Decreasing Soil Moisture Content Research Articles

Elevation, Soil and Environmental Factors Determine the Spatial and Quantitative Distribution of Qinghai Spruce Recruitment Biomass in Mountainous (Alpine) Watersheds

Soil heterogeneity observed in the alpine environment plays a very important role in the growth of forest recruitment. However, the mechanisms by which the biomass accumulation and allocation patterns of forest recruitment respond to such environmental differences are unclear, which hinders a thorough understanding of climate change’s impact on forest biomass. We hypothesized that soil heterogeneity influences the distribution of Qinghai spruce recruitment biomass along with elevation. In the frame of this study, carried out in the northern Tibetan Plateau, forest Qinghai spruce recruitment data were combined with soil data derived from 24 sample plots, while permutation multifactor ANOVA and multiple linear regression were utilized to reveal the characteristics of forest recruits’ above- and below-ground biomass and their allocation patterns in response to soil heterogeneity. According to the results, the soil heterogeneity mainly affected the distribution characteristics of recruits’ above- and below-ground biomass at different elevations, while the recruits’ root–shoot ratio variability was influenced by a combination of soil and other environmental factors. Soil organic carbon (SOC) had the greatest effect on the variability of the above- and below-ground biomass of spruce recruits, with R2 of 0.280 and 0.257, respectively. Soil organic carbon and soil moisture content (SMC) had a significant effect on the variability of the root–shoot ratio, with R2 of 0.168 and 0.165, respectively. Soil total nitrogen (TN) and soil organic carbon were the main influencing factors of the above-ground biomass of forest recruits, with contribution rates of 43.15% and 35.28%, respectively. Soil total nitrogen and soil organic carbon were also the main factors influencing the below-ground biomass of forest recruits, with contribution rates of 42.52% and 37.24%, respectively, and both of them had a positive effect on biomass accumulation, and the magnitude of the influence varied with the elevation gradient. Soil moisture content was the main influence factor of spruce recruits’ root–shoot ratio, with a contribution rate of 54.12%. Decreasing soil moisture content would significantly increase the root–shoot ratio of spruce recruits and promote plants to allocate more biomass to root growth. Changes in elevation not only affected the intensity of the effect of soil factors on spruce recruitment biomass and its allocation pattern but even led to a change in the positive and negative effects.

Field investigation of soil moisture profile in the seedbeds of clayey paddy fields composed of large clods (aggregates)

ABSTRACT Unstable germination and emergence of upland crops in clayey paddy fields is a pressing issue. As tillage leads to the formation of large clods measuring a few centimeters, the soil moisture content in the seedbed markedly decreases, potentially inhibiting germination of seeds. Although the effect of the clod size on the soil moisture profile was confirmed experimentally, the validity of this effect has not been tested in the field. In this study, we aimed to clarify the effect of clod size on the moisture profile and water balance in the seedbeds of clayey paddy field. We developed an apparatus for measuring soil moisture content in the soil layer with clods. This apparatus used a laser displacement sensor and large transparent plate horizontally fixed above the soil surface. Temporal changes in the soil moisture profile (0–10 cm depth) and evaporation rate of clayey paddy fields with different clod sizes were monitored during the sowing period of soybeans. We found that the larger the mean clod diameter (MCD), the greater the decrease in soil moisture content near the soil surface. In addition, soil moisture loss at the sowing depth (5 cm) was positively correlated with MCD. In terms of the water balance, the estimated upward water flux at a depth of 5 cm was less than 1 mm d−1 across all the plots and periods. By contrast, the estimated ratio of the apparent to molecular diffusion coefficient of water vapor in the dry soil layer of clayey paddy field with an MCD of 2.5 and 1.8 cm were 5.1 and 2.0, respectively. These results suggest that more significant soil moisture loss causing reduction of germination and emergence rate can occur in a clayey paddy field with large clods, likely owing to the increased enhancement of water vapor movement. To increase the germination and emergence rate, therefore, a numerical model that can evaluate the moisture profile of soil layer with clods should be developed and the sowing depth should be optimized based on the MCD.

Research on Temperature Field of Cement-Mixing Pile-Reinforced Soft Soil Foundation

To investigate the mechanism of reinforcing soft soil with cement-mixing pile, based on ABAQUS secondary development, a numerical simulation study of the hydration reaction of cement-mixing piles was conducted. In this study, the influence of ground temperature variations on the distribution patterns of the temperature field in and around the pile was also considered. The temperature field of the pile–soil model can be primarily divided into two stages: the temperature rise stage (0~5 d) and the temperature decrease stage (5~90 d). The following observations were made: (1) The temperature of the pile body rapidly increased within the first 5 days, dissipating heat to the surrounding soil, leading to an elevation of the temperature in the soil around the pile and a decrease in soil moisture content. Around the 5th day, the temperature reached its maximum value, and the heat release rate of the pile body was higher than that of the surrounding soil. (2) With a 15% cement admixture, under the influence of 425# cement hydration, the temperature inside the pile increased by 5 °C, and the temperature in the soil around the pile increased by 4.2 °C. After considering the ground temperature, the temperature in the soil around the pile increased by 4.6 °C. (3) The maximum temperature generated during the hydration of 425# Portland cement is higher than that of 525#; the temperature of the soil around piles made with 425# cement is consistently higher than that made with 525#. (4) The hydration temperature of piles with a 10% cement admixture increased by 4.4 °C; for piles with a 15% cement admixture, the hydration temperature increased by 6.6 °C; and for piles with a 20% cement admixture, the hydration temperature increased by 9.1 °C. The temperature field of this structure gradually stabilizes after 7 days with increasing time and cement admixture. The results indicate that the hydration of cement-mixing piles raises the temperature of the soil around the piles. Additionally, the temperature resulting from the hydration of cement-mixing pile increases with the addition of cement.

Soil Water Deficit Reduced Root Hydraulic Conductivity of Common Reed (Phragmites australis).

Alterations in root hydraulics in response to varying moisture conditions remain a subject of debate. In our investigation, we subjected common reeds (Phragmites australis) to a 45-day treatment with four distinct soil moisture levels. The findings unveiled that, in response to drought stress, the total root length, surface area, volume, and average diameter exhibited varying degrees of reduction. Anatomically, drought caused a reduction in root diameter (RD), cortex thickness (CT), vessel diameter (VD), and root cross-sectional area (RCA). A decrease in soil moisture significantly reduced both whole- and single-root hydraulic conductivity (Lpwr, Lpsr). The total length, surface area, volume, and average diameter of the reed root system were significantly correlated with Lpwr, while RD, CT, and RCA were significantly correlated with Lpsr. A decrease in soil moisture content significantly influenced root morphological and anatomical characteristics, which, in turn, altered Lpr, and the transcriptome results suggest that this may be associated with the variation in the expression of abscisic acid (ABA) and aquaporins (AQPs) genes. Our initial findings address a gap in our understanding of reed hydraulics, offering fresh theoretical insights into how herbaceous plants respond to external stressors.

Deciphering the Impact of Induced Drought in Agriculture Soils: Changes in Microbial Community Structure, Enzymatic and Metabolic Diversity

Prolonged drought stress may have a significant impact on the structure and activity of the soil microbial community. Our study aims to investigate the impact of short-term drought (2 months) on the microbial community structure, enzymes, and metabolic diversity in four agricultural soils (Gniewkowo (G), Lulkowo (L), Wielka Nieszawka (N) and Suchatówka (S) sites) in Poland. These four types of soil were selected based on differences in their texture (gleyic luvisol Phaeozem in G (rich in clay and humus), stagnic luvisol in L, fluvisol in N and haplic luvisol in S (sandy)). We investigated the (1) number of bacteria, actinomycetes (formally phylum Actinomycetota) and fungi; (2) microbial community (16S rRNA and ITS amplicon regions); (3) biological activity by community-level physiological profiling (CLPP); (4) soil enzyme activities (dehydrogenases (DH), phosphatases (acid ACP and alkaline ALP) and urease (UR)); and (5) soil chemical properties. At the end of our experiment, we observed a significant decrease in soil moisture content with the highest in the soil from the S site. Overall, there was no change in total bacteria, but actinomycetes and fungal numbers increased after the 1st week with a decrease in moisture content. ACP activity decreased in three out of four analyzed soil samples. The exception was in sample G, where activity increased for 1–2 weeks and then decreased. ALP activity significantly increased with a decrease in moisture in the 1st week and was lowest at the end of the experiment. DH activity increased up to the 4th week in the G and N samples and up to the 2nd week in the L and S samples. UR activity showed variations in the analyzed samples. A reduction in the utilization of carbon sources (except D-mannitol and L-asparagine) was noted with the highest reduction in the G sample followed by the L, N and S samples. Thus, the pattern of changes was different depending on the analyzed soil type. The 16S rRNA and ITS amplicon sequencing revealed a decrease in the relative abundance of Pseudomonadota, Basidiomycota, Apicomplexa, and increased abundance of Actinomycetota, Bacillota and Ascomycota under prolonged drought conditions. With this, we concluded that drought conditions resulted in a significant alteration of soil microbial communities, enzyme activities, and metabolic diversity in the investigated soils.

Effects of elevated temperature and decreased soil moisture content on triclosan ecotoxicity to earthworm E. fetida.

Emerging pollutants and climate change are two main challenges affecting soil organisms today. Changes in temperature and soil moisture with climate change are key factors determining activity and fitness of soil dwelling organisms. The occurrence and toxicity of antimicrobial agent triclosan (TCS) in terrestrial environment is of high concern, while no data are available on TCS toxicity changes to terrestrial organisms under global climate change. The study's aim was to assess the impact of elevated temperature, decreased soil moisture content, and their complex interaction on triclosan-induced changes in Eisenia fetida life cycle parameters (growth, reproduction, and survival). Eight-week TCS-contaminated soil (10-750 mg TCS kg-1) experiments with E. fetida were performed at four different treatments: C (21 °C + 60% water holding capacity (WHC)); D (21 °C and 30% WHC); T (25 °C + 60% WHC); and T + D (25 °C + 30% WHC). TCS had negative impact on the earthworm mortality, growth, and reproduction. Changing climate conditions have altered TCS toxicity to E. fetida. Drought and drought in combination with elevated temperature enhanced the adverse effects of TCS on earthworm survival, growth rate, and reproduction, while single elevated temperature slightly reduced TCS lethal toxicity as well as toxicity to growth rate and reproduction.

Variation of Soil Carbon, Nitrogen and Phosphorus and Ecological Stoichiometric Characteristics During Land Degradation in Coal Mining Subsidence Area

In order to explore the effects of land degradation on soil carbon, nitrogen and phosphorus and ecological stoichiometry in semi-arid coal mining subsidence area, the spatial pattern of soil carbon, nitrogen and phosphorus content, reserves and ecological stoichiometric ratio in the process of land degradation was studied by space-time substitution method with the soil in three stages of non-degradation, mild degradation and severe degradation as the research object. The results showed that :(1)Land degradation caused an average decrease of soil moisture content and porosity by 50.8% and 22.4%, respectively, resulting in an increase of soil pH and bulk density by 16.0% and 23.8%, respectively.(2)The soil organic carbon content and storage decreased by 55.6% and 50.7%, respectively, due to land degradation. The carbon loss in the surface soil was significant, and the nitrogen content and storage decreased by 21.8% and 13.9%, respectively. The soil nitrogen damage in the middle layer was the largest, and the phosphorus content and storage decreased by 37.9% and 31.8%, respectively.(3)Soil C/N decreased by 18.9%, C/P and N/P increased by 7.9% and 35.4%, respectively, after mild land degradation. Soil C/N and C/P decreased by 68.2% and 64.4%, respectively, while N/P increased by 16.1% after severe land degradation. (4) Soil water content and other environmental factors have different degrees of influence on soil carbon, nitrogen and phosphorus content, C/N and C/P, but no significant correlation with soil N/P. In summary, land degradation caused by multi-dynamic erosion damage in coal mining subsidence areas will significantly reduce soil environmental quality, cause soil drought, barrenness and salinization, and reduce the storage and supply capacity of ecosystem carbon, nitrogen and phosphorus.

Effect of moisture on photosynthesis and transpiration of buckwheat leaves

Currently, the issue of developing adaptive varieties of crops based on evolutionary principles is becoming urgent. The need to develop adaptive varieties for Russia is determined by the contrast of its natural and climatic conditions, global climate changes, and the increasing unpredictability of the weather. This task is highly relevant to the valuable food crop buckwheat, the yields of which are still low due to insufficient resistance of modern varieties to extreme environmental factors. Vegetation experiments to study the genotypic reaction of light and dark phases of photosynthesis of leaves on changes in soil moisture availability were carried out. During the period of buckwheat breeding from local samples to modern varieties the plants showed a significant trend in increasing the activity of photosynthesis and transpiration of plant leaves with a certain decrease in their resistance to moisture limitation. It was established that a decrease of soil moisture content from 70 to 30% of total moisture capacity caused, in modern cultivars, a mean decrease of fluorescence quantum yield by 52.5%, of electron-transport chain activity by 53.7%, of photosynthesis intensity by 66.5%, of transpiration intensity by 82.1%, whereas in local cultivars it decreased by 40.0%, 52.1%, 51.0%, and 76.1%, respectively.

Use of Impact Penetrometer to Determine Changes in Soil Compactness After Entracon Sioux EH30 Timber Harvesting

Wood harvesting with the use of wheeled harvesters is now common in Polish and Czech forests. While moving in the forest, the wheels of these machines affect the forest soil and the extent of this impact is interesting. The paper presents the results of measurements of the changes that occur in the soil on the operational trails after the timber harvesting using the Entracon Sioux EH30 thinning harvester. The measurements were taken on fragments of three operational trails, in and between the ruts and at a distance of 1.0 m off the trail. An impact penetrometer was used to measure the penetration resistance, soil samples were collected to determine the bulk density and moisture content, and soil deformations on the trail were measured with a profile meter. Unit pressures exerted by harvester wheels on the ground were determined. It was shown that in the places where the harvester wheels pass, even of a small weight (5.73 tons, 8 wheels) and with unit pressures of the wheels on the ground <50 kPa, changes in soil parameters occurred. A statistically significant increase in penetration resistance in relation to the control occurred at a depth of up to 35 cm, while at a depth of up to 5 cm the increase was more than 2-fold. There was also a slight decrease in soil moisture content (up to 7.9%) and an increase (up to 8.4%) in bulk density in the ruts, while rut depths were small and reached 4 cm. As it was shown, the impact penetrometer, simple in design, which was assumed to be used for measurements, and which is not used in this type of research in forestry, despite its limitations, can be used to determine the compactness of the soil and its changes resulting from machine work.

Role of climatic factors in the toxicity of fipronil toward earthworms in two tropical soils: effects of increased temperature and reduced soil moisture content.

The aim of this study was to assess the effect of temperature on the toxicity of fipronil toward earthworms (Eisenia andrei) in two Brazilian soils (Entisol and Oxisol) with contrasting textures. In the case of Entisol, the influence of soil moisture content on toxicity was also investigated. Earthworms were exposed for 56days to soils spiked with increasing concentrations of fipronil (8.95, 19.48, 38.22, 155.61, and 237.81mgkg-1 for Entisol; 12.99, 27.94, 48.42, 204.67, and 374.29mgkg-1 for Oxisol) under scenarios with different combinations of temperature (20, 25 and 27°C) and soil moisture content (60 and 30% of water holding capacity (WHC) for Entisol and 60% WHC for Oxisol). The number of juveniles produced was taken as the endpoint, and a risk assessment was performed based on the hazard quotient (HQ). In Entisol, at 60% WHC the fipronil toxicity decreased at 27°C compared with the other temperatures tested (EC50 = 52.58, 48.48, and 110mgkg-1 for 20, 25, and 27°C, respectively). In the case of Oxisol at 60% WHC, the fipronil toxicity increased at 27°C compared with other temperatures (EC50 = 277.57, 312.87, and 39.89mgkg-1 at 20, 25, and 27°C, respectively). An increase in fipronil toxicity was also observed with a decrease in soil moisture content in Entisol at 27°C (EC50 = 27.95 and 110mgkg-1 for 30% and 60% WHC, respectively). The risk of fipronil was only significant at 27°C in Entisol and Oxisol with water contents of 30% and 60% WHC, respectively, revealing that higher temperatures are able to increase the risk of fipronil toxicity toward earthworms depending on soil type and soil moisture content. The results reported herein show that soil properties associated with climatic shifts could enhance the ecotoxicological effects and risk of fipronil for earthworms, depending on the type of soil.

Impact of Elevated Soil Temperature on Physiological Parameters of Tea Plant Growing Adjacent to Gas Flaring Site

Gas flaring is now recognized as a major environmental problem. Smoking flare may be a significant contributor to overall particulate emissions. It also results in production of excessive heat in the nearby areas. The present investigation aims to study the impact of elevated soil temperature on physiological parameters of tea plant growing adjacent to Gas flaring site. The experimental plot was laid out in 5 x 2 factorial RCBD with two factors viz. different distances from the flare site and two seasons in two different tea gardens adjacent to Kathaloni OCS and Merbil Majuli OCS 6 in Dibrugarh district of Assam in 2019-20. Plant and soil samples were collected and estimation of some select plant physiological parameters was done. Significant increase in soil temperature and decrease in soil moisture content was observed in distance closer to the flare pit. The result of the study revealed that there was a gradual decline in relative turgidity, specific leaf weight, plucking point density, stomatal count, leaf area measurement, polyphenol content, chlorophyll content, caffeine content but an increase in water saturation deficit of the green tea leaves on plants existing at a distance moving closer to the flare pit. A significant increase in rain flushing season as compared to autumn was observed in all the plant parameters except water saturation deficit.

Physiological Response of Soybean Plants to Water Deficit.

Soybean is an important cash crop in the world, and drought is the main reason for the loss of soybean plants productivity, with drought stress during the most water-sensitive flowering period of soybeans. In this article, drought-tolerant variety Heinong 44 (HN44) and drought-sensitive variety Heinong 65 (HN65) were used as experimental materials. Drought treatment was carried out at the early flowering stage. The method of controlling soil moisture content was used to simulate different degrees of drought, and the physiological changes of these two varieties of soybean under different soil moisture contents were studied. The results showed that with a decrease in soil moisture content, the content of malondialdehyde (MDA) in soybean leaves increased significantly; the activities of peroxidase (POD), catalase (CAT), and ascorbic acid peroxidase (APX) increased first and then decreased; the content of proline, soluble sugar, and soluble protein increased; and the total antioxidant capacity (T-AOC) increased significantly. When the soil moisture content was 15.5%, the degree of membrane lipid peroxidation, osmotic regulatory substances, antioxidant enzyme activity, and T-AOC increased the most, and the decrease in drought-tolerant variety HN44 was significantly less than that of drought-sensitive variety HN65. Our research reveals the response law of soybean crops to physiological characteristics under water deficit and provides theoretical basis and guiding significance for drought-resistant cultivation and breeding of soybean.

Invasion of alien slugs in disturbed habitats: role of behavioural phenotype, plasticity and interspecific competition

Habitat disturbance can promote the invasion success of alien species, but the underlying mechanisms remain unclear, especially in animal species. Alien species may have trait values that facilitate invasion (ideal weed hypothesis) or greater phenotypic plasticity than native species (plasticity hypothesis), thus promoting their invasion success in disturbed habitats. Invasion success and ultimately alien species dominance in disturbed habitats can also be a direct consequence of competitive exclusion of native species. We performed experiments in controlled conditions to determine which of these mechanisms could explain the invasion success of Arion subfuscus s.l. (hereafter Arion ), an alien slug species complex that lives in various disturbed ecosystems of eastern Canada such as managed forests. To do so, we compared the behavioural response of Arion and native sympatric philomycid slugs (hereafter Philomycus ) to a decrease in soil moisture content, which often occurs after forest harvesting (i.e. habitat disturbance). We also investigated whether the presence of Arion alters the behaviour of Philomycus , which would indicate that Arion has a greater ability to compete by interference than these native species. Our findings show that Arion did not have higher boldness or locomotor activity (i.e. behaviours that promote invasion success) or greater plasticity than Philomycus , and that the presence of Arion did not affect the behaviour of Philomycus . However, Arion may be able to exploit resources more efficiently than native species since it mainly used the closest refuge from the food source in the present study. These findings are in line with the ideal weed hypothesis but do not support the phenotypic plasticity hypothesis or any role of interference competition in Arion invasion success in disturbed habitats such as harvested forests. Our results also suggest that the direction, but not the magnitude, of behavioural plasticity might be a key aspect in alien species invasion success in disturbed habitats. • Alien slugs were not bolder or more active than native species. • Plasticity of these behaviours was not higher in alien slugs than in native slugs. • Interference competition does not seem to be involved in alien slug invasion success. • Alien slugs may be more efficient in exploiting resources than native species.

Precedent meteorological driving forces of flash drought and their feasibility for flash drought simulation

Flash droughts are extreme events characterized by a short duration, strong intensity, and rapid onset. Owing to their unusually rapid occurrence, the use of current drought monitoring tools to capture them is still challenging. In this study, using ERA-Interim soil moisture reanalysis products from the European Center for Medium-Range Weather Forecast, an approach that considers the rate of decrease in soil moisture content during the onset stage of flash droughts was proposed for the identification of the flash droughts that occurred during the 1979-2018 period. Further, the anomalies associated with meteorological variables during the drought onset stage of these events were analyzed, and the feasibility of using precedent meteorological driving forces to realize flash drought simulation based on a multivariate linear regression model was investigated. The results obtained showed that the rate of soil moisture intensification during the onset state of flash droughts showed significant spatial discrepancy. Specifically, during this stage, soil moisture content declined much faster in the south of the Yangtze River than in Northwestern China. Additionally, the mean, peak, and variation ranges of the anomalies of the different meteorological variables exhibited more significant spatial discrepancies during this stage. Particularly, the peak values showed the most significant variation, and were half the standard deviation higher than the slowly-evolving drought. Furthermore, by integrating the anomalies associated with multiple meteorological variables during the early and onset stages of the flash drought events, the regression model provided satisfying simulations of the soil moisture intensification rate, suggesting that it is possible to simulate flash droughts from a meteorological perspective.

EMS Derived Wheat Mutant BIG8-1 (Triticum aestivum L.)-A New Drought Tolerant Mutant Wheat Line.

Drought response in wheat is considered a highly complex process, since it is a multigenic trait; nevertheless, breeding programs are continuously searching for new wheat varieties with characteristics for drought tolerance. In a previous study, we demonstrated the effectiveness of a mutant known as RYNO3936 that could survive 14 days without water. In this study, we reveal another mutant known as BIG8-1 that can endure severe water deficit stress (21 days without water) with superior drought response characteristics. Phenotypically, the mutant plants had broader leaves, including a densely packed fibrous root architecture that was not visible in the WT parent plants. During mild (day 7) drought stress, the mutant could maintain its relative water content, chlorophyll content, maximum quantum yield of PSII (Fv/Fm) and stomatal conductance, with no phenotypic symptoms such as wilting or senescence despite a decrease in soil moisture content. It was only during moderate (day 14) and severe (day 21) water deficit stress that a decline in those variables was evident. Furthermore, the mutant plants also displayed a unique preservation of metabolic activity, which was confirmed by assessing the accumulation of free amino acids and increase of antioxidative enzymes (peroxidases and glutathione S-transferase). Proteome reshuffling was also observed, allowing slow degradation of essential proteins such as RuBisCO during water deficit stress. The LC-MS/MS data revealed a high abundance of proteins involved in energy and photosynthesis under well-watered conditions, particularly Serpin-Z2A and Z2B, SGT1 and Calnexin-like protein. However, after 21 days of water stress, the mutants expressed ABC transporter permeases and xylanase inhibitor protein, which are involved in the transport of amino acids and protecting cells, respectively. This study characterizes a new mutant BIG8-1 with drought-tolerant characteristics suited for breeding programs.

Hydrothermal regime of the urban soils in the cold period of the hydrological year of Western Siberia (Russia).

This study analysed the temperature and humidity properties of urban soils in the territory of the Mikhailovskaya Embankment Park of Culture and Recreation in Novosibirsk, Russian Federation, in the cold period of the 2018-2019 hydrological year. Data on the temperature of the air and soil at various depths, winter and spring soil moisture and data on the dynamics of snow accumulation and snow distribution were analysed. This study found that, despite high levels of humidity in the autumn and the high snow reserves that accumulated during the winter, a decrease in soil moisture content was observed after the snow had melted. Temperatures in the range of -3 to -7 °С were recorded in the layer of soil from 0 to 30 cm below the ground surface. Systematic clearing of the pedestrian zones of the park of snow during the winter leads to both an increase in snow height and, accordingly, water reserves in the snow in adjacent areas, and to exposure of the surfaces of rabattes, or cement subterranean garden beds, in which perennial ornamental plants are grown. This study also revealed the presence of an additional cooling effect within these rabattes on the temperature regime of the soils within them during the cold period.

Drought-induced reduction in flower size and abundance correlates with reduced flower visits by bumble bees.

Reduced water availability can cause physiological stress in plants that affects floral development leading to changes in floral morphology and traits that mediate interactions with pollinators. As pollinators can detect small changes in trait expressions, drought-induced changes in floral traits could affect pollinator visitations. However, the linkage between changes in floral traits and pollinator visitations under drought conditions is not well explored. We, therefore, tested whether drought-induced changes in floral morphology and abundance of flowers are linked to changes in pollinator visitations. We conducted flight cage experiments with a radio frequency identification system for automated visitation recordings with bumble bees (Bombus terrestris) and common charlock (Sinapis arvensis) as the model system. In total, we recorded interactions for 31 foraging bumble bees and 6569 flower visitations. We found that decreasing soil moisture content correlated with decreasing size of all measured morphological traits except stamen length and nectar tube width. The reductions in floral size, petal width and length, nectar tube depth and number of flowers resulted in decreasing visitation rates by bumble bees. These decreasing visitations under lower soil moisture availability might be explained by lower numbers of flowers and thus a reduced attractiveness and/or by increased difficulties experienced by bumble bees in handling smaller flowers. Whether these effects act additively or synergistically on pollinator behaviour and whether this leads to changes in pollen transfer and to different selectionp ressures require further investigation.

Effect of soil moisture content and nitrogen fertilizer on survival, growth and some physiological characteristics of Platycladus orientalis seedlings

Given the important applications of oriental arborvitae (Platycladus orientalis /L./ Franco), we examined the interaction effects of soil moisture content (SMC) and urea fertilizer on survival, growth and some physiological characteristics of seedlings of this species. In this study, 270 uniform oriental arborvitae seedlings were transplanted in 2 kg containers filled with the top soil of the natural stand in Soorkesh forest reserve. After 2 months, 6 levels of SMC (100%, 75%, 50%, 25%, 15% and 10%) and 3 levels of urea [control: 0, low nitrogen (LN): 75 mg·kg<sup>–1</sup>, and high nitrogen (HN): 150 mg·kg<sup>–1</sup>] were used from June till the end of the first growing season in 3 replications and 5 seedlings per replication as subsamples. The results showed that all seedlings survived under SMC above 25% in control and urea fertilizer treatments. However, under 15% and 10% SMC, the seedling survival decreased significantly in control treatment, but adding urea fertilizer significantly increased the survival, especially in HN treatment. Growth and morphological properties of seedlings, including root and shoot length, number of first-order lateral roots and total biomass, showed a significant decrease at 75%. Seedling quality index gradually decreased with SMC reduction, but the addition of urea to the soil significantly increased it under all SMC treatments. The results also indicated that a decrease in SMC significantly decreased relative water content of leaves and total chlorophyll content, and urea fertilizer increased total chlorophyll under all SMC treatments, but it increased relative water content only at 100% to 25%. Moreover, water use efficiency of P. orientalis seedlings significantly increased under low soil moisture treatments, and urea significantly increased it, especially under HN treatment. In conclusion, urea fertilizer, especially in the higher amount (150 mg·kg<sup>–1</sup>), improved growth and quality of seedlings under different soil moisture conditions, and increased their survival under severe drought.

Evaluating and improving the sand storm numerical simulation performance in Northwestern China using WRF-Chem and remote sensing soil moisture data

This paper aims to test the ability of the WRF-Chem model to simulate sand storms in Northwest China and improve the simulation results by introducing remote sensing soil moisture data into WRF-Chem. We conducted sensitivity tests, including parameterization scheme tests and soil moisture tests using WRF-Chem. By comparing various combinations of parameterization schemes, which have considerable impacts on sand emissions, the most suitable parameterization scheme for WRF-Chem to simulate sand storms in Northwest China was selected for establishing models in future research. Based on the optimal combination of parameterization schemes, the sensitivity of sand emissions to soil moisture was tested, indicating that soil moisture has a substantial influence on sand emissions and revealing a nonlinear relationship between sand emissions and soil moisture. Although sand simulations are sensitive to soil moisture, the sand emission volume does not always increase with decreasing soil moisture content. Moreover, the soil moisture content simulated by WRF-Chem is quite different from that observed by satellites. Therefore, we selected ten sand storms that occurred in Northwest China in 2009–2018, including weak, moderate and strong sand storms, to explore the responses of sand storms of different intensities to soil moisture. Some experiments were conducted in two scenarios: scenario A was simulated only by WRF-Chem, and scenario B was designed by replacing the initial soil moisture field in WRF-Chem with soil moisture satellite data from AMSR2 and AMSR-E. Comparing the simulation results with in-situ ground-based and satellite-based measurements indicates that WRF-Chem can capture strong sand storms and some moderate sand storms, but the ability to simulate weak sand storms needs to be greatly improved. After introducing remote sensing soil moisture data into WRF-Chem, the simulation of sand emissions becomes more accurate, substantially improving the simulation results. Among the ten simulated sand storms, the AOD (aerosol optical depth) and PM10 simulation accuracies are improved for five and seven sand storms, respectively. After this improvement, the AOD correlation coefficient can reach 0.63, and the PM10 correlation coefficient can reach 0.60.

Forecasting Water Inflow into the Tsimlyansk Reservoir during Spring Flood under Current Climate Conditions: Problems and Reproducibility

Studies of water balance and variations of water regime of rivers in the Don Basin have shown a steady trend toward a decrease in spring flood volumes and an increase in runoff volume in winter since the mid-1980s. More frequent thaws have resulted in that snowmelt runoff formation can be seen almost throughout winter. A decrease in soil moisture content in the late October along with a decrease in the maximal freezing depth in the major portion of the basin increases water losses during thaws and at the early stages of spring flood. At a considerable decrease in the water equivalent of snow cover along with an appreciable increase in water losses, spring flood will not occur in some years. Therefore, changes in the climate and anthropogenic load considerably reduce the reliability of relationships developed in the XX century and used to forecast the spring inflow into the Tsymlyansk Reservoir.