Soil-water Environment Research Articles

Effect of low-molecular-weight organic acids on the transport of polystyrene nanoplastics in saturated porous media

Low molecular weight organic acids (LMWOAs) are extensively present as soluble organic matter in the environment, potentially influencing the transport of polystyrene nanoplastics (PSNPs) in soil and groundwater environments. In this study, we studied the impact of three LMWOAs (Acetic Acid (AA), Malic Acid (MA), and Citric Acid (CA)) on PSNPs migration under varied pH and Ionic Strength (IS) conditions in the saturated porous medium. The results demonstrated that the low LMWOAs concentrations (0.0001 mol L−1) promoted PSNPs migration rate, while high concentrations (0.001, 0.01 mol L−1) reduced the migration rate and increased the deposition. Due to the different relative molecular weights and number of functional groups of different LMWOAs, the order of promoting (0.0001 mol L−1) /inhibiting (0.001, 0.01 mol L−1) effects of LMWOAs on PSNPs migration rate under various physicochemical conditions in this study was AA < MA < CA. The decrease in IS and increase in pH promoted the migration of PSNPs. Electrostatic repulsion and spatial potential resistance affected PSNPs migration. This study offers theoretical support for the understanding of migration patterns and mechanisms of nanoparticles in soil-water environments.

Occurrence and emission characteristics of microplastics in agricultural surface runoff under different natural rainfall and short-term fertilizer application

Land-based microplastics (MPs) are considered the primary source of MPs in aquatic environments, with runoff being a major pathway for their transfer from soil to surface water. However, the transportation characteristics of MPs via agricultural surface runoff remain unclear. In this study, we investigated the occurrence and emission characteristics of MPs in agricultural surface runoff under various short-term fertilizer applications and natural rainfall events using laser direct infrared imaging analysis (LDIR). MPs from fertilizers and soils co-migrated with the agricultural runoff. The abundance and concentration of MPs in runoff were 145.90 ± 22.48–2043.38 ± 89.51 items·L−1 and 39.17 ± 21.94–523.04 ± 47.85 µg·L−1, respectively. Small and low-density MPs, such as polyethylene (PE), chlorinated polyethylene (CPE), and polyurethane (PU) in film/fragment form with 20–50 µm exhibited a higher mobility. No statistical differences were observed in the distribution of runoff MPs with the application of different fertilizers. There was a significant positive relationship between runoff MP abundance and rainfall intensity. The annual emission load in this study area was 116.73 g·hm−2, indicating that the transportation of MPs via agricultural surface runoff cannot be ignored. This study is conducive to understanding the migration behavior of MPs in soil-water environments in a better manner.

Impacts of unregulated dumpsites: a study on toxic soil contamination, associated risks, and call for sustainable environmental protection in Nnewi, Nigeria

The accumulation of leachates from unlined dumpsites laden soil-water environment with toxic elements poses imminent threats to both the environment and humans. This study evaluated the seasonal levels of potentially toxic elements (PTEs), their health-related risks, contamination factors (CF), pollution load index, geo-accumulation index (Igeo), ecological risk index, polymetallic contaminant index and Nemerow's synthetic pollution index of soils near a waste dump in Nnewi, Anambra State, Nigeria. The PTE results indicated that levels of Cd (1.54–3.40 mg/kg) were above the World Health Organization's threshold limit for soil. The studied soil samples had PTE levels higher than the control samples due to their proximity to the dumpsite. The CF of the PTE in the soil indicated moderate to considerable contamination, while the control areas showed moderate contamination for both seasons. The pollution load indices of the soil indicated heavy and moderate pollution for the study sample (2.207–2.517) and control samples (1.445–1.659). However, the ecological risk indices ranged from 85.72 to 164.84, indicating a low ecological risk. The Igeo of the PTE in the soil ranged from unpolluted, moderately polluted to very strongly polluted. The Nemerow's synthetic pollution index values ranged from 3.560 to 3.564 for the study samples and 2.070–2.502 for the control samples, indicating heavy and moderate pollution of the soil respectively. The polymetallic contaminant index values for the study samples (23.22–26.43) and control samples (15.02–17.23) showed high and considerable contamination respectively. Health risk examination highlighted that both adults and children have a low risk for non-cancer health threat via ingestion route, while a high risk was obtained for children for cancer health dangers via ingestion routes. For the dermal pathway, children and adults have minimal chances of exposure to cancer risks, while a high exposure to non-cancer risk was observed for children. Pearson's correlation and principal component loadings revealed the sources of pollution to be of similar origins linked to anthropogenic activities. Awareness programs are necessary to educate the populace about the dangers of using contaminated soil for farming or recreational activities. The use of sanitary dumpsites should be encouraged and adopted as a waste disposal method by the government to mitigate the spread of PTE into the environment.

Comparison of microstructure, mechanical, and electrochemical performance of laser-deposited FeCrV15 alloy at varying powder feed rates

In the realm of surface modification, repair, and reinforcement of components exposed to challenging operational conditions, such as tillage tools, laser cladding stands out as an innovative manufacturing technique. Employing this additive manufacturing approach, a functionally graded material with outstanding strength and properties is incorporated to enhance the desired attributes of the base material. This comparative investigation scrutinized and assessed the microstructural characteristics, hardness, wear resistance, and corrosion behavior of high carbon ferrochrome FeCrV15 coatings fabricated at two distinct powder feed rates, namely 5 and 6 g/min, respectively. The analysis delved into how the resultant coatings' molten bead deposition, microstructural evolution, hardness, wear resistance, and corrosion resistance were influenced by the powder feed rate. Evaluation of hardness was conducted using a Vickers microhardness testing apparatus, while phase identification was accomplished utilizing an X-ray diffractometer. The morphologies of the microstructures were scrutinized employing optical microscopy and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS). Furthermore, the corrosion response of the deposits in a soil–water environment was probed utilizing an Autolab potentiostat. A comprehensive assessment of the coatings' sliding wear performance was undertaken using an Anton Paar Tribometer. The findings of the study reveal that an escalation in the powder feed rate engenders heightened grain refinement within the microstructure, yielding a defect-free sample and augmenting the wear performance (with a wear rate of 2.42 × 10–6 mm3/N/m for sample B, surpassing 2.39 × 10–5 mm3/N/m for sample A and outstripping 1.72 × 10–3 mm3/N/m for the steel substrate). Additionally, the corrosion resistance is enhanced (with a corrosion rate of 0.0032 mm/yr for sample B, surpassing 0.0036 mm/yr for sample A, which, in turn, exceeds 0.1168 mm/yr for the steel substrate) in the case of sample B.

Unraveling the photochemical behavior of dissolved organic matter derived from hydrothermal carbonization process water: Insights from molecular transformation and photoactive species

Hydrothermal carbonization process water (HTPW) has been utilized as a substitute for chemical fertilizers in agricultural applications. However, the input of HTPW into paddy water, particularly the significant proportion of dissolved organic matter (DOM) in HTPW (DOM-HTPW), directly engages in photochemical transformations, a phenomenon often overlooked. This study observed a consistent decrease in humification (SUVA280, 7.7–53.9%) and aromaticity (SUVA254, 6.1–40.0%) of DOM-HTPW after irradiation. The primary active photobleaching components of DOM-HTPW varied depending on the feedstock, such as protein for chicken manure DOM-HTPW and lignin for rice straw DOM-HTPW. The photochemical activity of DOM-HTPW was augmented by its lower molecular weight and higher hydrophilic composition, particularly evident in chicken manure DOM-HTPW, which exhibited higher generation rates for 1O2 (35.1–37.1%), 3DOM* (32.8–43.9%), and O2•− (28.6–48.8%) as measured by molecular probes. DOM-HTPW effectively facilitated the phototransformation of tetracycline, with the contribution of O2•− being more significant than 3DOM* and 1O2. These findings shed new light on the understanding the photochemical processes of DOM-HTPW as exogenous DOM and the interconnected fate of contaminants in aquatic environments.

Transport behavior of microplastics in soil‒water environments and its dependence on soil components

Microplastic (MP) pollution has become a global concern, and the transport behavior of MPs in soil-water systems is vital in determining their distribution and potential risks to the subsurface environment. To reveal the role of various soil components on MP migration, the downward transport behavior of polystyrene (PS) MPs were explored in this study via column experiments with mono or multi-soil components as porous media. Compared with the selected soil mineral volcanic rock (VR) and fine river sand (RS), condensed soil organic matter (SOM) resulted in higher transport efficiencies for PS microparticles, with greater than 90% total mass recovery under the experimental conditions. The more surface charges of SOM than minerals contribute to the high migration efficiency of PS MPs, and electrostatic repulsion is assumed a significant driving mechanism in the migration of negatively charged PS particles in soils. The ionic strength of porewater influenced the PS migration behaviors by altering the electrostatic interactions between the MPs and soil grains. The uniform mixing of SOM with mineral grains significantly enhanced the transport efficiency of PS MPs in the columns. The results provide supports for the prediction and prevention of the risks of MPs to the subsurface environment.

Impact of calibrating a low-cost capacitance-based soil moisture sensor on AquaCrop model performance

Sensor data and agro-hydrological modeling have been combined to improve irrigation management. Crop water models simulating crop growth and production in response to the soil-water environment need to be parsimonious in terms of structure, inputs and parameters to be applied in data scarce regions. Irrigation management using soil moisture sensors requires them to be site-calibrated, low-cost, and maintainable. Therefore, there is a need for parsimonious crop modeling combined with low-cost soil moisture sensing without losing predictive capability.This study calibrated the low-cost capacitance-based Spectrum Inc. SM100 soil moisture sensor using multiple least squares and machine learning models, with both laboratory and field data. The best calibration technique, field-based piece-wise linear regression (calibration r2 = 0.76, RMSE = 3.13 %, validation r2 = 0.67, RMSE = 4.57 %), was used to study the effect of sensor calibration on the performance of the FAO AquaCrop Open Source (AquaCrop-OS) model by calibrating its soil hydraulic parameters.This approach was tested during the wheat cropping season in 2018, in Kanpur (India), in the Indo-Gangetic plains, resulting in some best practices regarding sensor calibration being recommended. The soil moisture sensor was calibrated best in field conditions against a secondary standard sensor (UGT GmbH. SMT100) taken as a reference (r2 = 0.67, RMSE = 4.57 %), followed by laboratory calibration against gravimetric soil moisture using the dry-down (r2 = 0.66, RMSE = 5.26 %) and wet-up curves respectively (r2 = 0.62, RMSE = 6.29 %). Moreover, model overfitting with machine learning algorithms led to poor field validation performance. The soil moisture simulation of AquaCrop-OS improved significantly by incorporating raw reference sensor and calibrated low-cost sensor data. There were non-significant impacts on biomass simulation, but water productivity improved significantly. Notably, using raw low-cost sensor data to calibrate AquaCrop led to poorer performances than using the literature. Hence using literature values could save sensor costs without compromising model performance if sensor calibration was not possible. The results suggest the essentiality of calibrating low-cost soil moisture sensors for crop modeling calibration to improve crop water productivity.

Influencing mechanisms of tartaric acid on adsorption and degradation of tetracycline on goethite: insight from solid and liquid aspects.

The interactions between organic pollutants and iron minerals play an important role in their environmental fate. In this study, the effects of low-molecular-weight organic acids (LMWOAs) on the adsorption and degradation of tetracycline (TC) on goethite were investigated. Tartaric acid (TA) was taken as the representative of LMWOAs to study the influencing mechanism through batch experiments and microscale characterization. In addition, the properties of TC-TA clusters under different pHs were determined by density functional theory (DFT) calculations. The results showed that all five LMWOAs inhibited TC adsorption and degradation. The preferential adsorption of TA on goethite changed TC adsorption from inner spherical to outer spherical complexation and mainly inhibited TC adsorption and degradation of the singly coordinated hydroxyl group. TC degradation rate decreased from 0.0287 to 0h-1 in the first stage. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results showed that TA could influence the interactions of amide groups, C = O on the A-ring, and dimethylamino group of TC with goethite, and the formation of ≡Fe(II) was inhibited. In addition to competing for the effective sites, the effects of complexation between TA and TC in solution should be considered. According to DFT calculations, hydrogen bonds could be formed between the carboxyl group of TA and the H atom of TC at different pH. These findings can provide evidence for estimating the contribution of adsorption and degradation to TC removal by iron oxides with the coexistence of LMWOAs in a soil-water environment.

Micro-ridge-furrow soil moisture regulation technology improves seedling quality and yield of winter rapeseed

Rapeseed (Brassica napus L.) is an important oil crop worldwide, and the Yangtze River Basin (YRB) region is one of the most vital rapeseeds producing areas in China. However, the uneven distribution of annual precipitation during the rapeseed seedling stage in this region often leads to droughts and waterlogging, resulting in declined rapeseed seedling quality and yield. Therefore, this study aimed to assess the impact of micro-ridge-furrow planting (MR) and conventional flat cropping planting (FC) under straw returning on rapeseed seedling growth and yield during two growing seasons: wet year (WY) and dry year (DY). In MR planting, rapeseed was sown either on the ridge surface (RS) or in the ridge furrow (RF). We found that MR planting had stronger regulation of soil temperature and humidity compared to FC. The average soil volume water content in RS was 19.2 % lower than FC, while in RF, it was 9.0 % higher than FC. Under MR planting, the daily temperature fluctuations in RF were smaller than in FC, whereas in RS, they were larger than in FC. Through the adjustment of temperature and humidity, MR increased the activities of β-glucosidase (β-Glu) and cellulose disaccharide hydrolase (CBH) in the soil, thereby accelerating rice straw decomposition. Importantly, MR led to improved root growth, seedling quality, precipitation water use efficiency (WUEP), and yield of rapeseed during both the WY and DY seasons. Notably, root morphological traits were significantly altered under straw returning (RT) in MR, particularly with an 11.0 % increase in root surface area, which showed a significant correlation with the indoleacetic acid and jasmonic acid contents in the root system. Furthermore, RT increased antioxidant enzymes activity in rapeseed roots. The H2O2 and ∙OH contents in MR were lower than in FC, indicating that the roots of MR were capable of self-protection and reducing the accumulation of superoxide radicals and peroxides by adapting actively to the soil water environment under straw returning. The yield and WUEP of MR were higher by 11.9 % and 21.0 %, respectively, compared to FC. In conclusion, MR planting has the potential to enhance seedling quality and increase rapeseed yield when combined with rice straw returning. This finding provides technical support for realizing the full and strong seedling establishment and improving the cultivation of direct-seeded rapeseed in the YRB region.

Micro-nano oxygenated irrigation improves the yield and quality of greenhouse cucumbers under-film drip irrigation

To study the influence mechanism of micro-nano oxygenated irrigation (MNOI) on greenhouse fruit cucumber in arid and semi-arid cold regions, the yield and quality of greenhouse fruit cucumber were evaluated and verified based on 2 years of observation data. Taking fruit cucumber in Ningxia solar greenhouse as the research object, three dissolved oxygen (DO) levels of MNOI (DO; 6, 7.5, and 9 mg L−1, O1, O2, and O3, respectively) and non-oxygenated irrigation (CK, 4 mg L−1) were set up as the control treatment. Through comparative design, the influence mechanism of different levels of aerobic irrigation on the yield and quality of greenhouse fruit cucumber was studied. The main indicators of fruit cucumber yield and quality increased with dissolved oxygen in irrigation water from 4 to 9 mg L−1. In spring–summer (autumn–winter), compared with CK, the leaf area index (LAI) and net photosynthetic rate (A) increased by 28.83% (28.77%) and 44.90% (35.00%), respectively, and Vitamin C, soluble protein, soluble sugar, soluble solids and total acid content increased by 100.00% (51.88%), 37.78% (61.11%), 34.17% (54.17%), 37.07% (78.72%) and 26.92% (30.67%) respectively, while nitrate content decreased by 44.88% (51.15%), and dry matter accumulation (DMA), soil respiration rate (SRR), microbial carbon (MC), and microbial nitrogen (MN) increased by 49.81% (127.25%), 55.22% (110.34%), 117.50% (90.91%) and 70.37% (74.42%) respectively, and yield, irrigation water use efficiency (IWUE) and soil oxygen content (SO) increased by 22.47% (28.04%), 22.39% (28.05%) and 33.21% (35.33%) respectively. A model of DO in irrigation water and SO was established and the applicability of the model was verified with an average relative error of 2% (less than 5%). MNOI increased SO and soil enzyme activity, enriched soil microorganisms, improved soil microenvironment, promoted water nutrient uptake and growth of root system, increased chlorophyll, photosynthesis and DMA, which improved fruit cucumber yield and quality, and the better DO concentration in irrigation water is 9 mg L−1. The research results provide theoretical support for regulating soil water, fertilizer and air environment, and at the same time, provide feasible ways to improve the quality and efficiency of crops in arid and semi-arid cold regions.

Long-term impacts of conservation pasture management in manuresheds on system-level microbiome and antibiotic resistance genes.

Animal manure improves soil fertility and organic carbon, but long-term deposition may contribute to antibiotic resistance genes (ARGs) entering the soil-water environment. Additionally, long-term impacts of applying animal manure to soil on the soil-water microbiome, a crucial factor in soil health and fertility, are not well understood. The aim of this study is to assess: (1) impacts of long-term conservation practices on the distribution of ARGs and microbial dynamics in soil, and runoff; and (2) associations between bacterial taxa, heavy metals, soil health indicators, and ARGs in manures, soils, and surface runoff in a study following 15 years of continuous management. This management strategy consists of two conventional and three conservation systems, all receiving annual poultry litter. High throughput sequencing of the 16S ribosomal RNA was carried out on samples of cattle manure, poultry litter, soil, and runoff collected from each manureshed. In addition, four representative ARGs (intl1, sul1, ermB, and blactx-m-32) were quantified from manures, soil, and runoff using quantitative PCR. Results revealed that conventional practice increased soil ARGs, and microbial diversity compared to conservation systems. Further, ARGs were strongly correlated with each other in cattle manure and soil, but not in runoff. After 15-years of conservation practices, relationships existed between heavy metals and ARGs. In the soil, Cu, Fe and Mn were positively linked to intl1, sul1, and ermB, but trends varied in runoff. These findings were further supported by network analyses that indicated complex co-occurrence patterns between bacteria taxa, ARGs, and physicochemical parameters. Overall, this study provides system-level linkages of microbial communities, ARGs, and physicochemical conditions based on long-term conservation practices at the soil-water-animal nexus.

Subsurface irrigation with ceramic emitters improves greenhouse tomato yield and resource utilization efficiency by stabilizing soil hydrothermal status

Maintaining a stable and suitable soil hydrothermal status is crucial for promoting the high quality and yield of greenhouse vegetables throughout the year. Irrigation by regulating soil moisture changes to soil heat capacity is an effective measure to alleviate the fluctuation of soil hydrothermal environment caused by interannual solar radiation. To investigate the soil hydrothermal status of greenhouse tomatoes under subsurface irrigation with ceramic emitters (SICE) and its impact on tomato growth and yield, we conducted a two-season greenhouse experiment with subsurface drip irrigation (SDI) as a control. The results showed that soil hydrothermal changes under SICE fluctuated less with time in the autumn and spring experiment than SDI; SICE could increase soil temperature in the tomato root zone profile in winter and decrease the profile temperature in summer. This indicates that SICE could reduce the direct effect of air temperature on soil temperature and maintain a stable and suitable soil hydrothermal condition. Furthermore, the underground and vegetative biomass of SICE stopped increasing with the rapid growth of water and heat resources to the inflection point. They shifted to the accumulation of reproductive biomass. However, the vegetative biomass of SDI continued to increase in the late stage of water and heat resources. Therefore, under similar total biomass conditions, SICE obtained more output. SICE increased tomato yields by 11.60 in autumn and 8.36 t hm−2 in spring compared to SDI. The regulation mechanism also improved the hydrothermal resource utilization efficiency under SICE, with SICE increasing water and heat resource use efficiency by 24.04 % and 3.73 % (in autumn) and 9.80 % and 6.00 % (in spring), respectively, compared to SDI. We conclude that SICE is an effective and promising irrigation method for greenhouse tomato cultivation for stabilizing the soil water and heat environment, promoting yield, and improving the utilization rate of solar radiation.

Optimization algorithm for determining working water head of subsurface irrigation with ceramic emitters based on soil wetting patterns

Appropriate working water head of subsurface irrigation systems with ceramic emitters (SICE) is crucial for providing a stable and suitable soil water environment to promote crop production and save water resources in intensive agriculture. However, working water head optimization of SICE is hindered by the uncertainties of the soil physic properties, increasing the risk of irrational irrigation. To effectively address this challenge, this study presented an optimization algorithm for optimizing the working water head of SICE based on soil wetting patterns, considering taking into account soil physical variables and management variables, and then the reliability of the algorithm was verified by three case studies. The results of three case studies showed that the relative error between the actual irrigation amount of SICE using the optimization algorithm, and the recommended irrigation amount was lower than 5%. In three case studies, the sand-based ceramic emitter and working water head of 40 cm, 30 cm, and 70 cm were recommended parameters for SICE. The crop yield under SICE with appropriate working water head for three case studies was 109.2 × 103 kg ha−1, 5643.3 kg ha−1, and 3182.6 kg ha−1, which were 8.01%, 30.56%, and 16.90% higher than that of subsurface drip irrigation, respectively. Our findings revealed that SICE with the appropriate working water head might be an efficient subsurface irrigation method for intensification agriculture with the goal of high crop production.

Afforestation reduced the deep profile soil water sustainability on the semiarid Loess Plateau

Insight into the response of deep soil moisture (SM) to land cover change is crucial for the sustainable management of regional water resources and ecosystems. However, the deep soil water budget and resilience after revegetation are not clear. In this study, seven typical land-cover patterns (artificial arbor, shrub, economic tree, pasture, abandon grassland, and natural grassland) were selected in four different study sites on the Loess Plateau of China. From May 2019 to December 2020, SM was monitored daily at ten depths along a 10 m profile in situ to assess the effect of revegetation on the vertical distribution, availability, and sustainability of soil water. The results indicated that the minimum SM moved to the deeper depth in the planted forest, while the maximum SM gradually moved to a shallower and deeper depth after the conversion of cropland to forestland and grassland, respectively. The difference in soil water use strategies under different revegetation types generated the opposite effect on deep SM availability, resilience, and sustainability. Conversion of cropland to grassland realized the deep soil available water (SAW) increment by 53.3% over the entire measurement period. Besides, the grassland promoting the deep soil water resilience (SWR) and soil water storage variation (ΔSWS) enhanced by 41.6% and 708.7% below 2 m depth, respectively. Whereas, compared to cropland, afforestation decreased the SAW, SWR, and ΔSWS by 17.2%, 10.5%, and 570.7% below 2 m depth, respectively. Furthermore, the deep SWR and ΔSWS were basically negative in the forestland, resulting in an unbalanced deep soil water budget within the year. Despite the significant disadvantages of sustaining the availability and water budget of deep soil water in artificial vegetation, constructing a reasonable land cover and vegetation structure could achieve the soil–water environment balance and the sustainable utilization of ecosystem water resources in the semiarid Chinese Loess Plateau (CLP). The findings of this study provide valuable references and guidance for sustainable vegetation conservation and water resource management and provide design and optimization solutions for vegetation restoration in similar areas of arid and semiarid regions around the world.

Balancing economic benefits and environmental repercussions based on smart irrigation by regulating root zone water and salinity dynamics

As a critical index for irrigation scheduling, plant water deficit index (PWDI) is defined as the ratio of water deficit to water demand to reflect the extent of abiotic stresses such as water and salinity. Recently, smart irrigation scheduling, according to PWDI thresholds to maintain desirable or acceptable stress levels, has been suggested to maximize yields while minimizing negative environmental effects under non-saline conditions. To investigate and quantify the potential for PWDI-driven irrigation on agricultural production under conditions of salinity, a two-year experiment with six specific thresholds was conducted in Shawan of Xinjiang for drip-irrigated cotton under film mulch. Results indicated that, with increasing PWDI threshold, irrigation depth per event increased, while irrigation frequency and total volume decreased. Consequently, the soil water and salt environment deteriorated, resulting in less nutrient uptake, slower growth, and lower yield and net profit. With particularly high PWDI thresholds leading to serious stress conditions, fiber quality was also negatively affected. Within a designed range of PWDI thresholds between 0.39 and 0.62, an elliptic function characterized the processes of water application, yield and net profit (R2 ≥ 0.95), and water productivity could be described by a parabolic function (R2 = 0.77). These quantitative results were used to provide guidelines for smart irrigation scheduling under local conditions considering water management measures and market prices of cotton. For a reference market price of 7.5 CNY kg-1, a PWDI threshold of 0.49 was found to optimize economic benefits while maximizing water productivity. When prices of cotton are prohibitively low, a lower threshold should be considered to obtain an acceptable net profit. Otherwise, a higher threshold would be preferable to use water more efficiently. Further verification and improvement are necessary to deal with more complex scenarios, such as, considering crop sensitivity to water and salinity stresses at different growth stages and optimizing irrigation depth per event.

Effects of forest structural and compositional change on forest microclimates across a gradient of disturbance severity

Forest structural diversity and community composition are key in regulating forest microclimates. When disturbance affects structural diversity or composition, forest microclimates may be altered due to changes in soil temperature, soil water content, and light availability. It is unclear however which structural or compositional components, when changed or to what extent, result in microclimatic change. To address this question, we used data from a large scale, manipulative stem-girdling experiment in northern, lower Michigan—the Forest Resilience and Threshold Experiment (FoRTE). FoRTE follows a factorial design with multiple levels of disturbance severity (0, 45, 65, 85%) based on targeted reductions in gross leaf area index via stem-girdling induced mortality. These disturbance severity treatments are applied in two ways: either as top-down (largest trees are killed) or bottom-up (small to medium trees killed) treatments. We examined how multiple components of structural diversity and community composition changed as a product of disturbance severity and type, and then tested for resulting effects on forest microclimates (light availability, soil temperature, and soil water), using a multivariate, Random Forest framework. We found that measures of community composition (species richness, species evenness, and Shannon-Wiener Diversity Index) and stand structure (basal area, standard deviation of DBH, tree size diversity) declined more following disturbance than did measures of canopy cover, heterogeneity, arrangement, or height. However, when changes in each variable from pre- to post-disturbance, measured as log change, were employed in a multivariate, Random Forest regression framework, structural diversity measures of heterogeneity (rugosity, top rugosity), cover (canopy cover), and arrangement (porosity) were the most influential variables, but with differences among bottom-up and top-down treatments We found that the death of large trees from disturbance impacts soil temperature, water, and light environments more substantially and uniformly across disturbance gradients than does the death of smaller trees. Our results have implications for both statistical and process-based modeling of forest disturbance.

Subsurface irrigation with ceramic emitters improves the yield of wolfberry in saline soils by maintaining a stable low-salt environment in root zone

The high salt concentration in soils depresses crop growth and saline soil reclamation. An appropriate irrigation method is essential to alleviate water shortage and promote wolfberry (Lycium barbarum L.) cultivation in saline soils. Subsurface irrigation with ceramic emitters (SICE) is a novel technique that maintains a stable soil water environment through adaptive outflow and holds a beneficial impact on saving water and increasing yield. However, the effect of SICE on salt leaching remains to be investigated. A field experiment was executed to investigate the salt leaching process in SICE and subsurface drip irrigation (SDI) in saline soils and their effect on wolfberry yield. HYDRUS-2D was calibrated and validated using experimental data to investigate the spatial-temporal variation of soil salinity. Subsequently, the salt leaching efficiency with different emitter discharges (0.10, 0.15, 0.24, and 0.33 L h−1) was assessed via HYDRUS-2D. Results indicated that SICE leached soil salt below the stress threshold after 50 days of irrigation, while SDI required 148 days. At the end of irrigation, SICE formed a low-salt zone that occupied 74.14% of the main root zone, while the zone with SDI was 60.69%. Generally, SICE provided a stable low-salt environment for wolfberry root system for 117.5 days (69.9% duration of growth period). SICE improved the wolfberry yield and root-zone soil desalination efficiency (DE) by 0.17 t ha−1 and 0.41% cm−1 than SDI, respectively. When emitter discharge increased to 0.24 L h−1, the root zone of wolfberry was protected from salt stress, but DE decreased gradually. SICE with an emitter discharge of 0.24 L h−1 was recommended for wolfberry in saline soils of Ningxia. The results reveal that SICE is an efficient salt leaching method for saline soil management and crop yield improvement.

Resupply, diffusion, and bioavailability of Hg in paddy soil-water environment with flood-drain-reflood and straw amendment

Mercury (Hg) poses a significant risk in paddy fields, particularly when it is converted to methylmercury (MeHg) and accumulates in rice. However, the bioavailability and resupply kinetics of Hg in the paddy soil-water environment are not well understood. In this study, the diffusive gradients in thin films (DGT) and the ‘DGT-induced fluxes in sediments’ model (DIFS) were first adopted to investigate the Hg resupply kinetics, diffusion fluxes and bioavailability in a paddy environment subjected to flood-drain-reflood treatment and straw amendment. Our results show that although the straw amendment limited the bioavailability of Hg (38.2%–47.9% lower than control) in porewater by decreasing its resupply capacity, especially with smaller straw particles, the net production of MeHg in paddy fields was significantly increased after straw amendment (73.5%–77.9% higher than control). The results of microbial sequencing indicate that enhanced methylators (e.g., family Geobacter) and non-Hg methylators (e.g., Methanosarcinaceae) played a crucial role in MeHg production following straw amendment. Moreover, Hg-containing paddy soils generally tend to release Hg into the overlying water, while drain-reflood treatment changes the direction of Hg diffusion fluxes in the paddy soil-water interface. The drainage-reflooded treatment decreases the Hg reactive and resupply capacity of the paddy soil, thereby hindering the release of Hg from soil into overlying water during the early stages of reflooding. Overall, this study provides novel insights into the behavior of Hg in paddy soil-water surface microlayers.

Deciphering the melatonin-mediated response andsignalling intheregulation ofheavy metal stress in plants.

Melatonin has a protective effect against heavy metal stress in plants by immobilizing HM in cell walls and sequestering them in root cell vacuoles, reducing HM's translocation from roots to shoots. It enhances osmolyte production, increases antioxidant enzyme activity, and improves photosynthesis, thereby improving cellular functions. Understanding the melatonin-mediated response and signalling can sustain crop production in heavy metal-stressed soils. Melatonin is a pleiotropic signal molecule that plays a critical role in plant growth and stress tolerance, particularly against heavy metals in soil. Heavy metals (HMs) are ubiquitously found in the soil-water environment and readily taken up by plants, thereby disrupting mineral nutrient homeostasis, osmotic balance, oxidative stress, and altered primary and secondary metabolism. Plants combat HM stress through inbuilt defensive mechanisms, such as metal exclusion, restricted foliar translocation, metal sequestration and compartmentalization, chelation, and scavenging of free radicals by antioxidant enzymes. Melatonin has a protective effect against the damaging effects of HM stress in plants. It achieves this by immobilizing HM in cell walls and sequestering them in root cell vacuoles, reducing HM's translocation from roots to shoots. This mechanism improves the uptake of macronutrients and micronutrients in plants. Additionally, melatonin enhances osmolyte production, improving the plant's water relations, and increasing the activity of antioxidant enzymes to limit lipid peroxidation and reactive oxygen species (ROS) levels. Melatonin also decreases chlorophyll degradation while increasing its synthesis, and enhances RuBisCO activity for better photosynthesis. All these functions contribute to improving the cellular functions of plants exposed to HM stress. This review aims to gain better insight into the melatonin-mediated response and signalling under HM stress in plants, which may be useful in sustaining crop production in heavy metal-stressed soils.

Elevated CO2 concentration regulate the stomatal traits of oilseed rape to alleviate the impact of water deficit on physiological properties

There is a limited understanding of how stomatal distribution and structure affect photosynthesis under elevated CO2 concentrations (e[CO2]) and variable soil water environments. This study investigated the effects of e[CO2] on stomatal morphology and distribution, gas exchange and growth parameters of oilseed rape plants under water deficit [soil moisture decreased from 80% field capacity (FC) (W; full irrigation) to 60% FC (D1), 40% FC (D2), and < 35% FC (D3)] and re-watering conditions in growth chambers with [CO2] controlled at 400 µmol mol−1 (a[CO2]) or 800 µmol mol−1 (e[CO2]). e[CO2] had a strong CO2 fertilization effect on the net photosynthetic rate (An) and growth of plants under water deficit. Under a[CO2], stomatal density and aperture on the adaxial leaf surface increased when soil moisture decreased from W to D1, while the stomatal aperture and regularity of the spatial distribution pattern of stomata decreased with decreasing soil moisture. Stomatal conductance (gs) were 47.1% and 26.1% capacity of anatomically determined maximum anatomical conductance (gsmax) with W under a[CO2] and e[CO2], respectively. e[CO2] enhanced plant recovery after re-watering through modifying stomatal traits. This study offers insights into the trade-off between stomatal traits and gas exchange for adapting plants to future climates.