根际中硅,铁,锰和铝的状况与水稻生长

本文以根盒试验与盆栽试验相结合的方法,研究了红壤性水稻土、淀浆白土、第四纪红土和赤红壤植稻后根际微生态系统中Si、Fe、Mn和Al等元素的状况及其与水稻生长的关系。结果表明,新垦红壤植稻后根际中活性Fe和Al富集;活性Mn量降低,但亏缺率小;活性Si则亏缺不明显,有时甚至富集。而熟化水稻土植稻后根际中活性Fe和Al则出现亏缺;Mn的亏缺较大,且差值明显;活性Si的亏缺现象更为显著。由于新垦红壤植稻后Fe和Al在根际微生态系统中富集,根茎叶中累积量较高,从而使Si、P和Mn等元素的吸收受阻,导致新垦红壤上水稻生长明显比熟化水稻土上的水稻要差。     

重金属在根际中的化学行为Ⅲ.土壤中铁形态转化的根际效应及其生态学意义

本文研究了两种熟化水稻土和两种新垦红壤植稻后根际中铁的形态转化。结果表明,水稻土植稻后根际中无定形铁、游离铁、络合态铁及铁的活化度均低于非根际;红壤中除络合态铁的根际内外分布趋势与水稻土相同外,其余均与水稻土相反。穆斯堡尔谱特征表明,根际中氧化铁的四极矩分裂较大,内磁场较低,即根际中氧化铁被活化。差热分析结果表明根际土的持水力强于非根际土。这对根际微生态系统的生态环境保护、物质流的调控及水分的保持和有效利用有重要作用。     

应用电子探针对植物根际和根内营养元素微区分布的探讨

用电子探针可检测出玉米、大豆根际和根内含有Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Fe,Cu和Zn 13种元素。这些元素在根际土壤、粘液层和根组织内的含量分布有一定的规律性。除Si,Al,Ca,Fe在根际土壤中峰值较高外,Ti仅在土壤中达到可检测量;S,Fe和Zn富集在粘液层,Mg,P,Cl只在根组织内才有较明显的峰。这些规律可作为区分根—土界面的参考指标。K含量在根内明显高于根际土壤,并由表皮层到中柱径向增加;Ca则与K不同,且受植物种类的影响。     

根际环境中铅的形态转化

用根际箱试验研究了红壤植麦和植稻后根际中Pb的形态转化 ,讨论了与Cd复合处理对Pb形态的影响 .结果表明 ,Pb在红壤根际、非根际的主要形态为酸解态 +碳酸盐态、交换态和铁锰氧化物结合态 .交换态Pb都是根际 >非根际 ;不同Pb处理浓度和Pb Cd交互作用都对Pb的形态分布产生影响 ,小麦根际随加入Cd浓度增大 ,根际交换态Pb和铁锰氧化物结合态Pb下降 ;水稻根际交换态Pb与Cd复合处理浓度密切相关 ,5mgCd·kg-1复合处理 ,根际交换态Pb的活化较单元素弱 ,10mgCd·kg-1复合处理 ,根际交换态Pb的活化较单元素要强 .     

根际环境中铅的形态转化

用根际箱试验研究了红壤植麦和植稻后根际中Pb的形态转化,讨论了与Cd复合处理对Pb形态的影响.结果表明,Pb在红壤根际、非根际的主要形态为酸解态+碳酸盐态、交换态和铁锰氧化物结合态.交换态Pb都是根际>非根际;不同Pb处理浓度和PbCd交互作用都对Pb的形态分布产生影响,小麦根际随加入Cd浓度增大,根际交换态Pb和铁锰氧化物结合态Pb下降;水稻根际交换态Pb与Cd复合处理浓度密切相关,5mgCd·kg^-1复合处理,根际交换态Pb的活化较单元素弱,10mgCd·kg^-1复合处理,根际交换态Pb的活化较单元素要强.     

烟草根际土壤硒、硫形态相互作用与烟草对硒、硫吸收的研究

通过烟草根际营养试验研究发现,烟草根际土壤Se总量及可溶态Se、交换态Se及有机Se均表现出明显的亏缺.而根际土中S总量及吸附性S、有机S则表现明显的富集.施S对根际土Se亏缺程度的影响与施Se处理有关,而施Se对根际土S富集程度的影响随施S的水平而有一定差异.未施Se处理时,施S降低了烟草根际土中相应几种Se形态的亏缺率,施Se处理时施S的影响则相反.不施S时,加入Se可以增加根际土全S量的富集程度;施S时,加入Se则减少根际全S量的富集程度.前期烟草的Se含量主要受根际土壤可溶态Se的影响,而Se积累量除受土壤可溶态Se的影响外,还受到根际土壤交换态Se、有机Se及酸溶态Se的影响.前期烟草地上部分中S含量主要受根际土壤可溶性S及有机S影响.     

三峡库区消落带典型植物根际土壤磷形态特征

三峡库区消落带生态系统演变对水库安全具有重要影响,其中植物群落演变与土壤氮磷形态转化及释放等广受关注。然而,消落带植物根际效应与土壤磷形态关系及潜在影响并不清楚。选择三峡库区澎溪河消落带为研究对象,分别在冲积潮土、紫色土和水稻土分布的消落区采集典型草本植物(狗牙根、香附子、苍耳)和农作物(玉米)根际、非根际土壤,分析无机磷和有机磷的形态特征,探讨了消落带典型植物生长对土壤磷形态的根际效应及潜在影响。结果表明,土壤类型对土壤磷含量及磷赋存形态具有显著影响,紫色土磷含量最高,且活性磷含量低于冲积潮土和水稻土,表现出磷库稳定性较高;4种植物根际土壤全磷、有效磷及不同形态无机、有机磷(弱吸附态磷WA-P、潜在活性磷PA-P、铁铝结合态磷Fe/Al-P、钙结合态磷Ca-P、残渣态磷R-P)含量均高于非根际,表现出明显的根际富集效应;不同植物根际土壤全磷和有效磷表现为狗牙根苍耳香附子玉米,但磷形态在不同植物根际富集水平不同:活性较高的WA-P、PA-P含量在玉米和苍耳覆盖区均高于狗牙根和香附子,而较稳定Ca-P_i、R-P_i、Fe/Al-P_o、Ca-P_o含量在狗牙根和香附子覆盖区更高,表明玉米和苍耳生长有利于稳定性磷的活化,提高消落带土壤磷流失风险。不同植物根际对不同形态磷富集率差异明显,且玉米根际对活性磷形态的富集率最高,表明农业活动可能加速土壤稳定性磷的活化。pH、土壤有机质、土壤容重与无机磷的赋存形态关系密切,而有机磷赋存形态受pH影响显著,植物根际有机质积累和有机酸分泌等是影响土壤磷形态变化的主要因素。消落带植物群落演变及恢复对土壤磷形态转化具有重要影响。     

泉州湾河口红树林湿地重金属的分布与迁移

通过测定泉州湾河口湿地2种红树植物(桐花树和秋茄)不同部位(根、枝和叶)及其根际沉积物中重金属酸可提取态含量,探讨该区域重金属元素的分布、在植物不同部位富集和迁移的情况。结果表明:2种红树植物根际沉积物中酸可提取态重金属含量顺序均为FeMnZnPbCuCrNi;秋茄根际沉积物中Cu、Zn、Pb、Ni和Cr两两之间呈正相关,桐花树根际沉积物中Cu与Zn呈正相关,Pb与其他重金属的相关性不显著;2种红树植物根中大多数重金属含量与根际沉积物中重金属酸可提取态含量之间呈正相关,而枝中的相关性不显著;2种红树植物重金属富集的情况较接近,Mn富集系数最大,其次是Cu和Zn;Mn、Cu、Zn、Cr主要富集在叶中,而Pb、Fe、Ni主要富集在根部;2种植物中Mn的迁移能力最强,易于从根部运输到叶中。     

荒漠盐生植物根际系统盐分分布特征

利用盐土和棉田土,采用水平根垫法对4种不同类型的荒漠盐生植物进行栽培实验,应用冰冻薄层切片法对距根表不同距离的土壤进行分层取样,并测定不同层次土壤中pH、总盐、Cl^-、SO₄^2-、Na⁺、K⁺、Ca²⁺和Mg²⁺的含量。结果表明: 在盐土中,距根表不同距离的土壤中,pH值呈有规律的梯度分布,即根际微区pH值较土体下降,且距根表越近,pH值越低;而在棉田土中却没有显著变化;总盐在根际出现较大的亏缺区,最大亏缺率位于距根表0～4 mm处;在盐土中,除芦苇外,其余3种盐生植物的根际土中Cl^-、SO₄^2-、Na⁺、K⁺、和Mg²⁺的含量在根际有明显的富集;在棉田土中,除K⁺外,这些离子在根际也有富集,但富集程度比盐土低,K⁺表现亏缺,而Ca²⁺却是富集的;4种植物尤其是稀盐盐生植物和泌盐盐生植物,地上部分的主要盐离子（如Cl^-、Na⁺、Ca²⁺和K⁺）含量比地下部分高,在根际富集程度最高的Cl^-和Na⁺,在植株的地上部分也增加的最多。     

有机物料对滨海盐渍土重金属根际效应的影响Ⅱ.土壤内源铁形态分布

研究了排水条件下施用腐熟有机物料、种稻改良滨海盐渍土内源铁形态分布．结果表明,单淹水利于土中无定形氧化铁、络合态铁、有效态铁以及氧化铁活化度升高,并且络合态铁与有效态铁升高程度,低盐土壤显著;晶形氧化铁变化不明显,土中可能存在其它形态铁向晶形氧化铁转化．种稻不施有机物料,根际络合态铁和有效态铁富集;无定形氧化铁和晶形氧化铁亏缺．根际氧化铁活化度稍低于非根际．增施有机物料利于两种盐渍土根际内外铁形态向络合态铁和无定形氧化铁转化;有效态铁和氧化铁活化度提高,低盐土壤根际较明显     

不同产地黄芩中无机元素含量及其与根际土壤无机元素的关系

药用植物中各无机元素含量的不仅影响药用植物的生长发育,也是药材有效成分的构成因子。通过对全国范围内16个不同产地(即居群)的92个野生黄芩(Scutellaria baicalensis Georgi)样本及其相应的根际土壤中10种无机元素含量的分析,发现不同产地黄芩及其根际土壤无机元素都有很大变异,且不同产地黄芩根际土壤中无机元素的变异远大于黄芩药材中无机元素的变异。总体来看,黄芩中Mg(9级)含量较其他植物含量高;P(1级)、K(2级)、Mn(3级)含量与其他植物相比处处较低水平;黄芩对Sr(富集系数达到3.52)有较强富集。并且通过无机元素分布曲线分析建立了无机元素指纹谱,主成分分析筛选出黄芩主要特征无机元素为Mg、K、Ca、Fe、Zn。本研究还表明,黄芩对各元素的吸收能力受产地的影响较大,提示黄芩对无机元素的吸收与各产地根际土壤无机元素有一定关联性。     

石灰性土壤上植物根际中Fe,Mn的形态分布及其与植物吸收的关系

研究了石灰性土壤上５种作物品种根际微生态环境中Ｆｅ、Ｍｎ的形态分布．结果表明,交换态Ｆｅ（ＥＸ－Ｆｅ）、碳酸盐结合态Ｆｅ（ＣＡＲＢ－Ｆｅ）、无定形氧化铁（ＡＯ－Ｆｅ）和交换态Ｍｎ（Ｅ－Ｍｎ）、碳酸盐结合态Ｍｎ（ＣＡＲＢ－Ｍｎ）在根际土壤中都呈现明显的累积．各品种根际中的累积量有较大差异．相关分析表明,黄潮土上植株含Ｆｅ量、吸Ｆｅ量与根际土壤ＡＯ－Ｆｅ含量呈显著正相关．根际有效态Ｆｅ累积不仅是根际ｐＨ作用的结果,与根系分泌物对难溶性Ｆｅ活化有关．根际有效态Ｍｎ累积则受到根际土壤Ｅｈ的影响．     

Distinct Weathering Ability and Populations of Culturable Mineral-Weathering Bacteria in the Rhizosphere and Bulk Soils of Morus Alba

In this study, we isolated and compared the weathering effectiveness and population of mineral-weathering bacteria from the rhizosphere and bulk soils of Morus alba grown in a mineral-rich soil. Eighty-four isolates could release Si, Al, K, and Fe from potash feldspar. Weathering effectiveness and pattern of the isolates differed between the rhizosphere and bulk soils. The proportion of the highly effective Si, Al, K, and Fe solubilizers was significantly higher in the rhizosphere soils than in the bulk soils. Notably, the proportion of the highly effective acid-producing isolates was also significantly higher in the rhizosphere soils. The 84 mineral-weathering isolates were affiliated with 15 bacterial genera. Distinct mineral-weathering genera were observed between the rhizosphere and bulk soils. The results suggested that the highly effective mineral-weathering bacteria were selected in the rhizosphere soils and the mineral-weathering bacteria from the rhizosphere and bulk soils might weather potash feldspar through different mechanisms.     

Aspects of the Fe-and Mn nutrition of rice plants

Summary The combination of low Mn levels and high Fe levels in tissues of lowland rice varieties, as often encountered when rice is grown on acid soils, is not likely to result from an antagonistic effect of Fe on the uptake of Mn.Experiments with rice plants growing on sand, supplied with Fe and Mn, and subjected to various pH levels and moisture regimes, made it clear that under acid anaerobic conditions the absorption of Mn by rice plants is little affected by the presence of large quantities of Fe, and that under acid aerobic conditions the absorption of Fe by rice plants is little affected by the presence of large quantities of Mn.     

New Insights into How Increases in Fertility Improve the Growth of Rice at the Seedling Stage in Red Soil Regions of Subtropical China

The differences in rhizosphere nitrification activities between high- and low- fertility soils appear to be related to differences in dissolved oxygen concentrations in the soil, implying a relationship to differences in the radial oxygen loss (ROL) of rice roots in these soils. A miniaturised Clark-type oxygen microelectrode system was used to determine rice root ROL and the rhizosphere oxygen profile, and rhizosphere nitrification activity was studied using a short-term nitrification activity assay. Rice planting significantly altered the oxygen cycling in the water-soil system due to rice root ROL. Although the oxygen content in control high-fertility soil (without rice plants) was lower than that in control low-fertility soil, high rice root ROL significantly improved the rhizosphere oxygen concentration in the high-fertility soil. High soil fertility improved the rice root growth and root porosity as well as rice root ROL, resulting in enhanced rhizosphere nitrification. High fertility also increased the content of nitrification-induced nitrate in the rhizosphere, resulting in enhanced ammonium uptake and assimilation in the rice. Although high ammonium pools in the high-fertility soil increased rhizosphere nitrification, rice root ROL might also contribute to rhizosphere nitrification improvement. This study provides new insights into the reasons that an increase in soil fertility may enhance the growth of rice. Our results suggest that an amendment of the fertiliser used in nutrient- and nitrification-poor paddy soils in the red soil regions of China may significantly promote rice growth and rice N nutrition.     

An overview of rhizosphere processes related with plant nutrition in major cropping systems in China

Rhizosphere processes of individual plants have been widely investigated since 1904 when the term “rhizosphere” was first put forward. However, little attention has been paid to rhizosphere effects at an agro-ecosystem level. This paper presents recent research on the rhizosphere processes in relation to plant nutrition in main cropping systems in China. In the peanut (Arachis hypogaea L.)/maize (Zea mays L.) intercropping system, maize was found to improve the Fe nutrition of peanut through influencing its rhizosphere processes, suggesting an important role of phytosiderophores released from Fe-deficient maize. Intercropping between maize and faba bean (Vicia faba L.) was found to improve nitrogen and phosphorus uptake in the two crops compared with corresponding sole crop. There was a higher land equivalent ratio (LER) in the intercropping system of maize and faba bean than the treatment of no root interactions between the two crops. The increased yield of maize intercropped with faba bean resulted from an interspecific facilitation in nutrient uptake, depending on interspecific root interactions of the two crops. In the rotation system of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) crops, Mn deficiency in wheat was caused by excessive Mn uptake by rice and Mn leaching from topsoil to subsoil due to periodic cycles of flooding and drying. However, wheat genotypes tolerant to Mn deficiency tended to distribute more roots to deeper soil layer and thus expand their rhizosphere zones in the Mn-deficient soils and utilize Mn from the subsoil. Deep ploughing also helped root penetration into subsoil and was propitious to correcting Mn deficiency in wheat rotated with rice. In comparison, oilseed rape (Brassica napus L.) took up more Mn than wheat through mobilizing sparingly soluble soil Mn due to acidification and reduction processes in the rhizosphere. Thus, oilseed rape was tolerant to the Mn-deficient conditions in the rice-oilseed rape rotation. Oxidation reactions on root surface of rice also resulted in the formation of Fe plaque in the rice rhizosphere. Large amounts of Zn were accumulated on the Fe plaque. Zinc uptake by rice plants increased as Fe plaque formed, but decreased at high amounts of Fe plaque. It is suggested that to fine-tune cropping patterns and optimize nutrient management based on a better understanding of rhizosphere processes at an agro-ecosystem level is crucial for increasing nutrient use efficiency and developing sustainable agriculture in China.     

Nutritional characteristics in leaves of native plants grown in acid sulfate,peat, sandy podzolic,and saline soils distributed in Peninsular Thailand

Acid sulfate soils, peat soils, sandy podzolic, and saline soils are widely distributed in Peninsular Thailand. Native plants adapted to such problem soils have grown well, and showed no symptom of mineral deficiency or toxicity. Dominant plants growing in low pH soils (acid sulfate and peat) were Melastoma marabathricum and Melaleuca cajuputi. Since M. marabathricum accumulated a huge amount of aluminum (Al) in leaves, especially in new growing leaves, it can be designated an Al accumulator plant. While M. cajuputi did not accumulate Al in shoot, it can be designated an Al excluder plant. Both plant species adapted well to low pH soils, though a different strategy was used for Al. On the other hand, in acid sulfate and peat soils, M. cajuputi, Panicum repens, Cyperus haspan, and Ischaemum aristatum accumulated large amounts of Na in the leaves (or shoots), even in soil with low exchangeable Na concentration. Thus, when growing in the presence of high Al and Na concentration in soils, plant species have developed two opposite strategies: (1) Al or Na accumulation in the leaf and (2) Al or Na exclusion from the leaf. Al concentration in leaves had a negative relationship with the other mineral nutrients except for N and Mn, and Na concentration in leaves also had a negative relationship with P, Zn, Mn, Cu, and Al. Consequently, Al and Na accumulator plants are characterized by their exclusion of other minerals from their leaves.     

水稻土中硫酸盐还原微生物研究进展

硫是水稻必需的营养元素之一.硫酸盐还原是硫元素生物地球化学循环中的关键步骤,在稻田土壤表层和水稻根际都十分活跃.介导硫酸盐还原过程的硫酸盐还原菌(sulfate- reducing bacteria, SRB)是稻田土壤中重要的功能菌群.它们不仅是硫元素生物地球化学循环的重要参与者,也是土壤中有机污染物降解的主要力量之一,发挥着重要的生态和环境功能.综述了稻田土壤中微生物参与的硫酸盐还原过程、SRB的生物多样性以及目前研究稻田土壤SRB主要采用的分子生态学方法,如末端限制性片段长度多样性(T-RFLP)、变性梯度凝胶电泳(DGGE)、实时荧光定量PCR(real-time PCR)、荧光原位杂交(FISH),并对水稻土壤中SRB的分子生态学研究方向进行了展望.     

Oxygen input controls the spatial and temporal dynamics of arsenic at the surface of a flooded paddy soil and in the rhizosphere of lowland rice (Oryza sativa L.): a microcosm study

The impact of oxygen (O₂) input at the soil surface and in the rhizosphere of rice (Oryza sativa L.) on the spatial and temporal dynamics of arsenic (As) was investigated in a flooded paddy soil. A soil microcosm and root-mat technique were designed to mimic submerged conditions of paddy fields. Water-filled containers with (planted) or without (unplanted) 27-day-old rice seedlings were fitted for 20 days on top of microcosms containing an As-affected soil (Bangladesh). After the initial establishment of strongly reduced conditions (?230 mV) in both planted and unplanted soils, the redox potential gradually increased until the day 8 to reach?+?50 mV at 2 mm from the surface of unplanted soils only. This oxidation was associated with an accumulation of NH₄-oxalate extractable As (25.7 mg kg^?1) in the 0.5-mm top layer, i.e. at levels above the initial total content of As in the soil (14 mg kg^?1) and a subsequent depletion of As in soil solution at 2 mm from soil surface. Root O₂-leakage induced the formation of an iron (Fe) plaque in root apoplast, with no evidence of outer rhizosphere oxidation. Arsenic content reached 173 mg kg^?1 in the Fe plaque. This accumulation induced a depletion of As in soil solution over several millimetres in the rhizosphere. Arsenic contents in root symplast and shoots (112 and 2.3 mg kg^?1, respectively) were significantly lower than in Fe plaque. Despite a large As concentration in soil solution, Fe plaque appeared highly efficient to sequester As and to restrict As acquisition by rice. The oxidation-mediated accumulation of As in the Fe plaque and in the oxidised layer at the top of the soil mobilised 21 and 3% of the initial amount of As in the planted and unplanted soils, respectively. Soil solution As concentration steadily decreased during the last 16 days of the soil stage, likely indicating a decrease in the ability of the soil to re-supply As from the solid-phase to the solution. The driving force of As dynamic in soil was therefore attributed to the As diffusion from reduced to oxidised soil layers. These results suggest a large mobility of As in the soil during the flooded period, controlled by the setting of oxic/anoxic interfaces at the surface of soil in contact with flooding water and in the rhizosphere of rice.