冻融交替对不同生物结皮土壤饱和导水率的影响

  目的  生物土壤结皮在干旱、半干旱地区分布广泛,能显著影响土壤饱和导水率的大小,为探明冻融交替对不同类型生物结皮土壤饱和导水率的变化。  方法  以神木六道沟流域混合结皮（藻结皮 + 苔藓结皮）和苔藓结皮土壤为研究对象,采用室内模拟冻融实验的方法,测定不同冻融交替次数和初始含水率共同作用下生物结皮土壤饱和导水率（Ks）的变化。  结果  （1）冻融条件下,苔藓结皮和混合结皮的存在相比裸土均降低了土壤Ks。（2）同一冻融次数下,苔藓结皮和混合结皮土壤Ks随初始含水率增加总体呈现先增大后减小的趋势;同一初始含水率下,两种结皮土壤Ks随冻融次数增加呈现逐渐增大的趋势。（3）冻融后苔藓结皮土壤Ks显著大于混合结皮土壤,在同一冻融条件下,初始含水率为8%时,冻融3次和7次后两种结皮土壤Ks相差最大,表现为苔藓结皮土壤Ks分别是混合结皮土壤的2.1和2.3倍。（4）冻融通过影响结皮层容重和结皮厚度及结皮下层土壤有机质和 > 0.25 mm团聚体含量进而影响Ks,冻融次数对结皮厚度及有机质含量有极显著影响（P < 0.01）,对结皮容重有显著影响（P < 0.05）,初始含水率对 > 0.25 mm团聚体含量有极显著影响（P < 0.01）。（5）冻融环境下苔藓结皮和混合结皮土壤的Ks均与冻融次数呈极显著正相关（P < 0.01）,与结皮容重呈极显著负相关（P < 0.01）。并对两种结皮Ks与其他因子进行偏最小二乘回归分析,结果表明苔藓结皮土壤Ks的主要影响因子依次为结皮容重 > 冻融次数 > 结皮厚度,而混合结皮土壤Ks的主要影响因子为冻融次数 > 结皮容重。  结论  冻融交替对生物结皮土壤饱和导水率有较显著影响,且冻融作用主要是通过影响结皮厚度、结皮容重及结皮下层土壤大团聚体颗粒及有机质含量来影响生物结皮土壤饱和导水率。     

Adaptation, tolerance, and evolution of plant species in a pyrite mine in response to contamination level and properties of mine tailings: sustainable rehabilitation

Purpose

The impacts of mining contaminations and physico-chemical properties and geochemistry of mine tailings on the density, richness, biodiversity, evolution and succession of plant species and vegetation recovery in the mining area is very poorly reported in the literature. Therefore, the present study conducted an investigation on vegetation development and succession of plant communities at the abandoned São Domingos pyrite mining area.

Materials and methods

We conducted the field survey to estimate the vegetation development and succession of plant communities, collect vegetation (plant species, lichen and moss) and tailing (and soil) samples, and finally analyzed the physico-chemical and geochemical properties and metal levels in mine tailings, soil and vegetation samples.

Results and discussion

The results showed that the communities of low height and biomass like grass, legume, shrub, moss and lichen were dominating on the mine tailings and waste dumps at the inner sites and center of the mine, and the vegetation coverage was explicitly very poor. The reddish brown colluvia had poor soil quality, but high acidity and metal concentrations. However, at the outer edge of the mine the loamy soil and relatively lower acidity and metal contamination favored the higher vegetation cover and a gradual increase in the number of species and plant succession, where the taller, higher biomass and broad leaf trees were abundantly grown forming a dense forest and canopy. The succession of several plant communities dominating in the mining area, vegetation coverage and species richness were strongly related to the different levels of contamination, soil properties and adverse factors of mine tailings.

Conclusions

Although the high concentrations of toxic trace elements and low pH soil are important factors for limiting the plant growth, however, proper soil development with enriched nutrients and properties on mining wastes, by either natural or external soil aided process, can help to promote the high vegetation growth, mine rehabilitation and ecological restoration of the mining degraded lands.     

Effects of super absorbent polymers on soil microbial properties and Chinese cabbage (Brassica chinensis) growth

Purpose

New water retention materials, super absorbent polymers (SAPs), have shown the potential to improve some soil physicochemical properties and promote growth of some crop species in arid and semi-arid areas. However, the impacts of SAPs on soil microbial properties are unclear. This study was conducted to clarify the effects of two SAPs on soil microbial properties and Chinese cabbage (Brassica chinensis) growth under different water conditions in the greenhouse.

Materials and methods

Experimental conditions included different irrigation conditions and different quantities of SAPs. Chinese cabbage was harvested after 1-month growth in the greenhouse. Meanwhile, soil samples were collected and sieved (<2-mm mesh). Some of the soils were kept at ?4 °C for analysis of soil physicochemical properties, and some at ?20 °C for analysis of soil microbial properties. Chinese cabbage samples were thoroughly washed with deionized water for the measurement of fresh weight, shoot length, and root length.

Results and discussion

The effects from SAPs were not obvious under water sufficient (WC1, watered every 2 days, and WC2, watered every 4 days) since plant properties were smaller in some SAP treatments than those in control. However, under water deficit (WC3, watered every 8 days), there were significant differences in plant shoot length and fresh weight between SAP treatments. There were also significant differences in relative soil water content between water condition (WC) or SAP treatments. The SAPs were beneficial for the formation of large aggregates. Under WC3, the soil organic matter (SOM) increased by 16.9 and 11.5 %, soil microbial biomass C (SMBC) by 32.5 and 19.3 %, and soil microbial respiration (SMR) by 52.1 and 37.2 % with Jaguar C (JC) and Jaguar S (JS), respectively. Under WC1 and WC2, significantly higher copy numbers of AOA in bulk treatment of JC were found compared with control treatment in this study. Under water deficit, the abundance of bacteria was significantly increased by application of SAPs. For almost every property of soil and plant, JC was showing better effects than JS.

Conclusions

Our results showed that cabbage growth was restricted under water-deficit conditions and the application of SAPs could conserve soil water and be useful for increasing cabbage growth under water deficit, improving SOM, SMBC, and SMR under different WC, and stimulating amoA gene AOA copy numbers and bacterial gene copy numbers. Thus, there should be no adverse effects of SAP application on soil microbial environment and Chinese cabbage growth.     

Effect of 7-year application of a nitrification inhibitor, dicyandiamide (DCD), on soil microbial biomass, protease and deaminase activities, and the abundance of bacteria and archaea in pasture soils

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO₃ ^?) leaching and nitrous oxide (N₂O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g^?1 soil) and biomass N (63 to 28 μg N g^?1), protease (361 to 694 μg tyrosine g^?1 soil h^?1) and deaminase (4.3 to 5.6 μg NH₄ ⁺ g^?1 soil h^?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?10⁹ to 2.77?×?10⁹ g^?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?10⁷ to 3.01?×?10⁸ g^?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.     

Soil Algal Colonization and Its Ecological Role in an Environment Polluted by Past Zn�CPb Mining and Smelting Activity

The research was carried out around dumps made at the beginning of twentieth century linked to Zn?CPb ore mining of deposits of Mississippi Valley type in Southern Poland. Soil algae communities were investigated near spoil dumps rich in Zn, Pb, Fe, Cd, and Tl. In algal crusts, Chlorophyta and Cyanophyta occur in filament forms such as Stichococcus bacillaris, Stichococcus chlorelloides, S. cf. fragilis, and Cylindrocapsa sp. The algal crusts form aggregates containing metal-bearing minerals and algal organic material. The development of the crusts occur on sandy-clayey soils poor in water and highly enriched in heavy metals (up to 68,800 mg kg^?1 for Zn, 85,060 mg kg^?1 for Pb, 369 mg kg^?1 for Cd and 355 mg kg^?1 for Tl). Algal-crust formation is an important initial stage which facilitates vascular plant succession and topsoil formation. The results of investigation of algal material with ESEM are presented and the mineral phases in the top soil layer based on the XRD and EDS are described. The results indicate the presence of secondary labile minerals of lead, e.g., anglesite and plumbojarosite and minerals of Zn, e.g., smithsonite and minrecordite.     

Short-term effects of prescribed burning on phosphorus availability in a suburban native forest of subtropical Australia

Purpose

Prescribed burning can alter nutrient availability to plants. Plant growth in tropical and subtropical forests is frequently phosphorus (P) limited. Soil P availability is influenced by a combination of multiple factors including soil chemical and biological properties. The aims of this study were to investigate the short-term effects of prescribed burning on soil P status and to evaluate the key drivers responsible for the variation in soil P fractions.

Materials and methods

Soil samples were collected at a depth of 0–10 cm at two sites in a suburban native forest. One site (the burnt site) was burned on 11 August 2011. The other site (the control site) was not burned but served as a reference. Sampling was conducted at four times: before burning, 12 days after burning (T1), 1 week after T1 (T2), and 1 month after T2 (T3). Soil pH, P fractions, microbial biomass carbon (C) and P, and activities of acid and alkaline phosphatase were measured.

Results and discussion

Total P was relatively low at both sites compared with other subtropical forests. Microbial biomass P accounted for approximately 10 % of soil total P at the two sites, suggesting that the turnover of microbial biomass is critical for soil P availability. Soil properties at the control site remained unchanged over the time. Soil organic forms of P at the burnt site were decreased by the prescribed burning, and the greatest reduction was found in moderately labile organic P (e.g., NaOH-extractable fractions). Soil inorganic forms of P, however, were not correspondingly increased by the prescribed burning. Microbial biomass P was closely related to the shifts in P fractions. These effects were only detected immediately after the fire.

Conclusions

Microbial biomass could serve as a sink of P in P-impoverished soils and play an important role in soil P transformation. Our results indicate that microbial biomass is an important factor that governs P status after prescribed burning. The rapid recovery of microbial biomass P could be beneficial to the P requirement for plant regrowth after prescribed burning.     

Use of blue-green algae and bryophyte biomass as a source of nitrogen for oil-seed rape

Summary Blue-green algal (Nostoc muscorum) or bryophyte (Barbula recurvirostra) growth on the surface of a brown earth silt loam contained in flooded columns significantly increased soil C (+20.9% and ±23.0%, respectively) and soil N (+25.1% and +9.6%, respectively) after 5 weeks in the surface 0.7-cm soil layer. Differences in the lower layers were not significant since there was no movement of C or N metabolites down the profile, even after 21 weeks. The input of C by the inoculated blue-green algae was estimated at 0.48 Mg C 100^-1 g soil or 0.45g C ha^-1; the bryophyte growth gave 0.5 Mg C ha^-1. N fixation by the blue-green algae alone was estimated at 60 kg N ha^-1 after 5 weeks of growth. Blue-green algae associated with bryophyte growth had fixed 23 kg N ha^-1 after 5 weeks, rising to 40 kg ha^-1 after 21 weeks. Decomposition of the bryophyte biomass led to a significant increase in the dry weight (+16.8%) and the N uptake (+27.5%) of spring oil-seed rape planted in homogenised soil. In contrast, soil incorporation of the blue-green algal biomass had no significant effect on yield. The equivalent mineralized N from the blue-green algal and bryophyte incorporation was estimated as 24 and 58 kg N ha^-1, respectively.     

Effect of application rate of a nitrification inhibitor,dicyandiamide (DCD), on nitrification rate,and ammonia-oxidizing bacteria and archaea growth in a grazed pasture soil: An incubation study

Purpose

Dicyandiamide (DCD) has been used commercially in New Zealand to reduce nitrate leaching and N₂O emissions in grazed pastures. However, there is a lack of information in the literature on the optimum rate of DCD to achieve the environmental benefits while at the same time reducing the cost of the technology. The objective of this study was to determine the effect of DCD application rate on its effectiveness to inhibit ammonia oxidizer growth and nitrification rate in a grazed pasture soil.

Materials and methods

The soil was a Templeton silt loam (Immature Pallic Soil; Udic Haplustepts) collected from Lincoln University Research Dairy Farm with a mixed pasture consisting of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) and was incubated alone (control) or with cow urine at 700 kg N/ha with 6 rates of DCD [0, 2.5, 5, 7.5, 10 (applied twice), 15 and 20 kg/ha] in incubation vessels. The incubation vessels were placed randomly in an incubator with a constant temperature of 12 °C. During 112 days of incubation, soil subsamples were taken at different time intervals to measure the concentrations of NO₃ ^?-N and NH₄ ⁺-N and the amoA gene copy numbers of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA).

Results and discussion

DCD applied at all the different rates inhibited nitrification in urine-treated soils, but the effectiveness increased with DCD application rate. In addition, AOB growth and the amounts of nitrate-N in the soil were significantly related to the application rate of DCD. However, AOA population abundance showed no relationship to the application rate of DCD. The DCD rate at which the AOB growth rate and nitrate-N concentration were halved (effective dosage that causes 50 % reduction in nitrification rate, or ED₅₀) was about 10 kg DCD/ha.

Conclusions

These results suggest that DCD applied at relatively low rates still slowed down the nitrification rate, and the current recommended rate of 10 kg DCD/ha for DCD use in New Zealand grazed pastures would result in a 50 % reduction in nitrification rate in this soil. The actual rate of DCD application used would depend on the cost of the product and the environmental and agronomic benefits that would result from its use.     

Toxic Effect of Certain Metals Mixture on Some Physiological and Morphological Characteristics of Freshwater Algae

The toxic effect of multi metals mixture which exist simultaneously in aquatic ecosystem on natural phytoplankton assemblages (green algae, blue-green algae and diatoms) was studied. For this purpose a laboratory scale unit was designed to evaluate the effect of continuous flow metals mixture in forms if triple and penta metals in Nile water algae. Clear changes in algal biomass in terms of chlorophyll a (chl a) took place when subjected to metals combination. The rise or decline in chl a was in relation with other algal pigments (chl b, chl c, carotenoides and phenophytin), protein and carbohydrate content of algal cells. Substantial changes in phytoplankton community structure was detected and the most tolerant group was blue-green algae followed by green algae while diatoms was the most sensitive group. The most dominant species in all cases were blue-green alga Oscillatoria mougeotii and green alga Scenedesmus quadricauda. In addition clear changes in morphological shape was observed for tolerant species belonging to the three algal groups. Nile water algae has ability to remove and accumulate metals in the following order therefore Zn > Cd > Ni > Cu > Cr. In addition, phytoplankton has ability to recovered from the stress of metals when eliminated from the media and the recovered biomass was nearly equivalent to that before exposing to metals stress. The overall effect of metals mixture depending on the type and number of metals, the algal community structure and ratio between different morphological forms of algae (unicellular, colonial and filamentous).     

Contrasting response of nitrification capacity in three agricultural soils to N addition during short-term incubation

Purpose

Human disturbance is a major culprit driving imbalances in the biological transformation of nitrogen from the nonreactive to the reactive pool and is therefore one of the greatest concerns for nitrogen (N) cycling. The objective of this study was to compare potential nitrification rates and the abundance of ammonia oxidizers responsible for nitrification, with the amendment of external N in different agricultural soils.

Materials and methods

Three typical Chinese agricultural soils, QiYang (QY) acid soil, ShenYang (SY) neutral soil, and FengQiu (FQ) alkaline soil, were amended with 0, 20, 150, and 300 μg NH₄ ⁺-N g^?1 soil and incubated for 40 days. The abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA) at the end of incubation in the soil microcosms was determined using the real-time PCR.

Results and discussion

There was a significant decrease in ammonium concentration in the QY soil from the highest to the lowest N-loading treatments, while no significant difference in ammonium concentrations was detected among the different N-loading treatments for the SY and FQ soils. A significantly higher potential nitrification rate (PNR) was observed in the FQ soil while lowest PNR was found in the QY soil. Quantitative PCR analysis of AOB amoA genes demonstrated that AOB abundance was significantly higher in the high N-loading treatments than in the control for the QY soil only, while no significant difference among treatments in the SY and FQ soils. A significant positive correlation between PNR and AOB amoA abundance, however, was found for the SY and FQ soils, but not for the QY soil. Little difference in AOA amoA abundance between different N-loading treatments was observed for all the soils.

Conclusions

This study suggested that ammonia oxidation capacity in the FQ and SY soils was higher than those in the QY soil with the addition of ammonium fertilizer for a short-term. These findings indicated that understanding the differential responses of biological nitrification to varying input levels of ammonium fertilizer is important for maximizing N use efficiency and thereby improving agricultural fertilization management.     

Soil microbial biomass and bacterial and fungal community structures responses to long-term fertilization in paddy soils

Purpose

Long-term fertilization can influence soil biological properties and relevant soil ecological processes with implications for sustainable agriculture. This study determined the effects of long-term (>25 years) no fertilizer (CK), chemical fertilizers (NPK) and NPK combined with rice straw residues (NPKS) on soil bacterial and fungal community structures and corresponding changes in soil quality.

Materials and methods

Soil samples were collected from a long-term field site in Wangcheng County established in 1981 in subtropical China between mid summer and early autumn of 2009. Terminal restriction fragment length polymorphism (T-RFLP) and the real-time quantitative polymerase chain reaction (real-time qPCR) of bacterial and fungal community and microbial biomass (MB-C, -N and -P) were analyzed.

Results and discussion

Redundancy analysis of the T-RFLP data indicated that fertilization management modified and selected microbial populations. Of the measured soil physiochemical properties, soil organic carbon was the most dominant factors influencing bacterial and fungal communities. The bacterial and fungal diversity and abundance all showed increasing trends over time (>25 years) coupling with the increasing in SOC, total N, available N, total P, and Olsen P in the fertilized soils. Compared to chemical fertilizer, NPKS resulted in the greater richness and biodiversity of the total microbial community, soil organic C, total N, MB-C, -N and -P. The high biodiversity of microbial populations in NPKS was a clear indication of good soil quality, and also indicated higher substrate use efficiency and better soil nutrient supplementation. Otherwise, unfertilized treatment may have a soil P limitation as indicated by the high soil microbial biomass N: P ratio.

Conclusion

Our results suggest that NPKS could be recommended as a method of increasing the sustainability of paddy soil ecosystems.     

Metal removal from and microbial property improvement of a multiple heavy metals contaminated soil by phytoextraction with a cadmium hyperaccumulator Sedum alfredii H.

Purpose

Effects of phytoextraction by Sedum alfredii H., a native cadmium hyperaccumulator, on metal removal from and microbial property improvement of a multiple heavy metals contaminated soil were studied under greenhouse conditions.

Materials and methods

A rhizobox experiment with an ancient silver-mining ecotype of S. alfredii natively growing in Zhejiang Province, China, was conducted for remediation of a multiple heavy metals contaminated soil. The rhizobox was designed combining the root-shaking method for the separation of rhizospheric vs near-rhizospheric soils and prestratifying method for separation of sublayers rhizospheric soils (0–10 mm from the root) and bulk soil (>10 mm from the root). Soil and plant samplings were carried out after 3 and 6 months of plant growth.

Results and discussion

Cadmium (Cd), zinc (Zn), and lead (Pb) concentrations in shoots were 440.6, 11,893, and 91.2 mg kg^?1 after 6 months growth, and Cd, Zn, and Pb removed in the shoots were 0.862, 25.20, and 0.117 mg/plant. Microbial biomass C, basal respiration, urease, acid phosphatase, and invertase activities of the rhizospheric soils were significantly higher than that of unplanted soils after 6 months growth. Microbial biomass carbon (MBC) of 0–2 mm and basal respiration (BR) rate of 0–8 mm sublayer rhizospheric soils were significantly higher than that of bulk soil after 6 months growth. So were the three enzyme activities of 0–4 mm sublayer rhizospheric soils. BR rate and urease were significantly negatively correlated with soluble Cd, so were MBC, acid phosphatase, and intervase activities with soluble Zn, MBC, BR rate, and three enzyme activities with soluble Pb.

Conclusions

Harvesting shoots of S. alfredii could remove remarkable amounts of Cd, Zn, Pb, and lower water-soluble Cd, Zn, and Pb concentrations in the rhizospheric soils. MBC, BR rate, and enzyme activities of the metal polluted soil, especially the rhizospheric soils increased with phytoextraction process, which is attributed to the stimulation of soil microbes by planting as well as the decrease in soil-soluble metal concentration.     

Controlling effects of surface crusts on water infiltration in an arid desert area of Northwest China

Purpose

Surface crusts are important features in arid desert areas and are critical to hydrological processes and ecosystem development. This paper aims to understand the effects of crusts on water movement in the soil and the factors that affect this and to provide the soil parameters for estimation of saturated hydraulic conductivity (K _s) in ecohydrological models.

Materials and methods

The study area was located in the middle and lower reaches of the Heihe River Basin, an arid desert area in Northwest China. There were three crust types in this region: physical soil crusts (PSCs, formed by water drop and erosion), biological soil crusts (BSCs, formed by microorganisms, moss, algae, lichen, and soil materials), and salt soil crusts (SSCs, formed by soluble salts). The infiltration rates of different soil and crust types and scalped soils were determined in situ in the field conditions using a disc infiltrometer with three repetitions. Crusts and soils were collected, and their properties were determined in the laboratory.

Results and discussion

The K _s of crust were significantly lower than that of scalped soils with a decrease of 13–70 %. The K _s of crusts were related to the type of crust and the properties of soil beneath the crusts. In this region, the soil textures are similar throughout, due to ubiquitous loess sedimentation, so textural differences had no significant effect on K _s. Soil organic matter (SOM) played a weak negative role on K _s because most crusts had higher SOM than the underlying soil. However, both crust thickness and electrical conductivity (EC, an index of salt concentration) showed significantly negative exponential relationship with K _s. Therefore, the SSC with high EC and thick crust have the lowest K _s among all crust types. Because soil development is related to salt accumulation, structure, and crust formation, the K _s follows the order of Solonchaks < Cambisols < Regosols, from lowest to highest.

Conclusions

Crusts have different characteristics compared with original soils and are the limiting layer of water infiltration in these arid soils. Therefore, the characteristics of crust must be considered in ecohydrological models. The main apparent controlling parameters of water infiltration rate in this area are crust thickness and EC.

     

Biochars immobilize soil cadmium, but do not improve growth of emergent wetland species Juncus subsecundus in cadmium-contaminated soil

Purpose

An addition of biochar mixed into the substrate of constructed wetlands may alleviate toxicity of metals such as cadmium (Cd) to emergent wetland plants, leading to a better performance in terms of pollutant removal from wastewater. The objective of this study was to investigate the impact of biochars on soil Cd immobilization and phytoavailability, growth of plants, and Cd concentration, accumulation, and translocation in plant tissues in Cd-contaminated soils under waterlogged conditions.

Materials and methods

A glasshouse experiment was conducted to investigate the effect of biochars derived from different organic sources (pyrolysis of oil mallee plants or wheat chaff at 550 °C) with varied application amounts (0, 0.5, and 5 % w/w) on mitigating Cd (0, 10, and 50 mg kg^?1) toxicity to Juncus subsecundus under waterlogged soil condition. Soil pH and CaCl₂/EDTA-extractable soil Cd were determined before and after plant growth. Plant shoot number and height were monitored during the experiment. The total root length and dry weight of aboveground and belowground tissues were recorded. The concentration of Cd in plant tissues was determined.

Results and discussion

After 3 weeks of soil incubation, pH increased and CaCl₂-extractable Cd decreased significantly with biochar additions. After 9 weeks of plant growth, biochar additions significantly increased soil pH and electrical conductivity and reduced CaCl₂-extractable Cd. EDTA-extractable soil Cd significantly decreased with biochar additions (except for oil mallee biochar at the low application rate) in the high-Cd treatment, but not in the low-Cd treatment. Growth and biomass significantly decreased with Cd additions, and biochar additions did not significantly improve plant growth regardless of biochar type or application rate. The concentration, accumulation, and translocation of Cd in plants were significantly influenced by the interaction of Cd and biochar treatments. The addition of biochars reduced Cd accumulation, but less so Cd translocation in plants, at least in the low-Cd-contaminated soils.

Conclusions

Biochars immobilized soil Cd, but did not improve growth of the emergent wetland plant species at the early growth stage, probably due to the interaction between biochars and waterlogged environment. Further study is needed to elucidate the underlying mechanisms.     

Remediation of a diesel-contaminated soil from a pipeline accidental spill: enhanced biodegradation and soil washing processes using natural gums and surfactants

Purpose

This paper addresses the application of bioproducts produced by plants (locust bean, guar, and mesquite seed gums) to enhance remediation processes of different nature: soil washing and biodegradation methodologies.

Materials and methods

These natural gums were tested at laboratory scale to remove total petroleum hydrocarbons-diesel fraction (TPH-diesel) from oil-contaminated volcanic soils sampled from a polluted site in an agricultural area of western Mexico. TPH-diesel removal by natural gums was compared to common synthetic surfactants.

Results and discussion

There is a strong evidence of contamination caused by the presence of TPH-diesel at a concentration of 32,100 mg/kg, which is above the legal limit of 1,200 mg/kg for agricultural soils in Mexico. Regarding the surfactant soil washing experiments, ionic surfactants showed removal rates above the control test of about 78.51 % (Maranil LAB), 71.27 % (Texapon 40), 60.13 % (SDS), and 48.19 % (Surfacpol G). In contrast, some nonionic surfactants showed removal rates below soil-washing background rate (40 %). On the other hand, natural gums showed interesting and promising results. Guar gum and locust bean gum showed efficiencies of 54.38 % and 53.46 %, respectively. Biodegradation experiments confirmed the effectiveness of natural gums as biodegradation enhancers in diesel-contaminated soils. Specifically, guar gum showed an excellent performance. An 82 % TPH-diesel removal rate was achieved for a very low gum concentration (2 ppm). In this particular context, reported surfactant concentrations to assist biodegradation are, in general, higher.

Conclusions

This work demonstrated the applicability of natural gums as soil remediation enhancers in diesel-contaminated systems. Particularly, guar gum might represent a cost-effective alternative for biodegradation enhancement processes.     

Rhizosphere effect has no effect on marker genes related to autotrophic CO2 fixation in paddy soils?

Purpose

The rhizosphere is a hotspot for microbial activities as well as microbial ecology studies. This study aimed to explore the “rhizosphere effect” on marker genes of CO₂ fixation autotrophic microorganisms.

Materials and methods

Microcosm experiments were conducted using two different types of paddy soil, planted with rice and added with urea. At tillering and ripening stages, bulk and rhizosphere soils were sampled separately for DNA extraction and quantitative PCR analyses.

Results and discussion

Six marker genes (cbbLG, cbbLR, cbbM, aclB, oorA, accA) of three autotrophic pathways (the Calvin cycle, the reductive tricarboxylic acid cycle, and the 4-hydroxybutyrate cycle) were detected, suggesting their pervasiveness in paddy soil. Redundancy analysis and variation partitioning based on partial redundancy analysis revealed higher contributions of growth stage (explaining 37 %) and soil type (explaining 19 %) on the variation of these genes, lower but significant impact of rhizosphere effect (explaining 12 %), and no significant effect of urea addition (P?>?0.05).

Conclusions

These results suggested that the composition of CO₂ fixation autotrophic microorganisms in the paddy soil was subject to combined actions of soil type and growth stage as well as rhizosphere effect.     

生物结皮发育对风沙土盐基离子释放和矿物风化的影响

为探明生物结皮发育对风沙土盐基离子释放和矿物风化的影响,以进一步明确生物结皮的风化成土作用。以典型风沙土上发育的生物结皮为对象,通过模拟淋溶试验比较不同类型生物结皮(藻结皮、藻—藓混生结皮和藓结皮)覆盖土壤的盐基离子释放规律,探究盐基离子释放量随淋溶液pH的变化趋势,以及量化生物结皮覆盖土壤的矿物风化速率。结果表明:矿物风化反应阶段不同种类盐基离子的淋出量均较为平缓,生物结皮覆盖土壤的各盐基离子总淋出量表现为Ca²⁺＞K⁺＞Mg²⁺＞Na⁺,其中藻结皮覆盖土壤的盐基离子总淋出量最高,比无结皮、混生结皮和藓结皮分别增加了112.0%,31.2%,27.1%。淋溶液pH显著影响盐基离子的淋溶释放,且其作用程度因离子种类和结皮类型而异。生物结皮覆盖提升了土壤的易风化矿物含量、风化程度和速率,藻结皮、混生结皮和藓结皮覆盖土壤的风化速率相比无结皮分别提升了61.2%,27.1%,152.6%,并且风化速率随淋溶液pH降低而提升。综上,生物结皮能显著促进风沙土矿物风化,其对风沙土改良和修复具有积极意义。     

Ammonia oxidizers and denitrifiers in response to reciprocal elevation translocation in an alpine meadow on the Tibetan Plateau

Purpose

Global climate change, in particular temperature variation, is likely to alter soil microbial abundance and composition, with consequent impacts on soil biogeochemical cycling and ecosystem functioning. However, responses of belowground nitrogen transformation microorganisms to temperature changes in high-elevation terrestrial ecosystems are not well understood.

Materials and methods

Here, the effects of simulated cooling and warming on the abundance and community composition of ammonia-oxidizing archaea (AOA) and bacteria (AOB), as well as the abundance of denitrifiers, were investigated using quantitative polymerase chain reaction and clone library approaches, on the basis of a 2-year reciprocal elevation translocation experiment along an elevation gradient from 3,200 to 3,800 m above sea level on the Tibetan Plateau.

Results and discussion

We found that, compared with the temperature variations caused by elevation translocation, the soil origin exerted a much stronger influence on AOA abundance. There were significant effects of both soil origin and elevation translocation on AOB abundance, which was particularly decreased by elevation-enhanced (simulated cooling) and increased by elevation-decreased (simulated warming) treatments. Altered temperature affected the abundance of nirK rather than nirS and nosZ genes, and the latter two seemed to be associated tightly with the soil origin. Furthermore, the results showed that temperature changes had obvious influences on the community structure and diversity of AOB, but not AOA. More apparent response of AOB to warming than in other studies on grassland and forest ecosystems may be attributed to higher elevation and lower mean annual temperature in this study.

Conclusions

Our findings thus suggest that, in comparison with AOA and denitrifying populations, AOB may respond more sensitively to natural temperature variation caused by elevation translocation in this alpine grassland ecosystem on the Tibetan Plateau.     

A sustained controlled release formulation of soil nitrogen based on nitrate-layered double hydroxide nanoparticle material

Purpose

Nitrate-layered double hydroxide material (nitrate-LDH) matrix can be considered as a potential formulation of delivering nitrogen into soil in a sustained manner.

Materials and methods

The nitrate-LDH matrix was formulated by a co-precipitation technique and subsequently characterized by scanning electron microscopy, X-ray analysis, and infrared spectroscopy. The release of nitrate was monitored in different buffer mediums: buffer A as a simulated acidic soil solution and buffer B as a simulated neutral soil solution.

Results and discussion

The stability of nitrate-LDH against thermal decomposition was evaluated by thermal gravimetric analysis. The nitrate-LDH supported a sustained controlled release process of nitrate during 16 days into acidic soil at 15 °C, while the release was continued to 20 days into neutral soil at the same temperature. The increase of soil temperature slightly enhanced the release of nitrate.

Conclusions

We offered a potential management strategy of soil nitrogen leaching process. The nitrate form of layered double hydroxide material was used as a nitrogen fertilizer in order to monitor the release of nitrate anion into soil at different conditions.     

Impact of organic matter addition on pH change of paddy soils

Purpose

The objective of the present study was to explore the effect of initial pH on the decomposition rate of plant residues and the effect of residue type on soil pH change in three different paddy soils.

Materials and methods

Two variable charge paddy soils (Psammaquent soil and Plinthudult soil) and one constant charge paddy soil (Paleudalfs soil) were used to be incubated at 45 % of field capacity for 105 days at 25 °C in the dark after three plant residues (Chinese milk vetch, wheat straw, and rice straw) were separately added at a level of 12 g?kg^?1 soil. Soil pH, CO₂ escaped, DOC, DON, MBC, MBN, NH ₄ ⁺ , and NO ₃ ^? during the incubation period were dynamically determined.

Results and discussion

Addition of the residues increased soil pH by 0.1–0.8 U, and pH reached a maximum in the Psammaquent and Plinthudult soils with low initial pH at day 105 but at day 3 in the Paleudalfs soil with high initial pH. Incorporation of Chinese milk vetch which had higher concentration of alkalinity (excess cations) and nitrogen increased soil pH more as compared with incorporation of rice and wheat straws. Microbial activity was the highest in Chinese milk vetch treatment, which resulted in the highest increase of soil pH as compared with addition of rice and wheat straws. However, nitrification seemed to be inhibited in the variable charge soils of Psammaquent and Plinthudult but not in the constant charge soil of Paleudalfs.

Conclusions

The effectiveness of increasing soil pH after incorporation of the plant materials would be longer in low initial pH soils of Psammaquent and Plinthudult than in high initial pH soil of Paleudalfs. In order to achieve the same degree of pH improvement, higher amounts of plant residues should be applied in constant charge soils than in variable charge soils.