Cations adsorbed to soil organic matter — A regulatory factor for the release of organic carbon and hydrogen ions from soils to waters

Surface waters in northern forest ecosystems receive a substantial amount of drainage water from superficial soil horizons enriched in organic matter (SOM). Chemical reactions in the interface between the soil solution andf organic colloides will therefore affect the surface water chemistry. The mobilization of total organic carbon (TOC) and pH was studied as a function of amounts of organically adsorbed Na, Ca and Al in two O and one A horizon, which differed in the likelihood of contributing to the chemistry in runoff, in a forested watershed in northern Sweden. The samples were hydrogen ion saturated, washed and titrated with NaOH, Ca(OH)₂ and Al(OH)₃ in a constant ionic medium of 0.01 M NaCl in order to give rise to a population of manipulated samples differing in the composition of adsorbed cations. The highly humified SOM accumulated in the O_h and A_h horizons of a Gleysol close to the draining stream was stabilized by flocculating Al (95% of adsorbed metal cations), which resulted in a low release of TOC. These horizons showed a high potential of organic carbon solubility when Al was changed for di- or monovalent cations. Calculations suggested that the release of TOC would increase more than ten times if Al was exchanged for Ca upon liming to pH 6.0. The pH values of all horizons were shown to be determined mainly by the composition of adsorbed mono-,di- and trivalent cations.     

磷对植物铝毒害作用研究中两种磷铝处理方法比较

由于磷和铝在溶液中的相互作用,研究磷对植物铝毒害作用的关键是选择合适的磷铝处理方法,本研究采用两种磷铝处理方法就磷对植物铝毒害的作用进行了比较。结果表明,采用计算铝活度的方法,磷能缓解铝对小麦的毒害,而采用磷铝交替处理的方法,磷则加重铝对小麦的毒害。尽管在计算铝活度的方法中不同磷浓度处理液中铝的活度相同(用GEOCHEM软件计算),但磷浓度越高的处理液,其毒性铝的浓度越低,在该方法中,磷可能是通过降低溶液中毒性铝的浓度而缓解铝毒的,不能很好地避免溶液中磷铝相互作用。磷铝交替处理彻底避免了磷铝在溶液中的相互影响,保证相同的磷和铝处理浓度,而且长期交替处理在一定程度上也降低了磷铝不能同时处理对试验结果准确性的影响,因而,该方法是一种研究植物磷铝关系比较可行的方法。在磷铝交替处理条件下,磷加重小麦的铝毒害,可能与磷促进铝在根尖的累积有关。     

Relationships between the Ratio of Plant-Available Phosphorus (P-AL) to Total Phosphorus and Soil Properties

Abstract

The relationships between the ratio of plant-available phosphorus (P-AL) to total P and soil properties were examined in 52 samples of mineral soils collected from different parts of Norway. The ratio P-AL/total P in the soils was used as a measurement of a soil's capacity to bind P in sparsely soluble forms and of the possibility for plants to utilize added P. Simple regression analysis showed that the ratio P-AL/total P was correlated with clay (r= ?0.60???, significant at the 0.1% probability level), Tamm acid oxalate extractable Fe (r= ?0.63???), and Tamm acid oxalate extractable Al (r-= ?0.44???), but not with organic C and pH. Variation of Fe, Al and clay content could explain 50% of the variation of the ratio of P-Al/total P. Partial correlation coefficients showed that Fe was the most important factor explaining the variation of the ratio of P-AL/total P.     

Soil aluminium availability in Andisols of southern Chile and its effect on forage production and animal metabolism

Soil acidification limits livestock production in many parts of the world. Two experiments were carried out to investigate the effect of aluminium (Al) on pasture yield and animal production. In experiment 1, the effect of raising soil pH (in water) from 5.1 (acid soil, A) to 5.6 (corrected soil, C) was tested on forage and animal production. In experiment 2, Friesian calves were individually fed either silage with or without the addition of 2000 mg kg^?1 of Al as aluminium sulphate. Al, P, Ca and Mg concentrations were measured in forage, and in animal blood and faeces. Live weight gain (LWG) was also measured. Soil acidification resulted in a 36% overall reduction in pasture yield in the A treatment (9.4 ± 0.31 and 14.7 ± 0.47 t ha^?1 year^?1 for the A and C treatments respectively) and in 15% reduction of the protein concentration in the herbage. No significant differences were found for the individual daily LWG (P > 0.05). Direct Al intake reduced animals daily LWG by 14% (P ≤ 0.05). The correction of soil acidification increased livestock production by 125% when stocking rate was strictly adjusted to grassland production.     

铝胁迫下不同耐铝性小麦根际pH值变化及其与耐铝性的关系

Al3＋是植物铝毒害的主要形态,而其活性受环境pH值的影响,H＋-ATPase通过调节根的质子分泌改变根际pH值。为探讨铝胁迫下根际pH值变化与小麦耐铝性的关系,以小麦品种ET8（耐铝型）、ES8（铝敏感型）为试验材料,采用溶液培养的方法对铝胁迫下根际pH值及根尖H＋-ATPase活性变化进行了研究。结果表明,铝处理条件下,小麦根际pH值随培养时间的延长而升高;随培养液中铝浓度的增加,根际pH值上升幅度下降,相同铝浓度处理条件下ET8根际pH值显著高于ES8。根际pH值与根尖铝含量呈极显著负相关（R2=0.932 1）,与根相对伸长率呈极显著正相关（R2=0.858 5）,表明小麦通过提高根际pH值降低根尖铝含量,减轻铝毒害。根尖H＋-ATPase活性随铝处理浓度升高而显著降低,100 μmol·L-1Al处理24 h ET8和ES8根尖H＋-ATPase活性分别为各自无铝处理的69.8%和60.0%,根尖H＋-ATPase相对活性与根际pH值呈极显著负相关（R2=0.831 9）。温度显著影响根的伸长,低温处理（9 ℃）根际pH值显著高于常温处理（25 ℃）,而根尖铝含量却显著低于常温处理。表明小麦通过根尖H＋-ATPase提高根际pH值降低铝毒害。综上所述,铝胁迫下小麦可通过提高根际pH值减轻铝毒害,不同耐铝性小麦品种根际pH值的显著差异是耐铝性差异显著的     

铵态氮/硝态氮对水稻铝吸收的影响及其机制研究

选用两个水稻品种武运粳7号（耐铝品种）和扬稻6号（铝敏感品种）作为实验材料,利用水培试验,通过长期和短期处理相结合的方式研究了NH4+-N和NO3--N对水稻Al吸收的影响及其作用机制。结果表明,与NH4+-N相比,NO3--N促进了水稻对Al的吸收。而且随着NO3--N浓度的提高,水稻根中Al含量显著增加,随着NH4+-N浓度的提高,水稻根中Al含量显著降低。这些结果表明NH4+-N和NO3--N对水稻Al吸收的影响具有浓度效应。当向Al溶液添加pH缓冲剂后,NH4+-N和NO3--N对根尖Al累积的影响变小,表明NH4+-N和NO3--N处理下溶液pH的变化可能是NH4+-N和NO3--N对水稻Al吸收影响不同的一个原因。     

盐碱胁迫及植物耐盐碱分子机制研究

土地盐碱化严重影响农业生产发展,是世界范围内农业发展所面临的重大问题。因此,了解盐碱胁迫对植物造成的危害、植物对盐碱胁迫的响应及耐盐碱植物的耐逆机制,将为增强作物的耐盐碱能力和开发利用盐碱地奠定坚实的理论研究基础。盐胁迫对植物造成的伤害主要包括离子胁迫、渗透胁迫和氧化胁迫,而碱胁迫在盐胁迫基础上还增加了高pH胁迫,对植物的伤害表现得更为严重和复杂。铁离子是植物生长发育不可或缺的重要金属离子,然而在盐碱土壤中植物对铁离子的吸收利用效率大大降低,严重影响了植物的正常生长和代谢。本文总结了盐碱胁迫对植物造成的生理伤害及耐盐碱植物资源的相关研究,综述了植物盐碱胁迫信号转导及分子机制研究进展,重点阐述了铁的转运吸收与盐碱胁迫的关系,以期为耐盐碱基因的挖掘、耐盐碱作物新品种的培育及开发利用改良盐碱地资源提供理论基础。     

Influence of soil pH on the toxicity of aluminium for Eisenia andrei (Oligochaeta: Lumbricidae) in an artificial soil substrate

Toxicity of aluminium for the earthworm Eisenia andrei was studied in artificial soil at different pH levels. In a range-finding test, effects of three different aluminium salts on earthworm survival were determined. AlCl₃ appeared to be most toxic, with LC₅₀ values of 316, 359 and >1000 mg Al/kg dry soil at pH_KCl of 3.5, 4.4 and 6.7, respectively in the control soils. Effects of this salt interfered with a strong decrease of soil pH with increasing aluminium concentration. Al₂(SO₄)₃ was less toxic with LC₅₀ values of 457, >4000 and >4000 mg Al/kg dry soil at pH 3.24, 4.86 and 7.22, respectively. Al₂O₃ did not affect earthworm survival at concentrations of 5000 mg Al/kg and pH levels between 2.4 and 7.1.In the main test, earthworms were exposed for 6 weeks to soils treated with Al₂(SO₄)₃. As in the range-finding test, aluminium sulfate was most toxic at a pH of 3.4 with an LC₅₀ of 589 mg Al/kg dry soil. At this pH, growth and cocoon production of earthworms were significantly reduced at 320 mg Al/kg dry soil, while at 1000 mg Al/kg dry soil all earthworms died. Survival was not affected by 1000 mg Al/kg dry soil at pH 4.3 and 7.3. At pH 4.3, growth was significantly reduced at 1000 mg Al/kg dry soil and cocoon production at 320 and 1000 mg Al/kg dry soil. At pH 7.3, aluminium only affected cocoon production at the two highest exposure levels. At the highest two exposure levels at pH 7.3, growth was significantly increased, suggesting a trade-off between growth and reproduction. These effects of aluminium at the highest soil pH could not be explained from the concentration of extractable, monomeric (labile) aluminium in soil, which decreased with increasing soil pH.     

低pH和铝毒对荞麦根边缘细胞特性的交互作用研究

采用悬空气培法,研究低pH(3.5、4.5、5.5)和铝毒(0、50、100μmolL-1)及其交互作用对荞麦根长、根边缘细胞活性及其分泌的黏液层厚度的影响。处理12h,Al3+浓度由50μmolL-1增至100μmolL-1时,pH3.5的根伸长量分别降低18.6%和31.9%,pH4.5时分别降低18.9%和26.8%,pH5.5时各降低8.5%。处理24h的根伸长量变化与12h类似。pH降低至3.5时,边缘细胞的活性下降28.6%,黏液层厚度无明显变化。Al3+浓度升高至100μmolL-1时,黏液层增厚64.6%,而边缘细胞活性变化不大。pH3.5与100μmolL-1Al3+的处理,边缘细胞活性最低,黏液层厚度最大,两者间存在极显著的交互作用。可见低pH加剧铝毒发生,外围黏液层产生可以减轻Al3+对边缘细胞的伤害。     

Beneficial effect of aluminum on growth of plants adapted to low pH soils

Plants in which growth was reduced by low and high Al applications were designated as Al-sensitive plant (Hordeum vulgare) and Al-medium tolerant plants (Leucaena leucocephala, Ischaemum barbatum, Stylosanthes guianensis, and Fagopyrum esculentum), respectively, while plants in which growth was not affected or was stimulated by Al application were designated as Al-tolerant plant (Brachiaria ruziziensis) and Al-stimulated plants (Melastoma malabathricum, Melaleuca cajuputi, Acacia mangium, Hydrangea macrophyila, Vaccinium macrocarpon, Polygonum sachalinense, and Oryza sativa), respectively. Plants tolerant to or stimulated by Al were further classified based on the criteria of Al accumulation: 1) Al-excluders such as M. cajuputi, A. mangium, L. leucocephala, I. barbatum, S. guianensis, and O. sativa, 2) Al root-accumulators such as V. màcrocarpon, B. ruziziensis, and P. sachalinense, and 3) Al-accumulators such as M. malabathricum, H. macrophylla, and F. esculentum. The growth and N, P, and K uptake in M. malabathricum, M. cajuputi, A. mangium, L. leucocephala, H. macrophylla, V. macrocarpon, I. barbatum, P. sachalinense, F. esculentum, and O. sativa were stimulated by Al application, especially P uptake, while in H. vulgare (Al-sensitive plant) they were reduced by Al application. Ca and Mg uptake of many plants was inhibited by Al application, while that of some plants adapted to low pH soils was not affected at all (Ca and Mg: M. cajuputi, H. macrophylla, V. macrocarpon, I. barbatum, and S. guianensis; Mg: B. ruziziensis and P. sachalinense). In M. malabathricum, the relationship between Al and Ca (or Mg) was antagonistic because the Ca and Mg contents decreased by Al application even though dry matter, N, P, and K accumulation was stimulated by Al application. Plants adapted to low pH soils grew poorly in the no-Al treatment. Since the effect of the pH on plant growth was less conspicuous than that of Al, growth stimulation by Al application was ascribed not only to the alleviation of H⁺ toxicity but also to the increase of root activity such as P uptake.     

Effect of B,Mn and Zn on nodulation and N2‐fixation in southernpeas

Abstract

Two greenhouse studies were conducted to evaluate the effect of B, Mn and Zn on nodulation and N₂‐fixation of southernpea (Vigna unguiculata (L.) Halp.) cultivars ‘Freezegreen’, ‘Mississippi Silver’ and ‘Pinkeye Purple Hull’. The cultivars were grown in plastic pots with a Norfolk sandy loam (fine, loamy siliceous thermic, Typic Paleudult) soil treated with B, Mn and Zn at rates of 0, 5, 10 and 20 kg/ha each at pH levels 5.5, 6.0 and 6.5. At pH 6.5 all micronutrient treatments significantly increased nodulation and N₂‐fixation over the control (no micronutrient applied). The effects of B, Mn and Zn on nodulation and N₂‐fixation depended on the cultivar and soil pH. For plants given the 5 kg/ha B and Mn treatments, ‘Mississippi Silver’ produced the highest number of nodules and ‘Pinkeye Purple Hull’ the least. At 20 kg/ha Zn, nodulation of ‘Freezegreen’ was highest and ‘Pinkeye Purple Hull’ the lowest. As a whole, maximum nodulation was at 5 kg/ha B and Mn and 20 kg/ha for Zn. Nitrogen fixation rates responded similarly except that the optimum rate for Zn was 10 kg/ha. Seed yield of plants peaked at 5 kg/ha for B and 10 kg/ha for Zn, indicating a possible relation of N₂‐fixation to seed yield.