淋洗与植物作用耦合对盐渍化土壤的改良效应

以甘肃秦王川引大灌区盐渍化土壤为背景,以当地5种耐盐植物为材料,采用根袋法盆栽试验动态研究了淋洗结合植物种植对盐渍化土壤改良的效应。结果表明:与种前相比,单纯的淋洗作用对土壤pH值影响不大,而淋洗结合植物种植明显降低了土壤pH值,且根际土壤pH值小于非根际土壤的,5种耐盐植物中霸王根际土壤pH值降低幅度最大,达0.6个单位。K+、Ca2+、Na+、Mg2+、Cl-和SO2-4在5种植物根际土壤中均有不同程度的富集,富集程度因物种的不同而不同,随培养时间的延长而呈波动状态。5种供试植物和对照组土壤中的6种主要的可溶性盐分离子随淋洗次数和培养时间的延长呈下降趋势。在培养120d后,单纯淋洗的土壤中K+、Ca2+、Na+、Mg2+、Cl-和SO2-4的含量相比种前平均分别降低了33.3%、26.1%、35.6%、32.5%、35.5%和36.3%,植物吸收带走的上述各离子的含量平均分别占种前的46.2%、8.1%、30.2%、7.2%和21.6%,其中霸王吸收带走的盐分离子最多,而淋洗结合种植植物的土壤中上述各离子的含量与种前相比平均分别降低了67.25%、63.73%、83.8%、67.5%、81.55%和78.46%,由此可见,淋洗结合植物种植的脱盐效果优于单纯淋洗,且土壤中主要的盐分离子Na+、Cl-和SO2-4的含量降低幅度最大,通过计算得出,在Cl-、SO2-4和Na+减少的总量中还有37.73%的Na+、38.22%的Cl-和35.14%的SO2-4的减少量是由植物根系的物理化学作用机制引起的。     

不同耐盐植物根际土壤盐分的动态变化

以甘肃秦王川引大灌区盐渍化土壤为研究背景,用盆栽根袋法对4种耐盐植物根际和非根际土壤pH和盐分离子的动态变化进行了分析比较。结果表明:4种待测植物随着培养时间的延长土壤pH和EC值呈降低趋势。新疆大叶(Medicago Sativa L.cv.Xinjiangdaye)、向日葵(Helianthus annuus)和霸王(Zygophyllum xanthoxylum)生长90 d后根际土壤pH明显低于非根际,而裸麦(Hordeum vulgare var. vulgare)根际较非根际pH差异不大。霸王和新疆大叶根际土壤EC值较非根际高,而裸麦和向日葵的根际与非根际差异不大。4种供试植物根际K⁺均出现亏缺,Ca²⁺、Na⁺、Mg²⁺、SO^2-₄和Cl^-在新疆大叶、霸王和向日葵3种植物根际均出现富集,对于裸麦:Ca²⁺、Mg²⁺和SO^2-₄ 3种离子在植物根际富集,而Cl^-和Na⁺在根际亏缺。随着待测植物培养时间的增加Na⁺/K⁺、Na⁺/Ca²⁺和Na⁺/Mg²⁺ 这3个比值呈降低趋势,说明Na⁺相对于K⁺、Ca²⁺和Mg²⁺的含量降低,生物措施对Na⁺的移除效果较显著。     

Soil solution chemistry in the rhizosphere of roots of sessile oak (Quercus petraea) as influenced by lime

This study describes the soil solution chemistry in the rhizosphere of fine roots of sessile oak ( Quercus petraea (M.) Liebl.) grown in rhizotrons. A control was compared with soils treated with an equivalent CaCO₃ of 1.4 t ha^-1 CaO. Solution samples were extracted from the B-horizon using micro suction cups with a suction of _∼40 kPa. Two series of experiments were carried out: one irrigated with rain water (age of seedling 2 to 4 months) and one irrigated with demineralized water (age of seedlings 1.5 to 2 months). Half of the sampling points were choosen close to the roots and half in the bulk soil. In both experiments there was generally no rhizospheric gradient after liming. In contrast, in the control, depletion in the rhizosphere occurred for most of the ions studied (Mg, Ca, Al, K, NO₃ ^-, NH₄ ⁺, Cl^-) in the demineralized water experiment, but this was different when rainwater was used. The latter effect is probably due to the higher solution concentrations in the rainwater experiment but could also be a result of root damage due to low Ca/Al ratios in the rhizosphere solution. It was concluded, that liming improved the chemical composition in the rhizosphere soil solution by increasing overall solute concentration to levels enabling sufficient and easier nutrient uptake by roots. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of nitrogen form and phosphorus source on the growth,nutrient uptake and rhizosphere soil property of Camellia sinensis L.

The effects of nitrogen form and phosphorus source on the growth, nutrient uptake and rhizosphere soil property of tea (Camellia sinensis L.) were investigated in a pot experiment. The experiment was performed with a compartmental cropping device, which enables the collection of rhizosphere soil at defined distances from the root of tea plant. Nitrogen was supplied as nitrate or ammonium in combination with soluble phosphorus as Ca(H₂PO₄)₂ or insoluble P as rock phosphate. The leaf dry matter production of tea was significantly greater in the treatments with NH₄ ⁺ than NO₃ ^-, whereas dry matter production of root and stem was not significantly affected. Addition of phosphorus as either source did not influence the dry matter production. The concentrations of K in root, Mg and Ca in both the shoot and root supplied with NO₃ ^- were significantly higher than in NH₄ ⁺ and influence of P sources was minor. On the contrary, Al and Mn concentrations were significantly larger in NH₄ ^--fed plants which could be attributed to remarkably increased availability of Al and Mn caused by acidification of the rhizosphere soil (the first 1-mm soil section from the root surface) with NH₄–N nutrition. The concentration of N in shoot was also significantly higher in NH₄- than in NO₃-fed plants, indicating higher use efficiency of NH₄–N. Whatever the phosphate source, rhizosphere pH declined in ammonium compared to in nitrate treatment. The pH decrease was much larger when no P or soluble P were applied and reached 0.85–1.30 units which extended to 3–5 mm away from the root surface. Exchangeable acidity, content of exchangeable Al and Mn were also considerably higher in the rhizosphere soils of NH₄ ⁺ fed tea plants. Significant amounts of P dissolved from rock phosphate accumulated in rhizosphere of NH₄ ⁺, not NO₃ ^-, suggesting that the dissolution of rock phosphate was induced by the proton excreted by tea root fed with ammonium. With soluble P addition, shoot and root P concentrations were greater in NH₄ ⁺ than in NO₃ ^- treatment and it appeared that this difference could not be sufficiently explained by the available P content in soil which was only slightly higher in NH₄ ⁺ treatment. With rock phosphate addition, the shoot and root P concentrations were hardly affected by nitrogen form, although the available P content was much higher and accumulated in the rhizosphere soil supplied with ammonium. The reason for this was discussed with regard to the inter-relationship of Al with P uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of litter incorporation and nitrogen fertilization on the contents of extractable aluminium in the rhizosphere soil of tea plant (Camallia sinensis (L.) O. Kuntze)

The effects of litter incorporation and nitrogen application on the properties of rhizosphere and bulk soils of tea plants (Camellia sinensis (L.) O. Kuntze) were examined in a pot experiment. Total of 8 treatments included four levels of tea litter additions at 0, 4.9, 9.8, and 24.5 g kg^–1 in combination with two N levels (154.6 mg kg^–1 and without). After 18 months of growth the rhizosphere soil was collected by removing the soil adhering to plant roots and other soil was referred to as bulk soil. The dry matter productions of tea plants were significantly increased by N fertilization and litter incorporation. The effect of litter was time-depending and significantly decreased the content of exchangeable Al (Al_ex, by 1 mol L^–1 KCl) and Al saturation at 9 months after litter incorporation whereas soil pH was not affected, although the litter contained high Al content. After 18 months, the contents of extractable Al by dilute CaCl₂, CuCl₂ + KCl, NH₄OAC, ammonium oxalate and sodium citrate (Al_CaCl2, Al_Cu/KCl, Al_NH4OAC, Al_Oxal, and Al_Cit respectively) and Al_ex, were not affected by litter application, except that of Al_CaCl2 in the rhizosphere soil which was decreased following litter additions. Nitrogen fertilization with NH₄ ⁺ (urea and (NH₄)₂SO₄) significantly reduced soil pH, the contents of exchangeable Ca, K, Mg and base saturation while raised extractable Al levels (Al_CaCl2, Al_Cu/KCl, Al_NH4OAC, and Al_ex). In the rhizosphere soils exchangeable K accumulated in all treatments while exchangeable Ca and Mg depleted in treatments without litter application. The depletions of Ca and Mg were no longer observed following litter incorporation. This change of distribution gradients in rhizosphere was possibly due to the increase of nutrient supplies from litter decomposition and/or preferable root growth in soil microsites rich in organic matter. Lower pH and higher extractable Al (Al_CaCl2, Al_ex, and Al_NH4OAC) in the rhizosphere soils, regardless of N and litter treatments, were distinct and consistent in all treatments. Such enrichments of extractable Al in the rhizosphere soil might be of importance for tea plants capable of taking up large amounts of Al.     

Depletion of Selenium in Soil Solution due to its Enhanced Sorption in the Rhizosphere of Soybean

The effect of plant roots on selenium (Se) mobility in soil was studied by a large-scale pot experiment in order to understand the environmental behavior of Se in agricultural soils under plant growth conditions. Soybean plants (Glycine max (L.) Merrill) were grown in a greenhouse for 84 d. The concentrations of Se and major elements (K, Ca, Mg, Na, and Al) in the soil solutions and in the plants were measured at different growth periods. Concentrations of Se and major cations in soil solution decreased as the soybean plants grew, while the concentrations of Al increased. It was assumed that the soybean roots released H⁺ with the uptake of cations; consequently, due to the acidification of the rhizosphere, Al³⁺ was released starting from the soil solid phase. The decreased Se concentration in the soil solution should be due to the enhancement of Se sorption onto the soil solid phase. The increase of Se sorption level in the rhizosphere was examined in a small-scale pot experiment. The soil–soil solution distribution coefficient of Se (K _d-Se) was observed as an index of Se sorption level. K _d-Se clearly increased in the rhizosphere soil after cultivation. The effects of pH and Al³⁺ in the rhizosphere on Se sorption were assessed by K _d-Se measurements at different levels of HCl and AlCl₃. In this third experiment, a decrease in pH increased K _d-Se values, but no specific effect was observed on Se sorption due to increased Al³⁺. These results show that the Se mobility in agricultural soil could be decreased by plant roots under plant growth conditions due to enhanced Se sorption in the rhizosphere.     

Mechanisms of Aluminum Tolerance in Wheat : An Investigation of Genotypic Differences in Rhizosphere pH, K, and H Transport, and Root-Cell Membrane Potentials

Control of rhizosphere pH and exclusion of Al by the plasma membrane have been hypothesized as possible mechanisms for Al tolerance. To test primarily the rhizosphere pH hypothesis, wheat cultivars (Triticum aestivum L. `Atlas 66' and `Scout'), which differ in Al tolerance, were grown in either complete nutrient solution, or 0.6 millimolar CaSO₄, with and without Al at pH 4.50. A microelectrode system was used to simultaneously measure rhizosphere pH, K⁺, and H⁺ fluxes, and membrane potentials (E_m) along the root at various distances from the root apex. In complete nutrient solution, the rhizosphere pH associated with mature root cells (measured 10-40 millimeters from the root apex) of Al-tolerant `Atlas 66' was slightly higher than that of the bulk solution, whereas roots of Al-sensitive `Scout' caused a very small decrease in the rhizosphere pH. In CaSO₄ solution, no significant differences in rhizosphere pH were found between wheat cultivars, while differential Al tolerance was still observed, indicating that the rhizosphere pH associated with mature root tissue is not directly involved in the mechanism(s) of differential Al tolerance. In Al-tolerant `Atlas 66', growth in a CaSO<sub>4</sub> solution with 5 micromolar Al (pH 4.50) had little effect on net K<sup>+</sup> influx, H<sup>+</sup> efflux, and root-cell membrane potential measured in cells of mature root tissue (from 10-40 mm back from apex). However, in Al-sensitive `Scout', Al treatment caused a dramatic inhibition of K⁺ influx and both a moderate reduction of H⁺ efflux and depolarization of the membrane potential. These results demonstrate that increased Al tolerance in wheat is associated with the increased ability of the tolerant plant to maintain normal ion fluxes and membrane potentials across the plasmalemma of root cells in the presence of Al.     

Occurrence and intensity of wild boar disturbances, effects on the physical and chemical soil properties of alpine grasslands

Background and aims

Physical and chemical soil properties determine local plant conditions and resources, affecting plants’ ability to respond to disturbances. In alpine grasslands, wild boar disturbances occur at different intensities, what may affect differently their soil properties. Alpine soils from five contrasted plant communities were explored within and outside disturbances, accounting for an overall and community scale effect. Additionally, we analysed the effect of disturbance intensity on soil NO₃ ^--N and NH₄ ⁺-N.

Methods

Soils were analyzed for physical (bulk density, moisture content and electrical conductivity), and chemical properties (pH, total N and C, oxidizable C, C:N ratio, available K, P, Ca²⁺, Na⁺ and Mg²⁺). Resin bags were used to compare the effect of the disturbance occurrence and intensity on soil NO₃ ^--N and NH₄ ⁺-N.

Results

Bulk density, total N and NO₃ ^--N concentration were significantly higher in disturbed areas, while soil moisture, C:N, NH₄ ⁺-N, Na⁺, Mg²⁺ and Ca²⁺ concentrations were significantly lower. However, low disturbance intensity reduced NO₃ ^--N and increased NH₄ ⁺-N concentrations.

Conclusions

Wild boar occurrence and intensity strongly alter physical and chemical conditions of alpine soils, increasing soil compaction, and altering the availability of N forms. These changes may affect most plant species, thus affecting the structure and dynamics of alpine plant communities.     

Influence of rhizosphere on the nutrient status of dwarf French beans

French bean seedlings grown on choline, ammoniacal and nitrate forms of nitrogen together with equivalent basal application of P as KH₂PO₄ were tested for nutrient uptake from the rhizosphere. Statistical tests on soil (rhizosphere and non-rhizosphere) and plant (root and shoot) revealed that with the exception of P, levels of all other estimated macro-(Na⁺, K⁺, Ca²⁺, Mg²⁺) and micro-nutrients (Fe²⁺, Mn²⁺, Zn²⁺) were significantly changed after 42 days growth as compared to 21 days growth period. The higher uptake into shoots of Na⁺, K⁺, Fe²⁺, Mn²⁺, Zn²⁺ and H₂PO₄ ⁻ and higher biomass accumulation in the rhizosphere were associated with lower rhizosphere pH. The uptake of Ca²⁺ and Mg²⁺ increased with higher rhizosphere pH. While ammoniacal and choline forms decreased rhizosphere pH and increased the P uptake, nitrate form reversed the trend showing significant inverse relationship between shoot phosphate and rhizosphere pH. Calcium and iron were associated with an inhibition of the translocation of P from root to shoot. However, no causal relationships could be established. Both shoot weight and shoot P content were closely associated with a number of rhizosphere soil parameters. The paper forms a part of the Ph. D thesis submitted by the first author to the University of Wales, 1977.     

Mobilization of aluminium in the rhizosphere soil solution of growing tree roots in an acidic soil

Chemical conditions in the rhizosphere in many respects are different from the bulk soil. Especially in acid forest soils aluminium chemistry at the soil root interface is of particular interest because of its importance for evaluating the risk of rhizotoxicity. In the present study we have used micro suction cups to collect soil solution from the rhizosphere of oak seedlings (Quercus robur L.) in high spatial resolution and capillary electrophoresis for the determination of major ions and Al³⁺. While the concentrations of nutrient cations, especially Ca²⁺ and Mg²⁺, decreased in the vicinity of growing roots the concentrations of Al³⁺ significantly increased. Al³⁺-ions were probably released when root-exuded protons were buffered by the soil. Their occurrence indicates, that the oak roots in our experiments had only limited capabilities to detoxify Al in their rhizosphere. The restriction of this effect to the very small soil compartment close to the roots suggests, that common soil analysis which neglect rhizosphere processes might greatly underestimate the in situ concentration of Al³⁺ near tree roots. Our experiments furthermore indicate, that also suberized roots have a significant influence on rhizosphere soil solution chemistry. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of aluminium on the peanut (Arachis hypogaea L.)/ Bradyrhizobium symbiosis

The effects of low activities of the monomeric Al species, Al³⁺, Al(OH)₂ ⁺ and Al(OH)²⁺, on the peanut/Bradyrhizobium symbiosis were examined in solution culture. In flowing solution culture, growth of the host plant was depressed at activities ≥5 μM. Neither shoot dry weight, root dry weight nor root length were inhibited by 3 μM Al, an activity which reduced nodule number by 70%. Low nodule number was compensated for, at this activity, by an increase in weight per nodule. In non-flowing solution culture of similar composition, survival of a streptomycin resistant mutant of Bradyrhizobium spp. NC92 in the bulk solution or in the rhizosphere of peanut roots was unaffected by 20 μM Al. The site of infection by Bradyrhizobium was examined by scanning electron microscopy. Lateral root axils of plants exposed to ≥2 μM Al did not display the rosette of multicellular root hairs which is characteristic in normal plants. The detrimental effects of Al on nodulation appear to be related to structural changes at the site of infection which are observed at Al activities too low to cause any depression in growth of the host plant, including root length, and at activities of Al which do not affect survival of the free-living Bradyrhizobium.     

杨树人工林生态系统降水再分配及主要离子特征

大气降水是森林生态系统养分输入的主要途径之一,对养分的生物地球化学循环有着重要的意义。对13年生杨树人工林林外雨、树干流、林内雨和地表径流等水文过程中的养分特征进行了调查分析,旨在了解该生态系统的养分输入与输出规律,为杨树人工林可持续经营提供依据。结果表明,从2013年11月至2014年10月,杨树人工林生态系统林外雨量为1154.1 mm,树干流量仅占大气降水量的2.3%,15.4%的大气降水被杨树人工林的冠层截留;林内雨、树干流与大气降水量(林外雨)的动态变化规律相似。各类降水年加权平均pH值表现为林内雨林外雨树干流;各类降水的离子浓度动态变化规律基本一致,即在降水量较小的11月至次年1月份,各阴阳离子的浓度普遍较高,在降水量较大的2—9月份,阴阳离子浓度普遍较低。SO_4~(2-)-S和Ca~(2+)分别是各类降水中的主要阴离子和阳离子;整体上,树干流的离子浓度林内雨大气降水;林内雨是养分输入的主要形式,通过林内雨输入林地较多的养分离子是Ca~(2+)和K~+,分别为70.83 kg hm~(-2)a~(-1)和63.31 kg hm~(-2)a~(-1);地表径流和土壤渗漏是养分输出的主要形式,输出林地较多的离子是Cl~-和Ca~(2+),分别为196.47 kg hm~(-2)a~(-1)和123.09 kg hm~(-2)a~(-1),其次为SO_4~(2-)-S、Mg~(2+)、Na~+、K~+;NH_4~+-N和NO_3~--N的输出量不足输出离子总量的1%。所以,从水文过程看,杨树人工林生态系统无机氮(NH_4~+-N和NO_3~--N)和K~+表现为净积累,净积累量分别为10.9 kg hm~(-2)a~(-1)和56.4 kg hm~(-2)a~(-1),其他离子表现为净损失,其中Cl~-的净损失量达179.8 kg hm~(-2)a~(-1)左右,其他离子损失量50 kg hm~(-2)a~(-1)。     

Is the Ca:Al ratio superior to pH,Ca or Al concentrations of soils in accounting for the distribution of plants in deciduous forest?

The distributions of vascular plants in south Swedish deciduous forests were related to exchangeable (exc) and soil solution concentrations of H⁺ (pH), Ca, Al and the Ca:Al ratios within these fractions. Topsoils (0–5 cm) of 172 sites with a pH_KCl of 3.2–3.9 (corresponding to 3.7–4.4 in soil solution) were used. In the soil solution both total Al_t and quickly reacting Al_r were determined. Exchangeable concentrations were generally well related to plant distributions, the highest correlation coefficients usually being given by pH_KCl>Ca_exc>Al_exc.>(Ca:Al)_exc. The (Ca:Al)_exc ratio was clearly inferior. Out of the soil solution variables studied, Ca concentration, followed by pH, was best correlated with plant distributions, Al_t, Al_r, and the Ca:Al ratios having similar and lower coefficients. It is concluded that the use of Ca:Al ratios as a general measure of Al toxicity in controlling plant distributions is rather problematic. It seems difficult to apply evidence for Ca-Al interactions from solution culture experiments to field conditions when measured as exchangeable or soil solution concentrations of the soil.     

Spatial and temporal variation of soil solution chemistry and ion fluxes through the soil in a mature Norway Spruce (Picea abies (L.) Karst.) stand

In this study we investigated the spatial and temporal variation in soil solution chemistry and of water and ion fluxes through the soil in a forest ecosystem. Our aim was to evaluate the relevance of these variations for the accuracy of average areal soil solution concentrations and ion fluxes with seepage at 90 cm depth.Twenty spatially distinct subcompartments of approximately 1 m² were established within a mature stand of Norway spruce and ceramic suction lysimeters were installed at depths of 20, 35 and 90 cm. A tensiometer was placed close to each suction lysimeter, and one throughfall sampler was established for each subcompartment.Soil solution samples were analysed for major ions (H⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Mn²⁺, Fe³⁺, Al³⁺, Cl^-, NO ₃ ^- , SO ₄ ^2- . We calculated water fluxes for each subcompartment separately by a numeric simulation of the soil water flux close to the lysimeters. The ion fluxes at each lysimeter were calculated by multiplying the simulated water fluxes with the ion concentrations on a fortnightly base. Averaging these 20 independent ion fluxes gave the areal average flux and an estimate of its statistical accuracy. The spatial variation of ion concentrations in the soil solution was high with coefficients of variance ranging from 5% to 128%. Part of the spatial variation was related to stem distance. Temporal variation of the concentrations was less than spatial for most ions. The spatial variation of water and ion fluxes with seepage was also substantial; for example the fluxes of SO ₄ ^2- -S calculated for each subcompartment ranged from 21 to 119 kg ha^-1 yr^-1, with an arithmetic average of 47 kg ha^-1 yr^-1. For H₂O, Mg²⁺, Cl^-, and SO ₄ ^2- , the spatial heterogeneity of seepage fluxes was largely explained by the heterogeneity of throughfall fluxes. No such relationship was found for nitrogen.Despite using 20 replicates, the 95% confidence intervals of the average annual areal fluxes with seepage were found to be 20–30% for most ions.     

Equilibrium solution composition and exchange properties of disturbed and undisturbed soil samples from an acid forest soil

Microscalic heterogeneity of soil chemical properties caused by soil structure has been reported for several soils. We investigated exchange properties and soil solution composition of disturbed and undisturbed samples of an acid forest soil lacking visible structure. Cation concentrations in the soil solution resulting from two extraction procedures and two analytical methods were compared. The effective cation exchange capacity (CEC_e) of the undisturbed sample represented 56–69% of the bulk soil CEC_e. Base saturation of undisturbed samples equalled that of disturbed samples for EA, Bhs, and Bsh horizons, and was higher for the Bw horizon. Contradicting the results of other authors, soil pore solution obtained by percolating soil cores under conditions of low water tension offered more favourable conditions for plant roots when compared to the equilibrium soil solution of the bulk soil sample in all except the Bsh horizon. Ca²⁺/Al³⁺ molar ratios were higher and fractions of H⁺ + Al³⁺ on total cationic charge were lower in the soil pore solution. These results were obtained employing soil: solution ratios of about 1:0.5 during the extraction of soil pore solution, and by determination of free cations. Other authors used a water extraction with soil:solution ratios up to 1:2 and took total metal for ion concentrations. The combination of the latter extraction and analytical method in our study, too, led to unfavourable Ca²⁺/Al³⁺ ratios and high tractions of H⁺ + Al³⁺. The choice of analytical and extraction method are thus decisive for the valuation of the soil solution composition in view of plant nutrition.     

Microscale heterogeneity of acidity related stress-parameters in the soil solution of a forested cambic podzol

Acid related stress in soils might be caused by high concentrations of H⁺ and Al³⁺ in soil solution. Sampling of soil solution so far integrates over a relatively large soil volume, in the range of dm³. In order to study the microscale heterogeneity of acidity related stress-parameters the soil profile of a podzolic cambisol was covered by a 10×6 matrix of micro suction cups with a grid distance of 2 cm. The soil solution collected at 10 sampling events was analyzed for free cations and anions by capillary electrophoresis and for total metal content by a micro injection technique on ICP-OES. pH and UV absorption were also measured.There was a general trend of increasing pH and decreasing UV absorption with increasing soil depth, however without a clear correlation of concentration isolines to soil horizon borders. The latter was also true for total Al (Al_tot) and Al³⁺, with the exception of the soil horizon border A_he/B_h,which was very well reflected by Al³⁺ and also by the fraction of bound Al. In the A_he horizon less than 30%, in deeper mineral soil less than 50% of Al_tot were present as free Al³⁺. This fact is critical when calculating Ca/Al ratios as a stress parameter, because total metal content measured by ICP clearly overestimates the risk of root damage, even in deeper horizons of acid forest soils, where organic complexation of Al is of minor importance. The heterogeneity of soil solution chemistry and toxicity parameters on the cm-scale was found to be significant, for example with gradients of more than 0,5 pH-units within 2 cm. Because plant roots also experience soil on a microscale, high resolution investigations of soil solution chemistry offer a new approach for looking at the chemical environment relevant for root growth and plant nutrition.     

Nutrient composition of Douglas-fir rhizosphere and bulk soil solutions

Rhizosphere soil solution is the direct source of nutrients for plant uptake. The nutrient composition of rhizosphere soil solution can be very different from that of bulk soil solution due to root exudation, nutrient uptake and rhizosphere microorganism activity. This study examined the nutrient composition of Douglas-fir rhizosphere soil solution in two soils belonging to the Nisqually and Pitcher soil series and compared rhizosphere solution with that of bulk soil solution. Fertilized and unfertilized Nisqually soils were also compared. Soil solutions were collected using centrifugation. Results indicated that nutrient concentrations in the rhizosphere solutions were typically higher than that of bulk soil solutions when no fertilizer was applied. Differences in the concentrations of nutrients between the rhizosphere and bulk soil solutions were masked by the addition of fertilizers. Rhizosphere solution pH also appeared to be affected by the concentration of NH₄ and NO₃ in the solution. With a higher concentration of NH₄ relative to NO₃ in the rhizosphere soil solution, the solution pH of the rhizosphere was lower than that of the bulk soil, but with a lower concentration of NH₄ relative to NO₃, the solution pH of the rhizosphere was higher than that of the bulk soil solution.     

Effects of limestone and gypsum application to a Malaysian ultisol on soil solution composition and yields of maize and groundnut

A field experiment was conducted on an Ultisol in Malaysia to assess changes in soil solution composition and their effects on maize and groundnut yields, resulting from limestone and gypsum application. The results showed that soil solution Ca in the lime treatment remained mainly in the zone of incorporation, but in the gypsum treatment some Ca moved into 15–30 cm zone. Al³⁺ and AlSO₄ ⁺ were dominant Al species in the soil solution of nil treatment. Liming decreased Al³⁺ and AlSO₄ ⁺, but increased hydroxy-Al monomer activities. However, gypsum application resulted in an increase of AlSO₄ ⁺ activity and in a decrease of Al³⁺ activity. Relative maize and groundnut yields were negatively correlated with Al³⁺, Al(OH)²⁺ and Al_sum activities. Likewise, relative yields were negatively correlated with Al concentration and the Al concentration ratio and positively correlated with soil solution Mg concentration and Ca/Al ratio.     

盐分胁迫对啤酒大麦幼苗生长、离子平衡和根际pH变化的影响

盐分胁迫不仅影响植物的生长,而且会影响植物根际微域环境。根际pH的改变对土壤养分的有效性和微生物群落组成的变化有重要影响。为了探究啤酒大麦幼苗对不同类型盐分胁迫的生理生态响应机制和根际pH变化影响的生理机制,采用水培法,通过不同类型盐分(对照、混合Na盐、混合Cl盐和NaCl)胁迫处理啤酒大麦幼苗,对其生长、离子平衡和根际pH变化进行了研究。结果表明,1)在3种不同类型盐分胁迫下,啤酒大麦幼苗地上部干重、含水量均有所降低,而根冠比增加,尤其在NaCl胁迫下啤酒大麦幼苗地上部干重较对照显著降低了17.88%,而根干重和根冠比则分别增加了19.12%和43.86%。不同类型盐分胁迫抑制了啤酒大麦幼苗根长的生长,尤其在混合Na盐胁迫下根长降低明显(P0.05),但促进了根表面积和根体积的增加,尤其在混合Cl盐胁迫下,根表面积和根体积分别增加了41.76%和84.38%。2)不同类型盐分胁迫下啤酒大麦幼苗地上部离子平衡发生改变,在混合Na盐和NaCl胁迫下啤酒大麦幼苗主要吸收Na~+,地上部K~+/Na~+、Ca~(2+)/Na~+和Mg~(2+)/Na~+显著降低;混合Cl盐和NaCl胁迫下则过量吸收Cl~-,抑制了H_2PO_4~-、NO_3~-和SO_4~(2-)的吸收。3)在混合Na盐、混合Cl盐和NaCl盐分胁迫下,啤酒大麦幼苗对阴离子的吸收总量高于对阳离子的吸收总量,离子平衡计算结果表明根际呈碱化现象,与原位显色结果一致,且在混合Cl盐胁迫下根际碱化程度最大。     

Atmospheric deposition, mass balances, and processes regulating streamwater solute concentrations in mixed-conifer catchments of the Sierra Nevada, California

Solute concentrations in atmospheric deposition and stream water were measuredfrom 1984 through 1993 to determine the fate and mobility of solutes in twogauged mixed-conifer catchments (Tharp's and Log creeks) located in theSierra Nevada, California. The two catchments contain mature forest standsdominated by Abies concolor (white fir), Sequoiadendron giganteum (giantsequoia), Abies magnifica (red fir) and Pinus lambertiana (sugar pine).Ammonium, Cl^-, Ca²⁺ and NO^- ₃were highest in concentration of the solutes measured in wet deposition;bulk deposition was highest in SO^{2- 4}, NH⁺ ₄,Cl^- and H⁺. Net retention ofH⁺, NO₃ ^-, NH₄ ⁺,SO₄ ^2- and Cl^- occurred in both catchments.Discharge was dominated by spring snowmelt with the largest export yieldsfor acid neutralizing capacity (ANC), SiO₂, andCa²⁺. Export yields of H⁺,NO₃ ^-, NH₄ ⁺ and PO₄ ^3-were relatively small (0.5 kg ha^-1 y^-1).Discharge-concentration relationships for ANC, SiO₂,Na⁺, K⁺, Ca²⁺ andMg²⁺ were inverse and their concentrations in stream waterwere primarily influenced by discharge and annual differences in the relativecontributions of snowmelt and groundwater. The mobility of these solutes iscontrolled by the rates of mineral weathering and ion exchange. The positiverelationship of SO₄ ^2- concentration with increasingdischarge suggests that atmospherically deposited SO₄ ^2-is temporarily stored and that its release is controlled by the extent of soilwater flushing.