南亚热带森林演替过程土壤水分、有机质和交换性阳离子的变化格局

Information on the distribution patterns of soil water content （SWC）, soil organic matter （SOM）, and soil exchangeable cations （SEC） is important for managing forest ecosystems in a sustainable manner. This study investigated how SWC, SOM, and SEC were influenced in forests along a successional gradient, including a regional climax （monsoon evergreen broad-leaved forest, or MEBF）, a transitional forest （coniferous and broad-leaved mixed forest, or MF）, and a pioneer forest （coniferous Masson pine （Pinus rnassoniana） forest, or MPF） of the Dinghushan Biosphere Reserve in the subtropical region of southern China. SWC, SOM, and SEC excluding Ca^2＋ were found to increase in the soil during forest succession, being highest in the top soil layer （0 to 15 cm depth） except for Na^＋. The differences between soil layers were largest in MF. This finding also suggested that the nutrients were enriched in the topsoil when they became increasingly scarce in the soil. There were no significant differences （P = 0.05） among SWC, SOM, and SEC. A linear, positive correlation was found between SWC and SOM. The correlation between SOM and cation exchange capacity （CEC） was statistically significant, which agreed with the theory that the most important factor determining SEC is SOM. The ratio of K^＋ to Na^＋ in the topsoil was about a half of that in the plants of each forest. MF had the lowest exchangeable Ca^2＋ concentration among the three forests and Ca^2＋：K^＋ in MPF was two times higher than that in MF. Understanding the changes of SWC, SOM, and CEC during forest succession would be of great help in protecting all three forests in southern China.     

Comparative toxicity of Al3+, Yb3+, and La3+ to root-tip cells differing in tolerance to high Al3+ in terms of ionic potentials of dehydrated trivalent cations

Abstract

Green manure legumes are often used to compare biomass production as well as nitrogen-fixing capacity. Mineral deficiency often limits the symbiotic nitrogen fixation of many legumes, thus limiting their productivity despite their high yielding potential (O’Hara et al. 1988; Flis et al. 1993). Leguminous species require large amounts of P for growth, nodulation, and nitrogen fixation. Consequently, they are often unable to grow in acid soils with low available P. The low P availability in tropical acid soils often arises from fixation of P by Al and Fe in soil. Generally, Al and Fe-phosphates are relatively unavailable to plants (McLachlan 1976; Ae et al. 1990).     

Distribution of exchangeable cations in a soil catena in the area of Baer mounds

The soil cover of the Baer mounds in Astrakhan oblast consists of brown solonetzes on the tops of the mounds, solonetzic brown and meadow brown soils on the slopes, and solonchaks at the footslopes. The exchangeable sodium percentage in the brown soils on the tops and slopes varies from 7 to 42%. However, the morphological features of the solonetzic process are weakly pronounced in these soils, except for some cementation of the soil mass and the poorly developed columnar structure in the B horizon. This is probably related to the coarse soil texture and the relatively low exchange capacity (<10 meq/100 g of soil). The portion of exchangeable sodium reaches 2–9%. A direct correlation between the sodium concentrations in the water extracts and in the soil exchange complex is clearly seen.     

Effects of salt stress on distribution of Na+ and some other cations in two soybean varieties differing in salt tolerance

In the course of investigations on the impact of salinity on mineral ion transport in differentially salt susceptible soybeans (“Lee” and “Jackson”) short-term experiments were conducted to elucidate the distribution pattern of Na⁺ and some other cations. The results showed that low salinity (7.5 mM NaCl) did not induce varietal differences in Na⁺ content during a 30 hrs uptake period. At 66.5 mM NaCl, however, the Na⁺ contents increased more in the leaves of the salt sensitive variety “Jackson” than in “Lee”. Both soybean varieties retained Na⁺ in the proximal root and stem. Furthermore, they extruded considerable amounts of Na⁺ from the roots to the medium. Increasing the level of salinity in the solution substantially reduced the Ca²⁺ uptake of both soybean varieties. In an experiment with the salt sensitive variety under constant salinity but increasing Ca²⁺ concentration in the medium, the plants showed a reduction in Na⁺ uptake and translocation to stem and leaves and an enhanced Ca²⁺ uptake and translocation to the shoots. It is suggested that the injury observed in “Jackson” after salt treatment is not only related to the insufficient control of Cl^? transport. At higher salinity levels the increasing accumulation of Na⁺ in the leaves and the varietally independant depression of Ca²⁺ uptake and translocation may enhance the development of leaf necrosis.     

The importance of exchangeable cations and resin-sink characteristics in the release of soil phosphorus

The significance of exchangeable cations in the release of phosphorus by sequential extraction with water was evaluated in 11 acid (_pH 5.0–6.3) New Zealand soils contrasting in P status and P retention. The release of P from Na-saturated soil exceeded that from the original Ca-dominated soils by up to four-fold. Possible explanations for the larger P release in the Na system include: (i) desorption of P induced by increased surface negative potential associated with the exchange of Na for Ca/Mg, and/or (ii) accelerated dissolution of Ca phosphate compounds or complexes resulting from the creation of a sink for Ca.
The potential of a series of anion- and cation-exchange resin systems (AER and CER, respectively) as sinks for labile soil P was also examined. For all soils studied, P extracted by AER-HCO₃ 3 and that removed by sequential extraction with water. Also, the amounts of P extracted by AER-OH/CER-H and NaCl/ H₂O were closely correlated ( r = 0.95**), suggesting similar release mechanisms. The results obtained indicate that charge-balancing cations, particularly Ca which is the predominant exchangeable cation in the majority of soils, exerts a more significant control on soil P equilibria in acid soils than is commonly recognized.     

Effects of acid deposition on acidity and exchangeable cations in podzols of the Kola Peninsula

Response of soil and soil water of podzols in the Kola Peninsula to acid deposition was estimated under both field and laboratory conditions. A significant increasing trend of exchangeable acidity in organic (O) horizons and exchangeable Al in podzolic (E) horizons of podzols with distance from the nickel smelter was observed. The simulated rain at pH 4.5 did not alter chemical properties of soils and soil solutions. As much as 95–99% of the applied H⁺ ions were retained by soils and appeared in the percolates after a treatment period that depended on acid load and soil thickness. Ca and Mg in soil solutions were highly sensitive to acid loading. Simulated acid rain enhanced the leaching of exchangeable base cations out of root zone. Acid inputs resulted in decreased pH, amount of exchangeable base cations and base saturation, in elevated exchangeable acidity and it's Al fraction in soil solid phase. The most significant changes occurred in O and E horizons. Substantial amounts of both Ca and Mg can be lost from the root zone of podzols in the north-western Kola, subjected to acid deposition, thus leading to forest productivity damage.     

Mutual relationships of biochar and soil pH,CEC, and exchangeable base cations in a model laboratory experiment

Purpose

The majority of biochar studies use soils with only a narrow range of properties making generalizations about the effects of biochar on soils difficult. In this study, we aimed to identify soil properties that determine the performance of biochar produced at high temperature (700 °C) on soil pH, cation exchange capacity (CEC), and exchangeable base cation (Ca²⁺, K⁺, and Mg²⁺) content across a wide range of soil physicochemical properties.

Materials and methods

Ten distinct soils with varying physicochemical properties were incubated for 12 weeks with four rates of biochar application (0.5, 2, 4, and 8% w/w). Soil pH, CEC, and exchangeable base cations (Ca²⁺, K⁺, and Mg²⁺) were determined on the 7th and 84th day of incubation.

Results and discussion

Our results indicate that the highest biochar application rate (8%) was more effective at altering soil properties than lower biochar rates. Application of 8% biochar increased pH significantly in all incubated soils, with the increment ranging up to 1.17 pH unit. Biochar induced both an increment and a decline in soil CEC ranging up to 35.4 and 7.9%, respectively, at a biochar application rate of 8%. Similarly, biochar induced increments in exchangeable Ca²⁺ up to 38.6% and declines up to 11.4%, at an 8% biochar application rate. The increment in CEC and exchangeable Ca²⁺ content was found in soils with lower starting exchangeable Ca²⁺ contents than the biochar added, while decreases were observed in soils with higher exchangeable Ca²⁺ contents than the biochar. The original pH, CEC, exchangeable Ca²⁺, and texture of the soils represented the most crucial factors for determining the amount of change in soil pH, CEC, and exchangeable Ca²⁺ content.

Conclusions

Our findings clearly demonstrate that application of a uniform biochar to a range of soils under equivalent environmental conditions induced two contradicting effects on soil properties including soil CEC and exchangeable Ca²⁺ content. Therefore, knowledge of both biochar and soil properties will substantially improve prediction of biochar application efficiency to improve soil properties. Among important soil properties, soil exchangeable Ca²⁺ content is the primary factor controlling the direction of biochar-induced change in soil CEC and exchangeable Ca²⁺ content. Generally, biochar can induce changes in soil pH, CEC, and exchangeable Ca²⁺, K⁺, and Mg²⁺ with the effectiveness and magnitude of change closely related to the soil’s original properties.

     

Effect of mono- and divalent cations on sorption of water-extractable organic carbon and microbial activity

Biology and Fertility of Soils - Sorption is an important process for retention of organic carbon (C) in soils. The effect of Na+ and Ca2+ on sorption of organic C has been studied in salt-affected...     

低分子量有机酸对可变电荷土壤铝活化动力学的影响

从动力学角度研究了几种低分子量有机酸对2种酸性土壤中铝的活化和活化铝在土壤固/液相之间分配的影响。结果表明:对于络合能力弱的醋酸和乳酸,主要通过质子作用活化铝,且活化作用明显小于盐酸。而络合能力较强的苹果酸、草酸和柠檬酸,主要通过络合作用促进铝的释放,且这种作用随有机酸根阴离子络合能力的增强而增加。在氧化铁含量较高的砖红壤中,苹果酸、草酸和柠檬酸通过专性吸附增加土壤表面负电荷,从而增加土壤交换态铝;但在氧化铁含量较低的红壤中,草酸和柠檬酸主要通过形成可溶性铝络合物降低交换态铝。活化铝在土壤固/液相间的分配主要决定于溶液中有机阴离子与土壤固相表面对铝离子的竞争。醋酸和乳酸活化的铝主要以交换态铝存在;而草酸和柠檬酸活化的铝主要以有机酸-铝络合物存在于溶液中,特别是在氧化铁低的红壤中,这将促进铝在土壤-水体中的迁移。     

A comparison of buffered and unbuffered ammonium salts to determine exchangeable base cations in acid soils

Abstract

In soil samples from two study sites in southern Norway, exchangeable cations were determined using two different ammonium (NH₄)‐salts as extractant. As expected, the cation exchange capacity (CEC) determined in 1M ammonium acetate (NH₄OAc), buffered at pH 7.0 was higher than the CEC measured in ammonium nitrate (NH₄NO₃). By contrast, the amount of exchangeable calcium (Ca), magnesium (Mg), and barium (Ba) was lowest in the NH₄OAc extract, in particular in the upper soil horizons high in organic matter (O‐ and E‐horizon). This suggests that NH₄ in 1M NH₄OAc does not compete effectively with multivalent base cations. The relatively high levels of exchangeable base cations in NH₄NO₃ could not be explained by increased weathering. An increase in selectivity of especially divalent cations may explain the relatively low amount of exchangeable base cations extracted by NH₄OAc, as this involves increased deprotonation and thus a higher negative charge.     

Proton interactions with soil organic matter: the importance of aggregation and the weak acids of humin

Samples of three organic‐rich soils (ombrotrophic peat, podzol H‐horizon, humic ranker) were extensively washed with dilute nitric acid, dialysed against deionised water, and then subjected to acid‐base titrations over the pH range 3–10, in 0.3–300 mm NaNO₃, and with soil concentrations in the range 2–150 g l^?1. The results for the three soils were quantitatively similar. Comparison of the titration data with previously published results for humic acids isolated from the same soils showed the soil organic matter to have a greater ionic strength dependency of proton binding and to possess relatively greater buffering capacity at high pH, attributable to weak acid groups (c. 2–5 mmol g^–1) in the humin fraction of the soils. To describe the soil titration data quantitatively, we modified Humic Ion‐Binding Model VI‐FD, which utilizes a fixed Donnan volume to describe counterion accumulation, by increasing the content of weak acid groups. When artefacts in pH measurement caused by the suspension effect were taken into account, the resulting Model VI‐FD2 provided good or fair simulations of all the titration data. The results suggest that soil structure, specifically aggregation, plays a significant role in cation binding by organic soils in situ. The lack of dependence of the titration results on soil suspension concentration suggests that the findings can be applied to soils in situ.     

铝(氢)氧化物对有机酸和磷酸根的竞争吸附研究

研究了磷 /草酸浓度比 (Cp/Cox)、草酸 (OX)与磷 (P)加入顺序、多种有机酸共存等条件下铝 (氢 )氧化物 (Al(OH)x)对有机酸和磷的吸附量变化。结果表明 :磷浓度一定时 ,随Cp/Cox减小 ,Al(OH)x吸附磷量降低 ,吸附OX量增高 ,吸附阴离子总量一般随浓度升高而增加 ;Cp/Cox相同时 ,5种加入方式吸P顺序为P/OX P -OX OX +P OX -P OX/P ;Cp/Cox不同时 ,Al (OH)x吸附配位体的总量也相应变化 ;几种有机酸共存时 ,Al(OH)x对体系中的各种阴离子均有吸附 ,且相互影响和制约 ,总吸附量取决于离子种类和浓度 ,3种有机酸影响P吸附量的顺序为柠檬酸 (CA) 草酸 (OX) 酒石酸 (Tar) ;Al (OH)x加磷后随平衡时间延长 ,先吸附的OX和CA对吸附P量的影响逐渐减弱 ,它们的相对亲合力越来越成为主导因素。     

Nitrogenase activity in relation to season,carbohydrates and organic acids in a temperate zone root association

Nitrogenase activity associated with grasses is commonly reported to be maximal during reproductive growth. For Spartina alterniflora, a perennial grass growing in salt marshes, seasonal changes in potential (excised root) N₂ase activity followed, by about 2 weeks, seasonal changes in ethanol soluble carbohydrate concentrations in roots and rhizomes. Both varied by about 3-fold during the year, declined rapidly with the onset of vegetative growth, and increased to previous levels during reproductive growth. N₂-ase activity measured on intact systems in situ was also maximal during reproductive growth, but the absolute rates were much lower than the potential N₂ase activities.     

Toxicity factors in acidic forest soils: attempts to evaluate separately the toxic effects of excessive Al3+ and H+ and insufficient Ca2+ and Mg2+ upon root elongation

The acidic soils of temperate forests and some pastures on former forest land characteristically contain large amounts of aluminium and hydrogen ions and small amounts of calcium and magnesium ions. The relative importance of these potential toxicity factors are assessed from published data from soils collected in the United States and Europe. Activities of ions in the soil solutions and at the surfaces of root‐cell plasma membranes were computed with electrostatic models. Activities of Al³⁺ in soil solutions ({Al³⁺}) peaked at pH 4.1, and Al³⁺ activities at the surface of the plasma membrane ({Al³⁺}₀) achieved a broad maximum between pH 4.1 and 4.8; thus, Al³⁺ intoxication is likely to be more severe in soils at pH 4.1 than in more acidic ones. Intoxication (assessed by root elongation) correlated somewhat ambiguously with ion activities, but Al³⁺‐ and H⁺‐induced depletion of Ca²⁺ and Mg²⁺, or both, from the cell surface appears to play a role in toxicity. By contrast, experiments in solution culture, where intercorrelation among {Al³⁺}, {H⁺}, and {Ca²⁺} could be avoided, clearly demonstrated the following extrinsic and intrinsic effects. 1 The ions Al³⁺ and H⁺ are intrinsic toxicants. 2 They are also extrinsic toxicants because of the electrostatic displacement of Ca²⁺ from the surface of the plasma membrane. 3 They are extrinsic ameliorants because each electrostatically displaces the other from the surface of the plasma membrane. 4 The ion Ca²⁺ is an extrinsic ameliorant because of the electrostatic displacement of Al³⁺ and H⁺ from the surface of the plasma membrane. 5 It is an intrinsic ameliorant of intrinsic H⁺ toxicity, but not intrinsic Al³⁺ toxicity. 6 It meets an intrinsic requirement. 7 The ion Mg²⁺ resembles Ca²⁺ in item 4 but not items 5 and 6 in short‐term cultures. In acidic soils, Al³⁺ may prevent H⁺ from becoming an intrinsic toxicant (item 3) and may induce an insufficiency of Ca²⁺ and Mg²⁺ (item 2). These findings have implications for the mechanisms by which woodland plants tolerate very acidic soils.     

Formation constants of cu2+ complexes with humic and fulvic acids

Formation constants for Cu²⁺ complexes with humic and fulvic acids were determined by a modification of the well-known Bjerrum potentiometric titration method. Highly stable complexes were formed with formation constants of the order of those observed for synthetic polycarboxylic acids. Overall formation constants for a two-step process (B₂) ranged from 2.5 · 10^?4 to 7.9 · 10^?3.     

Quantitation of volatiles and nonvolatile acids in an extract from coffee beverages: correlation with antioxidant activity

The antioxidant activities of a commercial brewed coffee were investigated by measuring malonaldehyde (MA) formation from oxidized cod liver oil using a gas chromatographic method (MA-GC assay) and a thiobarbituric acid method (TBA assay). The highest antioxidant activity obtained by the MA-GC assay was from regular whole brewed coffee (97.8%) at a level of 20%, and the highest antioxidant activity obtained by the TBA assay was from decaffeinated whole brewed coffee (96.6%) at a level of 5%. Among 31 chemicals identified in a dichloromethane extract, guaiacol, ethylguaiacol, and vinylguaiacol exhibited antioxidant activities, which were comparable to that of alpha-tocopherol. Among nine chlorogenic acids (three caffeoylquinic acids, three feruloylquinic acids, and three dicaffeoylquinic acids) identified, 5-caffeoylquinic acid contained the greatest amount both in regular (883.5 microg/mL) and in decaffeinated (1032.6 microg/mL) coffees; it exhibited 24.5% activity by the MA-GC assay and 45.3% activity by the TBA assay at a level of 10 microg/mL. Caffeic and ferulic acids showed moderate antioxidant activities in both assays.     

Determination of aluminium complexes of low molecular organic acids in soil solution from forest soils using ultrafiltration

Ultrafiltration (<1000 D) was evaluated as an analytical method for determination of Al bound to low molecular weight organic acids (LMWOA) in soil solutions from podzolised forest soils. The results were compared to those obtained by two chemical equilibrium models and a size exclusion chromatography method. The percentage of Al bound to LMWOAs was highest in the O horizon solutions (15–44%) and decreased in the deeper horizons. Citric acid was found to be the most important complex former. Generally the ultrafiltration method and modelling showed acceptable agreement. The method showed acceptable precision and good recovery of Al in the samples.