soil water-holding capacity, on the decay of European beech (Fagus sylvatica) wood specimens exposed to soil contact. The developed dose–response model represents a step forward in incorporating soil-level variables into the prediction of wood decay over time. This builds upon prior models such as those developed within the TimberLife software package, but also aligns with similar modeling methodology employed for wood exposed above ground. The model was developed from laboratory data generated from terrestrial microcosm trials which used test specimens of standard dimension, incubated in a range of soil conditions and temperatures, for a maximum period of 16 weeks. Wood mass loss was used as a metric for wood decay. The dose aspect of the developed function modelled wood mass loss in two facets; soil temperature against wood mass loss, and soil water-holding capacity and soil moisture content against wood mass loss. In combination, the two functions describe the wood mass loss as a function of a total daily exposure dose, accumulated over the exposure period. The model was deemed conservative, delivering an overprediction of wood decay, or underprediction of wood service-life, when validated on a similar, but independent dataset (R2 = 0.65). Future works will develop similar models for outdoor, field-trial datasets as a basis for service-life prediction of wooden elements used in soil contact.

Biocontrol of Wireworms (Coleoptera: Elateridae) Using Entomopathogenic Nematodes: The Impact of Infected Host Cadaver Application and Soil Characteristics.

Wireworms have become a significant menace to cereals in the Northern Great Plains. Therefore, research toward developing effective control methods such as biological control with entomopathogenic nematodes (EPNs) is warranted. Two strains, each of two EPN species, Steinernema carpocapsae (Weiser) and Steinernema riobrave Cabanillas, Poinar, and Raulston in the form of infected Galleria mellonella (L.) cadavers were evaluated against wireworms in field and greenhouse. In field experiments, none of the four EPN strains were found effective against wireworms. However, in the greenhouse test, three of the strains, S. carpocapsae (All and Cxrd) or S. riobrave (355) applied in cadavers killed 50-68% of the sugarbeet wireworm, Limonius californicus (Mannerheim) was associated with 8-24% plant damage at 35 d after treatment (DAT), when seeds were treated with imidacloprid. The mortality range was 40-56% with 57-75% plant damage observed at 35 DAT, when seeds were planted without imidacloprid treatment. Synergistic effect among imidacloprid and S. carpocapsae (Cxrd) or S. riobrave (355) was observed in regard to L. californicus mortality. Additionally, effects of soil texture, moisture, and temperature on the infection rate of EPNs against L. californicus were examined in the laboratory. Limonius californicus mortality was not significantly affected by either soil moisture or soil types maintained at field capacity moisture levels. However, soil temperature showed a significant effect on L. californicus mortality. Overall, imidacloprid enhanced the infection and killing ability of EPNs against L. californicus and S. carpocapsae (All and Cxrd) strains were the virulent strains in different soil experiments.

Projecting urban heat island effect on the spatial-temporal variation of microbial respiration in urban soils of Moscow megalopolis

Urbanization coincides with remarkable environmental changes including vegetation, soil and climate. An urban heat island is a well-known urban mesoclimatic anomaly, however its effect on functions of urban soils considering their spatial-temporal variability remain overlooked. The research aimed to explain the urban heat island effect on soil microbial respiration by linking meso-climatic CCLM and TERRA_URB models and the digital soil mapping approach for the case of Moscow megalopolis. Moscow megalopolis is the biggest city in Russia, which experiences on-going urbanization within the New Moscow project. As a result, a clear urbanization gradient was observed in land-use structure, climate and soil properties. For the study period (May–October 2019), the increase in average monthly temperature of urban soils compared to rural reached 1.7 and 2.0 °C in June and September with the maximal values obtained in the city center. The significant effect of soil temperature, carbon content and pH on soil microbial (basal) respiration was estimated based on the lab experiment with a representative sample of urban topsoils (n = 140). The resulting equation was integrated with the mesoclimatic data in two ways: i) considering urban heat islands (based on the modelled 500 m grid soil temperature maps) and ii) non-considering urban heat islands (based on the average monthly rural soil temperature). Comparison of the results showed that urban heat island increased microbial respiration by 5–10% on average and up to 25% in the most affected locations. The additional amount of CO2 which could be potentially emitted by soil microbes as a result of the urban heat island in Moscow megapolis was on average 0.2 Mg C ha−1 (0–10 cm layer; 1.1 g cm−3 bulk density). Small scale green zones in the city center (public gardens, residential court yards and green lawns along the roads) where high soil C contents coincided with the maximal urban heat island effect were the hotspots of microbial respiration. Although the estimated absolute values could be rather uncertain, the research highlights the vulnerability of urban topsoil C stocks to mineralization intensified by mesoclimatic anomalies.

Response of abiotic soil CO2 flux to the difference in air-soil temperature in a desert

Abiotic soil CO2 flux (Fa) has been observed in drylands worldwide, while its generation mechanism is not determined. The remarkable features for the occurrence time of Fa, that the positive Fa (CO2 emission from soil) and negative Fa (CO2 absorption by soil) generally occurred in the daytime and nighttime, respectively, suggested that the generation of Fa is related to temperature. Previous studies have focused on the sole effect of soil temperature (Ts) or air temperature (Ta) on Fa, but very little is regarding to the overall response of Fa to both Ta and Ts in the air-soil system. In the Mu Us Desert, China, we continuously measured the hourly Fa, Ts, Ta and the difference between Ta and Ts (Ta-Ts) at 4-day intervals from June to October 2016. During this period, soil abiotically absorbed atmospheric CO2 at a rate of 0.32 ± 0.19 g m−2 d−1. Fa was not correlated with Ts and was weakly correlated with Ta, however, it was strongly and positively correlated with Ta-Ts. A quadratic model adequately fitted the relationship between Fa and Ta-Ts, and similar relationships were also observed between positive Fa and Ta-Ts and between negative Fa and Ta-Ts. The results of Fa measurement highlight that desert soils can absorb CO2 from the atmosphere through abiotic processes. The relationships of Fa with Ts, Ta and Ta-Ts indicate that, abiotic CO2 exchange between soil and atmosphere depends on air-soil temperature gradient in desert. Furthermore, the thermal convection driven by Ta-Ts may play a major role in the generation of nocturnal negative Fa. Our findings provide a new possible perspective for revealing the reasons of Fa generation in drylands.

Methane and Carbon Dioxide Flux Heterogeneity Mediated by Termite Mounds in Moist Tropical Forest Soils of Himalayan Foothills, India

Termites are dominant soil macro-fauna in tropical forests, yet remain an uncertain component of the carbon budget in many regions. We investigated CH4 and CO2 flux patterns from termite mounds and background soils of moist tropical deciduous forests in Indian lower Himalaya from April 2015 till March 2016 using static closed chamber technique. The relation between gas fluxes and soil moisture as well as temperature were examined. Termite (Odontotermes obesus) mounds were significant localized source of CH4 (0.38 ± 0.01 mg m−2 h−1) and CO2 (1837 ± 40 mg m−2 h−1) amidst CH4 consuming (– 0.028 ± 0.001 mg m−2 h−1) or lower CO2 emitting (1120 ± 19 mg m−2 h−1) background forest soils. Gas fluxes from termite mounds were seasonally bimodal (monsoon flux being highest followed by a second mild peak in winter) and diurnally variable. Soil moisture was a significant determinant of CH4 and CO2 fluxes from termite mounds, explaining more than 50% variability. In the case of background forest soils, the combined effect of soil moisture and temperature best explained CO2 and CH4 flux variation. On scaling up, termite mounds contributed negligibly (0.3%) to total soil CO2 emission while mound-mediated CH4 emission offset net soil CH4 uptake by 2.0%. Our results suggest considerable role of termite mounds in influencing source–sink capacity of forest soils. Present data are crucial in reducing error and uncertainty due to spatiotemporal variations in case of large-scale predictions. We suggest careful future land use decisions to minimize the contribution of mound-building termites to net soil CO2 and CH4 flux from this region.

Effects of Soil Moisture and Temperature on Microbial Regulation of Methane Fluxes in a Poplar Plantation

Improved mechanistic understanding of soil methane (CH4) exchange responses to shifts in soil moisture and temperature in forest ecosystems is pivotal to reducing uncertainty in estimates of the soil-atmospheric CH4 budget under climate change. We investigated the mechanism behind the effects of soil moisture and temperature shifts on soil CH4 fluxes under laboratory conditions. Soils from the Huai River Basin in China, an area that experiences frequent hydrological shifts, were sampled from two consecutive depths (0–20 and 20–50 cm) and incubated for 2 weeks under different combinations of soil moisture and temperature. Soils from both depths showed an increase in soil moisture and temperature-dependent cumulative CH4 fluxes. CH4 production rates incubated in different moisture and temperature in surface soil ranged from 1.27 to 2.18 ng g−1 d−1, and that of subsurface soil ranged from 1.18 to 2.34 ng g−1 d−1. The Q10 range for soil CH4 efflux rates was 1.04–1.37. For surface soils, the relative abundance and diversity of methanotrophs decreased with moisture increase when incubated at 5 °C, while it increased with moisture increase when incubated at 15 and 30 °C. For subsurface soils, the relative abundance and diversity of methanotrophs in all samples decreased with moisture increase. However, there was no significant difference in the diversity of methanogens between the two soil depths, while the relative abundance of methanogens in both depths soils increased with temperature increase when incubated at 150% water-filled pore space (WFPS). Microbial community composition exhibited large variations in post incubation samples except for one treatment based on the surface soils incubated at 15 °C, which showed a decrease in the total and unique species number of methanotrophs with moisture increase. In contrast, the unique species number of methanogens in surface soils increased with moisture increase. The analysis of distance-based redundancy analysis (db-RDA) showed that soil pH, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), microbial biomass carbon (MBC), NO3−-N, and NH4+-N mainly performed a significant effect on methanotrophs community composition when incubated at 60% WFPS, while they performed a significant effect on methanogens community composition when incubated at 150% WFPS. Overall, our findings emphasized the vital function of soil hydrology in triggering CH4 efflux from subtropical plantation forest soils under future climate change.

Efficacy of nonfumigant nematicides against Meloidogyne javanica as affected by soil temperature under pasteurized and natural soil conditions.

Biotic and abiotic factors such as microbes and soil temperature can affect nematicide efficacy. Two experiments were conducted to test the effect of three soil temperatures on the efficacy of nonfumigant nematicides (fluopyram, fluensulfone, oxamyl and fluazaindolizine) against Meloidogyne javanica in pasteurized and natural soil in planta. The results showed that all tested nematicides were more efficacious in pasteurized than in natural soil. Temperature affected the nematicides differently with no effect of soil temperature on oxamyl and fluazaindolizine, whereas fluopyram and fluensulfone had greater efficacy at higher soil temperatures. Temperature effects were noted for some but not all nonfumigant nematicides. Fluopyram and fluensulfone were less effective when applied in cold soil, whereas oxamyl and fluazaindolizine were not affected by soil temperature. Although all nematicides resulted in almost complete control of M.javanica in pasteurized soil, this was not the case in natural soil, and much more root damage and nematode reproduction was noted in the latter. © 2021 Society of Chemical Industry.

Soil water content measurement using polymer optical fibre Bragg gratings

Measuring soil water content is crucially important and can affect soil strength, which is a key parameter in the analysis, design and monitoring of geo-structures. In this study, an optical fibre Bragg grating sensor inscribed in polymer optical fibre was developed, and for the first time, its ability to measure soil water content was investigated. The sensitivity of the sensor to different values of gravimetric soil water content under the different compaction conditions of loose and normal compaction was tested. The effect of soil temperature on the sensor’s performance was considered. To assess the sensor’s implementation, accuracy and reliability, a commercial soil water content probe (SM150), which measures volumetric soil water content was employed. The results indicate that the developed sensor, when calibrated correctly, is able to provide detailed data on any minor variation of soil water content (e.g. 0.5%) with high precision. The outcomes of this study define an additional capability of the polymer optical fibre Bragg grating sensors, which is significantly important for the long-term performance monitoring of geo-structures.

The influence of stocking levels, clone, fertilization, and weed control on surface CO2 efflux in a mid-rotation Pinus radiata D. Don plantation in Canterbury, New Zealand

Silvicultural practices applied in managed forest plantations may help counteract the effects of climate change by influencing soil surface CO2 efflux (Fs). Understanding the effects of silvicultural practices on Fs will provide unbiased estimates of carbon fluxes and allow better silvicultural decisions for carbon sequestration. Therefore, we assessed how Fs differed seasonally across silvicultural practices (i.e., stocking levels, clone, fertilization and weed control treatments) and evaluated the effects of soil temperature (Ts) and soil volumetric water content (θv) on Fs across these practices for a mid-rotation (14 year-old) Pinus radiata plantation in the Canterbury region of New Zealand. There were significant differences in Fs (p < 0.05) over the four seasons, three levels of stocking, and five clones. The effects of fertilization and weed control applied 12 years previously on Fs were insignificant. Annual estimate of Fs (mean ± 1 standard deviation) from the study site was 22.7 ± 7.1 t ha−1 a−1 in the form of CO2 (6.2 ± 2.1 t ha−1 a−1 in the form of C). Fs values were consistently higher in plots with 1250 stems ha−1 compared to 2500 stems ha−1, which may be related to a strong soil resource limitation because of the close spacing in the latter plantation. Significant differences in Fs across clones suggest that variations in carbon partitioning might explain their growth performance. Silvicultural treatments influenced Fs response to soil temperature (p < 0.05), resulting in models explaining 28–49% of the total variance in Fs. These findings provide insights into how silvicultural management decisions may impact Fs in mid-rotation radiata pine plantations, contributing towards developing more precise and unbiased plantation carbon budgets.

Photosynthesis, fluorescence, and biomass responses of white oak seedlings to urban soil and air temperature effects.

Urban forest patches can provide critical ecosystem services and their ability to regenerate native tree species is critical to their sustainability. Little is known about native tree seedling establishment and physiological function in urban ecosystems. This growth chamber study examined the effects of urban soil and air temperatures on white oak (Quercus alba L.) germination, seedling growth, and leaf-level physiology. A split-plot design tested effects of field collected soils from urban and reference forest sites in Baltimore, Maryland, and warm (urban) versus cool (rural) growth chamber temperature regimes. Seedlings were harvested at the end of the 23-week experiment to assess foliar chemistry and biomass allocation. Seed germination was unaffected by treatments and was high in both soil types and temperature regimes. Urban soils supported significantly higher total seedling biomass and had a significant effect on leaf-level physiological parameters, with seedlings grown in urban soils having greater Anet , Vcmax , ETRmax , Jmax , PNUE, gs , Anet /Rd , and PIabs (an integrated chlorophyll fluorescence parameter). PIabs measurements taken throughout the experiment revealed a significant time × temperature interaction effect. Baltimore urban forest patch soils were higher in nutrients than reference soils, but also higher in heavy metals. Despite higher levels of heavy metals, these results demonstrate that urban forest patch soils are able to support robust white oak seedling growth and enhanced seedling physiological parameters. However, interactions with temperature suggest that warming air temperatures may cause seedling stress and reduced growth.

Ensuring the effects of climate warming; the sensitivity of controlling factors on soil respiration in Sub-Tropical grassland

Prevailing climate change is expected due to carbon dioxide emission to the atmosphere through soil respiration and perhaps the alteration in the terrestrial carbon cycle. The measurements to establish the effect and sensitivity of soil temperature, soil water content and plant biomass on soil respiration was performed in the sub-tropical grassland located in Central Nepal. Field measurements of soil respiration was conducted by using the closed-chamber method, and soil temperature, soil water content and plant biomass were monitored in the years 2015 and 2016. The soil respiration showed positive significant exponential function which accounted for 74.6% (R2=0.746, p&lt;0.05) of its variation with the soil temperature. The temperature sensitivity of soil respiration, Q10 value obtained was 2.68. Similarly, soil respiration showed a positive significant exponential function that accounted for 37.2% (R2=0.372, p&lt;0.05) of its variation with the soil water content. Remarkable seasonal and monthly variations were observed in soil respiration, soil temperature and soil water content, and the plant biomass as well followed the seasonal trend in variation of the soil respiration. Average soil respiration during measurements period was observed 325.51 mg CO2 m-2 h-1 and the annual soil respiration of the grassland in the years 2015 and 2016 was estimated 592.35 g C m-2 y-1. The study confirmed that soil temperature is the most influential primary factor in controlling soil respiration along with the soil water content and plant biomass. This research indicates that through emissions under the increasing temperature and precipitation, in the changing climate, the sub-tropical grassland could be an additional source of carbon dioxide to the atmosphere that might spur risk for further warming.

Climatic drivers of Verticillium dahliae occurrence in Mediterranean olive-growing areas of southern Spain.

Verticillium wilt, caused by the soil-borne fungus Verticillium dahliae, is one of the most harmful diseases in Mediterranean olive-growing areas. Although, the effects of both soil temperature and moisture on V. dahliae are well known, there is scant knowledge about what climatic drivers affect the occurrence of the pathogen on a large scale. Here, we investigate what climatic drivers determine V. dahliae occurrence in olive-growing areas in southern Spain. In order to bridge this gap in knowledge, a large-scale field survey was carried out to collect data on the occurrence of V. dahliae in 779 olive groves in Granada province. Forty models based on competing combinations of climatic variables were fitted and evaluated using information-theoretic methods. A model that included a multiplicative combination of seasonal and extreme climatic variables was found to be the most viable one. Isothermality and the seasonal distribution of precipitation were the most important variables influencing the occurrence of the pathogen. The isothermal effect was in turn modulated by the seasonality of rainfall, and this became less negative as seasonality increases. Thus, V. dahliae occurs more frequently in olive-growing areas where the day-night temperature oscillation is lower than the summer-winter one. We also found that irrigation reduced the influence of isothermality on occurrence. Our results demonstrate that long-term compound climatic factors rather than "primary" variables, such as annual trends, can better explain the spatial patterns of V. dahliae occurrence in Mediterranean, southern Spain. One important implication of our study is that appropriate irrigation management, when temperature oscillation approaches optimal conditions for V. dahliae to thrive, may reduce the appearance of symptoms in olive trees.

Temperature dependence of volcanic ash soil aggregate stability: Effects of fertilizer application

Soil structures and associated physical properties are strongly affected by soil wetness and temperature, especially when physically treated for sterilization. Effect of soil temperature on soil aggregate stability under wet condition is, however, still not well understood. This study aimed to investigate the effect of temperature on aggregate stability of soils treated with chemical fertilizers (F plot) and organic fertilizers (M plot) originating from cattle manure. We proposed a two-step wet sieving method in which samples were wet sieved at 20 °C and then at an increased constant temperature during the second wet sieving step in a water column. Macro-aggregates (≥250 μm) collected from the M plot disaggregated less compared to those from the F plot, indicating that they were more stable. As opposed to the macro-aggregates, micro-aggregates (<250 μm) were generally stable against temperature regardless of the fertilizer type. The polysaccharide content in the suspension in the soil column after the second wet sieving increased more than twofold when the temperature was increased from 20 to 80 °C for the macro aggregates of the F plot, suggesting the importance of polysaccharides in aggregate stability against temperature.

Response of soil respiration to nitrogen fertilization: Evidence from a 6-year field study of croplands

Agroecosystems receive large amounts of nitrogen (N), which can have a profound impact on soil respiration (Rs). Although Rs is the largest carbon dioxide (CO2) flux from terrestrial ecosystems to the atmosphere, the potential effects of N fertilization on Rs and its components (heterotrophic respiration (Rh) and autotrophic respiration (Ra)) remain controversial, and information on the impacts of N fertilization on C emission from long-term experiments is lacking. In this study, we conducted a field experiment during 6 growing seasons (2012–2018) in which we applied N fertilizer at three rates (0, 180 and 360 kg N ha−1, referred to as N0, N180 and N360, respectively) to two wheat varieties (Changhan No. 58 (CH) and Zhengmai No. 9023 (ZM)) and investigated the effects of N fertilization on Rs and its components by continuous half-hourly observations. We found that over the 6 growing seasons, N180 and N360 increased the mean growing season soil C emission by 29.7% and 11.6%, respectively, due to the increased C emission through Ra under fertilization, which was related to an increased leaf area index (LAI) and canopy photosynthesis (Pn). Significant seasonal variations in the Rs rate were observed; both Rh and Ra contributed to these variations, and the variations were significantly correlated with both soil and air temperature and plant-related traits (LAI and canopy Pn). In addition, the C emission through Rs during the growing season increased throughout the experiment, mainly because of an increase in C emissions through Rh that was caused by increasing temperature during the observation period due to climate change at the experimental site. However, C emission through Rs increased relatively rapidly under the N180 treatment due to the increased Rh throughout the experiment. Furthermore, interaction effects of soil moisture and temperature on the Rs rate and its components were also observed. Overall, our findings highlight the significance of N fertilization in term of soil C emission and its feedback under global warming in agroecosystems.

Effects of soil organism interactions and temperature on carbon use efficiency in three different forest soils

Microbial carbon use efficiency (CUE) affects the soil C cycle to a great extent, but how soil organisms and the abiotic environment combine to influence CUE at a regional scale remains poorly understood. In the current study, microcosms were used to investigate how microbial respiration, biomass, and CUE responded to biotic and abiotic factors in natural tropical, subtropical, and temperate forests. Soil samples from the forests were collected, sterilized, and populated with one or a combination of three types of soil organisms (the fungus Botrytis cinerea, the bacterium Escherichia coli, and the nematode Caenorhabditis elegans). The microcosms were then kept at the mean soil temperatures of the corresponding forests. Microbial respiration, biomass, and CUE were measured over one-month incubation period. The results showed that microbial biomass and CUE were significantly higher, but microbial respiration lower in the subtropical and temperate forest soils than in tropical forest soil. Biotic factors mainly affected CUE by their effect on microbial biomass, while temperature affected CUE by altering respiration. Our results indicate that temperature regulates the interactive effects of soil organisms on microbial biomass, respiration, and CUE, which would provide a basis for understanding the soil C cycle in forest ecosystems.

Sorption and Desorption of the Model Aromatic Hydrocarbons Naphthalene and Benzene: Effects of Temperature and Soil Composition

Petroleum hydrocarbon (PHC) contamination is a global environmental issue. Understanding the key factors and mechanisms controlling the fate and mobility of PHCs in soils and aquifers is critical for environmental risk assessment, the development of remediation strategies, and policy decisions. This study focuses on the effects of soil composition and temperature on the sorption and desorption of two representative aromatic PHC compounds: benzene and naphthalene. The experiments were carried out using artificial sandy loam soil mixtures with temperatures ranging from 3 to 25℃. As expected, the sorption capacities of the soils were primarily controlled by the organic carbon (OC) content, while barely affected by the clay content. The sorption data for benzene and naphthalene followed linear to near-linear isotherms. Naphthalene sorption further increased with decreasing temperature, whereas temperature had little effect on benzene sorption. The latter was consistent with the very small magnitude of the sorption enthalpy of benzene. Under imposed dynamic temperature fluctuations, naphthalene sorption and desorption were shown to be reversible: model simulations demonstrated minimal kinetic limitation of the temperature-dependent soil-water partitioning. Our results imply that even in simple artificial soil systems, temperature variations can have complex, but predictable, effects on the soil-pore water partitioning of PHCs and, hence, on their mobility and bioavailability. Understanding the role of temperature is thus a prerequisite to unraveling the coupled abiotic and biotic processes that modulate the fate of PHCs in real-world soils.