The most cited articles published since 2009, extracted from Scopus
Volume 45, Issue 1, January 2009, Pages 28-35
Fabricio Darío Cassan | Diego Perrig | Verónica Sgroy | Oscar A. Masciarelli | Claudio A. Penna | Virginia Mitch Luna
Inoculants are biological formulations that combine a stable microorganism population and various types of compounds produced and released during fermentation, such as phytohormones and plant growth regulators. Azospirillum brasilense strain Az39 and Brayrhizobium japonicum strain E109 were previously shown to produce indole 3-acetic acid (IAA), gibberellic acid (GA3) and zeatin (Z). We tested the hypothesis that such compounds are responsible for early growth promotion in inoculated corn (Zea mays L.) and soybean (Glycine max L.) seedlings. Seeds were inoculated with Az39, E109, or both, and kept in a chamber at 20-30 °C under a controlled photoperiod to evaluate seed germination. To evaluate root and shoot length and dry weight, and number of nodules and percentage of nodulated seedlings, in soybean, seedlings were kept in a growth chamber for 14 days under similar photoperiod and temperature conditions. Az39 and E109, singly or in combination, showed the capacity to promote seed germination, nodule formation, and early development of corn and soybean seedlings. Both strains were able to excrete IAA, GA3 and Z into the culture medium, at a concentration sufficient to produce morphological and physiological changes in young seed tissues. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 46, Issue 1, January 2010, Pages 18-26
Jinping Jiang | Longhua Wu | Na Li | Yongming Luo | Ling Liu | Qiguo Zhao | Lei Zhang | Peter Christie
The threat of heavy metal contamination to food and human health in south and east China has become a public concern as industrial development continues. The aims of this study were to investigate the influence of repeated phytoextraction over a two-year period by successive crops of the Zn and Cd hyperaccumulator Sedum plumbizincicola on multiple metal contaminated soils and to assess recovery of soil quality. Total and NH4OAc-extractable Zn and Cd concentrations were significantly reduced in planted soils compared to unplanted soils. Microbial biomass C (Cmic), basal respiration and microbial quotient (qM) were significantly and positively correlated and soil metabolic quotient (qCO2) was negatively correlated with heavy metal concentrations in unplanted soils (P < 0.05). However, Cmic, basal respiration and qM values increased significantly after phytoremediation by five crops over two years compared to unplanted soil. Urease, β-glucosidase, neutral phosphatase and arylsulfatase activities also increased significantly with decreasing heavy metal contents and hydrolase activity was enhanced in planted soil (P < 0.05) compared to the unplanted control. The data indicate the capacity of S. plumbizincicola to extract Zn and Cd from contaminated soil and also that phytoremediation had beneficial effects on soil microbial and hydrolase activities, with the metal phytoextraction procedure restoring soil quality. © 2009 Elsevier Masson SAS. All rights reserved.
Volume 48, Issue , January 2012, Pages 1-10
Yasser Mahmoud Awad | Evgenia V. Blagodatskaya | Yong Sik Ok | Yakov V. Kuzyakov
Application of polymers for the improvement of aggregate structure and reduction of soil erosion may alter the availability and decomposition of plant residues. In this study, we assessed the effects of anionic polyacrylamide (PAM), synthesized biopolymer (BP), and biochar (BC) on the decomposition of 14C-labeled maize residue in sandy and sandy loam soils. Specifically, PAM and BP with or without 14C-labeled plant residue were applied at 400 kg ha -1, whereas BC was applied at 5000 kg ha -1, after which the soils were incubated for 80 days at 22 °C. Initially, plant residue decomposition was much higher in untreated sandy loam soil than in sandy soil. Nevertheless, the stimulating effects of BP and BC on the decomposition of plant residue were more pronounced in sandy soil, where it accounted for 13.4% and 23.4% of 14C input, respectively, whereas in sandy loam soil, the acceleration of plant residue decomposition by BP and BC did not exceed 2.6% and 14.1%, respectively, compared to untreated soil with plant residue. The stimulating effects of BP and BC on the decomposition of plant residue were confirmed based on activities of β-cellobiohydrolase, β-glucosidase, and chitinase in both soils. In contrast to BC and BP, PAM did not increase the decomposition of native or added C in both soils. © 2011.
Volume 47, Issue 4, July 2011, Pages 215-222
Pascal Jouquet | Saran Traoré | Chutinan Choosai | Christian Hartmann | David Edward Bignell
As soil engineers, termites play a key role in the functioning of many tropical and subtropical ecosystems. This reviews assesses advances in our knowledge of the beneficial influences of termites on ecosystem functioning and services. Termites are amongst the main macroinvertebrate decomposers in arid and semi-arid environments, and exert additional impacts through the creation of biostructures (mounds, galleries, sheetings, etc...) with different soil physical and chemical properties. They influence the distribution of natural resources such as water and nutrients in the landscape and consequently the diversity of soil microbes, plants and animals. Surprisingly, considering the wide range of ecosystem services provided by termites, few researches have been reported on the utilization of termite activity for the management of soil fertility or for the rehabilitation of degraded soils. In our final section, we discuss the main obstacles hampering the development of such approaches and we suggest that ecosystems services provided by termites are not sufficiently appreciated, especially in the context of long-term processes and possible biotechnologies derived from a detailed knowledge of their biology. © 2011 Elsevier Masson SAS.
Volume 45, Issue 1, January 2009, Pages 73-80
Mandira Malhotra | Sheela K. Srivastava
Plant growth promotion by Azospirillum brasilense SM has been attributed to its indole-3-acetic acid (IAA) production. Analysis of IAA biosynthesis by this strain under nutrient stresses, likely environmental fluctuations and long-term batch cultures suggested that they significantly influenced this function, with some conditions (fluctuations in temperature) triggering IAA accumulation. In long-term batch cultures (of 30 days), the bacterial population was maintained at a specific cell density and produced IAA even after a sharp decline in population size, albeit fluctuations were observed in both the parameters. Long-term bacterial cultures under nitrogen starvation showed the same trend in cell viability; however, a continuous increase in IAA accumulation was seen over time. This study has shown that A. brasilense strain SM has the potential to be a competent rhizospheric bacterium as it can beneficially influence the growth of sorghum. Further, it also has the ability to promote the growth of a number of other plants like mung bean, maize, and wheat. The benefit of this characteristic of strain SM can be directly accrued to a range of plants with which it may associate so as to improve their yield. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 1, January 2009, Pages 106-113
André Luiz Martinez Oliveira | Marion Stoffels | Michael W. Schmid | Verônica Massena Reis | José Ivo Baldani | Anton Hartmann
Micropropagated sugarcane plants have been used in Brazil for almost three decades. Besides the improvement in plant health, micropropagated sugarcane carries no endophytic plant growth-promoting bacteria. The Brazilian inoculation technology to reintroduce diazotrophic bacteria in micropropagated sugarcane plantlets revealed a synergistic-like effect in PGP-bacteria mixed inoculations. The infection model of single diazotrophic bacteria species in sugarcane was studied in detail, but still many questions remain open. In this study we used a combined fluorescence in situ hybridization (FISH) and a cultivation based approach (MPN) to evaluate the colonization of sugarcane plantlets by mixed inocula. The highest colonization for three out of the five species studied was obtained with a mixed inoculum, when the Azospirillum amazonense showed an increase by almost 100 times in colonization and Herbaspirillum spp. and Burkholderia tropica was determined at 107 cells per gram root fresh weight. All of the inoculated bacterial species could be detected using the FISH probes 12 h after bacterial inoculation. The FISH results confirmed the MPN counts and showed differences in the population numbers and colonization behavior of particular bacterial inoculum strains in the different mixed inocula. A putative antagonistic effect among the inoculated H. seropedicae and H. rubrisubalbicans strains was observed using FISH, as well as the better competitiveness of B. tropica as compared to the A. amazonense strain. The observed data probably reflect also specific interactions with the sugarcane variety used in this particular inoculation system, and may not be generalized as a rule. This is the first study about the competition for sugarcane colonization in a mixed bacterial inoculum. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 1, January 2009, Pages 88-93
Juan Pablo Hernandez | Luz E. De- Bashan | D. Johana Rodriguez | Yaneth Rodriguez | Yoav Bashan
Immobilization of Bacillus pumilus ES4 from arid land soils, a plant growth-promoting bacterium and the freshwater, green microalga Chlorella vulgaris enhanced microalgal growth only in the absence of combined nitrogen in synthetic growth medium (SGM), but not in medium with combined nitrogen. B. pumilus was able to fix nitrogen in N-free SGM and its growth yielded an accumulation of ammonium in the medium. On its own, B. pumilus is a poor agent for removing nitrogen and phosphorus from wastewater, while C. vulgaris is a capable microorganism. By jointly immobilizing the two microorganisms, the capacity to remove nitrogen and phosphorus from the medium by the microalgae culture was not enhanced, but, at the cell level, removal of these nutrients was significantly enhanced. It appears that growth promotion induced by B. pumilus on C. vulgaris is related to nitrogen fixation. © 2008.
Volume 45, Issue 1, January 2009, Pages 3-11
Martín Díaz-Zorita | María Virginia Fernández-Canigia
The beneficial effects of inoculating with Azospirillum brasilense on crop productivity have been widely described, but extensive use in typical agricultural field environments is scarcely documented. The objective of this study was to quantify the productivity of wheat (Triticum aestivum L.) whose seed was inoculated with a liquid formulation containing Azospirillum brasilense INTA Az-39 strain under typical dryland farming conditions. The study was performed in the 2002-2006 growing seasons, evaluating inoculated and non-inoculated seed at 297 experimental locations in the Pampas region of Argentina. The inoculated crops exhibited more vigorous vegetative growth, with both greater shoot and root dry matter accumulation (12.9 and 22.0%, respectively). The inoculation increased the number of harvested grains by 6.1%, and grain yield by 260 kg ha-1 (8.0%). Positive responses were determined in about 70% of the sites, depending mostly on the attainable yield and independently of fertilization and other crop and soil management practices. In general, more response to inoculation was observed in the absence of major crop growth limitations, suggesting the complementary contribution of the Azospirillum brasilense treatment to more efficiently developing higher yielding wheat. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 46, Issue 2, March 2010, Pages 97-104
Metabolic footprints provide metrics for the magnitudes of ecosystem functions and services provided by component organisms of the soil food web. Nematodes occupy various trophic roles and perform important functions within the web. They are convenient indicators of similar functions performed by other organisms in the web and are well-documented indicators of ecosystem condition. The generally vermiform shapes of nematodes, and the standardized morphometric characteristics used in their description, facilitate assessment of body volume and weight. Prescribed coefficients allow calculation of their carbon metabolism. Their production of body structure and eggs can be standardized for life course duration. Consequently, standardized metabolic activity levels, attributable to the abundance of nematodes performing various functional roles, can be calculated from existing and accessible morphometric data. Metabolic footprints of nematode assemblages provide measures of ecosystem services performed by each functional guild. © 2010 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 1, January 2009, Pages 114-122
Soumitra Paul Chowdhury | Michael W. Schmid | Anton Hartmann | Anil Kumar Tripathi
Lasiurus sindicus is a highly nutritive, drought tolerant, perennial grass, endemic to the Thar Desert of Rajasthan, India. In order to characterize the diversity of bacteria associated with roots of this grass that had survived severe drought stress, 16S-rRNA gene clone libraries were established from RT-PCR amplified products of the total RNA extracted from the washed roots and rhizosphere soil samples. Eight major bacterial taxa were identified in a total of 121 16S-rRNA gene clones. The majority of sequences belonged to Gram-positive bacteria, Actinobacteria being the most predominant ones, closely followed by Firmicutes. Most of the sequences showed similarity with sequences from cultivated bacteria or uncultivated environmental clones associated with arid, semi-arid environments, cold deserts and contaminated soils. PCR amplification of nifH genes using total DNA as template produced a total of 48 nifH clones from the rhizosphere soil and root samples and revealed a predominance of nifH sequences closely affiliated to Pseudomonas pseudoalcaligenes, isolated in a previous study from root samples of Lasiurus sindicus. Some nifH sequences showed close similarity to cultivated diazotrophs like Azospirillum brasilense, Rhizobium sp., and a variety of uncultured nitrogen fixing bacteria. Thus, this study provides us with evidence that L. sindicus harbors a diversity of bacteria with potential for nitrogen fixation. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 2, March 2009, Pages 138-145
Hanène Chérif | Fathia Ayari | Hadda Imen Ouzari | Massimo Marzorati | Lorenzo Brusetti | Naceur Jedidi | Abdennaceur A. Hassen | Daniele Daffonchio
The use of municipal solid waste compost (MSWC) as soil organic amendment is of an economic and environmental interest. However, little is known about the effectiveness of MSWC application on agricultural soil in northern Africa arid climate. We assessed the impact of five years' applications of different organic and mineral fertilizers on wheat grain yields and soil chemical and microbial characteristics. Soils were treated with MSWC at rates of 40 (C1) and 80 (C2) Mg ha -1, farmyard manure at a rate of 40 Mg ha -1 (M), chemical fertilizers (Cf) and the combinations (C1Cf, C2Cf, MCf). Wheat grain yield was enhanced with all amendments. Parallel increases of heavy metal levels and faecal coliform were also recorded except for Cf treatments. Based on wheat grain yield, heavy metal and faecal coliform data, we determined the treatment effectiveness index (E xx), calculated by dividing the pollutant increase ratio by the grain yield increase ratio. The treatment effectiveness index E C1 indicated lower faecal and heavy metal pollution with positive gains in wheat yields. Despite polluting effects on soil determined by the different treatments, no significant differences between treatments were observed in total bacterial count and soil bacterial community structure, as shown by 16S rRNA gene PCR-denaturing gradient gel electrophoresis banding patterns and 16S rRNA gene Length Heterogeneity-PCR analysis. According to the collected data, the use of MSWC at a rate of 40 Mg ha -1 might be recommended. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 1, January 2009, Pages 12-19
Fabricio Darío Cassan | Santiago Javier Maiale | Oscar A. Masciarelli | Alfonso A. Vidal | Virginia Mitch Luna | Oscar Adolfo Graciela Ruíz
Polyamines are considered as plant growth regulating compounds; among them, cadaverine has been correlated with root growth promotion or osmotic stress mitigation in some plant species. The purpose of this study was to evaluate the capacity of bacterial Azospirillum brasilense Az39 strain to produce cadaverine in chemically defined medium and inoculated plants, and to correlate this capacity with root growth promotion or osmotic stress mitigation in hydroponics conditions. To evaluate cadaverine production in chemically defined medium A. brasilense Az39 was cultivated aerobically at 30 °C and 80 rpm in NFb medium or NFb-l supplemented with the precursor l-lysine. To evaluate the bacterial cadaverine production and growth promotion in plants, rice (Oryza sativa L.) cv. El Paso 144 seedlings were inoculated and hydroponically cultured under optimal conditions in growth chamber. In both, cadaverine was identified and quantified by dansyl-derivative method using a fluorescence-HPLC system, and lysine decarboxylase (LDC) activity was determined by 14CO2 production in a closed tube system fed with [14C]-lysine. To evaluate the possible role of bacterial cadaverine in osmotic stress conditions, abscisic acid (ABA) production was analyzed in rice seedlings hydroponically cultured under 0 (no stress), -0.47 (stress) or -0.82 (severe stress) MPa osmotic potential generated by mannitol, with the addition of 1 nM or 1 μM cadaverine or A. brasilense Az39 inoculation. Our results indicate that A. brasilense Az39 promoted root growth and helped mitigate osmotic stress in rice seedlings, due in part to cadaverine production. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 46, Issue 1, January 2010, Pages 41-48
Rona Miethling-Graff | Susanne Dockhorn | Christoph C. Tebbe
A three-year experimental field study with a genetically engineered Bt maize (event MON88017) and three conventionally bred cultivars was conducted to quantify the recombinant Cry3Bb1 protein released into soil and detect effects on the diversity of soil bacteria. Protein extraction and an enzyme-linked immunosorbent assay (ELISA) allowed a threshold detection of 0.01 ng Cry3Bb1 g-1 soil. The maximum amount found in field plots with Bt maize was 1.0 ng Cry3Bb1 g-1 rhizosphere soil. Average concentrations during the growing seasons varied between years from 0.07 to 0.29 ng g-1. No accumulation of Cry3Bb1 in soil occurred over the three growing seasons. Four weeks after harvest, the major Cry3Bb1 reservoirs on the field were the remaining root stubbles, but their Cry3Bb1 concentration declined by 98.30-99.99% in the following seven months. During the three consecutive years of study there were never significant differences between the rhizosphere bacterial community structure of the Bt maize and the other cultivars, as detected by cultivation independent profiling of PCR-amplified 16S rRNA genes. The low concentrations of soil extractable Cry3Bb1, its degradation in decaying roots, and the lack of effects on rhizosphere bacteria give no indications of adverse effects of MON88017 cultivation on soil ecology. © 2009 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 1, January 2009, Pages 52-61
Phanthi Cong | Tran Dang Dung | Tran Minh Hien | Nguyen Thanh Hien | Abu Turab Mohmmad Ali Choudhury | Mihály L. Kecskés | Ivan Robert Kennedy
Field experiments were conducted during successive rainy seasons in 2006 in the Chau Thanh district of southern Vietnam to evaluate the effects of an inoculant plant growth promoter product called "BioGro" and N fertiliser rates on yield and N and P nutrition of rice. The results indicated that inoculation with BioGro, containing a pseudomonad, two bacilli and a soil yeast, significantly increased grain and straw yields and total N uptake in both seasons, as well as grain quality in terms of percentage N. Nitrogen fertilisation increased grain and straw yields as well as total N and P uptakes significantly in both cropping seasons. The estimated grain yield response to added N was quadratic in nature with and without added BioGro. In the first crop, BioGro out-yielded the control up to 90 kg urea N ha -1 whilst in the second season the beneficial effect of BioGro was observed up to 120 kg urea N ha -1, indicating either an interaction of the inoculant with higher yielding seasonal conditions or a cumulative effect of BioGro application. In the first season, the estimated N rate for maximum grain yield was 103 kg N ha -1 with BioGro while it was 143 kg N ha -1 without BioGro. The maximum estimated grain yields were 3.21 and 3.18 t ha -1 with and without BioGro, respectively. This information indicates that BioGro was able to save 40 kg N ha -1 with an additional rice yield of 30 kg ha -1 in the season. In the second rainy season, the estimated N rates for maximum grain yields were 94 and 97 kg N ha -1 with and without BioGro, respectively. The estimated maximum grain yields were 3.49 and 3.25 t ha -1 with and without BioGro, respectively. The two seasons' combined results indicate that application of BioGro improved the efficiency of N use by rice significantly, saving 43 kg N ha -1 with an additional rice yield of 270 kg ha -1 in two consecutive seasons at the experimental site. The extra efficiency was shown by the fact that the same yield of rice was obtained with about 40 and 60 kg less fertiliser-N that the maximum yields with urea alone in the two successive harvests on the same plots. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 1, January 2009, Pages 62-72
Bhavanath Jha | Mukund Chandra Thakur | Iti Gontia | Valérie Albrecht | Marion Stoffels | Michael W. Schmid | Anton Hartmann
A diversity of N2-fixing (diazotrophic) bacteria was isolated from two traditional rice cultivars, Sataria and Kartiki, from the rice growing area of Mithila region of North Bihar, India, where low levels of nitrogen fertilizers are applied. Nitrogen-free semisolid media NFb, JMV and LGI with different carbon sources and pH-values were used for enrichment and isolation of root-associated diazotrophs. The colonization density of roots by diazotrophs, as estimated from positive pellicle formation at highest dilution in nitrogen-free enrichment media, was 106-108 diazotrophic bacteria per g fresh root weight. Roots of the cultivar Kartiki were found to be more densely colonized endophytically by diazotrophs as detected after chloramine T (1%) surface disinfection. To ascertain the phylogenetic affiliation of the isolates, phylogenetic oligonucleotide probes and the Fluorescent in situ Hybridization (FISH) technique were applied. Using group-specific rRNA directed oligonucleotide probes, the majority of the isolates could be identified as alpha-, beta-, or gamma-proteobacteria. Using 16S and 23S rRNA-directed genus- or species-specific probes, Herbaspirillum seropedicae, Azospirillum amazonense, Burkholderia cepacia/vietnamiensis, Rhizobia and Pseudomonas spp. were found to be the most prominent root associated culturable diazotrophs. Diazotrophic Gluconacetobacter spp. were also demonstrated as colonizers of rice roots. Burkholderia cenocepacia, Pseudomonas sp. and three diazotrophic PGPR reference strains were used for the inoculation of axenically grown rice seedlings to determine the plant growth promoting potential. Significant increases in the shoot length (up to 60%), shoot dry weight (up to 33%) and the grain yield (up to 26%) per plant were observed in non-axenic pot and field trials. Using semisolid enrichment media after surface sterilization of field grown inoculated rice roots and oligonucleotide probing of the diazotrophic enrichment cultures, a sustainable colonization with the inoculated bacteria could be demonstrated. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 2, March 2009, Pages 146-152
Mohammad Miransari | Donald Lawrence Smith
For the onset of symbiosis process between soybean (Glycine max (L.) Merr.) and Bradyrhizobium japonicum, signals should be exchanged. Salinity has inhibitory effects on the symbiosis between the two partners. Hence, a greenhouse experiment was planned to: (1) determine the stressful effects of salinity on soybean and B. japonicum symbiosis, hypothesizing that they can inhibit the signal exchange process between the two partners, and (2) determine if the addition of genistein (a nod gene inducer) to B. japonicum (strain 532C) inocula could overcome the stressful effects of salinity on the Bradyrhizobium - soybean symbiosis. Three levels of salinity (control, 36 and 61 mmolar or 3.6 and 6.1 mmhos/cm) and three levels of genistein (0, 5 and 20 μM) were combined in a factorial fashion in four replicates. Soybean plants were harvested at three different times including 20, 40 and 60 days after inoculation (DAI). Genistein enhanced soybean nodulation and growth, and such effects became greater with time under high salinity levels. For example, at 60 DAI the enhancing effects of genistein on the symbiosis process in soybean was more pronounced at the highest level of salinity. The significant interaction effect between genistein 5 μM and salinity 61 mmolar may reveal the direct role of genistein 5 μM in overcoming the stressful effects of salinity on the symbiosis between B. japonicum and soybean, and hence, plant growth. This novel finding may be very useful to increase soybean yields in salty croplands. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 1, January 2009, Pages 36-43
Raúl Osvaldo Pedraza | Carlos H. Bellone | Silvia Carrizo de Bellone | Paulo Marcos Fernandes Boa Sorte | K. R S S Teixeira
We assessed the Azospirillum inoculation and N-fertilization effect on grain yield and on the phyllosphere endophytic diversity of nitrogen-fixing bacteria in a rice rainfed crop. We used cultivation-based techniques and cultivation-independent methods involving PCR-16S rRNA and denaturing gradient gel electrophoresis (DGGE). In general, we observed that grain yield was improved when inoculated with Azospirillum (depending on the genotype) and/or fertilized with urea. A similar behavior was observed in total N-content in grain and the MPN determination, as the highest values occurred when seeds were inoculated with A. brasilense REC3 (S1) than with A brasilense 13-2C (S2). A positive nitrogenase activity and PCR-nifH amplification suggests that the bacteria associated to inner tissues of rice phyllosphere could have contributed to the different N-contents detected. The bacterial diversity, observed in the number and intensity of DGGE profiles, showed a higher number of bands when total DNA was obtained using only CTAB than with CTAB + PVP. The DGGE profiles revealed great stability in the dominating bands, which presumably represent numerically dominant species. Application of A. brasilense strains as inoculants did not influence the dominant members of the endophytic microbial communities in the phyllosphere, but improved N-content and production of rainfed rice crop. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 3, May 2009, Pages 239-246
Yunfu Gu | Xiaoping Zhang | Shihao Tu | Kristina Lindström
Soil microbial biomass carbon (SMBC) and nitrogen (SMBN), soil microbial community structure, and crop yields were studied in a long-term (1982-2004) fertilization experiment carried out in Suining, Sichuan province of PR China. Eight treatments included three chemical fertilizer (CF) treatments (N, NP, NPK), three CF + farmyard manure (M) treatments (NM, NPM, NPKM), M alone and no fertilizer (CK) as control. The results showed that the soil microbial biomass was higher in soil treated with CFM than in soil treated with CF alone, and that NPKM gave the highest rice and wheat yields. The SMBC and SMBN were higher after rice than those after wheat cropping. SMBC correlated closely with soil organic matter. Average yields of wheat and rice for 22 years were higher and more stable in the fertilized plots than in control plots. Bacterial community structure was analyzed by PCR-DGGE targeting eubacterial 16S rRNA genes. A higher diversity of the soil bacterial community was found in soil amended with CFM than in other fertilizer treatments. Some specific band emerged in the soil amended with M. The highest diversity of bacterial communities was found in the NPKM treated soil. The bacterial community structures differed in rice and wheat plots. Sequencing of PCR products separated in DGGE showed that some of the common and dominant bands were closely related to Aquicella lusitana and to Acidobacteria. This study demonstrated that mixed application of N, P, and K with additional M amendment increased soil microbial biomass, diversified the bacterial communities and maintained the crop production in the Calcareous Purplish Paddy soil. © 2009 Elsevier Masson SAS. All rights reserved.
Volume 45, Issue 2, March 2009, Pages 176-183
Céline Pelosi | Michel Bertrand | Yvan Capowiez | Hubert Boizard | Jean Roger-Estrade
The role earthworms play in soil fertility is under increasing scientific scrutiny, especially in light of the fact that farmers are seeking to reduce soil tillage. However, there are many discrepancies in earthworm sampling methods. The aim of this study is to compare the efficiency of three chemical expellants (formaldehyde, commercial 'hot' mustard and allyl isothiocyanate, abbreviated AITC), with two sampling methods: (i) a simple method that consisted in spreading an expellant solution on the soil and retrieving earthworms that emerged at the soil surface, and (ii) a combined method that consisted in applying a chemical to expel earthworms and then hand-sorting the remaining earthworms from the block of soil. Sampling efficiency was measured in terms of earthworm density and biomass, for endogeic and anecic earthworms. With the simple method, a higher density of earthworms was sampled using formaldehyde and AITC than with mustard. Formaldehyde, AITC and mustard expelled not significantly different biomasses of 47.7, 31.9 and 20.5 g m-2, respectively, on average over the three plots. The combined method did not yield a significantly different density or biomass with the different chemicals. Formaldehyde is toxic and commercial 'hot' mustard is difficult to standardise and inefficient when used without hand-sorting. Accounting for the accuracy of the sampling methods as well as the toxicity of the chemicals to users and soil organisms, AITC appears to be a reliable and promising chemical expellant whether or not in combination with hand-sorting. Its use would be a step towards standardizing earthworm sampling methods. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 47, Issue 5, September 2011, Pages 279-287
Xingang Zhou | Gaobo Yu | Fengzhi Wu
Soil enzyme activities, soil bacterial and fungal community structures and cucumber yield as affected by different cropping systems were evaluated in a three-successive-growing-season experiment under greenhouse conditions. Intercropping systems, in which onion or garlic were planted on the side of cucumber in the first growing season, were compared to cucumber monoculture. Only cucumber was planted in the second and third growing seasons in order to see if the impacts of intercropping in the first growing season still exist in later growing seasons. Results showed that cucumber yield increased under both intercropping systems in these three growing seasons, compared with monoculture. Increases of soil urease activities under intercropping systems were detected in these three growing seasons. Soil polyphenol oxidase activities under intercropping systems also increased in the first two growing seasons. Soil catalase activity was higher under garlic-cucumber intercropping systems than under monoculture in the last two growing seasons. PCR-DGGE analysis showed that soil bacterial community band numbers and diversity indices decreased with growing seasons under monoculture. These indices were relatively stable under intercropping systems throughout these three growing seasons, and were higher than under monoculture. Garlic-cucumber system had a more obvious effect on soil fungal community structure than onion-cucumber system. This study demonstrated that intercropping cucumber with onion or garlic increased cucumber productivity and improved soil environment at different levels. These impacts of intercropping still existed in the second and third growing seasons. © 2011 Elsevier Masson SAS.
Volume 45, Issue 3, May 2009, Pages 220-228
José Luis Moreno | Felipe Bastida | Margarita Ros | Teresa Hernández | Carlos Díaz García
Traditionally, three threshold levels have been accepted for heavy metal concentrations in agricultural soils, depending on soil pH. The aim of this work was to ascertain how the three threshold values proposed for Cd (3, 6.5, and 12.5 mg kg-1) and Zn (300, 650, and 1300 mg kg-1) really affect soil microbial activity. Two soils, a scrubland soil and a forest soil, differing widely in their organic C content, were used in this study. Despite the different soil characteristics, the fractions of Cd and Zn extracted with a solution of diethylenetriaminepentaacetic acid (DTPA) showed little difference between soils. Parameters, such as microbial biomass C (Cmic), soil basal respiration (BR), adenosine triphosphate (ATP) content, dehydrogenase activity (DHA), urease activity (UA), alkaline phosphatase activity (APA), and β-glucosidase (β-GA), were less affected by heavy metals in the forest soil than in the scrubland soil. In general, the simultaneous addition of both metals had a synergistic effect on microbial activity, and this treatment produced a significant decrease of microbial activity of both soils with respect to control. The highest level (L3) of Cd, Zn and Cd + Zn treatments produced significant decrease of microbial and biochemical parameters in both soils. © 2009 Elsevier Masson SAS. All rights reserved.
Volume 49, Issue , March 2012, Pages 22-30
Gwenaël Imfeld | Stéphane Vuilleumier
Extensive application of industrially-produced pesticides in agriculture has resulted in contamination of soil ecosystems. A variety of both cultivation-dependent and cultivation-independent methods can be applied to measure and interpret the effects of pesticide exposure. We review here the expanding panel of these methods in the specific context of responses of the soil bacterial microflora to pesticide exposure, and of ongoing advances in microbial molecular ecology, including metagenomics and new approaches for DNA sequencing. Several issues still need to be addressed in order to routinely evaluate the effect of pesticides on bacterial communities in soil in the future, and to make way for a widely accepted framework for risk assessment in agro-ecosystems that include bacterial indicators. © 2011 Elsevier Masson SAS.
Volume 47, Issue 2, March 2011, Pages 77-87
Jan Dirk Van Elsas . | F. G Hidde Boersma
The availability of novel and advanced molecular methods based on soil nucleic acids has revolutionized our studies of the microbiota of soil. In particular, our understanding of the daunting diversity of soil microbes has grown to maturity, opening up a new box of challenging research questions about microbial functioning and interactions. We here review recent developments in, as well as the state-of-the-art of, the molecular methods applied to soil, and discuss a few salient cases in which they have enhanced our understanding of the soil microbiota and its functioning. In particular, we place a focus on the interface between soil fungal hyphae and the corresponding non-fungal-affected soil, i.e., the mycosphere. This selective environment may reduce the diversity of its inhabitants, allowing an improved picture of their ecology and functioning via molecular techniques. We present arguments for the contention that, to investigate testable hypotheses, a polyphasic approach is needed, in which work on the basis of molecular approaches such as metagenomics and metatranscriptomics is coupled to that based on culturable organisms. Thus, advances in our understanding of local functioning and adaptation of bacterial mycosphere inhabitants will be fostered by combined metagenomics/metatranscriptomics and cultivation-based approaches. © 2010 Elsevier Masson SAS.
Volume 45, Issue 1, January 2009, Pages 44-51
Andres D. Naiman | Alejandra Latrónico | Inés Eugenia García De Salamone
Scientific evidence recognizes that the operation of a terrestrial ecosystem depends on soil microbial activity. Some Azospirillum strains produce plant growth regulators, increase the development of roots, and fix atmospheric nitrogen (N2). Some Pseudomonas strains are capable of producing cytokinins and solubilizing organic phosphorus. A sustainability analysis requires a detailed knowledge of the interrelationships between the microorganisms added to the system and those present in the soil. This study examines the effect of three commercial inoculants Azospirillum brasilense Az1 and Az2 as well as Pseudomonas fluorescens Pf on biomass production, grain yield and rhizosphere colonization of wheat, combined with two levels of N-addition. Plate counts of rhizosphere soil showed that the inoculation and N-addition did not affect the number of P. fluorescens, whereas it significantly affected the number of Azospirillum. N-addition and inoculation did not change the communities of actinomycetes and bacteria but they changed the number of fungi at the rhizosphere of wheat plants. Community-level physiological profiles of carbon-source utilization of rhizosphere soil microbial communities were changed after inoculation with Az1, Az2 and Pf depending on the phenological stage of the crop. Although no significant responses were observed, in average, PGPB inoculation increased aerial biomass by 12%, root biomass by 40% and grain yield by 16%. These increases represent important earnings for the farmer and they may help to obtain a greater sustainability of the agroecosystems. © 2008 Elsevier Masson SAS. All rights reserved.
Volume 45, Issues 5-6, September 2009, Pages 488-495
Joséphine Peigné | Jean François Vian | Mario Cannavacciuolo | B. Bottollier | Rémi Chaussod
Microbial indicators exhibit a high spatial heterogeneity which often masks comparison of the effects of different soil management treatments. It is therefore desirable to use a proper sampling design which integrates spatial heterogeneity at field level. Thus, the objectives were: (1) to study the spatial heterogeneity of biological and chemical soil variables, and (2) with obtained maps of spatial variability to test different sampling strategies to assess the usefulness of this 'new' soil map unit. 63 soil samples were collected according to a 10 m × 10 m grid on a 0.48 ha plot. On each of these samples, 10 variables were measured: soil water content, cation exchange capacity (CEC), organic carbon (OC) and total nitrogen (N), C/N, soil microbial biomass (SMB), labile soil organic matter (LOM), mineralisable C (Cmin) and N (Nmin), inverse of specific respiratory activity (1/SRA = SBM/Cmin). The spatial heterogeneity of each variable was charted with geostatistics. The biological variables exhibited spatial variability of the same order of magnitude as physicochemical parameters. From the maps, zones with different levels of organic matter, microbial biomass and specific respiratory activity were identified. The spatial patterns of SMB and SRA were related to CEC (positively for SMB and negatively for SRA), pointing out the effects of soil protection on microbial biomass and availability of organic substrates. The definition of these zones for a pool of variables (OC, N, SMB, LOM, CEC) is useful at 3 levels: (1) to record the initial values of the measured variables for each plot, (2) to integrate these zones as blocks in experimental design for future experiments, and (3) to focus analysis of specific biological mechanisms such as activity of micro-organisms. © 2009 Elsevier Masson SAS. All rights reserved.