Soil Solution Research Articles

Optimization of innovative optical sensor for zirconium determination and capturing from environmental samples

A highly sensitive bulk optode membrane, specifically engineered for the identification of zirconyl (ZrO2+) ions, has been successfully created. The membrane is composed of plasticized polyvinyl chloride (PVC), dibenzodylmethane (DBM) acting as the chromoionophore, 2-amino-4-(3-chlorophenylazo)pyridine-3-ol (ACPAP) serving as the ionophore, and sodium tetraphenylborate (NaTPB) included as an ionic additive. The sensing membrane undergoes a color change from orange to blue when exposed to ZrO2+ ions at pH 6.5. The preparation parameters of the sensor and the determination of ZrO2+ ions were meticulously optimized. In addition to showcasing reproducibility, extended stability, and a comparatively long lifespan, the suggested sensor membrane displays remarkable selectivity for ZrO2+ ions, effectively discerning them from a spectrum of alkaline earth, heavy and transition metal ions, and actinides. The sensor delivers a calibration response tailored for ZrO2+ ions across a concentration spectrum spanning 7.5–185 ng mL−1, establishing limits of quantification and detection at 7.3 and 2.2 ng mL−1, respectively. Demonstrating a rapid response within a timeframe of under 5.0 min. The sensor consistently delivered highly reproducible results, as evidenced by relative standard deviation (RSD) of 1.67 % and 1.55 % for Zr4+ concentrations at 100 and 150 ng mL−1.This underscores the precision and reliability of the sensor. Regeneration of the optode can be easily accomplished by employing 0.05 M HCl. Effectively employed across a spectrum of samples, including water, soil, plant materials, and ore solutions, the proposed optical sensor proves to be a valuable instrument for determining ZrO2+ ions in diverse environmental and analytical scenarios.

Experiences of mine closure cover with geosynthetics in Peru

Peru is internationally recognized as one of the countries with significant mining reserves. According to the Department of Energy and Mines (MINEM), as of December 2021, a total of 672 mining concession holders were registered and declared in the Monthly Statistical Declaration (ESTAMIN). Likewise, 44 mining concessions are in the closure stage (progressive, post-closure and final). In addition, Peru has 7956 Mining Environmental Liabilities (MEL) as of 2020, according to the inventory approved by the Department of Energy and Mines, which need to be remediated as they constitute a permanent and potential risk to the health of the population, the surrounding ecosystem and property. As part of the closure of these MEL and closure of some mining components, the use of geosynthetics has increased in Peru, and we speak specifically of the closure cover in slopes, platforms, sidewalks and others, which has become relevant as an alternative solution for soils selected as part of a traditional closure, the objective of this work is to present a series of experiences of the application of geosynthetics in mine closure covers, which intervene in the physical, geochemical and hydrological stability. It is worth mentioning that geosynthetics have been applied in Peru for more than 30 years in mining projects.

Application of soil amendments: investigation of incubation time on some soil solution properties of Kien Giang, Vietnam

Soil amendments can affect soil properties such as pH, EC, available phosphorus (P), and ammonium nitrogen (NH4+). The aim of this study was to determine the potential influence of submergence incubation time on some soil properties using soil amendments under controlled laboratory conditions suitable to the characteristics of rice-growing areas in Kien Giang, Vietnam. The experiment included treating soil supplemented with lime (at ratios of 0.0, 0.4, 0.6, and 1.0%) and soil supplemented with lime (0.4%) combined with alkalized biochar (at ratios 0.0, 0.2, 0.4, and 0.8%). The treatments were incubated in the laboratory under submerged conditions, and pH, EC, available phosphorus (P), and ammonium nitrogen (NH4+) parameters were measured at 7, 14, 21, 35, and 60 days. The results showed that soil supplemented with lime improved pH and EC, and maintained high phosphorus release for 21 days, but did not improve NH4+ release. In contrast, soil supplemented with lime (0.4%) combined with alkalized biochar improved pH and EC, maintained high levels of phosphorus and NH4+ content up to 35 days. The results showed that using lime combined with alkalized biochar to improve soil in rice-growing areas has many advantages compared to using lime alone. Therefore, understanding the contribution of soil incubation time with amendments to soil properties is an important prerequisite for developing a strategy to ensure crop productivity.

Changes in the composition and concentration of soil solutions in seasonal dynamics of irrigated agriculture

Changes in the composition and concentration of soil solutions in seasonal dynamics of irrigated agriculture

The Median Isn’t the Message: soil nutrient hot spots have a disproportionate influence on biogeochemical structure across years, seasons, and depths

Soil nutrient distribution is heterogeneous in space and time, potentially altering nutrient acquisition by trees and microorganisms. Ecologists have distinguished “hot spots” (HSs) as areas with enhanced and sustained rates of nutrient fluxes relative to the surrounding soil matrix. We evaluated the spatial and temporal patterns in nutrient flux HSs in two mixed-conifer forest soils by repeatedly sampling the soil solution at the same spatial locations (horizontally and vertically) over multiple seasons and years using ion exchange resins incubated in situ. The climate of these forests is Mediterranean, with intense fall rains occurring following summers with little precipitation, and highly variable winter snowfall. Hot spots formed most often for NO3− and Na+. Although nutrient HSs often occurred in the same spatial location multiple times, HSs persisted more often for PO43− NH4+, and NO3−, and were more transient for Ca2+, Mg2+, and Na+. Sampling year (annual precipitation ranged from 558 to 1223 mm) impacted the occurrence of HSs for most nutrients, but season was only significant for PO43−, NH4+, NO3−, and Na+, with HSs forming more often after fall rains than after spring snowmelt. The frequency of HSs significantly decreased with soil depth for all nutrients, forming most commonly immediately below the surficial organic horizon. Although HSs accounted for less than 17% of the sampling volume, they were responsible for 56–88% of PO43−, NH4+, and NO3− resin fluxes. Our results suggest that macronutrient HSs have a disproportional contribution to soil biogeochemical structure, with implications for vegetation nutrient acquisition strategies and biogeochemical models.Graphical abstract

Modulation of soil aeration and antioxidant defenses with hydrogen peroxide improves the growth of winter wheat (Triticum aestivum L.) plants

Soils with subsurface drip irrigation are often characterized by hypoxia, which could impair the aerobic respiration of roots and the productive potential of crops. Irrigation with hydrogen peroxide oxygenated water (HPOW) is one way to improve soil aeration in the rhizosphere. However, few studies have focused on exploring the interaction of HPOW with soil aeration and productivity of crops. The current work aimed to investigate the effects of four levels of HPOW [0 ppm H2O2 solution (tap water) as a control (H0), 600 ppm, 800 ppm and 1000 ppm H2O2 solution (H600, H800 and H1000)] on irrigation water properties, soil aeration, antioxidant defenses, growth biomarkers and yield components in winter wheat (Triticum aestivum L.) plants. Results confirmed that dissolved oxygen (DO) concentrations in H600, H800 and H1000 were significantly increased by 52.10%–126.59% and surface tension coefficients were significantly decreased by 17.72%–31.60% as compared to H0. DO concentrations in soil solutions irrigated with H600, H800 and H1000 were significantly elevated by 9.78%–15.68% as compared to H0, and the maximum value equal to 7.44 mg L−1 was found at a soil depth of 20 cm. Further, H600 and H800 reduced concentrations of malondialdehyde and H2O2 in leaves, increased accumulation of proline and activities of antioxidant enzymes, and resulted in an enhancement in grain yield of 15.28% and 25.23%, respectively. Application of H1000 resulted in lower growth biomarkers and yield components due to oxidative stress induced by decreased activities of antioxidant enzymes and accumulation of proline as well as elevated levels of lipid peroxidation as compared to H600 and H800. The optimal regulation was achieved with the H800 treatment. Overall, HPOW improved the plants growth by modulating soil aeration and antioxidant defenses which enhanced tolerance to hypoxic stress.

Fractionation of stable boron isotopes in alfisols: Application of a novel tool for tracing boron behavior in two soil profiles

Available boron (AB) and total boron (TB) in soil have distinct isotopic values, which are mainly influenced by the pH, organic matter and clay minerals, and can be used to explore the chemical behaviors of boron (B) in adsorption, weathering and eluviation processes. The B isotopic compositions of AB and TB in brown soil (slightly acidic) and cinnamon soil (neutral to slightly alkaline) profiles were investigated by multicollector inductively coupled plasma mass spectrometry. Variations in pH value and organic matter in the two soils directly affected the adsorption of B isotopes (dissolved 11B(OH)3 or 10B(OH)4-) in the aqueous solution, as shown by AB having an average negative δ11B value of −1‰ and a great range of −10.83‰ to +8.32‰ in the cinnamon soil. Furthermore, the long-term effects of adsorption and transportation processes were evidenced by the large range of δ11BTB values (-24.22‰ to +21.07‰) in the two soils. The topsoil layers with more organic matter and higher δ11B values indicated that B isotope fractionation occurred as a result of the input of rainfall, recycling of plant litter and the adsorption of organic matter and clay minerals. The lower δ11B values, the higher B contents and the element ratios in the underlying layers resulted from the weathering of different minerals and the adsorption of AB in the leaching process. This finding is supported by the relationship between AB and the clay/silt ratio, with more negative δ11B values being associated with finer clay particles via the adsorption of 10B(OH)4- in a weakly alkaline soil solution. The δ11B values in soils may be a useful tool for distinguishing geochemical cycling and processes and characterizing long-term processes that are difficult to assess.

Soybean yield dependence on the timing of sowing in the conditions of the foothill zone of the RNO-Alania

The article presents the results of research on the reaction of soybean plants depending on the timing of sowing in the foothill zone of the Republic of North Ossetia-Alania. The need to improve the timing of sowing occurs with the introduction of new varieties of various ripeness in the main and intermediate crops. The purpose of the paper is to study the effect of sowing dates on the yield of soybean seeds in the conditions of the foothill zone of the RNO-Alania. The scientific novelty was to establish optimal sowing dates that would ensure optimal plant growth and development and high productivity. Our research was carried out in the experimental fields of the North Caucasian Research Institute of Mountain and Piedmont Agriculture of the VSC RAS in 2018-2021. The object of research was the varieties of breeding of the Federal scientific center "V.S. Pustovoit All-Russian Research Institute of Oil Crops. Two main types of soils prevail in the foothill zone: chernozems of varying degrees of leaching, as well as meadow and meadow-boggy soils. The arable layer contains from 3 to 4.4% humus. Down the profile, the amount of humus decreases gradually. The reaction of the soil solution in the upper horizons is neutral, in horizons deeper than 80-90 cm – slightly alkaline. The predecessor of the experimental plots was corn for grain. It was found that at early sowing dates (April 20 - May 5) resulted in higher field germination (87-93%), plant foliage of 46.9 thousand m2/ha and their survival rate for harvesting 84-91%. More nodules formed on the roots of the plants. The maximum yield is 2.6 t/ha, obtained during sowing on April 30.

Lime Management to Increase Soil pH in Semi‐Arid Regions of the U.S.

AbstractSoil acidification, a common issue in high‐rainfall areas of the U.S. and Canada, has become a more prevalent problem in the semi‐arid areas of the western U.S. Liming is an effective way to mitigate soil acidity as the carbonate reacts with hydrogen ions in the soil solution to increase the soil pH. However, questions exist about the type of liming product, lime rate, cost effectiveness, and how long the lime benefits last, especially in regions that have historically not needed lime, like much of the Great Plains. Earn 0.5 CEUs in Soil & Water Management by reading the article and taking the quiz at https://web.sciencesocieties.org/Learning‐Center/Courses.

ЭЛЕМЕНТЫ ТЕХНОЛОГИИ ВОЗДЕЛЫВАНИЯ СОИ В РСО-АЛАНИЯ

The author presents the results of research on the study of sowing dates for soybean yields in the conditions of the forest-steppe zone of the Republic of North Ossetia-Alania. With the introduction of new varieties of various ripeness in the main and intermediate crops, there is a need to improve the timing of sowing. The purpose of the work is to study the effect of sowing dates on the yield of soybean seeds in the conditions of the foothill zone of the Russian Federation. The scientific novelty was to establish optimal sowing dates that would ensure optimal plant growth and development and high productivity. Our research was carried out in the experimental fields of the North Caucasus Scientific Research Institute of Mountain and Foothill Agriculture of the VNC RAS in 2018-2021. The object of research was the varieties of breeding of the Federal Scientific Center of the V.S. Pustovoit Research Institute of Oilseeds. Two main types of soils prevail in the foothill zone: chernozems of varying degrees of leaching, as well as meadow and meadow-marsh soils. The arable layer contains from 3 to 4.4% humus. Down the profile, the amount of humus decreases gradually. The reaction of the soil solution in the upper horizons is neutral, deeper than 80-90 cm – slightly alkaline. The predecessor of the experimental plots was corn for grain. It was found that at early sowing dates (April 20 – May 5), higher field germination (87-93%), plant foliage of 46.9 thousand m2/ha and their survival rate for harvesting 84-91% were noted. More nodules formed on the roots of the plants. The maximum yield is 2.6 t/ha, obtained during sowing on April 30. In the forest-steppe zone, the yield of medium-ripened varieties decreased from early to late sowing periods by 0.44 and 0.58 t/ha, while in early-ripening varieties it was less significant. Fertilizers (R90K30) increased the yield of seeds, depending on the timing of sowing, by 0.24-0.58 t/ha.

Malting barley in the Northern Urals

The article presents the results of studying the yield and grain quality of malting barley varieties grown on different backgrounds of fertilizers. Barley grain is a valuable raw material for the cereal, brewing, and feed processing industries. In the Northern Trans-Urals, barley is the most important forage and food crop. The purpose of the research was to study the effect of increasing norms of mineral fertilizers on the yield and grain quality of malting barley varieties in the conditions of the northern forest-steppe of the Tyumen region. Studies were conducted in 2022 and 2023 with the varieties Acha, Despina, KVS Hobbs, Beatrice. The experiment options included: 1) control without fertilizers; 2) N30P30K30; 3) N60P60K60. The soil cover of the experimental field is leached chernozem, heavy loamy in granulometric composition. The chemical composition of the soil is characterized by an average humus content in the arable layer, an average supply of phosphorus, potassium, low nitrogen and a slightly acidic reaction of the soil solution. The conditions of the 2022 growing season were characterized by high air temperature and sufficient precipitation. Meteorological indicators in 2023 were characterized by excessively high air temperatures and uneven precipitation, which negatively affected the yield of barley varieties. In the conditions of 2022, the varieties showed responsiveness to fertilizers. The greatest increase in yield was obtained against an increased background (N60P60K60): in the Acha variety – 1.48 t/ha; in the Despina variety – 2.71 t /ha, in the KVS Hobbs variety – 2.12 t/ha, in the Beatrice variety - 1.60 t/ha. In 2023, reliable increases from the action of fertilizers were obtained in two varieties – Acha (+0.57 t/ha) and Beatrice (+0.67 t/ha) against an increased background of fertilizers. Barley varieties were characterized by high indicators of grain nature and germination ability. The protein content corresponded to the standards for brewing in the Despina and KVS Hobbs varieties in the version without fertilizers and in the N30P30K30 variant, in the Beatrice variety – in all variants, in the Acha variety – only in the version without fertilizers.

Investigation of Zinc Corrosion in Tropical Soil Solution

The paper presents a large experimental study on the corrosion of zinc in tropical soil and in the ground water at the various depths. Through this study, the corrosion rate prediction was done based on two methods the electrochemical method and the gravimetric. The electrochemical results showed that the corrosion rate is more important at the depth levels 0 m to 0.5 m and 0.5 m to 1 m and beyond these depth levels, the corrosion rate is less important. The electrochemical results indicated also that a passive layer is formed on the zinc surface. The found SEM and EDX micrographs displayed that the surface is extremely attacked and confirmed that a zinc oxide layer is present on the surface whose thickness and relief increase as the contact with soil increases.

A two-stage based model for partially-buried pile group response in cross-anisotropic saturated media adjacent to moving harmonic loads

The pile foundations are frequently affected by adjacent traffic loads except for general active loads. However, the dynamic responses of the pile groups under moving loads have been rarely reported before. In addition, the influence of material anisotropy is often neglected. In this paper, a three-dimensional (3D) analytical model for the dynamic analysis of partially buried pile groups in stratified saturated cross-anisotropic media under adjacent moving harmonic loadings is developed. Specifically, a 3D Bernoulli–Euler beam theory is adopted to simulate the monopile and then superimposed into the finite element (FE) formulation for the partially embedded pile groups. Subsequently, the basic solutions of layered saturated cross-anisotropic soils are derived by the analytical layer-element approach (ALEA). By combination with ALEA, the two-stage based boundary element (BE) equations for the pile-soil interface are obtained. Finally, by coupling the FE and BE formulations, the dynamical response equation of pile-soil is established. Based on the verification of the accuracy of the proposed methodology by comparisons with existing solutions and FE results from ABAQUS, the impacts of material anisotropy, pile buried length, loading velocity, and pile stiffness on the time-domain dynamic behavior of pile groups are analyzed. The results show that increasing the pile-buried ratio or pile stiffness reduces the magnitude of the dynamic response. Moreover, with the increase of material anisotropic parameters, the peak pile response decreases. And the peak dynamic response first increases and then reduces as the loading velocity increases.

The effect of using of organic and mineral origin raw materials in agriculture on soil fertility

The presented work relates to ecology, chemical technology, in particular, methods for the production of fertilizers from sewage sludge and agriculture.The scale of production activity increases with population growth, so the problem of optimizing the interaction between man and nature is relevant and its solution is of great importance in improving the environment. Wastewater is one of the by-products of anthropogenic activities. When it is cleaned, a precipitate (sludge) is formed. The volume and the toxicity of sludge are, of course, increasing due to urban growth and the intensification of industrial production. About 25-30 kg of dry sediment is formed per person per year in European countries.There is no single rational and environmentally safe, currently tested technology for sludge disposal in our republic, and its appearance is unlikely to be created shortly since the sediments of different treatment facilities have different physicochemical and biological properties, as well as entirely different qualitative and quantitative compositions of elements.Purifying and disposing of such waste (sludge) is a serious environmental problem. The main principles of its solution are a set of environmental and economic interests of society, environmentally safe disposal and use of sludge, and their involvement in the economic cycle. The problem of using waste for fertilizer has various aspects and it is inseparable from the problem of soil fertility and ecology.The exceptional importance of organic matter in increasing soil fertility has long been known. In this regard, application of organic-mineral complexes that affect the productivity and quality of plants, determination of effective fertilizer norms and application of new technologies are an urgent issue and are of great theoretical and practical importance.The fertility of the soil is very dependent on the intensity of the biological processes taking place in it. Sufficient moisture, organic matter and a favorable reaction of the soil solution are required for the activity of microorganisms in the soil.He worked on the technology of organic-mineral complex preparation and applied it under agricultural plants (cotton) in order to achieve the set goal in the direction of solving this issue.

Влияние применения дефеката на вредоносность проволочников и продуктивность подсолнечника в Краснодарском крае

Larvae of click beetles (Coleoptera: Elateridae) are wireworms, one of the most spreading polyphagous soil pests damaging the agricultural crops, including sunflower. They prefer soils having pH from 5.6–6.0 to 4.5–5.0 and humus content more than 3.3%. Liming is the primary means to optimized reaction of a soil solution. In 2016–2018, in the V.S. Pustovoit All-Russian Research Institute of Oil Crops, influence of filter cake (lime organic and mineral fertilizers produced after sugar beet processing) application in doses 3.9 and 5.9 t/ha on damaging of sunflower seedlings by larvae of beetles from an Elateridae family (wireworms) and crop productivity. The dry filter cake in the studied doses introduced 30 days before sunflower planting with further incorporation into the physically mature soil by tillers “Krot” on a depth of 12–15 cm decreased significantly a number of wireworms – from 15–21 (in control) to 6–10 pcs/m2. Thinning of sunflower crops due to wireworm damages on average reached 53.3% in control, as plant death in variants with application of an organic and mineral fertilizer in doses of 3.9 and 5.9 t/ha was at a level of 31.6 and 26.7%, respectively. The filter cake application in doses of 3.9 and 5.9 t/ha allowed obtaining yield increase of 0.86–0.87 t/ha. Oil content in sunflower seeds in these variants was equal to 51.3–52.1%.

Restricted colloidal-bound phosphorus release controlled by alternating flooding and drying cycles in an alkaline calcareous soil

Colloid-facilitated phosphorus (P) migration plays an important role in P loss from farmland to adjacent water bodies. However, the dynamics of colloidal P (Pcoll) release as influenced by irrigation in alkaline calcareous soil remains a knowledge gap. The present study, monitored the dynamic change of Pcoll under different water management strategies: 1) control, 2) flooding, and 3) alternating flooding and drying cycles. Soil water-dispersible colloids (0.6 nm-1 μm) were extracted by combining filtration and ultrafiltration methods. The contents of P, cation and organic carbon in the water-dispersible colloids were determined and the stability and mineral composition of colloidal fractions were characterized. The results showed that Pcoll ranged from 16.5 to 25.5 mg kg−1 and represented 42.8%–64.9% of the water-extracted P in the control. Flooding significantly decreased the Pcoll content by 16.0%–62.1% (mean 32.7%) and it may be attributed to the dissolution of colloidal iron (Fe) bound P. The alternating flooding and drying treatment significantly reduced the Pcoll content by 11.6%–88.0% (mean 67.6%). The Pcoll content of the flooding event was always greater than the Pcoll content of the drying event during flooding and drying cycles. Redundancy analysis and random forest modeling showed that the colloidal calcium (Ca) and ionic strength in soil solutions had negative correlations with the Pcoll content, and pH, ionic strength and truly dissolved P were the critical factors affecting Pcoll. Drying of the flooded soil led to the decrease of pH and the increase of ionic strength, colloidal Ca content and positive charges of colloid surfaces, which promoted colloid aggregation and enhanced soil P sorption capacity. This restricted the loss potential of Pcoll. In summary, controlled flooding and drainage when managed correctly have a role to play in mitigating Pcoll loss from P-enriched calcareous soils.

Advancing circular economy for the growth, root development and elemental characteristics of bamboo (Bambusa vulgaris) on galamsey-degraded soil

Landscape restoration of degraded mining sites, crucial for agroecology and carbon farming in Ghana, remains poorly understood and underutilized. Bamboo has historically played a role in restoring such sites, but there is a need to integrate circular economy principles fully into harnessing its ecosystem services potential. In this study, we evaluated the impact of biochar and poultry manure amendments on galamsey-degraded mining sites to operationalize circular economy principles in ecosystem restoration, using Bambusa vulgaris as the test crop.Conducted in the Asikasu mining area of the Amansie Central District of Ashanti, a randomized complete block design (RCBD) experiment was used comprising five treatments: 1) 10 tonnes/ha biochar, 2) 10 tonnes/ha poultry manure, 3) Combined biochar and poultry manure at 10 tonnes/ha each, 4) Galamsey-degraded soil control, and 5) Forest topsoil control. Each treatment and control type was replicated three times. The experiment spanned from February 2020 to March 2021.The combined application of biochar and poultry manure resulted in the highest root density and average root diameter, demonstrating the potential for restoring galamsey-degraded sites to support bamboo-based agroecology. The elemental profiles of the bamboo varied in response to different treatments, indicating differing availabilities of micro- and macro-nutrients in the soil solution following soil amendments.This study underscores the viability of circular economy principles in ecosystem restoration, offering a pathway to sustainable land use and agroecological practices in Ghana's mining-impacted landscapes.

Insight into the availability and desorption kinetics of Se and Cd in naturally-rich soils using diffusive gradients in thin-films technique

Cadmium (Cd) contamination of selenium (Se)-rich soils may jeopardize the nutritional benefits of Se-biofortified crops. This study employed diffusive gradients in thin-films (DGT) technique and DIFS (DGT-induced fluxes in soils) model to understand the interdependency and driving factors of Se and Cd distribution and desorption kinetics across 50 soils from south China with naturally elevated levels. DGT-labile Se was the highest (up to 2.66 μg L−1) in non-carbonate/shale-derived soils, while Cd was maximal (5.53 μg L−1) in carbonate-based soils, reflecting soil background concentrations and soil characteristics. Over one-third of the soils showed labile Se:Cd molar ratio below 0.7, suggesting Cd phytotoxicity risks. The DIFS-derived response times (Tc) and desorption rate constants (k−1) suggested that Se was resupplied to the soil solution faster than Cd in soils with higher pH and SOM level, but Se resupply was still restricted due to the rapid depletion of its labile pool. As the first study of Se and Cd release kinetics in soils, our results reveal dependence on soil parent materials, with low labile Se:Cd soils presenting greater Cd hazards. By elucidating Se and Cd lability and interactions in soils, our findings help to inform management strategies to balance reduced Cd risk with adequate Se availability.

Restored forested wetland surprisingly resistant to experimental salinization.

Salinization of coastal freshwater wetlands is an increasingly common and widespread phenomenon resulting from climate change. The ecosystem consequences of added salinity are poorly constrained and highly variable across prior observational and experimental studies. We added 1.8 metric tons of marine salts to replicated 200 m2 plots within a restored forested wetland in Eastern North Carolina over the course of four years. Based on prior small-scale experiments at this site, we predicted that salinization would lead to slower tree growth and suppressed soil carbon cycling. Results from this large-scale field experiment were subtle and inconsistent over space and time. By the fourth year of the experiment, we observed the predicted suppression of soil respiration and a reduction of water extractable carbon from soils receiving salt treatments. However, we found no cumulative effects of four years of salinization on total soil carbon stocks, tree growth, or root biomass. We observed substantial variation in soil solution chemistry (notably, pH and base saturation) across replicated treatment blocks; the effective salt levels, ionic composition, and pH varied following treatment depending upon pre-existing differences in edaphic factors. Our multi-year monitoring also revealed an underlying trend of wetland acidification across the entire site, a suspected effect of ecosystem recovery following wetland restoration on former agricultural land. The overwhelming resistance to our salt treatments could be attributed to the vigor of a relatively young, healthy wetland ecosystem. The heterogeneous responses to salt that we observed over space and time merits further investigation into the environmental factors that control carbon cycling in wetlands. This work highlights the importance of multi-year, large-scale field experiments for investigating ecosystem responses to global environmental change.

A trait-based framework linking the soil metabolome to plant-soil feedbacks.

By modifying the biotic and abiotic properties of the soil, plants create soil legacies that can affect vegetation dynamics through plant-soil feedbacks (PSF). PSF are generally attributed to reciprocal effects of plants and soil biota, but these interactions can also drive changes in the identity, diversity and abundance of soil metabolites, leading to more or less persistent soil chemical legacies whose role in mediating PSF has rarely been considered. These chemical legacies may interact with microbial or nutrient legacies to affect species coexistence. Given the ecological importance of chemical interactions between plants and other organisms, a better understanding of soil chemical legacies is needed in community ecology. In this Viewpoint, we aim to: highlight the importance of belowground chemical interactions for PSF; define and integrate soil chemical legacies into PSF research by clarifying how the soil metabolome can contribute to PSF; discuss how functional traits can help predict these plant-soil interactions; propose an experimental approach to quantify plant responses to the soil solution metabolome; and describe a testable framework relying on root economics and seed dispersal traits to predict how plant species affect the soil metabolome and how they could respond to soil chemical legacies.