Copper uptake by four Elsholtzia ecotypes supplied with varying levels of copper in solution culture

The effects of copper (Cu) on the yield and Cu uptake of three ecotypes of Elsholtzia splendens and one of Elsholtzia argyi were studied using solution culture. Three Cu concentrations were compared: 0.31 (control), 50 and 100 micromol L(-1). Although E. argyi took up more Cu in the aboveground parts, typical visual symptoms of Cu toxicity appeared when the plants grew in 50 and 100 micromol Cu L(-1). In contrast, plants from all three populations of E. splendens showed high Cu tolerance and substantial shoot Cu accumulation of 58-144 mg kg(-1). Shoot Cu concentrations were about 16-27 times higher than root Cu concentrations. Root-to-shoot ratio of the E. argyi ecotype was halved when Cu was supplied at a level of 100 mg L(-1) compared to the control (0.31 mg L(-1)) but the ratio increased by 6-47% in the three E. splendens ecotypes. The increase in root-to-shoot ratio in E. splendens may be a mechanism by which the plants can tolerate high Cu concentrations. There were few differences in morphology among the three E. splendens ecotypes in response to added Cu. The results are discussed in relation to the possible use of E. splendens as a pioneer species in the phytostabilization of Cu-contaminated soils.     

Selenium bioavailability and uptake as affected by four different plants in a loamy clay soil with particular attention to mycorrhizae inoculated ryegrass

The aim of this study was to investigate the influence of plant species, especially of their rhizosphere soil, and of inoculation with an arbuscular mycorrhizal (AM) fungus on the bioavailability of selenium and its transfer in soil-plant systems. A pot experiment was performed with a loamy clay soil and four plant species: maize, lettuce, radish and ryegrass, the last one being inoculated or not with an arbuscular mycorrhizal fungus (Glomus mosseae). Plant biomass and Se concentration in shoots and roots were estimated at harvest. Se bioavailability in rhizosphere and unplanted soil was evaluated using sequential extractions. Plant biomass and selenium uptake varied with plant species. The quantity of rhizosphere soil also differed between plants and was not proportional to plant biomass. The highest plant biomass, Se concentration in plants, and soil to plant transfer factor were obtained with radish. The lowest Se transfer factors were obtained with ryegrass. For the latter, mycorrhizal inoculation did not significantly affect plant growth, but reduced selenium transfer from soil to plant by 30%. In unplanted soil after 65 days aging, more than 90% of added Se was water-extractable. On the contrary, Se concentration in water extracts of rhizosphere soil represented less than 1% and 20% of added Se for ryegrass and maize, respectively. No correlation was found between the water-extractable fraction and Se concentration in plants. The speciation of selenium in the water extracts indicated that selenate was reduced, may be under organic forms, in the rhizosphere soil.     

Phytoremediation of polychlorinated biphenyl-contaminated soils: the rhizosphere effect

The objective in the first phase of this study was to screen alfalfa, flatpea, sericea lespedeza, deertongue, reed canarygrass, switchgrass, and tall fescue for phytoremediation of polychlorinated biphenyl (PCB)-contaminated soil. During the second phase, the focus was rhizosphere characterization to optimize PCB phytoremediation. Aroclor 1248 (PCB) was added to soil at 100 mg x kg(-1) of soil. In the first phase, all of the plant species treatments showed significantly greater PCB biodegradation compared to the unplanted controls and the two most effective species were selected for further study. During the rhizosphere characterization study, soil irradiation did not affect PCB biodegradation, but planting significantly increased PCB biodegradation; 38% or less of the initial PCB was recovered from planted pots, compared to more than 82% from the unplanted control soils. Presence of plants significantly increased the biological activity (microbial counts and enzyme activity) of both irradiated and unirradiated soils. Greater bacterial counts and soil enzyme activity were closely related to higher levels of PCB biodegradation. The data showed that Aroclor 1248 biodegradation in soil seem to be positively influenced by the presence of plants and plant-bacteria interactions. Our results suggested that phytoremediation could be an environmentally friendly alternative for PCB-contaminated soils.     

Climate change driven plant–metal–microbe interactions

Various biotic and abiotic stress factors affect the growth and productivity of crop plants. Particularly, the climatic and/or heavy metal stress influence various processes including growth, physiology, biochemistry, and yield of crops. Climatic changes particularly the elevated atmospheric CO₂ enhance the biomass production and metal accumulation in plants and help plants to support greater microbial populations and/or protect the microorganisms against the impacts of heavy metals. Besides, the indirect effects of climatic change (e.g., changes in the function and structure of plant roots and diversity and activity of rhizosphere microbes) would lead to altered metal bioavailability in soils and concomitantly affect plant growth. However, the effects of warming, drought or combined climatic stress on plant growth and metal accumulation vary substantially across physico–chemico–biological properties of the environment (e.g., soil pH, heavy metal type and its bio-available concentrations, microbial diversity, and interactive effects of climatic factors) and plant used. Overall, direct and/or indirect effects of climate change on heavy metal mobility in soils may further hinder the ability of plants to adapt and make them more susceptible to stress. Here, we review and discuss how the climatic parameters including atmospheric CO₂, temperature and drought influence the plant–metal interaction in polluted soils. Other aspects including the effects of climate change and heavy metals on plant–microbe interaction, heavy metal phytoremediation and safety of food and feed are also discussed. This review shows that predicting how plant–metal interaction responds to altering climatic change is critical to select suitable crop plants that would be able to produce more yields and tolerate multi-stress conditions without accumulating toxic heavy metals for future food security.     

Soil organic horizons as a major source for radiocesium biorecycling in forest ecosystems

Here we review some of the main processes and key parameters affecting the mobility of radiocesium in soils of semi-natural areas. We further illustrate them in a collection of soil surface horizons which largely differ in their organic matter contents. In soils, specific retention of radiocesium occurs in a very small number of sorbing sites, which are the frayed edge sites (FES) born out of weathered micaceous minerals. The FES abundance directly governs the mobility of trace Cs in the rhizosphere and thus its transfer from soil to plant. Here, we show that the accumulation of organic matter in topsoils can exert a dilution of FES-bearing minerals in the thick humus of some forest soils. Consequently, such accumulation significantly contributes to increasing 137Cs soil-to-plant transfer. Potassium depletion and extensive exploration of the organic horizons by plant roots can further enhance the contamination hazard. As humus thickness depends on both ecological conditions and forest management. our observations support the following ideas: (1) forest ecosystems can be classified according to their sensitivity to radiocesium bio-recycling, (2) specific forest management could be searched to decrease such bio-recycling.     

Effects of forms and rates of potassium fertilizers on cadmium uptake by two cultivars of spring wheat (Triticum aestivum, L.)

A greenhouse pot experiment was conducted to study the influence of potassium fertilizers in different forms and rates on cadmium (Cd) uptake by two cultivars of spring wheat (Triticum aestivum, L.): Brookton and Krichauff. Potassium fertilizers were added to soil at four levels: 0, 55, 110 and 166 mg K kg(-1) soil as KNO(3) (N), KCl (C) or K(2)SO(4) (S). CdCl(2) was added to all the treatments at a uniform rate equivalent to 15 mg Cd kg(-1) soil. Plant shoot and root dry weights (DW) of both cultivars were reduced significantly by the addition of K-fertilizer in C and S treatments but there were only marginal changes in the N treatments. The Cd concentrations in shoots and whole plants increased significantly (P<.001) with increasing K addition, from 37.5 to 81.4 mg kg(-1) and from 42.9 to 86.8 mg kg(-1) for Brookton and Krichauff, respectively. However, no obvious effect was observed in the N treatments, except for the highest K level (K3) where there was a sharp increase in Cd concentration compared to the lower additions. Forms of K-fertilizers significantly influenced the Cd concentrations in plant shoots and roots (P<.001), but there was no significant difference between C and S treatments. This experiment showed that anions Cl(-) and SO(4)(2-) increase Cd uptake by plants, which can be interpreted as Cl(-) and SO(4)(2-) complexing readily with Cd(2+) and thereby increasing the bioavailability of Cd(2+) in soils. The effect of potassium itself on plant uptake of Cd was also observed. We suggest that when applying potassium fertilizer to Cd-contaminated soils, the forms and rates should be considered.     

Hyperaccumulation of Pb, Zn and Cd in herbaceous grown on lead-zinc mining area in Yunnan, China

A field survey of herbaceous growing on lead-zinc mining area in Yunnan, China were conducted to identify species accumulating exceptionally large concentrations of Pb, Zn and Cd in shoots. In total, 220 plant samples of 129 species of 50 families and 220 soil samples in which the plants were growing were collected. According to accumulation concentration in plant shoots and the concentration time levels compared to plants from non-polluted environments, 21 plant samples of 16 species were chosen as best-performing specimens, 11 plant samples of 10 species for Pb, 5 plant samples of 4 species for Zn and 5 plant samples of 5 species for Cd. Sonchus asper (L.) Hill in Qilinkeng had hyperaccumulation capacity to Pb and Zn. Corydalis pterygopetala Franch in Paomaping had hyperaccumulation capacity to Zn and Cd. All 5 Cd hyperaccumulators came from Lanping lead-zinc mining area. Out of 11 Pb hyperaccumulators, 7 came from Minbingying of Huice lead-zinc mining area. The average of the concentration time levels compared to plants from non-polluted environments were higher than 10 times in all plant samples, the concentration time levels changed from 203 times to 620 times for Pb, from 50 times to 70 times for Zn and from 145 times to 330 times for Cd. Out of 21 plant samples, translocation factor changed from 0.35 to 1.90, only translocation factor of 7 plant samples were higher than 1. Enrichment coefficients of all samples were lower than 1. These plant species were primarily heavy metal hyperaccumulator, and will be used in phytoremediation of the metallic pollutants in soils after further research in accumulation mechanism.     

Retention and phytoavailability of radioniobium in soils

Radioniobium is present in long-lived nuclear waste as a result of the activation of zirconium pellets associated with the nuclear fuel. The behaviour of niobium (Nb) in the environment and especially its fate in the soil-plant system has not been thoroughly investigated so far. In safety assessment of French long-lived nuclear waste disposal, data concerning the mobility and the bioavailability of Nb in soils are needed as well as general trends of its fate in the specific environment around the site of French underground research laboratory. Therefore, we investigated the mobility of 95Nb in three different soils typical of the area of north-eastern France and its uptake by two plants, rye grass (Lolium perenne L.) and winter wheat (Triticum aestivum L.). Soil:solution distribution of 95Nb was observed in 1:10 batch experiments with deionized water for a 3-day period. Results showed that K(d) values were high (in the order of 10(3) L kg(-1)) and were still significantly increasing after 3 days. A mathematical model, fitted to describe the decrease of the radioactivity after 3 days, is proposed to calculate sorption ratios--SR--(rather than K(d) values as equilibrium was not reached) over longer periods. Soil-to-plant concentration ratios (CR) were measured in shoots and roots of the two plants after cultivation on two soils spiked with (95)Nb (406kBqkg(-1)). Soil-to-root dry weight CR were high (0.30-1.52) and could probably be due to efficient uptake into the roots. However, no transfer of Nb to plant shoots was detected in any of the soils. Nb is thus a rather immobile element in soils and its transfer to plants seems limited to underground parts. It would therefore tend to accumulate in surface horizons of soils in case of long-term continuous surface release.     

Micronutrient composition of plants in the Polar Urals under contrasting geochemical conditions

Natural variation in the level of micronutrients in plants and soils of the Polar Urals depending on the types of bedrocks has been evaluated. The contents of Fe, Mn, Zn, Cu, Ni, Cr, and Co have been determined by the atomic absorption method in 156 plant species of 25 families and in 38 soil samples. It has been found that the mineral composition of plant species varies depending on edaphic conditions. Taxon-specific features in the accumulation of chemical elements in plants of the Polar Urals have been revealed for the first time on the basis of a large amount of data.     

Yield and arsenate uptake of arbuscular mycorrhizal tomato colonized by Glomus mosseae BEG167 in As spiked soil under glasshouse conditions

A glasshouse pot experiment was conducted to study the effect of arbuscular mycorrhizal (AM) colonization by Glomus mosseae BEG167 on the yield and arsenate uptake of tomato plants in soil experimentally contaminated with five As levels (0, 25, 50, 75 and 150 mg kg(-1)). Mycorrhizal colonization (50-70% of root length) was little affected by As application and declined only in soil amended with 150 mg As kg(-1). Mycorrhizal colonization increased plant biomass at As application rates of 25, 50 and 75 mg kg(-1). Shoot As concentration increased with increasing As addition up to 50 mg kg(-1) but decreased with mycorrhizal colonization at As addition rates of 75 and 150 mg kg(-1). Shoot As uptake increased with mycorrhizal colonization at most As addition levels studied, but tended to decrease with addition of 150 mg As kg(-1). Total P uptake by mycorrhizal plants was elevated at As rates of 25, 50 and 75 mg kg(-1), and more P was allocated to the roots of mycorrhizal plants. Mycorrhizal plants had higher shoot and root P/As ratios at higher As application rates than did non-mycorrhizal controls. The soil of inoculated treatments had higher available As than uninoculated controls, and higher pH values at As addition levels of 25, 50 and 75 mg kg(-1). Mycorrhizal colonization may have increased plant resistance to potential As toxicity at the highest level of As contamination studied. Mycorrhizal tomato plants may have potential for phytoextraction of As from moderately contaminated soils or phytostabilization of more highly polluted sites.     

Species-specific effects of P-solubilizing and N<Subscript>2</Subscript>-fixing bacteria on seedling growth of three salt-tolerant trees

Coastal afforestation suffers from low survival and slow growth due to harsh conditions and lack of robust seedlings. Inoculation of P-solubilizing bacteria (PSB) or N₂-fixing bacteria (NFB) are effective in promoting plant growth and thus potentially helpful for coastal afforestation. However, it remains unclear about the generality and specificity of these plant-growth-promoting-bacteria (PGPB) on the growth of salttolerant trees. We inoculated seedlings of two mangrove trees and one terrestrial salt-tolerant tree with pure cultures of PSB or mixed cultures of PSB and NFB. Plant biomass, height, base diameter and N and P concentrations were determined six months after bacterial inoculation. We found that inoculation of PGPB had an overall promoting effect on the seedling growth of three tree species, but the effects differed greatly (3–280% increase) among plant species and bacterial isolates or bacterial combinations. Only in the terrestrial tree, co-inoculations of PSB and NFB showed greater promoting effects than monocultures of PSB. Root: shoot ratios of seedlings were not changed by bacterial inoculation. Inoculation treatments moderately elevated N concentrations in shoots and roots and P concentrations only in roots of seedlings. Our results suggest that PGPB might have a general promoting effect on the seedling growth of salt-tolerant trees. Nevertheless, the magnitude of promoting effects and the comparative advantage of dual inoculation over single inoculation are species-specific. The generality and specificity of the plant-PGPB relationship are similar to the plantmycorrhizal symbiosis. In addition, tissue nutrient improvement might not be the main mechanism of the promoting effects by PGPB.     

Modelling 137Cs uptake in plants from undisturbed soil monoliths

A model predicting 137Cs uptake in plants was applied on data from artificially contaminated lysimeters. The lysimeter data involve three different crops (beans, ryegrass and lettuce) grown on five different soils between 3 and 5 years after contamination and where soil solution composition was monitored. The mechanistic model predicts plant uptake of 137Cs from soil solution composition. Predicted K concentrations in the rhizosphere were up to 50-fold below that in the bulk soil solution whereas corresponding 137Cs concentration gradients were always less pronounced. Predictions of crop 137Cs content based on rhizosphere soil solution compositions were generally closer to observations than those based on bulk soil solution composition. The model explained 17% (beans) to 91% (lettuce) of the variation in 137Cs activity concentrations in the plants. The model failed to predict the 137Cs activity concentration in ryegrass where uptake of the 5-year-old 137Cs from 3 soils was about 40-fold larger than predicted. The model generally underpredicted crop 137Cs concentrations at soil solution K concentration below about 1.0 mM. It is concluded that 137Cs uptake can be predicted from the soil solution composition at adequate K nutrition but that significant uncertainties remain when soil solution K is below 1 mM.     

Accumulation of Pb, Cd, Cu and Zn in plants and hyperaccumulator choice in Lanping lead-zinc mine area, China

A field survey of higher terrestrial plants growing on Lanping lead-zinc mine, China were conducted to identify species accumulating exceptionally large concentrations of Pb, Cd, Cu and Zn of 20 samples of 17 plant species. Concentrations of Pb and Zn in soil and in plant were higher than that of Cu and Cd. Significant difference was observed among the average concentrations of four heavy metals in plants (except Cd and Cu) and in soil (except Pb and Zn) (P<0.05). For the enrichment coefficient of the four heavy metals in plant, the order of average was Pbtree>herbaceous, and herbaceous grew in soil with the highest concentrations of four heavy metals. In different areas, the concentrations of Pb, Cd, Cu and Zn in plants and soils and enrichment coefficient were different. Plants in Paomaping had more accumulating ability to Pb, Cd and Zn, and plants in Jinfeng River had more accumulating ability to Cu. Six plant species, i.e. S. cathayana, Lithocarpus dealbatus, L. plyneura, Fargesia dura, Arundinella yunnanensis and R. annae in Paomaping, had high accumulation capacity. R. annae in Paomaping had hyperaccumulating capacity to Pb, Cd and Zn, L. plyneura to Pb and Cd, and S. cathayana to Cd, respectively.     

Effects of soil amendments on lead uptake by two vegetable crops from a lead-contaminated soil from Anhui, China

Previous studies have documented that phosphate compounds of lead (Pb) [e.g., pyromorphite Pb5(PO4)3-(X), where X=OH, F or Cl] are comparatively insoluble, and their formation in Pb-contaminated soil may be a means of reducing the bioavailability and chemical lability of Pb in soil. In this study, the effect of phosphate compound amendments on the bioavailability of Pb in a polluted alkaline soil was examined. A Pb-contaminated soil was treated with hydroxyapatite (HA), phosphate rock (PR), water-soluble P fertilizer (single superphosphate, SSP) and the combination of HA with SSP. The bioavailability of Pb was determined in plant uptake studies with vegetables (Brassica campetris L. var. communis, BC) and Brassica oleracea L. var. acephala, BO) and sequential extraction. The results indicated that the Pb concentrations in both shoots and roots of two vegetable plants decreased with increasing quantities of added P compound, and the HA treatment had the best effect at the level of 5000 mg of P kg(-1)as compared with other treatments in which the Pb concentrations in shoots of BO and BC decreased 51.9% and 65.5%, respectively, and the Pb concentrations in roots of BO and BC decreased 67.3% and 57.2%, respectively, as compared with the control treatment. The SSP treatment had little effect on the Pb concentrations in plant tissues. Sequential extraction results indicated that the addition of soil amendments transform soil Pb from nonresidual fractions to residual fraction substantially. The effect of treatments followed this order at the equivalent P addition: HA>PR>HA+SSP>SSP. The results suggested that HA amendments can lower the bioavailability and increase the geochemical stability of soil Pb, so it has the potential for in situ remediation in Pb-contaminated soils.     

Uptake and distribution of natural radioactivity in wheat plants from soil

The uptake of naturally occurring uranium, thorium, radium and potassium by wheat plant from two morphologically different soils of India was studied under natural field conditions. The soil to wheat grain transfer factors (TF) were calculated and observed to be in the range of 4.0 x 10(-4) to 2.1 x 10(-3) for 238U, 6.0 x 10(-3) to 2.4 x 10(-2) for 232Th, 9.0 x 10(-3) to 1.6 x 10(-2) for 226Ra and 0.14-3.1 for 40K. Observed ratios (OR) of radionuclides with respect to calcium have been calculated to explain nearly comparable TF values in spite of differences in soil concentration of the different fields. They also give an idea about the discrimination exhibited by the plant in uptake of essential and nonessential elements. The availability of calcium and potassium in soil for uptake affects the uranium, thorium and radium content of the plant. The other soil factors such as illite clays of alluvial soil which trap potassium in its crystal lattice and phosphates which form insoluble compounds with thorium are seen to reduce their availability to plants. A major percentage (54-75%) of total 238U, 232Th and 226Ra activity in the plant is concentrated in the roots and only about 1-2% was distributed in the grains, whereas about 57% of 40K activity accumulated in the shoots and 16% in the grains. The intake of radionuclides by consumption of wheat grains from the fields studied contributes a small fraction to the total annual ingestion dose received by man due to naturally existing radioactivity in the environment.     

Habitat function of agricultural soils as affected by heavy metals and polycyclic aromatic hydrocarbons contamination

Ecotoxic activity of soils polluted with polycyclic aromatic hydrocarbon (PAH) and heavy metals (HM) was evaluated in pot and laboratory experiments. Plants and soil microorganisms were chosen as test organisms and six different soil materials were used in the study. The applied levels of HM and PAH were aimed to reflect environmental conditions in the "worst case" situation. Zn(2+), Pb(2+) and Cd(2+) were introduced to the soils as an aqueous solution of the mixture of salts at the concentrations corresponding to 1000, 500 and 3 mg kg(-1), respectively. Mixture of four PAH compounds (flourene, anthracene, pyrene and chrysene) as a CH(2)Cl(2) solution was applied at levels of 10-100 mg summation operator 4PAH kg(-1). Population and activity of soil microflora was evaluated as measured of total bacteria counts, intensity of respiration and enzyme activity (dehydrogenases and phosphatases). Effect on plants was evaluated on the base of the growth (plant at an early stage of their development) and yield (mature plant) measurements. The results indicate that combined effect of PAH and heavy metals on soil microorganisms activity and on some plants at an early stage of their development can be stronger than in soils amended with HM or PAH separately. Reaction of tested organisms was related to soil properties, PAH concentration, time and plant species. Mature plants (maize) were insensitive to the applied levels of both group of contaminants.     

巢湖陆向湖滨带常见野生植物对磷缓冲能力的影响

湖泊陆向湖滨带缓冲磷扩散的机制尚未得到充分地研究。系统分析了2011年4~7月巢湖陆向湖滨带5种野生植物的生长状况与根际土不同形态磷的含量和吸附行为。结果表明土壤磷的吸附行为可用Langmuir方程加以描述。与对照相比,艾草和小飞蓬根际土总磷含量明显较低,磷的最大吸附量（Qmax）明显较高,而小蓟和狗尾巴草根际土速效磷含量明显较高,Qmax与磷吸附强度明显较低。植物根与茎长均随季节增加,相应的土壤磷饱和度下降。因此,植物吸收与土壤吸附是陆向湖滨带缓冲磷扩散的重要机制。有机质可通过增加速效磷含量和Qmax值调节土壤磷平衡浓度（EPC0）。小飞蓬和艾草根际土的EPC0值明显较低,磷吸附能力较强。而小蓟和早熟禾根际土的EPC0值明显较高,故易成为向湖泊扩散的磷源     

Plant induced changes in concentrations of caesium, strontium and uranium in soil solution with reference to major ions and dissolved organic matter

For a better understanding of the soil-to-plant transfer of radionuclides, their behavior in the soil solution should be elucidated, especially at the interface between plant roots and soil particles, where conditions differ greatly from the bulk soil because of plant activity. This study determined the concentration of stable Cs and Sr, and U in the soil solution, under plant growing conditions. The leafy vegetable komatsuna (Brassica rapa L.) was cultivated for 26 days in pots, where the rhizosphere soil was separated from the non-rhizosphere soil by a nylon net screen. The concentrations of Cs and Sr in the rhizosphere soil solution decreased with time, and were controlled by K+NH(4)(+) and Ca, respectively. On the other hand, the concentration of U in the rhizosphere soil solution increased with time, and was related to the changes of DOC; however, this relationship was different between the rhizosphere and non-rhizosphere soil.     

Plant uptake of 134Cs in relation to soil properties and time

134Cs uptake by sunflower and soybean plants grown on seven different soils and its relation to soil properties were studied in a greenhouse pot experiment. Soil in each pot was contaminated by dripping the 134Cs in layers, and sunflower and soybean plants were grown for three and two successive periods, respectively. 134Cs plant uptake was expressed as the transfer factor (TF) (Bq kg(-1) plant/Bq kg(-1) soil) and as the daily plant uptake (flux) (Bq pot(-1) day(-1)) taking into account biomass production and growth time. For the studied soils and for both plants, no consistent trend of TFs with time was observed. The use of fluxes, in general, provided less variable results than TFs and stronger functional relationships. A negative power functional relationship between exchangeable potassium plus ammonium cations expressed as a percentage of cation exchange capacity of each soil and 134Cs fluxes was found for the sunflower plants. A similar but weaker relationship was observed for soybean plants. The significant correlation between sunflower and soybean TFs and fluxes, as well as the almost identical highest/lowest 134Cs flux ratios, in the studied soils, indicated a similar effect of soil characteristics on 134Cs uptake by both plants. In all the studied soils, sunflower 134Cs TFs and fluxes were significantly higher than the respective soybean values, while no significant difference was observed in potassium content and daily potassium plant uptake (flux) of the two plants.     

滨海芦苇湿地土壤微生物数量对长期模拟增温的响应

采用开顶式生长室(Open-top chamber,OTC)连续8 a(2008~2015年)长期模拟温度升高,研究滨海芦苇湿地不同土壤深度,及两种代表植物芦苇(Phragmites australis)和白茅(Imperata cylindrical)根际、非根际土壤可培养微生物数量变化对长期增温的响应。结果表明:(1)相对于对照,长期增温导致土壤可培养微生物的数量显著增加。其中,增温对土壤表层细菌、真菌的数量影响显著,细菌在第一层的增幅最大,增加率为34.16%,真菌在第三层的增幅最大,增加了64.42%。增温对20~40 cm土层放线菌影响显著,其中在第二层达到最大增加率59.47%;(2)长期增温对芦苇根际土壤微生物的根际效应变化的影响不大,表现为各土层芦苇根际效应增温对照,而白茅根际真菌和放线菌分别在第二层和第三层有显著差异;(3)不同的植物类型,其根际可培养微生物数量及根际效应对长期增温的响应不一致,表现为芦苇和白茅根际土壤可培养微生物数量及根际效应的增加幅度不同,这可能与植物不同类型,根际分泌物种类、数量的差异有关。