Why plants grow poorly on very acid soils: are ecologists missing the obvious?

Factors associated with soil acidity are considered to be limiting for plants in many parts of the world. This work was undertaken to investigate the role of the toxicity of hydrogen (H(+)) which seems to have been underconsidered by ecologists as an explanation of the reduced plant growth observed in very acid soils. Racial differences are reported in plant growth response to increasing acidity in the grass Holcus lanatus L. (Yorkshire-fog) and the tree Betula pendula Roth (Silver Birch). Soils and seeds were collected from four Scottish sites which covered a range of soils from acid (organic and mineral) to more base-rich. The sites and their pH (1:2.5 fresh soil:0.01 M CaCl(2)) were: Flanders Moss (FM), pH 3.2+/-0.03; Kippenrait Glen (KP), pH 4.8+/- 0.05; Kinloch Rannoch (KR), pH 6.1+/-0.16; and Sheriffmuir (SMM), pH 4.3+/-0.11. The growth rates of two races of H. lanatus, FM and KP, and three races of B. pendula (SMM, KP and KR) were measured in nutrient solution cultures at pH 2.0 (H. lanatus only), 3.0, 4.0, 5.0, and 5.6. Results showed races from acid organic soils (FM) were H(+)-tolerant while those from acid mineral soils (SMM) were Al(3+)-tolerant but not necessarily H(+)-tolerant. These results confirmed that populations were separately adapted to H(+) or Al(3+) toxicity and this was dependent upon the soil characteristics at their site of collection. The fact of plant adaptation to H(+) toxicity supports the view that this is an important factor in very acid soils.     

Root surface phosphatase activity in ecotypes of Aegilops peregrina

The relationships between root surface phosphatase activity and the edaphic factors of their native habitats were investigated in four ecotypes of Aegilops peregrina (Hack.) Maire et Weil. In one set of experiments plants were grown in phosphate-deficient nutrient solution cultures (5 μ M ) with three pH values: 5.5, 6.5 and 7.5. In a second series, plants were grown in both P-poor and P-rich soils.
Results showed an optimal activity of the commonly-described root surface acid phosphatase of pH 4.5–5.0 in the ecotypes Meron (a P-poor montmorillonitic, typical mediterranean Terra-Rossa soil) and Har-Hurshan (a P-rich calcareous soil). However, in the ecotypes Malkiya (a P-rich kaolinitic Terra-Rossa) and Bet-Guvrin (a P-rich calcareous soil) the optimal activity of the phosphatase occurred at pH 6.0. The pH level of the growth solution had no effect on the pH of optimal activity of the phosphatase in the ecotypes Malkiya and Bet-Guvrin, but it somewhat affected their level of activity.
Phosphatase activity was stimulated when plant roots were grown in a P-poor soil, as compared to the activity of those which were grown in a P-rich soil. Plants of the Malkiya ecotype exhibited the strongest activation of phosphatase as compared to the other three ecotypes. It seems that ecotypes which have evolved in P-rich soils may regulate their root surface phosphatase activity better than those which have evolved in P-poor soils.     

Exudation of low molecular weight organic acids by germinating seeds of two edaphic ecotypes of Silene nutans L.

Two parapatric ecotypes of Silene nutans, exhibiting distinct allozyme patterns, morphology and autecology were investigated for differences in exudation of low molecular weight organic acids from germinating seeds, and for differences in seed phosphorus content. The calcicolous ecotype is restricted to calcareous soils, and the silicicolous one predominantly occurs on acid soils, and sometimes, although less frequently, on neutral to alkaline soils. No clear difference was found between ecotypes. However, within the silicicolous ecotype seed samples showed marked differences in exudation pattern and seed phosphorus content depending on origin along the soil acidity gradient. Seeds of low-pH origin exuded more dicarboxylic acids (malic + succinic acid, oxalic acid) and had a lower phosphorus content than seeds of high pH origin. The exudation of dicarboxylic acids from seeds of low pH origin is probably an adaptation to adverse conditions (aluminium toxicity) on acid soils. The pattern is similar to that found among different cultivars of wheat. It is contrasted to the pattern found on comparison of a suite of calcifugous and calcicolous species, where exudation of di- and tricarboxylic acids is associated with solubilisation of recalcitrantly bound phosphorus and iron in calcareous soils.     

Effects of aluminium on the growth and mineral composition of Betula pendula Roth

Aluminium (Al) is rhizotoxic and is often present in acidic soils at activities high enough to inhibit root elongation. The objectives of the present study were to assess the level of Al tolerance in different races of Betula pendula Roth (Silver Birch) and to investigate how growth and nutrient acquisition were affected by Al. A solution culture technique was employed which simulated natural soil solutions. Aluminium at low concentrations (2 and 5 mg l(-1)), enhanced the growth of two races of B. pendula originating from soils poor in Al (FM and KP). In contrast, Al, at all concentrations tested, inhibited growth in an Al-sensitive race (KR) whose provenance was a calcareous soil. At concentrations >/=10 mg l(-1), Al reduced growth in FM and KP races, while growth increased with increasing Al (up to 25 mg l(-1)) in the Al-tolerant, SMM, race. Aluminium altered both root and leaf architecture. Low Al concentrations (<5 mg l(-1)) significantly increased leaf expansion, and high concentrations (>25 mg l(-1)) reduced leaf expansion. In the Al-sensitive race, KR, there was a loss of apical dominance, and both lateral and primary roots were stunted and swollen, with increasing Al concentrations. These results demonstrated pronounced racial differences in tolerance to Al by B. pendula that could be predicted from the soil environment of each race.     

环渤海湾地区连作苹果园土壤中酚酸类物质变化

分析了山东昌邑、栖霞、蓬莱,辽宁大连、抚宁、绥远,河北昌黎、青县等地苹果园连作土壤中酚酸物质的组成和含量,结果表明:连作障碍发生的苹果园土壤中酚酸类物质的组成和含量在不同地区、不同土层厚度间存在显著差异。苹果园土壤中酚酸类物质的含量从春季到秋季随时间的延长逐渐减少,但过程缓慢。且非连作园土壤中酚酸类物质含量显著少于连作土。连作土壤中酚酸物质的组成和含量在不同季节间差异显著,尤其春季土壤中酚酸物质的种类与夏季和秋季显著不同。这可能是因为植物在不同季节分泌的酚酸类物质种类和含量有差别.不同土层中酚酸物质的分布因季节不同而有显著差异。夏季土壤中酚酸物质主要分布在浅层土壤中,而秋季则主要分布在深层土壤中。这可能是由于浇水等果园管理措施和自然降水对土壤中的酚酸物质产生的淋溶作用,使得大量的酚酸物质向深层土壤运动,最终造成了秋季果园连作土中随土层加深而酚酸物质含量增加的现象。不同地区苹果园连作土中,对羟基苯甲酸、(+)-儿茶素、咖啡酸、阿魏酸含量与非连作土无显著差异,而焦性没食子酸、绿原酸和根皮苷显著高于非连作土。焦性没食子酸、绿原酸和根皮苷可能是引起山东、辽宁、河北地区苹果园连作障碍的关键酚酸物质。     

采煤沉陷区不同造林树种恢复土壤酚酸物质对土壤微生物的影响

酚酸物质是影响微生物群落和结构的最重要因子之一,研究酚酸物质在不同造林树种土壤中的变化规律及其与微生物群落结构的关系,有助于更好地了解和揭示采煤沉陷区恢复造林条件下微生物群落变化的机制.本研究在双鸭山宝山采煤沉陷区的撂荒地基础上营造三针一阔(红松、落叶松、樟子松和杨树)人工林,测定这4种造林地土壤酚类物质、11种酚酸物质和微生物群落结构.结果表明: 复合态酚含量总体表现为人工林显著高于撂荒地,其中,落叶松人工林和杨树人工林的复合态酚含量较高,落叶松人工林和红松人工林的总酚含量显著高于撂荒地,红松人工林的水溶性酚含量显著高于撂荒地;在11种酚酸物质中,阿魏酸、松香酸、β-谷甾醇、齐墩果酸、莽草酸、亚油酸和硬脂酸的含量在人工林土壤中较高.土壤酚类物质与土壤微生物生物量不存在显著的相关关系,个别的酚酸物质与土壤微生物的相关关系显著,其中,阿魏酸、松香酸和β-谷甾醇对土壤微生物生物量有明显的促进作用,与真菌和真菌/细菌存在显著的正相关关系.杨树人工林的酚酸物质含量较高,说明营造杨树人工林对采煤沉陷区的土壤恢复有益.     

Influence of phenolic acids on phosphorus mobilisation in acidic and calcareous soils

Phenolic acids and phenols are abundant in soils. However, little information is available on the role of these compounds in mobilisation of soil phosphorus (P). The present study examined the effects of three phenolics on P mobilisation in comparison with citric acid in three soils differing in chemical properties. The soils were incubated with organic compounds at concentrations of 0 to 100 mol g^–1 soil for 30 min. While the addition of phenolic acid anions and phenol decreased soil pH, citrate either increased or did not affect soil pH depending on the soil type. All the organic compounds increased the amounts of easily-mobilised P fractions in the order of catechol citric acid proto-catechuic acid caffeic acid for the acid soils and citric acid > catechol = proto-catechuic acid > caffeic acid for the calcareous soil. Phosphorus mobilisation did not correspond to the amounts of Ca, Fe or Al ions released from the soils. These results suggest that organic acids and phenols altered the P fractions from stable, sparingly-soluble forms to easily dissolvable forms, and that chelation or precipitation of cations with organic ligands occur before biodegradation of the ligands.     

连作花生土壤中酚酸类物质的检测及其对花生的化感作用

研究了南方红壤区不同连作年限花生土壤中酚酸物质的种类、含量,及其对花生生长的影响。结果表明:连作花生土壤中对羟基苯甲酸、香草酸和香豆酸随着连作年限的增加而增加,连作10a后3种酚酸总量达11.09mg·kg-1干土,显著高于连作3a和6a的土壤;而土壤中香豆素和苯甲酸含量比较低,且变化没有规律。所有酚酸处理组对花生幼苗的株高和根长表现出抑制作用,对花生幼苗地下部的干鲜重均表现出"低促高抑"的特点。香草酸和香豆酸处理组对花生幼苗地上部的干鲜重表现出"低促高抑"的特点,其他处理组均表现出抑制作用。花生幼苗根系活力随着酚酸处理浓度的增加而降低,花生幼苗的超氧化物歧化酶活力(SOD)、过氧化物酶活力(POD)、丙二醛含量(MDA)则随着酚酸浓度的增加而增加。与只用茄腐镰刀菌孢子悬液浸泡花生种子的对照相比,加入酚酸后,花生种子的病原菌的感染率随着酚酸浓度的增加而增加,发芽率则随着酚酸浓度的增加而下降。以上结果说明,酚酸物质可以抑制花生幼苗的生长和提高花生的发病率,可能是因为酚酸物质破坏花生细胞膜的完整性而使病原菌入侵,影响花生生长,产生连作障碍。     

Allelopathic Interactions Involving Phenolic Acids

A major concern regarding allelopathic interactions involving phenolic acids in no-till systems pertains to the fact that concentrations of individual phenolic acids recoverable from field soils are well below levels required for inhibition of germination and seedling growth in laboratory bioassays. Field soils contain a variety of phenolic acids as well as other toxic and nontoxic organic compounds that are available to interact with seeds and roots; whereas in laboratory bioassays, with few exceptions, single phenolic acids have been tested. Studies of mixtures of phenolic acids and other toxic (e.g., methionine) and nontoxic (e.g., glucose) organic compounds in laboratory bioassays indicate that the action of a single phenolic acid is not representative of the actions of such mixtures. Specifically, as the number of phenolic acids added to soil increased, concentrations of the individual phenolic acids required to bring about a growth inhibition declined. The addition of other organic compounds (e.g., glucose, methionine) to the soil also reduced the concentration of a phenolic acid (e.g., p-coumaric acid) required for growth inhibition. These results support the hypothesis that in the field mixtures of phenolic acids and other organic compounds can cause inhibitory effects even though the concentrations of individual compounds are well below their inhibitory levels.     

连作障碍与根际微生态研究Ⅲ.土壤酚酸物质及其生物学效应

以黑龙江省大豆重茬 5年与正茬土壤和根系为主要研究对象 ,采用高效液相色谱法 ,研究土壤和根系浸提液中的酚酸物质的含量及其生物学效应 .结果表明 ,重茬土壤中对羟基苯甲酸和香草酸的含量 (1mol·L-1NaOH提取 )大于正茬土壤 ,且差异达到极显著水平 ,香草醛含量差异不显著 ;重茬大豆根系水提液中对羟基苯甲酸、香草酸、阿魏酸、香草醛、香豆素含量均高于正茬 .大豆连作条件下土壤多酚氧化酶活性高于正茬土壤 .重茬大豆根系水提液及在水培条件下外加对羟基苯甲酸对大豆幼苗生长发育有一定的抑制作用 ;酚酸物质加入土壤 1周后 ,对羟基苯甲酸、香草酸、香草醛、阿魏酸、苯甲酸、香豆素残留率分别为 10 .4%、15 .3 %、4.1%、2 .3 %、5 .0 %、17.5 % ;且外加酚酸浓度与土壤中真菌数量呈极显著指数相关 .     

Arbuscular mycorrhizal adaptation,spore germination,root colonization,and host plant growth and mineral acquisition at low pH

Arbuscular mycorrhizal (AM) fungi colonize plant roots and often enhance host plant growth and mineral acquisition, particularly for plants grown under low nutrient and mineral stress conditions. Information about AM fungi and mycorrhizal ( +AM) host plant responses at low pH ( < 5) is limited. Acaulospora are widely reported in acid soil, and Gigaspora sp. appear to be more common in acid soils than Glomus sp. Spores of some AM fungi are more tolerant to acid conditions and high Al than others; t Acaulospora sp., Gigaspora sp., and Glomus manihotis are particularly tolerant. Root colonization is generally less in low than in high pH soils. Percentage root colonization is generally not related to dry matter (DM) produced. Maximum enhancement of plant growth in acid soil varies with AM fungal isolate and soil pH, indicating adaptation of AM isolates to edaphic conditions. Acquisition of many mineral nutrients other than P and Zn is enhanced by +AM plants in acid soil, and the minerals whose concentration is enhanced are those commonly deficient in acid soils (Ca, Mg, and K). Some AM fungal isolates are effective in overcoming soil acidity factors, especially Al toxicity, that restrict plant growth at low pH.     

Mechanisms of microbially enhanced Fe acquisition in red clover (Trifolium pratense L.)

Soil microorganisms may play an important role in plant Fe uptake from soils with low Fe bioavailability, but there is little direct experimental evidence to date. We grew red clover, an Fe-efficient leguminous plant, in a calcareous soil to investigate the role of soil microbial activity in plant Fe uptake. Compared with plants grown in non-sterlie (NS) grown plants, growth and Fe content of the sterile(s) grown plants was significantly inhibited, but was improved by foliar application of Fe EDTA, indicating that soil microbial activity should play an important role in plant Fe acquisition. When soil solution was incubated with phenolic root exudates from Fe-deficient red clover, a few microbial species thrived while growth of the rest was inhibited, suggesting that the Fe-deficient (-Fe) root exudates selectively influenced the rhizosphere's microbial community. Eighty six per cent of the phenolic-tolerant microbes could produce siderophore [the Fe(III) chelator] under -Fe conditions, and 71% could secrete auxin-like compounds. Interestingly, the synthetic and microbial auxins (MAs) significantly enhanced the Ferric reduction system, suggesting that MAs, in addition to siderophores, are important to plant Fe uptake. Finally, plant growth and Fe uptake in sterilized soil were significantly increased by rhizobia inoculation. Root Fe-EDTA reductase activity in the -Fe plant was significantly enhanced by rhizobia infection, and the rhizobia could produce auxin but not siderophore under Fe-limiting conditions, suggesting that the contribution of nodulating rhizobia to plant Fe uptake can be at least partially attributed to stimulation of turbo reductase activity through nodule formation and auxin production in the rhizosphere. Based on these observations, we propose as a model that root exudates from -Fe plants selectively influence the rhizosphere microbial community, and the microbes in turn favour plant Fe acquisition by producing siderophores and auxins.     

A comparison of some populations of Eucalyptus viminalis Labill. growing on calcareous and acid soils in Victoria,Australia

A study of populations of Eucalyptus viminalis found on both acid and alkaline soils showed that seedlings differ in their tolerance of calcareous soils and their susceptibility to lime chlorosis. Seedlings from an open-forest population on calcareous dunes in the Otway Ranges, Victoria, averaged a significantly greater yield than seedlings of three other populations found on acid soils when all were grown on calcareous soil of pH 6.8. A tall ribbon gum form of E. viminalis, from Paradise gully in the Otways, was the least tolerant of alkaline conditions and showed severe signs of chlorosis and reddening of leaf margins. The latter appeared to be related to high uptake of phosphorus. This population showed rapid growth on a fertile acid loam. The data presented also emphasize the need to consider the variation in soils which can occur at any one site. Population differences were most marked when seedlings were grown on soils of pH near 7.0. Yield was reduced in the Otways calcareous population when seedlings were grown on the more leached soil from swales (pH 6.5) between dunes and on the highly calcareous soil from the dune crests (pH 7.8–8.0). The failure of any of the populations of E. viminalis studied to grow well on soils of high pH suggest that this species is not tolerant of highly calcareous soils. This may in part explain the absence of this species from the drier calcareous areas on the Mornington Peninsula and the Yanakie Isthmus, Victoria. Since seedlings had reduced root development on the soil collected from the Peninsula, E. viminalis may be restricted, in effect because of drought stress, to non-calcareous sites in the eastern part of Victoria.     

Phenolic acids: Possible agents of modifying N2-fixing symbiosis through rhizobial alteration?

Phenolic acids, low molecular weight phenolics, are precursors of a variety of antimicrobial compounds, root signalling molecules, and phytoalexins that play an important role in plant defence responses. In agro ecosystem, a large amount of litter is turned over during the cropping season, fallow period and land preparation. This releases a flush of phenolic acids, amounts of which exceed very much the quantities released in root exudation. In rhizobial inoculation of legumes, these phenolic acids, depending on the concentration, may affect the persistence of rhizobia in the soil and their symbiotic efficiency, in terms of N₂ fixation. The present study evaluates the effects of different concentrations of four phenolic acids (protocatechuic, p-coumaric, ferulic and vanillic) on population size of four rhizobial strains (Bradyrhizobium elkanii SEMIA 5019, B. japonicum TAL 102 and TAL 620, and Azorhizobium caulinodans ORS 571). Culture media with different concentrations of phenolic acids in the presence or absence of manitol were used to evaluate rhizobial population size on day 6. Rhizobial total proteins were extracted and electrophoresed on polyacrylamide gels. Further, the effects of phenolic acid-affected rhizobia on N₂ fixing capacity were also investigated by inoculating two of those strains to soybean. Phenolic acid-treated B. elkanii SEMIA 5019 and B. japonicum TAL 102 were inoculated to soybean, and plant growth, N accumulation and nodule dry weight were assessed in a pot experiment. The population size of TAL 102 was induced when the culture medium was supplied with different phenolic acids as the sole carbon source. In many cases, the presence of manitol in the medium masked the differential effects of phenolic acids on the rhizobial population size. All four phenolic acids used in our study suppressed the population size of TAL 620. Strain ORS 571 showed low population size at low concentrations followed by a growth recovery at high phenolic acid concentrations. Strain SEMIA 5019 treated with 0.03 mM ferulic acid produced the highest increase in shoot growth of soybean, (ca. 65%). Treating strain SEMIA 5019 with 9 mM protocatechuic acid produced the largest decrease in nodule dry weight (ca. 50%) without any significant changes in shoot N accumulation. P-coumaric acid, even at 0.12 mM, could stimulate the N₂ fixing activity of SEMIA 5019, whereas the same concentration reduced the effectiveness of TAL102 in a soybean-rhizobium symbiosis. Phenolic acid interactions with rhizobia led to biochemical, and hence physiological changes, resulting in an alteration in their symbiotic ability. Different leguminous plants secrete different phenolic compounds other than phenolic acids during root exudation. Further studies should therefore be conducted to evaluate the effects of those compounds on the symbiosis. It is concluded from this study that the effect of phenolic acids is concentration and structure dependant, and strain-specific. The effect will also be pH dependant. Thus, phenolic acids are possible agents for modifying the legume-rhizobial symbiosis.     

Iron accumulation in seed of common bean

The effect of soil and genotype on iron concentration [Fe] in common bean (Phaseolus vulgaris L.) seed was studied in the greenhouse. Liming an acid soil increased soil pH from 6.0 to 7.3 but had no effect on seed [Fe] of three bean genotypes (Voyager, T39, UI911) from the Middle American gene pool in North Dakota. However, liming decreased seed-manganese concentration [Mn]. The influence of FeEDDHA on Fe accumulation in seed of the three bean genotypes, grown on acid (pH=6.0) and naturally calcareous (pH=8.2) soils, was also studied in North Dakota. Seed from the acid soil contained 25% higher [Fe] than seed from the calcareous soil. FeEDDHA increased seed [Fe] only on the calcareous soil, but reduced seed [Mn] on both soils. Voyager seed, characterized by a relatively low [Fe] in the seed coat, had a higher seed [Fe] than the other two genotypes. The hypothesis that high seed [Fe] is characterized by a low seed-coat [Fe] was next investigated. Voyager, T39 and 10 diverse Latin American genotypes from the Middle American gene pool were grown on a soil (pH=7.0) with Andic properties in Mexico in the presence and absence of FeEDTA. FeEDTA increased seed [Fe]. Seed of Voyager and a Mexican genotype (Bayo 400) had the highest seed [Fe]. However, Bayo 400, unlike Voyager, contained a high percentage of its seed Fe in the seed coat. Consequently, a high seed [Fe] genotype does not necessarily have a low seed-coat [Fe]. Both soil and genotype affect Fe accumulation in bean seed.     

Ecotypes of Holcus lanatus Tolerant to Zinc Toxicity also Tolerate Zinc Deficiency

Genotypes tolerant to zinc (Zn) toxicity, if they accumulateZn in their roots, may grow better than Zn-sensitive genotypes,even in Zn-deficient soil. In the present study, Holcus lanatusL. ecotypes differing in tolerance to Zn toxicity were grownin Zn-deficient Laffer soil which was amended with Zn to createa range of conditions from Zn deficiency to Zn toxicity. IncreasingZn additions to the soil, up to the sufficiency level, improvedgrowth of all ecotypes. At toxic levels of added Zn, the Zn-sensitiveecotype suffered a greater decrease in growth than the Zn-tolerantecotypes. All ecotypes accumulated more Zn in roots than inshoots, with root concentrations exceeding 8 g Zn kg^-1dry weightin extreme cases. When grown in Zn-deficient or Zn-sufficientsoil (up to 0.5 mg Zn kg^-1soil added), ecotypes tolerant toZn toxicity took up more Zn, grew better and had greater rootand shoot Zn concentration than the control (Zn-sensitive ecotype).Zn-tolerant ecotypes transported more Zn, copper (Cu) and iron(Fe) from roots to shoots in comparison with the Zn-sensitiveecotype. The average Zn uptake rate from Zn-deficient soil (noZn added) was greater in the Zn-tolerant ecotypes than in theZn-sensitive ecotype. In conclusion, ecotypes of H. lanatusthat are tolerant to Zn toxicity also tolerate Zn deficiencybetter than the Zn-sensitive ecotype because of their greatercapacity for taking up Zn from Zn-deficient soil. This is thefirst report of the coexistence of traits for tolerance to Zntoxicity and Zn deficiency in a single plant genotype. Copyright2000 Annals of Botany Company Copper, heavy metal, Holcus lanatus, iron, zinc deficiency, zinc toxicity     

内生真菌对花生残茬腐解及土壤酚酸含量的影响

土壤中花生残茬是导致连作障碍的原因之一。为了探讨施加内生真菌Phomopsis liquidambari(B3)对加速花生残茬腐解、改善连作花生土壤环境、缓解花生连作障碍的作用及其可能机理,通过向土壤中添加花生(Archis hypogaea)残体,利用盆栽试验探讨了施加B3对花生残茬腐解率、土壤部分酚酸物质和酶活性的影响。结果表明:与CK相比,在萌发期和苗期,添加B3处理显著加快残茬腐解,提高纤维素木质素降解率,增加土壤中对羟基苯甲酸、香草酸和香豆酸的含量;在花生整个生育期,施加B3显著调节了土壤中漆酶、锰过氧化物酶(Manganese peroxidase,Mn P)、木质素过氧化物酶(Lignin peroxidase,Li P)和多酚氧化酶(Polyphenol oxidase,PPO)活性的动态变化,这种变化有利于花生残茬快速腐解和酚酸类化感物质的及时转化。开花期之后施加B3处理土壤酚酸含量显著降低,花生荚果增产19.9%。实时定量PCR结果表明内生真菌B3在土壤中30 d内可以被检测,并对复杂多样的酚酸类物质具有广谱高效的降解能力。由此说明,施加内生真菌B3可以显著加快连作土壤中花生残茬腐解,进而通过减少土壤酚酸含量来缓解由残茬腐解引起的连作障碍。     

酚酸类物质的化感作用研究进展

酚酸类物质是普遍存在于高等植物组织并与植物生长密切相关的次级代谢产物。几十年来,人们对酚酸类化合物的认识逐渐加深,但关于其在生物学、生态学以及农业上的作用机制仍不是很清楚。因此,进一步了解这些生物分子将有助于生态系统的维持与保护。重点介绍了酚酸类物质的来源及化感作用,微生物对酚酸类物质的降解机理,代谢途径及相应分子水平的研究,指出了酚酸类物质研究中存在的问题,同时展望了酚酸类物质的研究方向与前景。     

Copper bioavailability and rhizosphere pH changes as affected by nitrogen supply for tomato and oilseed rape cropped on an acidic and a calcareous soil

Vineyard soils have been contaminated by long-term applications of copper salts as fungicides against mildew, raising the question of the bioavailability (and toxicity) of such accumulated Cu to cultivated plants which can replace vines. The aim of this study was to assess, in an acidic and a calcareous Cu-contaminated soil, how the extractability and bioavailability of soil Cu was affected by pH changes in the rhizosphere of two plant species (oilseed rape and tomato), in response to various forms of nitrogen supply (nitrate only or both nitrate and ammonium). Besides shoot analysis, the experimental approach used in the present work provided an easy access to both roots and rhizosphere soil. Roots of tomato and rape induced a systematic acidification in the calcareous soil while root-induced alkalinization occurred in the acidic soil. Whilst few differences were found between treatments in the calcareous soil, oilseed rape took up more Cu and also alkalinized its rhizosphere more strongly than tomato in the acidic soil. The growth of tomato roots was restricted in the acidic soil, while that of oilseed rape was not, suggesting that tomato was either more sensitive to soil acidity and/or Cu toxicity. A major finding was that, in the acidic soil, Cu bioavailability increased with increasing rhizosphere pH. This was largely due to the enhanced accumulation of Cu in the root compartment of both species with increasing rhizosphere pH. The hypothetical explanation proposed here is that Cu binding to root cell walls played a major role in the accumulation of Cu into the plant. Apoplasmic Cu (Cu bound to cell walls) would indeed be expected to increase with increasing pH as a consequence of the pH-dependency of the charges of cell wall constituents.     

Overcoming Fe deficiency by a transgenic approach in rice

Iron (Fe) is an essential microelement for plant growth. Fe availability is particularly limited on calcareous soils, which have high pH. Approximately 30% of the world's soils are considered calcareous with low Fe availability, which results in extensive areas of Fe deficiency in plants. Some graminaceous plants are known to secrete high amounts of mugineic acid family phytosiderophores (MAs) under Fe deficiency. This Fe acquisition system is called the Strategy-II mechanism. Tolerance to Fe deficiency in graminaceous plants is thought to depend on the quantity of MAs secreted by plants under Fe deficiency stress. This system was utilized to enhance the tolerance of rice to low Fe availability. Transgenic rice expressing the barley naat genes, one of the genes for the enzymes on the biosynthetic pathway of MAs, showed tolerance to low Fe availability when grown in a calcareous soil.