首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 109 毫秒
1.
The aim of the present review is to define the various origins of root-mediated changes of pH in the rhizosphere, i.e., the volume of soil around roots that is influenced by root activities. Root-mediated pH changes are of major relevance in an ecological perspective as soil pH is a critical parameter that influences the bioavailability of many nutrients and toxic elements and the physiology of the roots and rhizosphere microorganisms. A major process that contributes root-induced pH changes in the rhizosphere is the release of charges carried by H+ or OH to compensate for an unbalanced cation–anion uptake at the soil–root interface. In addition to the ions taken up by the plant, all the ions crossing the plasma membrane of root cells (e.g., organic anions exuded by plant roots) should be taken into account, since they all need to be balanced by an exchange of charges, i.e., by a release of either H+ or OH. Although poorly documented, root exudation and respiration can contribute some proportion of rhizosphere pH decrease as a result of a build-up of the CO2 concentration. This will form carbonic acid in the rhizosphere that may dissociate in neutral to alkaline soils, and result in some pH decrease. Ultimately, plant roots and associated microorganisms can also alter rhizosphere pH via redox-coupled reactions. These various processes involved in root-mediated pH changes in the rhizosphere also depend on environmental constraints, especially nutritional constraints to which plants can respond. This is briefly addressed, with a special emphasis on the response of plant roots to deficiencies of P and Fe and to Al toxicity. Finally, soil pH itself and pH buffering capacity also have a dramatic influence on root-mediated pH changes.  相似文献   

2.
落叶松根限土壤磷的有效性研究   总被引:29,自引:7,他引:22  
野外用剥落法采集落叶松(Larix gmelini)根际土与非根际土,分析P浓度的变化,结果表明,落叶松根际土与非根际土全P浓度无明显差异,但根际土有效P却明显高于非根际土,12年生时根限土有效P增加12.6%,40年生时增加23.4%,表明落叶松根限对土壤中的P具有活化作用,落叶松根限土无机P各组分与非根际土亦有差异,表现出根际土O-P低于非要际土,Al-P,Fe-P,Ca-P和NH4Cl-P则高于非根际土的趋势,落叶松根限土的pH低于非根际土,但落叶松根限并未发生明显酸化,落叶松要际有效P与pH变化相关不显著。  相似文献   

3.
The effects of liming and inoculation with the arbuscular mycorrhizal fungus, Glomus intraradices Schenck and Smith on the uptake of phosphate (P) by maize (Zea mays L.) and soybean (Glycine max [L.] Merr.) and on depletion of inorganic phosphate fractions in rhizosphere soil (Al-P, Fe-P, and Ca-P) were studied in flat plastic containers using two acid soils, an Oxisol and an Ultisol, from Indonesia. The bulk soil pH was adjusted in both soils to 4.7, 5.6, and 6.4 by liming with different amounts of CaCO3.In both soils, liming increased shoot dry weight, total root length, and mycorrhizal colonization of roots in the two plant species. Mycorrhizal inoculation significantly increased root dry weight in some cases, but much more markedly increased shoot dry weight and P concentration in shoot and roots, and also the calculated P uptake per unit root length. In the rhizosphere soil of mycorrhizal and non-mycorrhizal plants, the depletion of Al-P, Fe-P, and Ca-P depended in some cases on the soil pH. At all pH levels, the extent of P depletion in the rhizosphere soil was greater in mycorrhizal than in non-mycorrhizal plants. Despite these quantitative differences in exploitation of soil P, mycorrhizal roots used the same inorganic P sources as non-mycorrhizal roots. These results do not suggest that mycorrhizal roots have specific properties for P solubilization. Rather, the efficient P uptake from soil solution by the roots determines the effectiveness of the use of the different soil P sources. The results indicate also that both liming and mycorrhizal colonization are important for enhancing P uptake and plant growth in tropical acid soils.  相似文献   

4.
Changes of metal concentration that occur in the rhizosphere may arise from several processes including variation in the concentration of complexing ligands, pH or redox potential that can be influenced by the Fe status of the plant. The aim of this study was to assess for both acidic and calcareous, Cu-contaminated soils how Cu concentration in plants and in the rhizosphere was affected by the Fe status of a strategy I plant species. The change of soil solution pH, total solution Cu concentration and soil redox potential was monitored for 8 days in the rhizosphere of tomato (Lycopersicon esculentum L.) in response to contrasting Fe supply. The concentration of Cu in roots was enhanced under Fe deficiency in the acidic soils. Shoot Cu however did not vary with the Fe status of the plant. The plant Fe status had little effect on rhizosphere pH, redox potential or Cu concentration in solution in either acidic or calcareous soils. Marked differences in pH and solution Cu concentration were observed between rhizosphere and uncropped soils. Roots induced an increase in pH of acidic soils and a decrease in solution Cu concentration in all soils. The decrease in solution Cu concentration in acidic soils may be explained by the increase in rhizosphere pH. The proposed device provided new data on the fate of Cu in the rhizosphere and showed a positive correlation for the four soils considered together between the total Cu concentration in soil solution and root Cu concentration.  相似文献   

5.
Seedlings of two cultivars of wheat (Triticum aestivum L.) differing in tolerance to aluminium (Al) were grown using a split-root sand/soil culture technique. Each culture tube was divided horizontally into a surface (0–150 mm) compartment and a subsurface (150–250 mm) compartment separated by a root-permeable paraffin wax barrier. Thus phosphorus (P) supplied to surface roots could not percolate or diffuse into the soil in the subsurface compartment. The soil in the subsurface compartment was divided into ‘rhizosphere’ and ‘non-rhizosphere’ zones using a porous (5 μm) membrane. Root growth of both cultivars into the subsurface zone was enhanced by increased P supply to surface roots, but did not conform to known relationships between root growth and soil pH, extractable-Al, or pH, Al or P concentrations in soil solution. Concentrations of Al in soil solution in the rhizosphere were greater than those in solution in the bulk soil. Concentrations of Al reactive with pyrocatechol violet (30s-RRAI) in the rhizosphere soil solution were generally greater than those in non-rhizosphere soil. With the Al-sensitive cultivar, root dry weight and length increased as concentrations of RRAl in the rhizosphere soil solution increased. Increased concentrations of Al in rhizosphere soil solutions were not related to the presence of organic ligands in solution. The effect of P in promoting root penetration into the acidic subsurface stratum was not related to differential attainment of maturity by the plant shoots, but appeared to be related to the effect of P in enhancing the rate of root growth. Thus, suboptimal supply of P to the surface roots of a plant, even at levels sufficient to preclude development of nutritional (P) stress symptoms, may seriously reduce tolerance to Al, and hence diminish the ability of roots to penetrate into acidic subsoils.  相似文献   

6.
Root exudates as mediators of mineral acquisition in low-nutrient environments   总被引:39,自引:3,他引:36  
Plant developmental processes are controlled by internal signals that depend on the adequate supply of mineral nutrients by soil to roots. Thus, the availability of nutrient elements can be a major constraint to plant growth in many environments of the world, especially the tropics where soils are extremely low in nutrients. Plants take up most mineral nutrients through the rhizosphere where micro-organisms interact with plant products in root exudates. Plant root exudates consist of a complex mixture of organic acid anions, phytosiderophores, sugars, vitamins, amino acids, purines, nucleosides, inorganic ions (e.g. HCO3 , OH, H+), gaseous molecules (CO2, H2), enzymes and root border cells which have major direct or indirect effects on the acquisition of mineral nutrients required for plant growth. Phenolics and aldonic acids exuded directly by roots of N2-fixing legumes serve as major signals to Rhizobiaceae bacteria which form root nodules where N2 is reduced to ammonia. Some of the same compounds affect development of mycorrhizal fungi that are crucial for phosphate uptake. Plants growing in low-nutrient environments also employ root exudates in ways other than as symbiotic signals to soil microbes involved in nutrient procurement. Extracellular enzymes release P from organic compounds, and several types of molecules increase iron availability through chelation. Organic acids from root exudates can solubilize unavailable soil Ca, Fe and Al phosphates. Plants growing on nitrate generally maintain electronic neutrality by releasing an excess of anions, including hydroxyl ions. Legumes, which can grow well without nitrate through the benefits of N2 reduction in the root nodules, must release a net excess of protons. These protons can markedly lower rhizosphere pH and decrease the availability of some mineral nutrients as well as the effective functioning of some soil bacteria, such as the rhizobial bacteria themselves. Thus, environments which are naturally very acidic can pose a challenge to nutrient acquisition by plant roots, and threaten the survival of many beneficial microbes including the roots themselves. A few plants such as Rooibos tea (Aspalathus linearis L.) actively modify their rhizosphere pH by extruding OH and HCO3 to facilitate growth in low pH soils (pH 3 – 5). Our current understanding of how plants use root exudates to modify rhizosphere pH and the potential benefits associated with such processes are assessed in this review.  相似文献   

7.
Zoysa  A.K.N.  Loganathan  P.  Hedley  M.J. 《Plant and Soil》1997,190(2):253-265
Rhizosphere studies on tree crops have been hampered by the lack of a satisfactory method of sampling soils at various distances in the rhizosphere. A modified root study container (RSC) technique developed for annual crops, grasses and legumes was used to study the mechanisms by which camellia plants (Camellia japonica L.) utilise soil P in the glasshouse and field. Plants belonging to the Camellia family (e.g. tea) have the ability to utilise P from relatively unavailable native P sources and for this reason camellia plants were selected for this study.In the glasshouse trial, the RSCs were filled with a Recent soil, treated with P fertilisers; North Carolina phosphate rock (NCPR), diammonium phosphate (DAP), mono calcium phosphate (MCP) and single superphosphate (SSP) at 200 g P g-1 soil. A planar mat of roots was physically separated by a 24 m polyester mesh and the soil on the other side of this mesh was cut into thin slices parallel to the rhizoplane and analysed for pH, and different forms of P (organic, Po and inorganic, Pi) to understand P depletion at different distances from camellia roots. In the field trial this technique was modified and used to study the rhizosphere processes in mature camellia trees fertilised with only SSP and NCPR.In both field and glasshouse trials, all P fertilisers increased all the bulk soil P fractions except NaOH-Po over unfertilised soil with the greatest increases being in the H2SO4-Pi fraction in the NCPR treatment and NaOH-Pi in the SSP treatment. Resin-P, NaOH-Pi and H2SO4-Pi were significantly lower in the rhizosphere soil compared to the bulk soil whereas NaOH-Po was higher in the rhizosphere soil than in the bulk soil. Plant and microbial P uptake were thought to be the major causes for the low resin-P rather than P fixation by Fe and Al because the NaOH-Pi fraction which is a measure of Fe-P and Al-P, also decreased in the rhizosphere soil. The rhizo-deposition of NaOH-Po suggests that labile inorganic P was immobilized by rhizosphere microbes which were believed to have multiplied as a result of carbon exudates from the roots. A marked reduction in pH (about 0.2–0.4 in the glasshouse and 0.2 in the field trial) was observed near the rhizoplane compared to that in the bulk soil in all treatments. The pH near the rhizoplane as well as in the bulk soil was highest for NCPR treated soil. The increase in pH in the NCPR treatment over the control was consistent with the number of protons consumed during the dissolution of NCPR. In both trials, the dissolution of NCPR in the rhizosphere was higher than in the bulk soil due to lower pH and plant uptake of solution P in the rhizosphere. The RSC technique proved to be a viable aid to study the rhizosphere processes in tree crops.  相似文献   

8.
Plant-soil interactions result in a special rhizosphere soil chemistry, differing from that of the bulk soil found only a few mm from the root. The aim of this study was to investigate adaptation mechanisms of herbs growing in acid soils through studying their rhizosphere chemistry in a greenhouse experiment and in a field study. Ten herbs were grown in acid soil (pH 4.2 in the soil solution) in the greenhouse. The concentrations of NO3 -, SO4 2-, phosphates, Ca2+, Mg2+, Mn2+, K+, Na+, NH4 + and pH were analysed in soil solutions obtained by centrifugation. The general pattern found was a depletion of nutrients in the rhizosphere compared with their concentrations in the bulk soil. The pH increase (up to 0.7 units) in the rhizosphere soil appeared to be caused by plant uptake of NO3 - (r2=0.88). The ion concentrations in the soil solution of the rhizosphere were dependent on plant species and biomass increase. Although species with a larger biomass and higher growth rates showed a higher degree of ion depletion (except for Na+, SO4 2-) in the rhizosphere, there were also species specific responses. A field study of five herbs at five oak forest sites in Southern Sweden (Scania) was also carried out. In addition to the soil solution concentrations, the loss on ignition (LOI) and the concentrations of 0.1 M BaCl2 extractable K+, Mg2+, Mn2+, Ca2+, and Al ions were measured. The amount of soil solution Al was determined as free ionic (quickly reacting) Al. For all species and sites, the LOI and the concentrations of exchangeable cations were higher in the rhizosphere than in the bulk soil, apparently due to the roots preferably growing at organic-rich microsites. The concentrations of the ions as measured in the centrifuged soil solution, were either higher in the rhizosphere than in the bulk soil or were the same in both, except for NO3 - and quickly reacting Al. The lower concentrations of quickly reacting Al in the rhizosphere, compared with the bulk soil could indicate the uptake of Al by the plant or the exudation of complexing substances. The pH differences were only small and mostly non-significant. Plant-soil interactions and the ability of plants to utilise heterogeneity of the soil appear to be more important for plant growth in acid soils than recognised heretofore. Rhizosphere studies provide an important means of understanding plant strategies in acid soils. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

9.
Application of organic manure (OM) and crop residues in agricultural soils can potentially influence positively or negatively the availability of soil phosphorus (P) through soil mineralization, sorption, or desorption of soil-bound P. Traditionally, the addition of OM can reduce the capacity of the soil colloids to adsorb P, thus increasing the release of P in soil solution, but also added OM can increase the adsorption site and increase the fixation or sorption of P to soil colloids, thus reducing the availability of P in soil solution and loss to the environment. The highly weathered tropical soils (HWTS) are susceptible to P insufficiency because HWTS have high P adsorption and fixation; this is mainly due to high concentration of P adsorbent. The main P adsorbents in HWTS include Al, Fe, Ca, and clay minerals, which are principally the same binding or adsorbent for OM compounds, but in excess, are toxic (Al and Fe) to crops. Thus, the presence of OM in HWTS can compromise the adsorption and availability of P in agricultural soils following phosphatic fertilizer applications. In this study, the influence of OM on P adsorption and availability was characterized to have a clear understanding of how OM influences P availability in agricultural soils, especially in highly weathered tropical soil. It is clearly outlined that the application of OM and crop residues can positively or negatively influence the availability of P in agricultural soils for plant uptake and dictate the P that is available for loss to the environment. Thus, the addition of organic matter as a strategy to increase P bioavailability for plant uptake must be treated with care because their contribution is not strait forward to be positive in many agricultural soils.  相似文献   

10.
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.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号