Changes in soil biological activities under reduced soil pH during Thlaspi caerulescens phytoextraction

Phytoextraction of soil Cd and Zn may require reduction in soil pH in order to achieve high metal uptake. Reducing the pH of high metal soil, however, could negatively affect soil ecosystem function and health. The objectives of this study were to characterize the quantitative causal relationship between pH and soil biological activities in two Zn and Cd contaminated soils and to investigate the relationship between metals and soil biological activities under low pH. Soils were adjusted to five or six different pH levels by sulfur addition, followed by salt leaching. Thlaspi caerulescens was grown for 6 months, and both the rhizosphere and non-rhizosphere soil biological activities were tested after harvest. Reducing pH significantly lowered soil alkaline phosphatase activity, arylsulphatase activity, nitrification potential, and respiration. However, acid phosphatase activity was increased with decreasing pH. The relationship between soil biological activities and pH was well characterized by linear or quadratic regression models with R² values ranging from 0.57 to 0.99. In general, the three enzyme activities, nitrification potential, and the ratio of alkaline phosphatase to acid phosphatase activity were very sensitive indicators of soil pH status while soil respiration was not sensitive to pH change. The rhizosphere soil had higher biological activities than non-rhizosphere soil. The negative effects observed in the non-rhizosphere soil were alleviated by the rhizosphere influence. However, rhizosphere soil after 6 months phytoextraction showed lower nitrification potential than non-rhizosphere soil, probably due to substrate limitation in our study.     

Apparent Cation – Exchange Equilibria and Aluminium Solubility in Solutions Obtained from Two Acidic Forest Soils by Centrifuge Drainage Method and Suction Lysimeters

Apparent cation–exchange equilibria and solubility of aluminium were analysed in two acidic forest soils: a Cambisol and a Cambic Podzol. Soil solution was obtained by a centrifuge drainage method from fresh soil samples and with suction lysimeters. The total positive charge of the measured cations as well as the concentrations of the cations were generally much larger in the centrifugates than in the lysimeter solutions, which implies that total charge of soil solution is larger in small pores than in large pores. Hydrogen ion in particular was concentrated in some of the centrifugates, the ratio centrifugate:lysimeter solution being over 10. The total positive charge of the measured cationsdecreased with increasing depth with both methods. Theapparent cation–exchange coefficients K _H-Ca, K _Al-Ca, and K _K-Ca had different values in the methods, and the variation in the cation exchange coefficients was larger in the lysimeter method than in the centrifuging method. The coefficient K _Mg-Ca had similar values in both methods. The results imply that mobile solution could not have cation–exchange equilibria with bulk exchangeable cations in the soils, although solution in small pores seemed to have equilibria. Solubility of Al did not follow the solubility of an Al(OH)₃ phase in the centrifugates, and the centrifugates with a H⁺ activity larger than 60 μmol were undersaturated with respect to the gibbsite. Solubility of Al was between gibbsite and amorphousAl(OH)₃ in the lysimeter solutions. Differencesbetween the centrifugates and the lysimeter solutionsin the ion concentrations and in the apparent chemicalequilibria were similar for both soils studied.     

间作五指毛桃土壤和根主要中微量元素含量及其相关性

为了解在成龄胶园间作的五指毛桃根际与非根际土壤及其根中主要中、微量元素含量情况，测定了实验区根际与非根际土壤各30个和对应五指毛桃根的钙、镁、铁、锰、铜和锌含量，分析了两者之间的关系，并评价了根际与非根际土壤中、微量元素丰缺状况。结果表明，非根际土壤钙、镁、铁、锰含量的平均值都高于根际土壤的，而铜、锌含量的平均值都低于根际土壤的。土壤钙、镁含量80%以上处于缺水平，而铁、锰含量处于丰或很丰水平，铜和锌含量处于适中水平。五指毛桃根际与非根际土壤中、微量元素存在空间上的广泛变异。五指毛桃根中、微量元素的平均值从大到小的排序是钙>镁>锰>铁>锌>铜。土壤中、微量元素与五指毛桃根中相对应的中、微量元素的相关性不强，且表现复杂。本研究结果揭示，在成龄胶园间作五指毛桃应当适量施用钙肥、镁肥和喷施一些铜元素叶面肥，并实行科学施肥，减少养分淋失。     

Use of a chemical equilibrium model to understand soil chemical processes that influence soil solution and surface water alkalinity

A chemical equilibrium model was applied to soil chemistry data (Spodosols) collected from 30 and 21 forested watersheds in New York and Maine, respectively, during the EPA Pilot Soil Survey. Chemistry data were evaluated between states using lumped series and within New York using three series (Adams, Becket, and Canaan). All New York horizons had soil characteristics that tend to cause lower solution alkalinity in comparison to Maine horizons. Negative alkalinities were produced in all E horizons (? 69 to ? 37 μmol LU^?1) at each of the pCO₂ levels used (0.3 to 2%). All B horizons had negative alkalinities at low PCO₂ levels, which became positive at higher levels, except for the Canaan B and New York Bh horizons, which were negative at all pCO₂ levels. C horizons generated positive alkalinities (1 to 67 μmol L^?1) at most pCO₂ levels. Results indicate the importance of water contact with different horizons and soil series in determining solution alkalinity. Because of degassing effects, solutions with a positive alkalinity will increase in pH after leaving the soil, whereas solutions with a negative alkalinity will remain at low pH (pH < 5.5) and cause the surface water to be acidic. Application of the model to soil chemistry data collected in the northeastern U.S. illustrates the importance of various factors such as pCO₂, Al solubility, base saturation, and exchange coefficients in determining surface water chemistry.     

湘中紫色丘陵区不同植被类型根际与非根际土壤理化特征

[目的]探索湘中紫色丘陵区不同植被类型根际与非根际土壤的理化特征,为湘中地区生态修复提供理论依据。[方法]以典型抽样方法调查湘中丘陵区草丛(G)、草灌(GS)、灌木(S)和乔灌(AS)4种典型植被,研究其根际与非根际土壤理化性质的差异,通过典型相关分析揭示根际与非根际土壤理化指标间的耦合关系。[结果]研究区草丛和灌木根际土壤中细砂粒(0.25~0.05mm)含量分别显著(p0.05)低于乔灌63.84%和76.97%;粉粒(0.02~0.002mm)含量表现为草和灌木分别显著高于乔灌的38.48%和37.66%。根际土壤0.25~0.05mm微团聚体含量均表现为乔灌高于其他植被,0.02~0.002mm微团聚体含量均表现为灌木高于其他植被。草灌与灌木非根际土壤有机质含量显著(p0.05)低于根际土壤148.05%和121.92%,灌木和草灌根际土壤有机质含量显著(p0.05)高于乔灌土壤84.28%和92.08%;草灌根际土壤全氮含量显著(p0.05)高于非根际土壤83.33%,草灌根际土壤碱解氮含量显著(p0.05)高于乔灌土壤200.83%;不同植被类型根际/非根际土壤磷含量差异不明显,总体来看,同一植被根际土壤全磷含量低于非根际土壤,而有效磷表现为乔灌最低;乔灌根际土壤速效钾含量分别显著(p0.05)低于草丛和草灌土壤125.15%和137.71%,除草灌外,其余植被类型根际土壤全钾含量均低于非根际土壤。典范相关分析表明土壤有机质和全量养分含量,2~1,1~0.5,0.25~0.05mm土粒含量,2~1,1~0.5mm团聚体3组理化性状间相互关系密切。[结论]改善土壤理化性质,促进湘中丘陵地区生态恢复,应注重协调土壤养分、颗粒组成及团聚体之间的耦合关系。     

冬小麦-夏玉米轮作体系中不同施氮水平对玉米生长及其根际土壤氮的影响

在河北衡水潮土上进行田间试验,以当地习惯高氮用量(小麦季施N 300 kg/hm2,玉米季施N 240 kg/hm2)为对照,研究冬小麦-夏玉米轮作体系中减少氮肥用量对玉米季植株生长、氮素吸收及根际土壤中无机氮与微生物量氮的影响。结果表明,两季作物氮肥施用量减少25%和40%,对玉米产量、生物量及植株体内氮累积量未产生明显影响,氮肥利用率提高。不同氮肥施用量对根际和非根际土壤铵态氮含量的影响不显著;减少氮肥施用量,对玉米根际土壤硝态氮含量也没有明显影响。在玉米苗期、抽雄期和成熟期,习惯高施氮量处理的非根际土壤硝态氮含量较高,其中抽雄期,非根际土壤硝态氮含量较氮肥减施40%用量处理高出近一倍,但非根际土壤微生物量氮水平含量明显降低。氮肥减施未影响根际土壤微生物量碳、氮含量,反而增加了非根际土壤微生物量碳、氮水平。在高肥力的潮土上,冬小麦/夏玉米轮作体系中适当减施氮肥并未影响玉米根际土壤氮素水平,可保证玉米稳产,实现减氮增效。     

Concentrations of 60 elements in the soil solution as related to the soil acidity

Little is known about solubility and soil solution concentrations of most elements occurring in the solid phase of soils. This study reports changes in solution concentrations of 60 mineral elements following CaCO₃ addition to a moderately acid semi‐natural soil, and possible mechanisms accounting for the differing solubility patterns as related to soil acidity are discussed. Soil solutions were obtained by high‐speed centrifuging and ultrafiltration (0.2 μm) of samples at 60% water‐holding capacity of the A horizon of a Cambisol developed from a shale–gneiss moraine and supplied with CaCO₃ at 20 rates to yield a soil solution pH range of 5.2–7.8. Concentrations of elements were determined in the solutions by ICP‐AES or (for most elements) ICP‐MS. Several distinct patterns of soil solution concentrations as a function of soil solution pH were demonstrated. Positively related to pH and CaCO₃ supply were soil solution concentrations of As, Br, Mo, S, Sb, Se, U, and W, and to a lesser degree, Co, Cr, Hg, Mg, and Sr. Inversely related to pH were concentrations of Al, B, Ba, Bi, Cs, Ce, Eu, Ga, Ge, Fe, Li, K, Rb, Na, Th, and Ti; less distinctly inversely rated were Dy, Er, Gd, Hf, La, Lu, Mn, Nd, Pr, Sm, Sc, Si, Tl, Tm, and Yb. ‘U‐shaped’ relationships to pH were demonstrated for the concentrations of Ag, Cd, Nb, Ni, P, V, and Zr. There were no or irregular relations between pH and concentrations of Be, Cu, Ho, Pb, Ta, and Tb. Differences between elements in their soil solution concentrations as related to total (HNO₃‐digestible) concentrations and the solubility of organic C were also treated. Increasing the pH of a soil by adding CaCO₃ changes the solubility of most mineral elements substantially, the several distinct patterns observed being governed by, for example, ionic properties and charge, affinity for organic compounds, and pH‐dependent formation and solubility of complexes.     

Fractionation of metal complexes with dissolved organic matter in a rhizosphere soil solution of a humus-rich Andosol using size exclusion chromatography with inductively coupled plasma-mass spectrometry

To better understand the behavior of metals in soil–plant systems, their physicochemical forms in rhizosphere soil should be elucidated. The dissolved organic matter (DOM) in a soil solution influences the mobility and bioavailability of metals in soil. The present study examined the effects of plant growth on DOM–metal complexes in a rhizosphere soil solution using size exclusion chromatography combined with an inductively coupled plasma-mass spectrometer system (SEC–ICP-MS) and an ultrafiltration technique. Humus-rich volcanic ash soil from the surface of an agricultural field was used in a pot cultivation experiment. Brassica rapa nothovar. was cultivated in a pot in which rhizosphere soil (R) was separated by a nylon net screen from non-rhizosphere soil (NR). Soil solutions were collected using a high-speed centrifugation method 3 weeks after sowing and analyzed using SEC–ICP-MS. Some peaks of DOM with a high molecular size were detected in the ultraviolet-absorbing chromatograph (280 nm) of the soil solution samples. Their concentrations were much higher in the R solution than in the NR solution. Metals including Al, Fe, Cu, Zn, Pb, Y, La and U were detected at the ultraviolet peak positions of the DOM. The ultrafiltration experiment showed that the size distributions of the organic materials to which the metals were combined differed between the R and NR soil solutions. These results suggest that plant growth enhanced the dissolution of metals adsorbed with organic matter from the solid phase in rhizosphere soil.     

Identification of organically bound iodine in soil humic substances by size exclusion chromatography / inductively coupled plasma mass spectrometry (SEC / ICP-MS)

Abstract

Sulfur transformation in riee rhizosphere was investigated. Soil enzyme arylsulfatase in rhizosphere and non-rhizosphere soil, whieh is responsible for mineralization of organic sulfur to sulfate sulfur, was studied. The Michaelis constants of arylsulfatase from Maahas c1ay and Pila c1ay loam were 3.04 × 10^-4 M and 3.97 × 10^-4 M, respectively. The arylsulfatase of rhizosphere soil showed higher activity than that of non-rhizosphere soil. Applieation of sulfate had no marked elTect on the enzyme aetivity either in rhizosphere or non-rhizosphere soil under the submerged condition. This indieates that arylsulfatase activity under the submerged condition is not inhibited by applieation of sulfate. The amount of HI-reducible sulfur in the rhizosphere and non-rhizosphere soi! inereased with time. However, rhizosphere soil had a higher amount of HI-reducible sulfur than did non-rhizosphere. Thc ditl'erence in arylsulfatase activity between the rhizosphcre and non-rhizosphere soil was not directly associated with thc number of sulfur-redueing and -oxidizing bacteria.     

石灰土地区几种作物根际与非根际土壤养分特征对比研究——以重庆市中梁山为例

以重庆市中梁山石灰土地区为研究区,选择莴笋、红菜苔、白菜、瓢儿菜和桔子5种不同的作物,通过野外采样和室内实验分析的方法,分别测定了5种作物的根际与非根际土壤的全氮、全磷、全钾、水解氮、速效磷、速效钾、有机质的含量以及土壤pH值,并进行了对比分析。结果表明,根际与非根际土壤的全氮、全磷、全钾、水解氮、速效磷、速效钾、有机质和pH值之间均表现出显著的差异性（p<0.05）。这5种作物的养分含量除了桔子树的根际土壤速效磷出现亏缺外,其余4种作物根际土壤的全氮、全磷、全钾、水解氮、速效磷以及速效钾都高于非根际土壤,不同作物出现了不同程度的富集现象。另外,根际土壤的pH值均低于非根际土壤;根际土壤有机质含量均高于于非根际土壤。     

The effect of pH upon the copper and cupric ion concentrations in soil solutions

Soil samples whose pH had been adjusted to between 4.5 and 7.5 either for long periods in the field or short periods in the laboratory were incubated after wetting with water or 0.01 m CaCl₂. Copper concentrations in the soil solutions decreased only slightly as the solution pH increased, but free cupric ion concentrations decreased considerably. The copper concentrations were smaller and the proportion of copper present in solution as cupric ion at a given pH was larger when CaCl₂ rather than water was used. Complexed organic species made up most of the copper in all solutions. The duration of pH adjustment did not affect these results. Copper adsorption isotherms were determined on the soils using low equilibrium solution concentrations. As a given copper concentration the quantity of copper adsorbed increased and the proportion of copper in solution present as cupric ion decreased with pH increase; again the duration of pH adjustment did not affect the results.     

长期保护性耕作可提高表层土壤碳氮含量和根际土壤酶活性

【目的】 研究不同长期耕作措施对作物根际和非根际土壤碳氮元素含量和土壤酶活性的影响,以及土壤碳氮元素与碳氮转化相关酶之间的相互联系,对认识土壤酶响应土壤碳氮变化的机制和选择合理有效的耕作技术具有重要的理论和实践意义。 【方法】 长期耕作试验始于1999年,位于河南孟津县,属于黄土高原东部边缘,土层深厚 (50—100 m),土壤类型是壤质黄绵土。试验处理有草地 (GL)、传统耕作 (CT)、免耕覆盖 (NT)、深松覆盖 (SM),于2016年采集根际土和非根际土0—20 cm、20—40 cm,分析了土壤总碳、有机碳和总氮含量,以及β-葡萄糖苷酶 (BG)、β-纤维二糖苷酶 (CBH)、β-木糖苷酶 (BXYL)、乙酰氨基葡萄糖苷酶 (NAG) 和亮氨酸氨基肽酶 (LAP) 的活性,并进行了土壤碳氮元素含量与酶活性的相关性分析。 【结果】 1) 与传统耕作相比,免耕和深松显著提高了根际和非根际0—20 cm土壤的总碳、有机碳和总氮含量,显著降低了非根际20—40 cm土壤的总碳、有机碳和总氮含量。草地显著提高了根际土壤总碳、有机碳和总氮含量,显著提高了非根际0—20 cm土壤的有机碳含量,显著降低了非根际土壤的总碳含量和非根际20—40 cm土壤中的有机碳含量。深松显著降低了作物根际和非根际土壤C/N,免耕和草地处理显著降低了作物非根际20—40 cm土壤中的C/N,但草地处理显著提高了作物非根际0—20 cm土壤C/N。2) 与传统耕作相比,草地、免耕和深松显著提高了根际土壤中β-葡萄糖苷酶、β-纤维二糖苷酶、β-木糖苷酶和乙酰氨基葡萄糖苷酶的活性。草地显著提高了根际土壤的亮氨酸氨基肽酶活性,免耕和深松显著降低了根际土壤的亮氨酸氨基肽酶活性。3) 碳氮转化相关酶之间均存在正相关关系 (除β-纤维二糖苷酶与亮氨酸氨基肽酶之间)。碳氮转化相关酶与土壤总碳、总氮和有机碳之间均存在正相关关系 (除亮氨酸氨基肽酶与总碳之间),与C/N之间均存在负相关关系。 【结论】 土壤碳氮转化酶之间存在相互促进的关系,共同参与土壤碳氮的转化。长期保护性耕作 (免耕和深松) 可以有效提高土壤表层的总碳、有机碳和总氮含量,提高根际土壤酶活性,有利于营养元素 (有机质、碳氮元素) 的循环转化和作物的吸收利用,以深松效果最好,免耕次之。      

复合污染土壤中水稻根际元素特性及效应研究

【目的】以广东大宝山重金属复合污染农田为生长介质,通过研究水稻不同部位生长量、 金属含量、 对金属的富集系数,及其与根际、 非根际土金属含量、 形态变化的相关关系,探讨根际效应可能对水稻体内金属积累转运以及生物量的影响。【方法】选取了广东大宝山稻田重金属复合污染(As、 Pb、 Fe、 Cu、 Zn)土壤及当地常见的20个水稻品种进行根际袋试验,即将根际袋内的土视为根际土,根际袋外的土视为非根际土,将供试水稻品种种植于根际袋土壤中60天后收获,测定水稻各部位的生长量、 不同金属的含量,根际土和非根际土中各金属有效态的含量。【结果】Fe、 Cu、 Pb、 Zn、 As在根部的富集系数均大于其在茎叶的富集系数,各金属在茎叶和根部的富集能力排序分别为Zn Cu As ≈ Pb ≈ Fe和Fe Zn As Cu Pb。根际土和非根际土中各种金属有效态含量均为Fe Cu Pb Zn As。研究还发现,有效态Fe、 Cu和Zn浓度对整株干重的影响显著,作用强弱顺序为Cu Zn Fe,对水稻生长影响作用显著的三种有效态金属Fe、 Cu和Zn均为植物生长所必需的元素。供试土壤中有效态Cu浓度对水稻的生长所起的作用最强。根际土有效态Fe浓度对根系Fe的积累作用效果显著,有效态As浓度显著抑制了根系Fe的积累,且有效态As浓度的作用强于有效态Fe。【结论】根际土中有效态Fe对株高、 根干重、 茎叶干重和整株干重均起着抑制作用,有效态Cu对水稻生长起到了促进作用。根际土有效态As和非根际土有效态Zn对根部Fe的积累起到了抑制作用,根际土有效态Fe和非根际土有效态Cu则起到了促进作用。非根际土有效态Fe和有效态Zn对水稻根长的增加均起到了促进作用。     

Effects of enhanced supplies of nitrogen and sulphur on rhizosphere and soil chemistry in a Norway spruce stand in SW Sweden

Rhizophere and bulk soil chemistry were investigated in a Norway spruce stand in SW Sweden. The rhizosphere and bulk soil chemistry in water extracts in control plots (C) and plots repeatedly treated with ammonium sulphate (NS) were compared. Treatment regime was started in 1988. Cylindrical core samples of the LFH-layer and mineral soil layers were collected in 1992 and used for water extract analyses. Samples of soil from LFH-layer and mineral soil layers were taken in 1991 and 1993 for determination of CEC and base saturation. Soil pH and NH₄-N, NO₃-N and SO₄-S, Al, Ca, K and Mg concentrations in water extracts were measured for rhizosphere and bulk soils. The pH-values of bulk and rhizosphere soils in NS plots decreased compared with those in control plots, whereas concentrations of NH₄-N, NO₃-N, SO₄-S, base cations and Al in water extract increased. In both bulk and rhizosphere soils the concentration of NH₄-N was much higher than that of NO₃-N. A significant difference in the pH and Mg concentration of bulk and rhizosphere soil between the treated and control plots was found only in the 0–10 cm layer. For all layers, there was a significant difference in NH₄-N concentrations in the bulk and rhizosphere soil between the NS treatment and control plots. Concentrations of exchangeable base cations and the base saturation level in the LFH-layer decreased in the NS plots. The concentration of extractable SO₄-S increased in the NS plots. The NS treatment enhanced the amount of litter in L-layer, owing to increases in needle biomass and litterfall but led to losses of base cations, mainly K and Mg, from LFH-layer. It was concluded that the NS treatment displaced cations from exchangeable sites in the LFH-layer leading to higher concentrations of these elements in both rhizosphere and bulk soil.     

Conditions related to solubility of rare and minor elements in forest soils

Soil solutions expelled by high‐speed centrifugation (13900 g) of intact soil sample cores at field moisture from 30 forest topsoils (A horizons of mainly Dystric and Eutric Cambisols, according to the FAO‐Unesco system) low in clay were subjected to analysis of 60 elements, using ICP‐MS and ICP‐AES. Concentrations measured were related to soil and soil solution properties assumed to be important for the solubility of elements, using stepwise regression analysis. On an average two thirds of the variability in soil solution concentration of elements were accounted for by, in particular, organic C concentrations, pH and/or nitrate concentrations of the solutions, varying among elements from 19 to 90 %. Concentrations of elements strongly positively related to soil solution acidity were Al, Be, Ge, Li, Ni, Pb, and Zn, strongly negatively related to acidity were Ca, Mo, and W. Most positively related to nitrate concentrations in soil solutions were B, Ba, Cd, Mg, Mn, and Sr; negatively were Nb, Ta, and Ti. Concentrations of organic C in the soil solutions correlated positively, often quite closely, with most of the other elements studied, including La, all the lanthanides, and with Ag, Br, Cr, Fe, Ga, Hf, Hg, In, P, Th, U, Y, and Zr. Soluble organic compounds were apparently ’︁carriers’ of these elements in the soil solution. The concentrations of elements in HNO₃ digests of the soils usually accounted for just little or no statistical variability of their soil solution concentrations.     

施肥对I-107杨树人工林土壤根际效应的影响

 通过研究施用有机肥、化学肥料和生物菌肥对I-107杨树人工林根际和非根际土壤微生物数量和土壤酶活性的影响,分析土壤酶活性与土壤微生物数量的关系。研究结果表明:不同种类肥料使用后3个月,林地根际土壤和非根际土壤微生物总量均有显著增长,其中有机肥处理土壤微生物数量增长幅度最大,菌肥处理最小。施肥处理显著提高土壤脲酶、碱性磷酸酶、过氧化氢酶、过氧化物酶活性,但尿素和菌肥处理土壤多酚氧化酶活性降低。施用有机肥处理对土壤微生物和土壤酶根际效应值影响最明显,菌肥处理影响最小。尿素处理土壤pH值高于对照,有机肥和菌肥处理小于对照,但不同处理间土壤pH值的根际效应值差异性不明显。土壤微生物数量与土壤酶活性之间存在一定的相关性,其中:土壤脲酶活性与好气性纤维素分解菌之间、土壤碱性磷酸酶活性与氨化细菌、真菌、放线菌、亚硝酸细菌之间,土壤过氧化氢酶与好气性纤维素分解菌、真菌、放线菌之间相关性显著。     

Effect of soil heating on the dynamics of soil available nutrients in the rhizosphere

The effect of soil heating on the dynamics of soil available nutrients in the rhizosphere was evaluated. A pot experiment was carried out by using a rhizobox; a pot which enables to sample soils and soil solutions not only temporally with plant growth but also spatially depending on the distance from the root-accumulating compartment. The experiment consisted of 4 treatments; soils with or without heating treatment (150°C, 3 h), each of which was either planted with maize (Zea mays L.) or not. During the 17-d experiment, soil solutions at 0–2 mm from the root-accumulating compartment were collected 5 times. Soils depending on the distance from the root-accumulating compartment and plants were also collected after the experiment. The ionic concentrations of the soil solutions and soil water extracts, and the nutrient contents of plants were analyzed. Immediately after soil heating, the concentrations of cations, SO₄ ^2-, CI^-, water-soluble P, and water-soluble organic carbon increased significantly. With plant growth, the total ionic concentration in the rhizosphere soil solution increased for heated soil, whereas it decreased for unheated soil. The increase of the concentrations of cations and SO₄ ^2- in the rhizosphere of heated soil was appreciable, suggesting that the movement of cations such as Ca²⁺ and Mg²⁺ by mass flow was regulated by that of SO₄ ^2-. Moreover soil heating inhibited nitrification, resulting in the supply of N mainly in the form of NH₄ ⁺ within 10 mm from the root-accumulating compartment. As a result, the soil pH decreased in the rhizosphere of heated soil. The amount of nutrients absorbed by plants, on the other hand, did not change significantly by soil heating except for an increase of P uptake. The increase of P uptake could be explained not only by the immediate increase of the water-soluble P concentration but also by the dissolution of Ca-bound P and the hydrolysis of water-soluble organic P in the rhizosphere.     

铜胁迫对白茅根际和非根际土壤酶活性影响的研究

通过盆栽实验研究了重金属Cu递进胁迫对白茅根际和非根际土壤酶活性的影响。结果表明,随着Cu浓度的增加,根际和非根际土壤的pH值下降、土壤酸化,而电导率呈持续上升,但根际土壤的pH值持续高于非根际土壤且更接近于中性。在梯度浓度的重金属Cu胁迫下,根际和非根际蔗糖酶活性随Cu浓度增加均表现出先升后降的趋势,但根际土壤的蔗糖酶活性在Cu浓度为1000 mg kg-1时达到峰值,而非根际土壤则在Cu浓度为500 mg kg-1时已到达峰值。白茅根际和非根际土壤中磷酸酶、脲酶和过氧化氢酶活性受Cu离子的影响均表现出持续下降的趋势,但各酶受抑制率各不相同。对梯度浓度Cu胁迫下的白茅根际和非根际土壤酶活性而言,四种酶在根际土壤中的活性普遍高于非根际土壤,且Cu2+对根际酶活性的抑制率也大于非根际土壤酶。对重金属单Cu污染敏感的土壤酶类依次为磷酸酶>蔗糖酶>脲酶>过氧化氢酶,其中磷酸酶可作为检测污染土壤的指示酶。     

Phenotypic structure of Pseudomonas populations is altered under elevated pCO2 in the rhizosphere of perennial grasses

The increasing atmospheric CO₂ content (pCO₂) is likely to modify the ecosystem functioning including rhizosphere bacteria that are directly dependent on rhizodeposition. This may include alteration of Pseudomonas populations that display phenotypic traits in relation with plant fitness. In the present study, 1228 Pseudomonas strains were isolated from the non-rhizosphere soil, rhizosphere soil and root fractions of perennial grassland systems: Lolium perenne and Molinia coerulea. Both plants were grown under ambient (36 Pa) and elevated (60 Pa) pCO₂ in the Swiss Free Air CO₂ Enrichment (FACE) system. Pseudomonas spp. were tested for their ability to produce auxin, siderophores and hydrogen cyanide, and to dissimilate nitrate. No effect of root proximity and elevated pCO₂ was observed on the proportions of auxin producers. For L. perenne and M. coerulea, siderophore and hydrogen cyanide Pseudomonas producers were stimulated in the root fraction. In contrast lower frequencies of nitrate reducers were observed in the root fraction compared to non-rhizosphere soil. The frequencies of siderophore producers and nitrate dissimilating strains were higher, and those of hydrogen cyanide producers lower, under elevated pCO₂ for L. perenne. This alteration of the phenotypic structure of Pseudomonas guild in the root fraction is discussed in relation with the physico-biochemical modifications of the rhizosphere condition via rhizodeposition and environmental changes occurring under elevated pCO₂.     

Phosphorus Speciation and Nutrient Stoichiometry in the Soil-Plant System During Primary Ecological Restoration of Copper Mine Tailings

The effects of plant vegetation on phosphorus(P) speciation, pH, total carbon concentration, total nitrogen concentration, and alkaline phosphatase activities were investigated to explore the P uptake strategy of plants in low-P soil and to determine the nutrient stoichiometric ratio changes in the rhizosphere of plants(Imperata cylindrica, Miscanthus floridulus, Zoysia sinica, Artemisia lavandulaefolia, Indigofera pseudotinctoria, and Conyza canadensis) which had grown for approximately 15 years in copper mine tailings, East China. The results showed that the average pH values in the rhizosphere decreased by 0.06–1.37 compared with those in the non-rhizosphere. The alkaline phosphatase activities of the rhizosphere were significantly higher than those in the non-rhizosphere.The mean concentrations of aluminum(Al)-and iron(Fe)-bound P and Ca_2-P(CaHPO_4) in the rhizosphere of all plants were 5.4% to 87.7%, 49.2% to 214.2%, and 86.6% to 147.6% higher than those in the non-rhizosphere, respectively. Except for Ca_8-P(Ca_8H_2(PO_4)_6)and Ca_(10)-P(Ca_(10)(PO_4)_6(OH)_2) in the rhizosphere, all kinds of inorganic P forms were negatively correlated with pH. Significant correlation was also observed among the concentrations of dominant forms of inorganic P, C, and N and alkaline phosphatase activities in the rhizosphere. Among the studied species, I. pseudotinctoria showed the most significant effect on enhancing soil available P concentration. The stoichiometric ratios of C:P and N:P were apparently higher in the rhizosphere than the non-rhizosphere, whereas these ratios were far below the ratios commonly observed in Chinese soils. These results indicated that the plant growth effectively affected P fractions possibly by changing pH, C and N concentrations, and alkaline phosphatase activity, in the rhizosphere in copper mine tailings.