Arbuscular Mycorrhizal Fungi, Bacillus cereus, and Candida parapsilosis from a Multicontaminated Soil Alleviate Metal Toxicity in Plants

We investigated if the limited development of Trifolium repens growing in a heavy metal (HM) multicontaminated soil was increased by selected native microorganisms, bacteria (Bacillus cereus (Bc)), yeast (Candida parapsilosis (Cp)), or arbuscular mycorrhizal fungi (AMF), used either as single or dual inoculants. These microbial inoculants were assayed to ascertain whether the selection of HM-tolerant microorganisms can benefit plant growth and nutrient uptake and depress HM acquisition. The inoculated microorganisms, particularly in dual associations, increased plant biomass by 148% (Bc), 162%, (Cp), and 204% (AMF), concomitantly producing the highest symbiotic (AMF colonisation and nodulation) rates. The lack of AMF colonisation and nodulation in plants growing in this natural, polluted soil was compensated by adapted microbial inoculants. The metal bioaccumulation abilities of the inoculated microorganisms and particularly the microbial effect on decreasing metal concentrations in shoot biomass seem to be involved in such effects. Regarding microbial HM tolerance, the activities of antioxidant enzymes known to play an important role in cell protection by alleviating cellular oxidative damage, such as superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase, were here considered as an index of microbial metal tolerance. Enzymatic mechanisms slightly changed in the HM-adapted B. cereus or C. parapsilosis in the presence of metals. Antioxidants seem to be directly involved in the adaptative microbial response and survival in HM-polluted sites. Microbial inoculations showed a bioremediation potential and helped plants to develop in the multicontaminated soil. Thus, they could be used as a biotechnological tool to improve plant development in HM-contaminated environments.     

Effect of arbuscular mycorrhizal fungal inoculation on heavy metal accumulation of maize grown in a naturally contaminated soil

A pot culture experiment was carried out to study heavy metal (HM) phytoaccumulation from soil contaminated with Cu, Zn, Pb, and Cd by maize (Zea mays L.) inoculated with arbuscular mycorrhizal (AM) fungi (AMF). Two AM fungal inocula--MI containing only one AM fungal strain (Glomus caledonium 90036) and MII consisting of Gigaspora margarita ZJ37, Gigaspora decipens ZJ38, Scutellospora gilmori ZJ39, Acaulospora spp., and Glomus spp.--were applied to the soil under unsterilized conditions. The control received no mycorrhizal inoculation. The maize plants were harvested after 10 wk of growth. MI-treated plants had higher mycorrhizal colonization than MII-treated plants. Both MI and MII increased P concentrations in roots, but not in shoots. Neither MI nor MII had significant effects on shoot or root dry weight (DW). Compared with the control, shoot Cu, Zn, Pb, and Cd concentrations were decreased by MI but increased by MII. Cu, Zn, Pb, and Cd uptake into shoots and roots all increased in MII-treated plants, while in MI-treated plants Cu, Zn, and Pb uptake into shoots and Cd uptake into roots decreased but Cu, Zn, and Pb uptake into roots and Cd into shoots increased. MII was more effective than MI in promoting HM extraction efficiencies. The results indicate that MII can benefit HMphytoextraction and, therefore, show potential in the phytoremediation of HM-contaminated soils.     

Effects of nutrient and soil moisture on competition between shape Carex stricta,shape Phalaris arundinacea,and shape Typha latifolia

We investigated the importance of nutrients, soil moisture, arbuscular mycorrhizal fungi (AMF), and interspecific competition levels on the biomass allocation patterns of three wetland perennial plant species, Carex stricta Lam., Phalaris arundinacea L., and Typha latifolia L. A factorial experiment was conducted with high-low nutrient levels, high-low soil moisture levels, and with and without AMF inoculation. Under the experimental conditions, plant inoculation by AMF was too low to create a treatment and the AMF treatment was dropped from the total analysis. P. arundinacea and T. latifolia biomass were 73% and 77% higher, respectively, in the high nutrient treatment compared to the low nutrient treatment. Biomass allocation between shoots and roots remained relatively constant between environmental treatments, although shoot:root ratios of P. arundinacea declined in the low nutrient treatment. For C. stricta, the high nutrient and soil moisture treatments resulted in an increase in biomass of 50% and 15%, respectively. Shoot:root ratios were nearly constant among all environmental conditions. Biomass of T. latifolia and C. stricta was greatly decreased when grown with P. arundinacea. The rapid, initial height growth of P. arundinacea produced a spreading, horizontal canopy that overshadowed the vertical leaves of T. latifolia and C. stricta throughout the study. This pattern was repeated in both high and low nutrient and soil moisture treatments. When grown with P. arundinacea, C. stricta and T. latifolia significantly increased their mean shoot height, regardless of the nutrient or soil moisture level. The results of this experiment suggest that C. stricta and T. latifolia were light limited when growing with P. arundinacea and that canopy architecture is more important for biomass allocation than the other environmental conditions tested. The results also suggest that Phalaris arundinacea is an inherently better competitor (sensu Grime 1979) than C. stricta or T. latifolia.     

丛枝菌根真菌与植物共生对植物水分关系的影响及机理

自1885年Frank首次提到菌根(mykorhiza)概念以来,大量的试验证实了丛枝菌根真菌(AMF)与植物根系之间形成具有一定结构和功能的共生体,促进植物生长并提高干旱耐受能力,在干旱生态系统中发挥重要的作用。该研究多集中在对宿主植物生理生态的影响及其机制方面,然而菌根共生对宿主植物水分吸收和信号产生、传递的影响研究少而分散,缺少系统总结。综述了最近四十多年丛枝菌根真菌与植物共生体对宿主植物干旱适应性影响研究进展,讨论了菌根共生对植物根冠通讯的影响及机理。干旱胁迫下AMF与植物共生,通过影响宿主植物一系列生理生态过程,提高宿主植物横向根压和纵向蒸腾拉力。经典的Ohm吸水模型是该方向最有代表性的研究成果,该模型揭示了菌根共生的根外菌丝具有不同于根细胞的细胞结构和水分运输性能,这为宿主植物提供一种特殊的快速吸水方式,可提高植物对土壤水分的吸收和运输能力。研究表明,AMF会影响宿主植物根冠通讯过程,如诱发信号级联反应,诱导根系尽早感知水分胁迫并产生非水力根源信号,提高宿主对干旱的耐受性。讨论了AMF在根冠通讯分子机制研究方面存在的问题及可能的解决途径,展望了AMF在干旱农业生产中的应用潜力。     

Moderating mycorrhizas: arbuscular mycorrhizas modify rhizosphere chemistry and maintain plant phosphorus status within narrow boundaries

Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbuscular mycorrhizal fungi (AMF) in the uptake of P from a pulse. Five legumes (Kennedia prostrata, Cullen australasicum, Bituminaria bituminosa, Medicago sativa and Trifolium subterraneum) were grown in a moderate P, sterilized field soil, either with (+AMF) or without (?AMF) addition of unsterilized field soil. After 9–10 weeks, half the pots received 15 mg P kg^?1 of soil. One week later, we measured: shoot and root dry weights; percentage of root length colonized by AMF; plant P, nitrogen and manganese (Mn) concentrations; and rhizosphere carboxylates, pH and plant‐available P. The P pulse raised root P concentration by a similar amount in uncolonized and colonized plants, but shoot P concentration increased by 143% in uncolonized plants and 53% in colonized plants. Inoculation with AMF decreased the amount of rhizosphere carboxylates by 52%, raised rhizosphere pH by ～0.2–0.7 pH units and lowered shoot Mn concentration by 38%. We conclude that AMF are not simply a means for plants to enhance P uptake when P is limiting, but also act to maintain shoot P within narrow boundaries and can affect nutrient uptake through their influence on rhizosphere chemistry.     

Phosphorus efficiencies and responses of barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) to arbuscular mycorrhizal fungi grown in highly calcareous soil

Two experiments were carried out to investigate phosphorus efficiencies and mycorrhizal responsiveness in an improved cultivar (Clipper) and a landrace (Sahara) of barley (Hordeum vulgare L.). In experiment 1, two pot sizes were used to evaluate the effect of soil volume on P uptake and mycorrhizal responsiveness. In experiment 2, a compartmented ("cross-pot") system was used to monitor (32)P delivery by external hyphae of arbuscular mycorrhizal fungi (AMF) to the host plant. Results showed that, irrespective of growth conditions, Sahara had much larger root biomass than Clipper and consequently substantially more P was allocated to roots in Sahara than in Clipper. Specific root length in Clipper was much longer than in Sahara. Increase in soil volume enhanced percentage root length colonised by AMF, plant growth and P uptake, and Sahara was more sensitive to changes in soil volume than Clipper. Pot size (soil volume) used to assess responsiveness to AMF by different plant species or genotypes with different root/shoot ratios might be a confounding factor. Clipper was more responsive to AMF than Sahara in terms of tissue P concentrations, which is partly related to their differences in root/shoot ratios. However, increases in SPU [specific P uptake, mg P (g root biomass)(-1)] caused by AMF were bigger in Clipper, suggesting that AMF played a larger role in P uptake. In accordance with the larger increase in SPU, Clipper took up more (32)P via AMF hyphae than Sahara. The compartmented system using radioactive P might be an alternative approach to directly investigate mycorrhizal responsiveness of different plant species or varieties than conventional pot experiments, provided that the same AM fungus is used.     

丛枝菌根真菌对豆科作物生长和生物固氮及磷素吸收的影响

本研究以大豆为材料,采用盆栽和田间试验,探讨丛枝菌根真菌(AMF)对豆科作物生长的影响。盆栽试验设置了接种(+AMF)和不接种(-AMF)丛枝菌根真菌处理,田间试验设置了AMF菌丝非限制与限制处理。盆栽试验结果表明: 接种AMF显著提高了大豆地上部生物量(16.5%)和大豆根瘤数(131.4%),地上部磷含量、磷吸收量、氮含量和氮吸收量也显著增加。田间试验中,AMF菌丝非限制处理下大豆的地上部生物量、根系生物量、根瘤数量分别比限制处理下显著提高了123.6%、61.5%和212.5%,地上部和根系磷吸收量、氮含量、氮吸收量均显著高于限制处理,大豆根际土壤速效氮和有效磷含量也均显著高于限制处理。本研究可为进一步认识豆科作物与AMF的共生关系及田间磷肥高效利用提供理论参考。     

西藏高原天然长芒草地丛枝菌根真菌接种效应

采用草地均匀打孔方法,就草地土壤未消毒条件下接种丛枝菌根（AM）真菌对长芒草(Stipa bungeana)的侵染效应以及对植物生长、吸磷效率、土壤微生物区系等的影响进行研究.结果表明,1)接种处理、不接种处理的菌根效应存在着明显的差异,多数接种处理根围土壤AM真菌孢子密度、菌根侵染率和侵染强度显著提高,但对丛枝丰度的影响相对较低.2)接种后AM真菌孢子密度对菌根侵染率具有极显著影响(r=0.7679**);随菌根侵染率的增加,植株总干物重和吸磷总量均呈极显著提高,r值分别为0.7556**、0.8018**.3)与植株地上部相比,接种AM真菌对提高根系干物重、根系吸磷量和含磷量的促进作用相对较大.4)多数接种处理根际土壤酸性磷酸酶、碱性磷酸酶活性均呈一定程度的提高,根际土壤细菌数量显著增加,真菌、放线菌的数量变化则不甚明显.5)各接种处理对寄主植物的综合侵染效应在总体上呈Glomus mosseae+G. intraradices+Scutellospora calospora＞G. mosseae+G. aggregatum＞Glomus sp.＞G. mosseae＞G. mosseae+ G. etunicatum+G. intraradices+S. erythropa＞G. geosporum的趋势.     

内生真菌和丛枝菌根真菌对羊草生长的影响

该研究比较了摩西球囊霉(Glmous mosseae)和幼套球囊霉(Glmous etunicatum)两种丛枝菌根真菌和内生真菌单独及混合接种对羊草(Leymus chinensis)生长的影响。结果表明, 内生真菌对2种菌根真菌的侵染均无显著影响, 内生真菌可极显著增加羊草的分蘖数、地上生物量、总生物量。内生真菌与菌根真菌之间的相互作用因菌根真菌种类而不同, 幼套球囊霉对宿主植物生长无明显影响且和内生真菌之间也无明显的相互作用; 单独接种摩西球囊霉显著增加羊草的地上、地下和总生物量, 当其与内生真菌共同存在时, 二者之间存在一定的拮抗作用。冗余分析结果表明, 在内生真菌-AM真菌-羊草共生体中, 内生真菌对宿主植物生长的影响最大, 摩西球囊霉对宿主植物生长也有一定的贡献, 幼套球囊霉对宿主植物生长无明显影响。     

Bioremediation of Cadmium-Contaminated Soil through Cultivation of Maize Inoculated with Plant Growth–Promoting Rhizobacteria

A pot experiment was conducted to study the effect of single and co-inoculation of Bacillus mycoides and Micrococcus roseus strains, indigenous to heavy metal (HM)–contaminated soils, on the growth and essential-nutrient and Cd uptake of maize in a soil polluted with 100 and 200 mg Cd kg^?1. Increasing Cd levels significantly decreased shoot and root dry weights, and shoot P, Fe, Zn, and Mn uptake. All bacterial treatments significantly increased biomass and shoot nutrient uptake of plant compared with control in the soil polluted with Cd. Inoculation of plants with B. mycoides and consortium of two bacteria significantly increased, whereas M. roseus significantly decreased, shoot and root Cd uptake, and Cd transfer and translocation factors compared with control in Cd-polluted conditions. The results showed that B. mycoides and consortium of two bacteria had an effective role in phytoextraction and M. roseus was the most effective treatment in phytostabilization of Cd.     

Mycorrhizal symbiosis and phosphorus fertilization effects on Zea mays growth and heavy metals uptake

Arbuscular mycorrhizal fungi (AMF) can promote plant growth and reduce plant uptake of heavy metals. Phosphorus (P) fertilization can affect this relationship. We investigated maize (Zea mays L.) uptake of heavy metals after soil AMF inoculation and P fertilization. Maize biomass, glomaline and chlorophyll contents and uptake of Fe, Mn, Zn, Cu, Cd and Pb have been determined in a soil inoculated with AMF (Glomus aggregatum, or Glomus intraradices) and treated with 30 or 60 µg P-K₂HPO₄ g^?1 soil. Consistent variations were found between the two mycorrhizal species with respect to the colonization and glomalin content. Shoot dry weight and chlorophyll content were higher with G. intraradices than with G. aggregatum inoculation. The biomass was highest with 30 µg P g^?1 soil. Shoot concentrations of Cd, Pb and Zn decreased with G. aggregatum inoculation, but that of Cd and Pb increased with G. intraradices inoculation. Addition of P fertilizers decreased Cd and Zn concentrations in the shoot. AMF with P fertilization greatly reduced maize content of heavy metals. The results provide that native AMF with a moderate application rate of P fertilizers can be exploited in polluted soils to minimize the heavy metals uptake and to increase maize growth.     

Mycorrhizae formation and nutrient uptake of new corn (Zea mays L.) hybrids with extreme canopy and leaf architecture as influenced by soil N and P levels

A study was conducted to evaluate the effect of N and P supply levels on mycorrhizal formation and nutrient uptake in corn hybrids with different architectures and to determine arbuscular mycorrhizal fungal (AMF) development in relation to shoot N/P ratio and shoot:root ratio. Corn pot cultures with a pasteurized medium of two parts sand and one part sandy loam soil were grown in the greenhouse. Marigold plants inoculated or not with Glomus intraradices Schenck & Smith were used to establish an AMF hyphal network in the designated soil pots. Corn hybrids were seeded after removal of the marigold plant. Mycorrhizal colonization of corn hybrids and the quantity of extraradical hyphae produced in soil were greatest at the lowest P level and at the intermediate N level. Root colonization was correlated with shoot N/P ratio only at the intermediate N level. The shoot concentrations of P, Mg, Zn and Cu were significantly higher in mycorrhizal plants than in non-mycorrhizal plants. The corn phenotype with the highest shoot:root ratio had the highest root colonization. The corn hybrid with a leafy normal stature architecture had a greater mycorrhizal colonization than that of other two corn hybrids. This experiment showed that N level in soil influenced shoot N/P ratio, root colonization and extraradical hyphal production, which in turn influenced uptake of other nutrients. This revised version was published online in June 2006 with corrections to the Cover Date.     

Heavy metal uptake by arbuscular mycorrhizas of Elsholtzia splendens and the potential for phytoremediation of contaminated soil

A pot culture experiment and a field experiment were carried out separately to study heavy metal (HM) uptake from soil contaminated with Cu, Zn, Pb and Cd by Elsholtzia splendens Nakai ex F. Maekawa inoculated with arbuscular mycorrhizal (AM) fungi and the potential for phytoremediation. The HM-contaminated soil in the pot experiment was collected from the field experiment site. Two AM fungal inocula, MI containing only one AM fungal strain, Glomus caledonium 90036, and M II consisting of Gigaspora margarita ZJ37, Gigaspora decipens ZJ38, Scutellospora gilmori ZJ39, Acaulospora spp. andGlomus spp., were applied to the soil under unsterilized conditions. In the pot experiment, the plants were harvested after 24 weeks of growth. Mycorrhizal colonization rate, plant dry weight (DW) and P, Cu, Zn, Pb, Cd concentrations were determined. MI-treated plants had higher mycorrhizal colonization rates than MII-treated plants. Both MI and MII increased shoot and root DW, and MII was more effective than MI. In shoots, the highest P, Cu, Zn and Pb concentrations were all observed in the plants treated with MII, while MI decreased Zn and Pb concentrations and increased P but did not alter Cu, and Cd concentrations were not affected by either of two inocula. In roots, MII increased P, Zn, Pb concentrations but did not alter Cu and Cd, and MI did not affect P, Cu, Zn, Pb, Cd concentrations. Cu, Zn, Pb, Cd uptake into shoots and roots all increased in MII-treated plants, while in MI-treated plants, Cu and Zn uptake into shoots and Cu, Zn, Pb, Cd into roots increased but Pb and Cd uptake into shoots decreased. In general, MII was more effective than MI in promoting plant growth and HM uptake. The field experiment following the pot experiment was carried out to investigate the effects of MII under field conditions. The 45-day-old nonmycorrhizal and MII-colonized seedlings of E. splendens were transplanted to HM-contaminated plots and harvested after 5 months. MII-inoculation increased shoot DW and shoot P, Cu, Zn, Pb concentrations significantly but did not alter shoot Cd concentrations, which led to higher uptake of Cu, Zn, Pb, Cd by E. splendens shoots. These results indicate that the AM fungal consortium represented by MII can benefit phytoextraction of HMs and therefore play a role in phytoremediation of HM-contaminated soils.     

Flax (Linum usitatissimum L.) depends on arbuscular mycorrhizal fungi for growth and P uptake at intermediate but not high soil P levels in the field

The contribution of indigenous arbuscular mycorrhizal fungi (AMF) to growth and phosphorus (P) uptake by oilseed flax (Linum usitatissimum L.) was examined in two field experiments covering soil P levels from 20–86 mg kg-1 NaHCO3-extractable P. The fumigant dazomet was applied to the soil in half of the plots to obtain control plants with reduced mycorrhiza formation. An extensive AMF colonization of up to 48% of the root length was established in untreated soil of both experiments, although P fertilization reduced colonization to 28–39% at the latest harvests. Fumigation markedly decreased or totally prevented AMF colonization throughout the experiments. Root growth responded to fumigation by increased total and specific root length. Shoot P uptake was decreased by fumigation at soil P levels lower than ca. 50 mg kg-1 whereas shoot growth was reduced by fumigation at soil P levels lower than ca. 40 mg kg-1. The effects of fumigation were ascribed to the suppression of mycorrhiza formation. The effect of the AMF increased with decreasing soil P levels. Phosphorus inflow through roots (based on shoot P uptake) was reduced more strongly by fumigation than total P uptake. The P inflow through fungal tissue in roots was estimated to 4 × 10-14 mol P cm-1 s-1. We conclude that AMF are essential to flax growth at soil P levels below ca. 40 mg P kg-1, which is representative of the conditions under which most flax is grown.     

The Role of Mycorrhizae Associated with Vetiver Grown in Pb-/Zn-Contaminated Soils: Greenhouse Study

The effects of mycorrhizae on growth and uptake of N, P, Zn, and Pb by plants were investigated in a greenhouse trial using vetiver grass (Vetiveria zizanioides) as host. Inoculation of the host plants with arbuscular mycorrhizal fungi (AMF), Glomus mosseae and G. intraradices spores, significantly increased the growth and P uptake. Mycorrhizal colonization increased Pb and Zn uptake by plants under low soil metal concentrations (at 0 and 10 mg/kg of Pb or Zn), whereas under higher concentrations (at 100 and 1,000 mg/kg of Pb or Zn), it decreased Pb and Zn uptake. P concentration in soil was negatively correlated with mycorrhizal colonization as well as Zn or Pb concentrations. The results showed that inoculation of the host plants with AMF protects them from the potential toxicity caused by increased uptake of Pb and Zn, but the degree of protection varied according to the fungus and host plant combination. The potential of arbuscular mycorrhizae in phytoremediation of the Zn‐ or the Pb‐contaminated soils is discussed in this article.     

Arbuscular mycorrhiza infection enhances the growth response of Lolium perenne to elevated atmospheric pCO(2)

Elevated atmospheric pCO(2) increases the C-availability for plants and thus leads to a comparable increase in plant biomass production and nutrient demand. Arbuscular mycorrhizal fungi (AMF) are considered to play an important role in the nutrient uptake of plants as well as to be a significant C-sink. Therefore, an increased colonization of plant roots by AMF is expected under elevated atmospheric pCO(2). To test these hypotheses, Lolium perenne L. plants were grown from seeds in a growth chamber in pots containing a silica sand/soil mixture for 9 weeks with and without inoculation with Glomus intraradices (Schenck and Smith). The growth response of plants at two different levels of N fertilization (1.5 or 4.5 mM) combined with ambient (35 Pa) and elevated atmospheric pCO(2) (60 Pa) was compared. The inoculation with G. intraradices, the elevated atmospheric pCO(2) and the high N fertilization treatment all led to an increased plant biomass production of 16%, 20% and 49%, respectively. AMF colonization and high N fertilization increased the plant growth response to elevated atmospheric pCO(2); the plant growth response to high N fertilization was also increased by AMF colonization. The root/shoot ratio was reduced by high N fertilization or elevated atmospheric pCO(2), but was not affected by AMF colonization. The unchanged specific leaf area indicated that if AMF colonization represented an increased C-sink, this was fully covered by the plant. Elevated atmospheric pCO(2) strongly increased AMF colonization (60%) while the high N fertilization had a slightly negative effect. AMF colonization neither improved the N nor P nutrition status, but led to an improved total P uptake. The results underline the importance of AMF for the response of grassland ecosystems to elevated atmospheric pCO(2).     

Chemical defense,mycorrhizal colonization and growth responses in <Emphasis Type="Italic">Plantago lanceolata</Emphasis> L.

Allelochemicals defend plants against herbivore and pathogen attack aboveground and belowground. Whether such plant defenses incur ecological costs by reducing benefits from plant mutualistic symbionts is largely unknown. We explored a potential trade-off between inherent plant chemical defense and belowground mutualism with arbuscular mycorrhizal fungi (AMF) in Plantago lanceolata L., using plant genotypes from lines selected for low and high constitutive levels of the iridoid glycosides (IG) aucubin and catalpol. As selection was based on IG concentrations in leaves, we first examined whether IG concentrations covaried in roots. Root and leaf IG concentrations were strongly positively correlated among genotypes, indicating genetic interdependence of leaf and root defense. We then found that root AMF arbuscule colonization was negatively correlated with root aucubin concentration. This negative correlation was observed both in plants grown with monocultures of Glomus intraradices and in plants colonized from whole-field soil inoculum. Overall, AMF did not affect total biomass of plants; an enhancement of initial shoot biomass was offset by a lower root biomass and reduced regrowth after defoliation. Although the precise effects of AMF on plant biomass varied among genotypes, plants with high IG levels and low AMF arbuscule colonization in roots did not produce less biomass than plants with low IG and high AMF arbuscule colonization. Therefore, although an apparent trade-off was observed between high root chemical defense and AMF arbuscule colonization, this did not negatively affect the growth responses of the plants to AMF. Interestingly, AMF induced an increase in root aucubin concentration in the high root IG genotype of P. lanceolata. We conclude that AMF does not necessarily stimulate plant growth, that direct plant defense by secondary metabolites does not necessarily reduce potential benefits from AMF, and that AMF can enhance concentrations of root chemical defenses, but that these responses are plant genotype-dependent.     

Seasonal dynamics of arbuscular mycorrhizal fungi in differing wetland habitats

The dynamics and role of arbuscular mycorrhizal fungi (AMF) have been well described in terrestrial ecosystems; however, little is known about how the dynamics of AMF are related to the ecology of wetland ecosystems. The seasonal dynamics of arbuscular mycorrhizal (AM) colonization within different wetland habitats were examined in this study to determine the factors that influence AM associations and to further assess the ecological role of AMF in wetlands. Fen and marsh habitats of four wetlands in west central Ohio were sampled monthly from March to September. AMF were found at all four sites for each month sampled and were present in all of the dominant plant species. A significant effect of month (P<0.001) on AM colonization did occur and was attributable to maximum colonization levels in the spring and minimum levels in late summer. This trend existed in all four wetlands in both fen and marsh habitats, regardless of variation in water levels, percent soil moisture, or available phosphorus levels. Because abiotic factors had minimal influence on AM colonization variation and the level of AM colonization paralleled plant growth patterns, we conclude that the AM seasonal dynamic was in response to plant phenology. Our data suggest that AM associations in temperate fen and marsh habitats are prevalent in the spring during new root and vegetative growth, even for plants experiencing flooded conditions. Evidence of an overriding AM seasonal trend indicates that future studies should include a seasonal component to better assess the role and distribution of AMF in wetland ecosystems.     

水位调控对崇明东滩围垦区滩涂湿地芦苇和白茅光合、形态及生长的影响

于2011年植物生长季,研究了长江口崇明东滩围垦区滩涂湿地3个地下水位梯度(低水位、中水位和高水位)下芦苇和白茅的光合、形态和生长特征,以及土壤温度、湿度、盐度和无机氮含量等土壤因子.结果表明： 在生长旺期,芦苇叶片光合能力在高水位显著低于低水位和中水位,白茅叶片光合能力在3个水位梯度间无显著差异.整个生长季内,在单株水平,芦苇形态和生长指标总体上在中水位最优,白茅大多数形态和生长指标在3个水位梯度间差异不显著;在种群水平,芦苇植株密度、叶面积指数和单位面积地上生物量在高水位最大,白茅植株密度、叶面积指数和单位面积地上生物量在低水位最大.生长季初期,3个水位梯度间0～20 cm土层芦苇根状茎生物量差异不显著,而0～20 cm土层白茅根状茎生物量在高水位显著低于低水位和中水位.作为围垦前的原生湿生植物,芦苇在3个水位梯度下表现的差异性可能是由于不同水位梯度下土壤因子和白茅竞争强度不同.合理调控围垦区滩涂湿地水位可以抑制中生草本植物白茅的生长和繁殖,有助于以芦苇为单优势种的原有湿地植物群落的恢复.