Effect of the size of variable charge soil particles on cadmium accumulation and adsorption

Purpose

The size of soil particles strongly affects the accumulation and adsorption of heavy metals which partly controls the co-transport of heavy metals by soil colloids. However, the effect of the size of soil particles on the accumulation and adsorption of heavy metals in the colloidal dimension has seldom been studied. In this study, variable charge soils were selected and separated into five size fractions to elucidate the effect of the size of soil particles on Cd accumulation and adsorption.

Materials and methods

Five soil particle size fractions (>10, 10–1, 1–0.45, 0.45–0.2 and <0.2 μm) were obtained from Cd-contaminated soil by natural sedimentation and fractional centrifugation. The concentrations and species of Cd were measured in various sized soil particles. Batch adsorption experiments of Cd on the obtained soil particles were conducted under different pH values and concentrations of NaCl.

Results and discussion

Generally, the concentration of Cd increased with decreasing soil particle sizes, and the Cd proportion of exchangeable and carbonate fraction decreased from 43.84 to 17.75% with decreasing particle size. The soil particles with a size of 10–1 and <0.2 μm possessed a stronger adsorption ability than the other fractions in most cases. Moreover, the Cd adsorption capacities of the soil particles increased with increasing pH values and decreasing concentrations of NaCl, especially for soil particles containing more organic matter (OM) and variable charge minerals.

Conclusions

Smaller soil particles are more capable of accumulating Cd and make Cd more stable. The adsorption capability of Cd is negatively related to the particle size and NaCl concentration and is positively related to the pH. The effects of the size of variable charge soil particles on Cd accumulation and adsorption are attributed to the differences in the physicochemical properties among various soil particle size fractions. This study contributes to the understanding of the co-transport of heavy metals in soil by soil colloids.

     

Dynamics of soil labile carbon and nitrogen pools in riparian zone of Wyaralong Dam in Southeast Queensland,Australia

Purpose

Soil labile carbon (C) and nitrogen (N) pools are considered to be sensitive indicators of changes in soil C and N pools. In this study, we examined possible factors affecting spatial and seasonal variations in soil labile C and N pools in the riparian zones in Southeast Queensland, Australia.

Materials and methods

Soil and sediment samples were collected from two sites in the riparian areas. The spatial and seasonal variabilities of soil moisture, hot-water extractable organic C and total N (HWEOC and HWETN), microbial biomass C and N (MBC and MBN), and the relationships among them were examined.

Results and discussion

Soil labile C and N pools decreased along the transects in both soil depths of the two soil types, with the peak or bottom of values detected between upland slope and the riparian zone. Other factors rather than soil moisture were more important in regulating seasonal changes of soil HWEOC and HWETN except the dry-rewetting influence in November 2013. Soil moisture played a significant role in the seasonal variations of MBC and MBN. Soil labile C (HWEOC and MBC) and N (HWETN and MBN) pools at Site 1 (S₁; heavy texture), which were significantly higher than those at Site 2 (S₂; light texture).

Conclusions

Soil moisture would be an important driving factor for the spatial and seasonal distributions of soil labile C and N pools. Our study highlighted the importance of riparian zones as the hot spot of soil C and N dynamics, especially at the onset of rewetting dry soil in subtropical Australia.

     

Effects of biomass ash,bone meal,and alkaline slag applied alone and combined on soil acidity and wheat growth

Purpose

The purpose of this study is to examine the effects of combined application of biomass ash (BA), bone meal (BM), and alkaline slag (AS) on soil acidity, nutrient contents, uptake of the nutrients by wheat, and wheat growth.

Materials and methods

A pot experiment with an Ultisol collected from Anhui province, China, was conducted to compare the effects of BA, BM, and AS applied alone and combined on soil acidity; soil nutrient contents; uptake of N, P, K, Ca, and Mg by wheat, and wheat growth.

Results and discussion

Application of BA, BM, and AS alone and combined increased soil pH and decreased soil exchangeable Al³⁺. BA + BM + AS showed the greatest ameliorating effect on soil acidity, and soil pH of the treatment increased by 1.24 units compared with control. Application of BA + BM + AS reduced soil exchangeable Al³⁺ and increased soil exchangeable calcium and magnesium to a greater extent than BA + BM and single application of the amendments. The BM-containing amendments substantially increased soil available phosphorous by 66–93% compared with control. Application of the amendments alone and combined enhanced the uptake of N, P, K, Ca, and Mg by wheat and thus promoted wheat growth and increased yield of wheat grains. Application of BA + BM + AS and BA + BM showed greater effects on nutrient uptake and wheat growth than single application of the amendments. Wheat straw weights of the two treatments were 11.1 and 10.1 times greater than that of control. The data were 2.7, 4.8, and 5.6 times for the treatments of BA, AS, and BM. The contents of Cd, Cr, Zn, and Cu in wheat grains were lower than standard limits, except for the single BA treatment.

Conclusions

BA + BM + AS is the best choice for amelioration of acid soils and promotion of crop production.

     

Simultaneous immobilization of lead,cadmium, and arsenic in combined contaminated soil with iron hydroxyl phosphate

Purpose

Combined contamination of lead (Pb), cadmium (Cd), and arsenic (As) in soils especially wastewater-irrigated soil causes environmental concern. The aim of this study is to develop a soil amendment for simultaneous immobilization of Pb, Cd, and As in combinative contaminated soil.

Materials and methods

A soil amendment of iron hydroxyl phosphate (FeHP) was prepared and characterized, and its potential application in simultaneous immobilization of Pb, Cd, and As in combined contaminated soil from wastewater-irrigated area was evaluated. The effects of FeHP dosage, reaction time, and soil moisture on Pb, Cd, and As immobilization in the soil were examined.

Results and discussion

The immobilization efficiencies of Pb, Cd, and As generally increased with the increasing of FeHP dosage. With FeHP dosage of 10 %, the immobilization percentages of NaHCO₃-extractable As and DTPA-extractable Pb and Cd reached 69, 59, and 44 %, respectively. The equilibrium time required for immobilization of these contaminants was in the following order: NaHCO₃-extractable As (0.25 days) < DTPA-extractable Cd(3 days) < DTPA-extractable Pb (7 days). However, the immobilization efficiencies of Pb, Cd, and As have not changed much under soil moisture varied from 20 to 100 %. According to the results of the sequential extraction, the percentages of Pb, Cd, and As in residual fractions increased after the application of FeHP amendment, while their percentages in exchangeable fractions decreased, illustrating that FeHP can effectively decrease the mobilities and bioavailabilities of Pb, Cd, and As in the soil. Moreover, the application of FeHP will not have soil acidification and soil structure problem based on the soil pH measurements and soil morphology.

Conclusions

FeHP can immobilize Pb, Cd, and As in the combinative contaminated soil from wastewater irrigation area simultaneously and effectively. Thus, it can be used as a potential soil amendment for the remediation of Pb, Cd, and As-combined contaminated soil.

     

An efficient approach towards the bioremediation of copper,cobalt and nickel contaminated field samples

Purpose

The synthetic soil based bioremediation approach as reasonable and sustainable practice at the farming level where desired bioremediation could be established at lower cost.

Materials and methods

Metal-tolerant bacteria from different environmental field samples, (a) a municipal dump site, (b) an agricultural field and (c) sludge of electro-plating industries, were screened and characterized. Bioremediation of metal contaminants through isolated bacteria was compared under two different conditions, synthetic soil and basic minimal media containing copper, cobalt and nickel.

Results and discussion

The pollutants arising from industrial effluents are imparting a huge negative impact on agricultural land. Microbes are predominant in heavy metal-contaminated sites, which signifies as a potential opportunity for the researchers towards bioremediation. Three bacterial species showed high metal tolerance; 16S ribosomal DNA (rDNA) analysis revealed that the organisms were Proteus vulgaris strain, Stenotrophomonas sp. and Bacillus thuringiensis. Percentage removal of metals was also analysed under different concentrations and pH.

Conclusions

The current tested methods are helpful in streamlining the natural compliance of fragile elements and its uptake into the microbial system under in vitro and in situ conditions.

     

The effect of biochar loading rates on soil fertility,soil biomass,potential nitrification,and soil community metabolic profiles in three different soils

Purpose

Biochar is increasingly being used as a soil amendment to both increase soil carbon storage and improve soil chemical and biological properties. To better understand the shorter-term (10 months) impacts of biochar on selected soil parameters and biological process in three different textured soils, a wide range of loading rates was applied.

Materials and methods

Biochar derived from eucalypt green waste was mixed at 0, 2.5, 5, 10 % (wt/wt) with a reactive black clay loam (BCL), a non-reactive red loam (RL) and a brown sandy loam (BSL) and placed in pots exposed to the natural elements. After 10 months of incubation, analysis was performed to determine the impacts of the biochar rates on the different soil types. Also, microbial biomass was estimated by the total viable counts (TVC) and DNA extraction. Moreover, potential nitrification rate and community metabolic profiles were assayed to evaluate microbial function and biological process in biochar-amended soils.

Results and discussion

The results showed that biochar additions had a significant impact on NH₄ and NO₃, total C and N, pH, EC, and soil moisture content in both a soil type and loading-dependent manner. In the heavier and reactive BCL, no significant impact was observed on the available P and K levels, or the total exchangeable base cations (TEB) and CEC. However, in the other lighter soils, biochar addition had a significant effect on the exchangeable Al, Ca, Mg, and Na levels and CEC. There was a relatively limited effect on microbial biomass in amended soils; however, biochar additions and its interactions with different soils reduced the potential nitrification at the higher biochar rate in the two lighter soils. Community metabolic profile results showed that the effect of biochar on carbon substrate utilization was both soil type and loading dependent. The BCL and BSL showed reduced rates of substrate utilization as biochar loading levels increased while the opposite occurred for the RL.

Conclusions

This research shows that biochar can improve soil carbon levels and raise pH but varies with soil type. High biochar loading rates may also influence nitrification and the function and activity of microbial community in lighter soils.

     

Bioenergy-derived waste biochar for reducing mobility,bioavailability, and phytotoxicity of chromium in anthropized tannery soil

Purpose

This study was aimed to investigate the potential of biochar (BC), a waste byproduct of a bioenegy industry, Sri Lanka, as a soil amendment to immobilize and reduce the phytotoxicity of Cr in tannery waste-polluted soil (TWS).

Materials and methods

The TWS and bioenergy waste BC were characterized for physio-chemical parameters. A pot experiment was conducted by adding three BC application rates, 1, 2.5, and 5 % (w/w) to investigate the immobilizing capacity and bioaccumulation of chromium (Cr) in tomato plants (Lycopersicon esculentum L.). Soils and plants were digested via microwave digestion and analyzed for total Cr. Further, sequential extraction was conducted to assess the fractionation of Cr before and after the application of bioenergy waste BC on TWS.

Results and discussion

The total Cr concentration in TWS was 12,285 mg/kg. The biomass of tomato plants grown in the 5 % BC amendment doubled compared to the biomass in BC-unamended soil. Bioaccumulation of Cr in plants grown in 5 % BC-amended TWS showed a decrease by 97 % compared to that of the BC-unamended soil. The CaCl₂ extractability of Cr indicated that the bioavailability of Cr in the 5 % BC amendment has decreased by 68 % compared to the control. Sequentially extracted Cr in the exchangeable fraction decreased by 98 % in the 5 % BC amendment.

Conclusions

Pore diffusion, and adsorption via π-π electron donor-acceptor interactions were the primary mechanisms to be involved in the Cr retention in BC. Results suggested that the addition of BC to TWS reduces the mobility, bioavailability, and phytotoxicity of Cr in tomato plants.

     

Spatial and temporal variability of urban soil water dynamics observed by a soil monitoring network

Purpose

Urban soils’ variability in the vertical direction presumably affects hydrological parameters at the timescale. Moreover, horizontal soil alterations at small spatial scales are common in urban areas. This spatio-temporal variability and heterogeneity of soil moisture and the possible influencing factors were to be described and quantified, using data of a soil monitoring network in the city of Hamburg, Germany.

Materials and methods

Soil moisture data from ten observation sites within the project HUSCO was evaluated for two different years. The sites were located within districts with different mean groundwater table depths and characteristic urban soil properties. Soil hydrological simulations with SWAP were calculated for a selected site.

Results and discussion

The temporal evolution of soil water content and tension for the sites was very distinct, related to soil substrate, organic matter content, and groundwater table depth. Impacts of different vegetation rooting depths, the soil substrates’ type, and to some extent the degree of disturbance on soil water dynamics could be identified. An impact of groundwater table depth on the water content of the topsoil during low-precipitation periods could be assumed. The comparison of the results of soil hydrological simulations with empirical data indicated an overestimation of infiltration and percolation for the given soil substrates.

Conclusions

While soil properties are mainly determinant for the long-term progression of soil hydrology, local site factors affect the short-term regime. A shallow groundwater table contributes to more constant water dynamics while the relative decrease of water during a dry phase is diminished.

     

The forms and distribution of aluminum adsorbed onto maize and soybean roots

Purpose

The Al forms on maize and soybean roots were investigated to determine the main factors affecting the distribution of Al forms and its relationship with Al plant toxicity.

Materials and methods

Solution culture experiments were conducted to obtain the fresh roots of maize and soybean. KNO₃, citric acid, and HCl were used to extract the exchangeable, complexed, and precipitated forms of Al on the roots.

Results and discussion

The complexed Al was higher than the exchangeable and precipitated Al. Root CECs of soybean and maize were 77 and 55 cmol kg^?1, and functional groups on the soybean roots (262.4 cmol kg^?1) were greater than on maize roots (210.8 cmol kg^?1), which resulted in more exchangeable and complexed Al on soybean roots than on maize roots, and was one of the reasons for the increased Al toxicity to soybean. The total and exchangeable Al were the highest on the plant root tips and decreased gradually with increasing distance from the tips. Ca²⁺, Mg²⁺, and NH₄ ⁺ cations reduced the exchangeable Al on the roots. Oxalate and malate also reduced the adsorption and absorption of Al by roots, and the effect of oxalate was greater than malate.

Conclusions

Higher exchangeable and complexed Al on plant roots led to increased Al plant toxicity. Ca²⁺, Mg²⁺, and NH₄ ⁺ and oxalate and malate can effectively alleviate Al plant toxicity.

     

Sorption and transport of sulfonamides in soils amended with wheat straw-derived biochar: effects of water pH,coexistence copper ion,and dissolved organic matter

Purpose

Sulfonamides are widely used for the prevention and treatment of bacterial infections, hard-degraded contaminants distributed in the environment if they are discharged into the soil and water. Biochar could probably influence the geochemical behavior of ionized antibiotics in the soils.

Materials and methods

To determine the sorption/desorption of three representative sulfonamides (SAs) in soils amended with biochar, we investigated the effects of water pH, Cu²⁺, and dissolved humic acid on the sorption of sulfamethoxazole (SMX), sulfamethazine (SMZ), and sulfadiazine (SD) onto two different soil samples (S1 pH?=?5.13 and S2 pH?=?7.33) amended with wheat straw-derived biochar (size 0.5～0.6 mm).

Results and discussion

Batch experiments showed that the sorption/desorption isotherms of SAs on soil with/without biochar followed the Freundlich model. The biochar had a strong adsorption potential for SMX, SMZ, and SD both in S1 and S2 at low water pH. Except for SMX, the presence of Cu²⁺ inhibited the sorption of SMZ and SD through competing hydrophobic adsorption region in soils. HA suppressed the sorption of three sulfonamides in soil S2 by electrostatic repulsion under alkaline condition. The soil leaching column experiments showed the SA transport in soils, and S1 and S2 amended with biochar (0.5 and 1.0 wt%) brought about 12–20 % increase in SMX, SMZ, and SD retention compared to the untreated soil.

Conclusions

The results indicated that the presence of biochar effectively mitigated the mobility of ionized antibiotics such as SMX, SMZ, and SD in soils, which helps us reconsider the potential risk of antibiotics in the environment.

     

Comparison of field portable XRF and aqua regia/ICPAES soil analysis and evaluation of soil moisture influence on FPXRF results

Purpose

Field portable X-ray fluorescence (FPXRF) technology can offer a rapid and cost-effective determination of the total elemental concentrations in soils. The aims of this study were (i) to test the capability of FPXRF to predict the element concentrations of a very large soil sample set and (ii) to assess the influence of soil moisture, known to strongly affect the quality of FPXRF analyses.

Materials and methods

A large set of 215 soil samples were analysed for Ba, Ca, Cr, Cu, Fe, Mn, Pb, Rb, Sn, Sr and Zn by inductively coupled plasma atomic emission spectroscopy (ICPAES) after aqua regia digestion and with a FPXRF analyser using a short acquisition time. Soil samples were then saturated with ultrapure water to test the influence of soil water content on FPXRF signal.

Results and discussion

For all of the elements, the total concentrations obtained with ICPAES and FPXRF showed a very high degree of linearity, indicating that FPXRF can effectively predict element concentrations in soils. A Lambert-Beer law was successfully used to describe the decrease in the FPXRF concentrations with increasing soil moisture. The attenuation coefficient obtained for each element allowed us to satisfactorily predict the FPXRF concentrations of samples for water contents as high as 136.8 %.

Conclusions

These results show that the effect of water on signal attenuation can be corrected and that FPXRF may gradually replace chemical methods for the analysis of environmental samples.

     

Use of biochar-compost to improve properties and productivity of the degraded coastal soil in the Yellow River Delta,China

Purpose

Nutrient deficiency and salt stress (sodium, Na⁺) strongly limited the productivity of the degraded coastal soils in the Yellow River Delta. Biochar-based functional materials have been considered as a promising amendment to solving the problem of global soil security (e.g., erosion, fertility loss, acidification, and salinization). Therefore, this study aimed to explore the potential of using a biochar-compost amendment (BCA) to improve the coastal soil properties and productivity.

Materials and methods

The BCA was produced from composting of biochar and additives including seafood shell powder, peanut shell, commercial humate, and inorganic nutrients. Two halophytes, sesbania (Sesbania canabina (Retz.) Pers) and seashore mallow (Kosteletzkya virginica), were chosen as the tested plants in a 52-day pot experiment. BCA was added as the rates of 0, 1.5, 5, and 10 % (w/w). At the end of the incubation, the shoot height, biomass, and root morphological parameters including length, tips, and surface area were measured, as well as the properties (e.g., soil organic matter (SOM) content and cation exchange capacity (CEC)) of the rhizosphere and non-rhizosphere soils.

Results and discussion

The BCA application at 1.5 % enhanced the growth of sesbania and seashore mallow and increased their total biomass by 309 and 70.8 %, respectively, while significantly inhibited both the halophyte growths at 10 %. Similarly, both the halophyte root morphologies (e.g., length and tips) significantly increased by BCA addition at 1.5 %. The promoting growth of the both halophytes could be resulted from the improvement of soil properties such as the increased SOM and CEC, the decreased amount of the exchangeable sodium (Ex-Na) and exchangeable sodium percentage (ESP), and the rhizosphere effect (e.g., decreased soil pH). The higher rate of BCA addition (e.g., 10 %) sharply increased soil salinity, responsible for the inhibition of both the halophyte growths. Although BCA addition may directly supply much nitrogen (N) for the soils, N bioavailability for both halophytes was not largely improved.

Conclusions

The short-term laboratory pot experiments revealed that producing the biochar-compost with desired properties (e.g., BCA) could be a feasible alternative to remediate the degraded coastal soil in the Yellow River Delta. Moreover, the addition of BCA should be kept at an optimal level, which may produce expected positive results. Our results will be helpful for supporting the strategy of designing right biochar-compost for the right soil.

     

Effect of tea plantation age on the distribution of fluoride and its fractions within soil aggregates in the hilly region of Western Sichuan,China

Purpose

Long-term tea plantation (Camellia sinensis L.) could markedly change the pools of total fluoride (T-F) in soil extractable fractions. However, the effects of different chronosequence phases on the changes of fluoride fractions in these plantations are poorly understood.

Materials and methods

In this study, we have investigated the distribution of extractable fluoride fractions in four differently aged tea plantations (16, 23, 31, and 53 years old, respectively), in Zhongfeng Township of Ming-shan County, Sichuan, Southwest China. This study aimed to determine the effects of the age of various tea plantations with respect the contents of T-F, also considering the water-soluble fluoride (Ws-F), the exchangeable fluoride (Ex-F), the Fe/Mn oxide-bound fluoride (Fe/Mn-F), the organic matter-bound fluoride (Or-F), and the residual fluoride (Res-F) within soil aggregates.

Results and discussion

The T-F, Ws-F, Ex-F, and Res-F contents increased with the decreasing of particle size except for Fe/Mn-F and Or-F. Along with the increase of tea plant life, the contents of Ws-F and Ex-F within soil aggregates gradually increased. In addition, the trends of extractable Fe/Mn-F and Or-F were opposite to that of highly available fluoride after 23 years.

Conclusions

The results of this study show that fluoride is easily transformed into highly available phases in long-term tea plantations, improving the absorption of fluoride for tea plants.

     

Topography-soil relationships in a hilly evergreen broadleaf forest in subtropical China

Purpose

Topography-soil relationships usually vary with climate, vegetation type, degree of human disturbance, type of parent material, and the scale being studied. In this paper, we studied the topography-soil relationship in a hilly forest in subtropical China.

Materials and methods

The influence of topography on soil properties (soil moisture, organic carbon (C), total nitrogen (N) and total phosphorus contents, C:N ratio, and pH) was evaluated using a recursive partitioning conditional inference tree (CIT) as well as a multiple linear regression (MLR) method.

Results and discussion

The CIT models generally performed better than MLR in describing the topography-soil relationships. Topographic parameters chosen by the CIT models, which indicate the mechanisms at play for the spatial variation of the soil properties, varied with the soil property of concern. The soil moisture, organic C, and total N models contained only primary terrain attributes, the soil C:N ratio and pH models contained both primary and secondary terrain attributes, while the total phosphorus model contained mostly secondary terrain attributes.

Conclusions

The CIT method worked well for exploring the topography-soil relationships in the studied undisturbed hilly forest. We conclude that (1) soil moisture, organic C, and total N were strongly affected by location-specific topographic features such as gravitational potential, the amount of precipitation, temperature, and vegetation type; (2) total phosphorus was affected by catchment-related hydrological activities and soil C:N ratio; and (3) pH was affected by location-specific topographic features and catchment-related hydrological activities.

     

Soil pH,organic matter,and nutrient content change with the continuous cropping of <Emphasis Type="Italic">Cunninghamia lanceolata</Emphasis> plantations in South China

Purpose

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important native tree species in China. Consecutive cropping traditionally occurs in Chinese fir plantations (CFPs), but this practice has resulted in productivity declines in subsequent rotations. This study was designed to better understand the change of soil properties in the continuous cropping CFPs.

Materials and methods

We investigated soil pH, soil organic matter (SOM), and nutrient contents in different soil layers and in rhizosphere soil (RS) and non-rhizosphere soil (NRS) under CFPs of different ages and in different rotations.

Results and discussion

In the upper (0–20 cm) soil layer, soil pH decreased, while SOM increased, beneath mature CFPs with consecutive rotations. Total nitrogen (TN), available potassium, and available phosphorus contents in the upper soil layers did not differ significantly with consecutive rotations. Soil pH in RS was significantly lower than in NRS under mature plantations of the third rotation. Soil organic matter, TN, and available nitrogen did not differ between RS and NRS. Available phosphorus in RS was consistently lower than in NRS, and was highly deficient in the third rotation.

Conclusions

We conclude that no severe soil nutrient degradation occurred in the continuous cropping CFPs examined in this study, with soil acidification and phosphorus deficiency being two primary problems observed.

     

Role of woody biochar and fungal-bacterial co-inoculation on enzyme activity and metal immobilization in serpentine soil

Purpose

In this study, we investigated the effect of biochar (BC) and fungal bacterial co-inoculation (FB) on soil enzymatic activity and immobilization of heavy metals in serpentine soil in Sri Lanka.

Materials and methods

A pot experiment was conducted with tomatoes (Lycopersicon esculentum L.) at 1, 2.5, and 5 % (w/w) BC ratios. Polyphenol oxidase, catalase and dehydrogenase activities were determined by idometric, potassium permanganate oxidisable, and spectrophotometric methods, respectively. Heavy metal concentrations were assessed by 0.01 M CaCl₂ and sequential extraction methods.

Results and discussion

An increase in BC application reduced polyphenol oxidase, dehydrogenase, and catalase activity. The application of FB increased soil dehydrogenase activity, with the maximum activity found in 1 % BC700?+?FB treatment. Moreover, the CaCl₂ extractable metals (Ni, Mn, and Cr) in 5 % BC700 amended soil decreased by 92, 94, and 100 %, respectively, compared to the control. Sequential extraction showed that the exchangeable concentrations of Ni, Mn, and Cr decreased by 55, 70, and 80 % in 5 % BC700, respectively.

Conclusions

Results suggest that the addition of BC to serpentine soil immobilizes heavy metals and decreases soil enzymatic activities. The addition of FB to serpentine soil improves plant growth by mitigating heavy metal toxicity and enhancing soil enzymatic activities.

     

Contrasting response of two grassland soils to N addition and moisture levels: N<Subscript>2</Subscript>O emission and functional gene abundance

Purpose

Nitrification and denitrification processes dominate nitrous oxide (N₂O) emission in grassland ecosystems, but their relative contribution as well as the abiotic factors are still not well understood.

Materials and methods

Two grassland soils from Duolun in Inner Mongolia, China, and Canterbury in New Zealand were used to quantitatively compare N₂O production and the abundance of bacterial and archaeal amoA, denitrifying nirK and nirS genes in response to N additions (0 and 100 μg NH₄ ⁺–N g^?1 dry soil) and two soil moisture levels (40 and 80 % water holding capacity) using microcosms.

Results and discussion

Soil moisture rather than N availability significantly increased the nitrification rate in the Duolun soil but not in the Canterbury soil. Moreover, N addition promoted denitrification enzyme activities in the Canterbury soil but not in the Duolun soil. The abundance of bacterial and archaeal amoA genes significantly increased as soil moisture increased in the Duolun soil, whereas in the Canterbury soil, only the abundance of bacterial amoA gene increased. The increase in N₂O flux induced by N addition was significantly greater in the Duolun soil than in the Canterbury soil, suggesting that nitrification may have a dominant role in N₂O emission for the Duolun soil, while denitrification for the Canterbury soil.

Conclusions

Microbial processes controlling N₂O emission differed in grassland soils, thus providing important baseline data in terms of global change.

     

Effects of temperature on soil organic carbon fractions contents,aggregate stability and structural characteristics of humic substances in a Mollisol

Purpose

Under a global warming scenario, understanding the response of soil organic carbon fractions and aggregate stability to temperature increases is important not only for better understanding and maintaining relevant ecosystem services like soil fertility and crop productivity, but also for understanding key environmental processes intimately related with the maintenance of other regulatory ecosystem services like global climate change mitigation through carbon sequestration. An increase in temperature would accelerate the mineralization of soil organic carbon. However, the properties of organic carbon remained in soil after mineralization is not well known.

Materials and methods

Mollisol was collected at 0–20-cm depth from maize (Zea mays L.) field in Northeast China. A 180-day incubation experiment was conducted at three different temperatures (10, 30, and 50 °C) under constant soil moisture (60 % water holding capacity). Soil samples were assayed for total organic carbon (TOC), water-soluble organic carbon (WSOC), easily oxidizable organic carbon (EOC), humic fractions carbon, aggregate-associated carbon, and water stability of aggregates. Elemental analysis and solid-state ¹³C nuclear magnetic resonance spectroscopy were used to characterize humic acid and humin fractions.

Results and discussion

The contents of soil TOC, EOC, humic fractions carbon, and aggregate-associated carbon decreased with the increase in temperature. The proportion of 2–0.25-mm macroaggregate and the mean weight diameter (MWD) of aggregates also decreased. The C, H, N, S, alkyl C, and O-alkyl C contents of humic acid and humin decreased, whereas the O, aromatic C, and carbonyl C contents increased. The H/C, aliphatic C/aromatic C, and O-alkyl C/aromatic C ratios in humic acid and humin fractions decreased.

Conclusions

The increase in temperature has a negative impact on soil organic carbon content, soil aggregation, and aggregate stability. Moreover, humic acid and humin molecules become less aliphatic and more decomposed with the increase in temperature.

     

Climate change affects soil labile organic carbon fractions in a Tibetan alpine meadow

Purpose

Changes in bioactive soil C pools and their temperature sensitivities will dominate the fate of soil organic C in a warmer future, which is not well understood in highland ecosystems. This study was conducted in order to evaluate climate change, especially cooling effects, on soil labile organic C (LOC) pools in a Tibetan alpine meadow.

Materials and methods

A short-term reciprocal translocation experiment was implemented to stimulate climate warming (downward translocation) and cooling (upward translocation) using an elevation gradient on the Tibetan Plateau. Variations in soil microbial biomass C (MBC), dissolved organic C (DOC) and LOC were analyzed.

Results and discussion

Over the range of soil temperature from 0.02 to 5.5 °C, warming averagely increased soil MBC, DOC and LOC by 15.3, 17.0 and 3.7 % while cooling decreased them by 11.0, 11.9 and 3.2 %, respectively. Moreover, warming generally increased the proportion of DOC in LOC but cooling had an opposite effect, while the response of the MBC proportion to DOC and LOC varied depending on vegetation type. Soil MBC, DOC and LOC pools were positively related to soil temperature and showed a hump-shaped relationship with soil moisture with a threshold of about 30–35 %. Although soil DOC was more sensitive to warming (5.1 % °C^?1) than to cooling (3.0 % °C^?1), soil LOC showed a symmetrical response due to regulation by soil moisture.

Conclusions

Our results indicated that climate change would not only change the size of soil LOC pools but also their quality. Therefore, cooling effects and regulation of soil moisture should be considered to evaluate the fate of soil organic C in Tibetan alpine meadows in a warmer future.

     

Soil properties and plant community relationship in a saltmarsh of the Grado and Marano lagoon (northern Italy)

Purpose

The relationship between soil properties and plant communities was investigated in a saltmarsh of the Grado and Marano lagoon (northern Italy), where hydrology and micromorphology strongly influence the features of the ecosystem. A multidisciplinary approach was used to assess the change of soil properties and plant communities in relation to the submergence of soil.

Materials and methods

The plant community and soil profile surveys were both carried out along a transect in six sampling sites of the Gran Chiusa saltmarsh (Grado and Marano lagoon). The morphological and physicochemical parameters of soil profiles were investigated, and soils were classified according to Soil Taxonomy. The concentration of macronutrients in both soils and plants was analysed by inductively coupled plasma-optical emission spectrometry. Cluster and linear discriminant analysis were used to assist the interpretation of the data of plant communities and soil properties, respectively. The bioconcentration factor explored the macronutrient relationship between plant community and soil.

Results and discussion

A high, middle and low zone were identified by clustering the different plant communities along the studied transect. Discriminant analysis showed how the increase in soil submergence supported the accumulation of S and Ca content and depletion of Fe and Na. The development of different plant communities was linked to both soil water saturation and to the capacity of halophytes to tolerate anoxic conditions or salinity, by extrusion or bioconcentration strategies.

Conclusions

This study demonstrates that tide level plays an important role in the pedological development and chemical transformations along a soil hydrosequence. The micromosaic vegetation pattern may therefore represent a useful index of the hydrological and nutritional status of the underlying soils and could be used to predict changes in coastal ecosystems.