Aluminum tolerance of wheat does not induce changes in dominant bacterial community composition or abundance in an acidic soil

Aims

Aluminum-tolerant wheat plants often produce more root exudates such as malate and phosphate than aluminum-sensitive ones under aluminum (Al) stress, which provides environmental differences for microorganism growth in their rhizosphere soils. This study investigated whether soil bacterial community composition and abundance can be affected by wheat plants with different Al tolerance.

Methods

Two wheat varieties, Atlas 66 (Al-tolerant) and Scout 66 (Al-sensitive), were grown for 60 days in acidic soils amended with or without CaCO₃. Plant growth, soil pH, exchangeable Al content, bacterial community composition and abundance were investigated.

Results

Atlas 66 showed better growth and lower rhizosphere soil pH than Scout 66 irrespective of CaCO₃ amendment or not, while there was no significant difference in the exchangeable Al content of rhizosphere soil between the two wheat lines. The dominant bacterial community composition and abundance in rhizosphere soils did not differ between Atlas 66 and Scout 66, although the bacterial abundance in rhizosphere soil of both wheat lines was significantly higher than that in bulk soil. Sphingobacteriales, Clostridiales, Burkholderiales and Acidobacteriales were the dominant bacteria phylotypes.

Conclusions

The difference in wheat Al tolerance does not induce the changes in the dominant bacterial community composition or abundance in the rhizosphere soils.     

Simultaneous assessment of the effects of an herbicide on the triad: rhizobacterial community, an herbicide degrading soil bacterium and their plant host

Aims

This work addresses the relevant effects that one single compound, used as model herbicide, provokes on the activity/survival of a suitable herbicide degrading model bacterium and on a plant that hosts this bacterium and its bacterial rhizospheric community.

Methods

The effects of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), on Acacia caven hosting the 2,4-D degrading bacterium Cupriavidus pinatubonensis JMP134, and its rhizospheric microbiota, were simultaneously addressed in plant soil microcosms, and followed by culture dependent and independent procedures, herbicide removal tests, bioprotection assays and use of encapsulated bacterial cells.

Results

The herbicide provokes deleterious effects on the plant, which are significantly diminished by the presence of the plant associated C. pinatubonensis, especially with encapsulated cells. This improvement correlated with increased 2,4-D degradation rates. The herbicide significantly changes the structure of the A. caven bacterial rhizospheric community; and it also diminishes the preference of C. pinatubonensis for the A. caven rhizosphere compared with the surrounding bulk soil.

Conclusions

The addition of an herbicide to soil triggers a complex, although more or less predictable, suite of effects on rhizobacterial communities, herbicide degrading bacteria and their plant hosts that should be taken into account in fundamental studies and design of bio(phyto)remediation procedures.     

Pyrosequencing reveals how pulses influence rhizobacterial communities with feedback on wheat growth in the semiarid Prairie

Background and Aims

Evidence shows that plants modify their microbial environment leading to the “crop rotation effect”, but little is known about the changes in rhizobacterial community structure and functionality associated with beneficial rotation effects.

Methods

Polymerase chain reaction (PCR) and 454 GS FLX amplicon pyrosequencing were used to describe the composition of the rhizobacterial community evolving under the influence of pea, a growth promoting rotation crop, and the influence of three genotypes of chickpea, a plant known as an inferior rotation crop. The growth promoting properties of these rhizobacterial communities were tested on wheat in greenhouse assays.

Results

The rhizobacterial communities selected by pea and the chickpea CDC Luna in 2008, a wet year, promoted durum wheat growth, but those selected by CDC Vanguard or CDC Frontier had no growth-promoting effect. In 2009, a dry year, the influence of plants was mitigated, indicated that moisture availability is a major driver of soil bacterial community dynamics.

Conclusion

The effect of pulse crops on soil biological quality varies with the crop species and genotypes, and certain chickpea genotypes may induce positive rotation effects on wheat. The strength of a rotation effect on soil biological quality is modulated by the abundance of precipitation.     

A modified model for estimating soil redistribution on grassland by using 7Be measurements

Background and aims

⁷Be has been used as a powerful tracer for estimating short-term soil redistribution by virtue of its short half-life. However, the existing conversion model associated with this radionuclide means that it can only be applied to bare soils because vegetation will intercept a large proportion of ⁷Be fallout. A modified model which takes into consideration the impact factor of vegetation was reported in this paper and the estimation of soil redistribution was compared by using both the conventional and the modified models.

Methods

Field experiment on ⁷Be distribution in above-ground grasses and soils was carried out on a 100 m² grass-covered slope. The vegetation interception factor (P) was determined and the soil redistribution rates were calculated by using the previous model and the modified model.

Results

The result shows that nearly 40 % of the atmospherically deposited ⁷Be will be sequestered by leaf surfaces of herbaceous plants. Soil loss rates on grassland will be remarkably overestimated by using the previous model.

Conclusions

The net soil loss estimated from the modified model is more accurate than that derived from the conventional model and the modified model will be more appropriate to estimate soil redistribution rates on soils with significant vegetation cover by using ⁷Be technique.     

Effects of condensed tannins in conifer leaves on the composition and activity of the soil microbial community in a tropical montane forest

Background and aims

Condensed tannins, a dominant class of plant secondary metabolites, play potentially important roles in plant-soil feedbacks by influencing the soil microbial community. Effects of condensed tannins on the soil microbial community and activity were examined by a short-term tannin-addition experiment under field and laboratory conditions.

Methods

Condensed tannins were extracted from the leaves of a dominant conifer (Dacrydium gracilis) in a tropical montane forest on Mt. Kinabalu, Borneo. The extracted tannins were added to soils beneath the conifer and a dominant broadleaf (Lithocarpus clementianus) to evaluate the dependence of the response to tannin addition on the initial composition of the soil microbial community.

Results

Enzyme activities in the field tannin-addition treatment were lower than in the deionized-water treatment. Carbon and nitrogen mineralization were also inhibited by tannin-addition. The fungi-to-bacteria ratio after tannin-addition was higher compared with the distilled-water treatment in the laboratory experiment.

Conclusions

Based on our results, we suggest that the higher concentration of condensed tannins in the leaf tissues of Dacrydium than in those of Lithocarpus is a factor influencing the microbial community and activity. This may have influences on subsequent plant performance, which induces plant-soil feedback processes that can control dynamics of the tropical montane forest ecosystem.     

Weeds influence soil bacterial and fungal communities

Background and aims

Vineyards harbour a variety of weeds, which are usually controlled since they compete with grapevines for water and nutrients. However, weed plants may host groups of fungi and bacteria exerting important functions.

Methods

We grew three different common vineyard weeds (Taraxacum officinalis, Trifolium repens and Poa trivialis) in four different soils to investigate the effects of weeds and soil type on bacterial and fungal communities colonising bulk soil, rhizosphere and root compartments. Measurements were made using the cultivation-independent technique Automated Ribosomal Intergenic Spacer Analysis (ARISA).

Results

Weeds have a substantial effect on roots but less impact on the rhizosphere and bulk soil, while soil type affects all three compartments, in particular the bulk soil community. The fungal, but not the bacterial, bulk soil community structure was affected by the plants at the late experimental stage. Root communities contained a smaller number of Operational Taxonomic Units (OTUs) and different bacterial and fungal structures compared with rhizosphere and bulk soil communities.

Conclusions

Weed effect is localised to the rhizosphere and does not extend to bulk soil in the case of bacteria, although the structure of fungal communities in the bulk soil may be influenced by some weed plants.     

Restoration of high altitude forests in an area affected by a wildfire: Polylepis australis Bitt. seedlings performance after soil inoculation

Key message

Outplanted Polylepis australis seedling growth, survival and mycorrhizal response were not influenced by inoculation with soil from different vegetation types. Seedling inoculation would not be essential for reforestation practices.

Abstract

Polylepis forests are one of the most endangered high mountain ecosystems of South America and reforestation with native Polylepis species has been recommended. To determine whether native soil inoculation could help in reforestation success, a field trial was set up to evaluate the response of outplanted P. australis seedlings to the inoculation with soils from three vegetation types (a grassland, a mature forest and a degraded forest) and a sterile soil, used as control. We evaluated seedlings performance: growth and survival for 18 months, root/shoot ratio, phosphorous content and arbuscular mycorrhizal fungal (AMF) colonization. To interpret performance patterns we evaluated the colonization potential of the three inoculum soils and the changes of the AMF community composition of the seedlings rhizosphere in relation to inoculation treatment and season. Our main results showed no significant differences in seedlings survival and growth between treatments. The colonization potential of grassland and degraded forest soils was ~25 times greater than mature forest soil and specific spore density of some morphospecies varied with season. However, AMF spore community of seedlings rhizosphere became homogenized after outplanting and was similar between treatments after 12 months. Therefore, we conclude that soil inoculation is not essential for outplanted P. australis survival and increase in height, and thus all the tested soils could be used as inocula, including grassland soils which in practice are the easiest to collect.     

Soil retention of 15N in a simulated N deposition study: effects of live plant and soil organic matter content

Background and aims

The impacts of atmospheric nitrogen (N) deposition on terrestrial ecosystem processes remain controversial, mostly because of the uncertainty regarding the fates of deposited N. We conducted a 16-week simulated deposition study to experimentally trace N in a greenhouse plant-soil system.

Methods

Using a two-way factorial design, we added (¹⁵NH₄)₂SO₄ solution twice a week to pots containing different soil organic matter (SOM) content and with or without a live plant (Salix dasyclados). The recoveries of ¹⁵N in soil, plant biomass, and leaching solution were quantified.

Results

We found most ¹⁵N was retained in soil (18.0–59.2%), with significantly more ¹⁵N recovered from high-SOM soils than from low-SOM soils. Plant presence significantly increased ¹⁵N retention in soil. Plant biomass accounted for 10–20% of the ¹⁵N input, with proportionally more ¹⁵N assimilated when plants were grown in low-SOM soils. Leaching loss of ¹⁵N was relatively low (10–17%).

Conclusion

Our study suggests that SOM content and plant presence significantly affect the fates of deposited N. Indeed, N would be preferentially retained in soils with high SOM content and live plant, while plants would assimilate more deposited N when grown in low SOM soils. Global biogeochemical models thus need to incorporate such soil-specific N retention and plant N assimilation.     

Influence of agricultural practices and seasons on the abundance and community structure of culturable pseudomonads in soils under no-till management in Argentina

Background and aims

Members of the genus Pseudomonas are common inhabitants of rhizospheres and soils, and it is known that soil types and crop species influence their population density and structure. 20?×?10⁶ ha are cultivated under no-tillage in Argentina and there is a need to find new biologically-based soil quality indexes to distinguish between sustainable and non-sustainable agricultural practices. Pseudomonads abundance and community structure were analyzed in no-till soils with different agricultural practices, in productive fields along 400 km of Argentinean Pampas.

Methods

We sampled soils and root systems from agricultural plots in which sustainable or non-sustainable agricultural practices have been applied. Samples were collected in summer and winter during 2010 and 2011. Culturable fluorescent and total pseudomonads were enumerated by plating on Gould’s selective medium S1. Colonies from these plates served as DNA source to carry out PCR-RFLP community structure analysis of the pseudomonads-specific marker genes oprF and gacA.

Results

Abundance of total and fluorescent culturable pseudomonads in bulk soils was influenced by seasonal changes and agricultural practices. Rhizospheric counts from the same crop were affected by agricultural treatments. Also, crop species influenced pseudomonads density in the rhizosphere. Combined PCR-RFLP profile of both genes showed a seasonal grouping of samples.

Conclusions

Sustainable soil management seems to promote pseudomonads development in soils, favoring root colonization of crops from those plots. Crop species influence total pseudomonads load of rhizospheres and its community structure. Total or relative pseudomonads load could function as soil quality indicator of good agricultural practices.     

Effects of exotic and native tree leaf litter on soil properties of two contrasting sites in the Iberian Peninsula

Aims

We assessed the effects of native and exotic tree leaf litter on soil properties in two contrasting scenarios. The native Quercus robur and Pinus pinaster tree species coexist with the aliens Eucalyptus globulus and Acacia dealbata in acid soils of NW Spain. The native trees Fraxinus angustifolia and Ulmus minor coexist with the aliens Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila in eutrophic basic riparian soils in Central Spain.

Methods

Four plastic trays per species were filled with homogenized top-soil of the site and covered with leaf litter. Before and after 9?months of incubation, litter mass, soil pH, organic matter, mineral and total N were measured. Available mineral N (NO ₃ ^? -N and NH ₄ ⁺ -N) was assessed every 2?months.

Results

Soil biological activity was higher in the basic than in the acid soil. Litter of the exotic trees tended to decompose less than litter of native species, probably due to the presence of secondary metabolites in the former. Soil pH, mineral and total N responded differently to different litter types, irrespective of their exotic or native origin (acid soil), or was similar across litter treatments (basic riparian soil). The similar response of the basic soil to the addition of different litter types may be due to the low contrast of litter quality between the species. E. globulus litter inhibitied soil microbial activity much more than the rest of the studied litter types, leading to a drastic impoverishment of N in soils.

Conclusion

Litter of exotic N-fixing trees (A. dealbata and R. pseudoacacia) did not increase soil N pools because of the inhibition of microbial activity by secondary compounds. Therefore, secondary metabolites of the litter played a major role explaining exotic litter impact on soil properties.     

Dynamics of plant metal uptake and metal changes in whole soil and soil particle fractions during repeated phytoextraction

Aims

Phytoextration of metal polluted soils using hyperaccumulators is a promising technology but requires long term successive cropping. This study investigated the dynamics of plant metal uptake and changes in soil metals over a long remediation time.

Methods

A soil slightly polluted with metals (S1) was mixed with highly polluted soil (S4) to give two intermediate pollution levels (S2, S3). The four resulting soils were repeatedly phyto-extracted using nine successive crops of Cd/Zn-hyperaccumulator Sedum plumbizincicola over a period of 4 years.

Results

Shoot Cd concentration decreased with harvest time in all soils but shoot Zn declined in S1 only. Similar shoot Zn concentrations were found in S2, S3 and S4 although these soils differed markedly in metal availability, and their available metals decreased during phytoextraction. A possible explanation is that plant active acquisition ability served to maintain plant metal uptake. Plant uptake resulted in the largest decrease in the acid-soluble metal fraction followed by reducible metals. Oxidisable and residual fractions were less available to plants. The coarse soil particle fractions made the major contribution to metal decline overall than the fine fractions.

Conclusion

Sedum plumbizincicola maintained long term metal uptake and the coarse soil particles played the most important role in phytoextraction.     

Differential responses of native and exotic coastal sage scrub plant species to N additions and the soil microbial community

Background and aims

Native shrub species of southern California have a long history of displacement by exotic annual herbs and forbs. Such invasions may be mediated by interactions with the microbial community and changes in the N cycle as a result of N pollution. However, the simultaneous effects of the soil microbial community status and N fertilization on dominant native and exotic plant species growth have not been thoroughly explored in this ecosystem.

Methods

Three species of native shrubs and of exotic annuals were grown in an orthogonal two-factor greenhouse experiment. To assess the importance of the soil microbial community pre-sterilized soils were inoculated with sterilized or non-sterilized field soil; to assess the importance of N type pots were fertilized with nitrate, ammonium or glycine solutions. Plant shoot and root biomass was measured after harvesting.

Results

The natives Artemisia californica and Eriogonum fasciculatum had lower growth in sterilized soil, suggesting microbial facilitation of these species, and E. fasciculatum higher growth with ammonia than either nitrate or glycine. Salvia apiana had equal growth under all conditions. The exotics Brassica nigra and Bromus madritensis grew equally in sterilized and unsterilized soil, and B. madritensis greater growth with ammonia fertilizer. Centaurea melitensis had greater growth in sterilized soil, and with either form of inorganic N.

Conclusions

These results highlight the importance of the soil microbial community in contributing to relative success of native vs. exotic species, and could inform restoration approaches for these species.     

Rhizobacterial inoculants can improve nickel phytoextraction by the hyperaccumulator Alyssum pintodasilvae

Aim

Rhizobacteria can influence plant growth and metal accumulation. The aim of this study was to evaluate the effect of rhizobacterial inoculants on the Ni phytoextraction efficiency of the Ni-hyperaccumulator Alyssum pintodasilvae.

Method

In a preliminary screening 15 metal-tolerant bacterial strains were tested for their plant growth promoting (PGP) capacity or effect on Ni bioaccumulation. Strains were selected for their Ni tolerance, plant growth promoting traits and Ni solubilizing capacity. In a re-inoculation experiment five of the previously screened bacterial isolates were used to inoculate A. pintodasilvae in two contrasting Ni-rich soils (a serpentine (SP) soil and a sewage sludge-affected agricultural (LF) soil).

Results

Plant growth was greater in serpentine soil (where it grows naturally) than in the LF soil, probably due to Cd phytotoxicity. Rhizobacterial inoculants influenced plant growth and Ni uptake and accumulation, but the effect of the strains was dependent upon soil type. The increase in plant biomass and/or Ni accumulation significantly promoted shoot Ni removal.

Conclusion

One strain (Arthrobacter nicotinovorans SA40) was able to promote plant growth and phytoextraction of Ni in both soil types and could be a useful candidate for future field-based trials.     

Carbon sequestration and soil fertility of tropical tree plantations and secondary forest established on degraded land

Purpose

Much tropical land requires rehabilitation but the capacity of reforestation with plantations or naturally regenerating secondary forests for overcoming soil degradation remains unclear. We hypothesised that desirable effects, including improved soil fertility and carbon sequestration, are achieved to a greater extent in Acacia mangium plantations and secondary forests than in Eucalyptus urophylla plantations.

Methods

We tested our hypothesis across soil and climate gradients in Vietnam with linear mixed-effect models and other, comparing A. mangium and E. urophylla plantations, secondary forests and pasture.

Results

A. mangium plantations and secondary forests showed a positive correlation between biomass production and desirable soils properties including increased soil carbon, nitrogen and phosphorus, and reduced bulk density. All plantations, but not secondary forests, caused increases in soil acidity. Eight-year old A. mangium plantations contained most carbon in biomass+soil, and secondary forests and pastures had similar or higher soil carbon. E. urophylla plantations had the lowest soil carbon status, raising doubt about their sequestration capacity in current 6–8 year rotations.

Conclusions

The study demonstrates that appropriate reforestation enhances soil fertility and promotes carbon sequestration on degraded tropical lands and that unmanaged secondary forests are effective at improving soil fertility and sequestering carbon at low cost.     

Combined effects of soil properties and Phytophthora cinnamomi infections on Quercus ilex decline

Aims

The importance of soil properties as determinants of tree vitality and Phytophthora cinnamomi root infections was analysed.

Methods

The study comprised 96 declining stands in western Spain, where declining and non-declining holm oak (Quercus ilex L.) trees were sampled. Soil properties (soil depth, Ah horizon thickness, texture, pH, redox potential, soil bulk density and N-NH₄ ⁺ and N-NO₃ ^? concentrations) and P. cinnamomi infections were assessed.

Results

Tree mortality rates increased with low soil bulk densities, which were also associated with more P. cinnamomi-infected trees. Occurrence of infected trees was higher in fine textured soils and in thick Ah horizons. Fine textured soils favoured trees, but with the presence of P. cinnamomi their health status deteriorated. Soil under declining trees had higher N-NO₃ ^?/N-NH₄ ⁺ ratio values than under non-declining trees. Additional soil properties changes associated to grazing were not related to decline and P. cinnamomi infections.

Conclusions

The implications of P. cinnamomi in holm oak decline and the influence of soil properties as contributors to pathogen activity were demonstrated. Fine soil textures and thick Ah horizons, usually favourable for vigour and vitality of trees growing in the Mediterranean climate, were shown to be disadvantageous soil properties if P. cinnamomi was present. Fine soil textures and thick Ah horizons are frequently related with higher levels of soil moisture, which increase the inoculum of the pathogen and favours root infection. Grazing does not seem to be directly linked to Q. ilex health status or P. cinnamomi root rot.     

Arbuscular mycorrhizas and their role in plant growth, nitrogen interception and soil gas efflux in an organic production system

Background and aims

Roots and mycorrhizas play an important role in not only plant nutrient acquisition, but also ecosystem nutrient cycling.

Methods

A field experiment was undertaken in which the role of arbuscular mycorrhizas (AM) in the growth and nutrient acquisition of tomato plants was investigated. A mycorrhiza defective mutant of tomato (Solanum lycopersicum L.) (named rmc) and its mycorrhizal wild type progenitor (named 76R) were used to control for the formation of AM. The role of roots and AM in soil N cycling was studied by injecting a ¹⁵N-labelled nitrate solution into surface soil at different distances from the 76R and rmc genotypes of tomato, or in plant free soil. The impacts of mycorrhizal and non-mycorrhizal root systems on soil greenhouse gas (CO₂ and ¹⁴⁺¹⁵N₂O and ¹⁵N₂O) emissions, relative to root free soils, were also studied.

Results

The formation of AM significantly enhanced plant growth and nutrient acquisition, including interception of recently applied NO ₃ ^? . Whereas roots caused a small but significant decrease in ¹⁵N₂O emissions from soils at 23?h after labeling, compared to the root-free treatment, arbuscular mycorrhizal fungi (AMF) had little effect on N₂O emissions. In contrast soil CO₂ emissions were higher in plots containing mycorrhizal root systems, where root biomass was also greater.

Conclusions

Taken together, these data indicate that roots and AMF have an important role to play in plant nutrient acquisition and ecosystem N cycling.     

Longleaf and loblolly pine seedlings respond differently to soil compaction,water content,and fertilization

Aims

Longleaf pine (Pinus palustris Mill.) is being restored across the U.S. South for a multitude of ecological and economic reasons, but our understanding of longleaf pine’s response to soil physical conditions is poor. On the contrary, our understanding of loblolly pine (Pinus taeda L.) root and shoot growth response to soil conditions is well established.

Methods

We performed a comparative greenhouse study which modeled root length density, total seedling biomass, and the ratio of aboveground:belowground mass as functions of volumetric water content, bulk density and soil fertility (fertilized or not).

Results

Root length density was about 35 % greater in longleaf pine seedlings compared to loblolly pine seedlings, and was reasonably well modeled (R ²?=?0.54) for longleaf pine by bulk density (linear), volumetric water content (quadratic), soil fertility, and the interactions of bulk density, volumetric water content, species, and soil fertility. The aboveground:belowground mass ratio (ABR) increased at both extremes of water content.

Conclusions

This research indicates that young longleaf pine seedling root systems respond more negatively to extremes of soil physical conditions than loblolly pine, and compacted or dry loamy soils should be ameliorated in addition to normal competition control, especially on soils degraded by past management.     

Interaction between root growth allocation and mycorrhizal fungi in soil with patchy P distribution

Aims and Background

Many plants preferentially grow roots into P-enriched soil patches, but little is known about how the presence of arbuscular mycorrhizal fungi (AMF) affects this response.

Methods

Lotus japonicus (L.) was grown in a low-P soil with (a) no additional P, (b) homogeneous P (28 mg pot^?1), (c) low heterogeneous P (9.3 mg pot^?1), and (d) high heterogeneous P (28 mg pot^?1). Each P treatment was combined with one of three mycorrhiza treatments: no mycorrhizae, Glomus intraradices, indigenous AMF. Real-time PCR was used to assess the abundance of G. intraradices and the indigeneous AMF G. mosseae and G. claroideum.

Results

Mycorrhization and P fertilization strongly increased plant growth. Homogeneous P supply enhanced growth in both mycorrhizal treatments, while heterogeneous P fertilization increased biomass production only in treatments with indigenous AMF inoculation. Preferential root allocation into P-enriched soil was significant only in absence of AMF. The abundance of AMF species was similar in P-enriched and unfertilized soil patches.

Conclusion

Mycorrhization may completely override preferential root growth responses of plants to P- patchiness in soil. The advantage of this effect for the plants is to give roots more freedom to forage for other resources in demand for growth and to adapt to variable soil conditions.     

Effect of the aerenchymatous helophyte Glyceria maxima on the sulfate-reducing communities in two contrasting riparian grassland soils

Aims

The research aimed at studying the effect of flooding with sulfate-rich water on the activity, abundance and diversity of sulfate-reducing micro-organisms present in the root zone of an oxygen-releasing plant growing on two riparian grassland soils with contrasting amounts of iron.

Methods

A series of microcosms was used to investigate the effects. Plants were grown under controlled conditions in microcosms containing a rhizosphere and bulk soil compartment for a period of 12 weeks in the presence of sulfate-rich flood water. Molybdate-treated systems served as non-sulfate-reducing controls.

Results

At harvest, activity and numbers of sulfate-reducing micro-organisms were higher in the absence of molybdate, but a rhizosphere effect and an impact of the presence of high levels of iron were not observed on activity and numbers. Both soils had in common a diverse community of sulfate-reducing micro-organisms covering all major cultured bacterial taxa. The appearance of members of the Desulfovibrionaceae exclusively in the rhizosphere of G. maxima was the only unambiguous indication of a plant effect.

Conclusion

The presence of sulfate-rich flood water stimulated the activity and growth of a part of the sulfate-reducing community leading to a change in community composition. The proximity of aerenchymatous plant roots and the abundance of iron in the soil had a negligible effect on the sulfate-reducing community.