Description: Background and aims   Some elephant grass ( Pennisetum purpureum ) genotypes are able to produce large amounts of biomass and accumulate N derived from BNF when growing in soil with low N levels. However, information about the diazotrophic bacteria colonizing this C4 plant is still very scarce. This study aimed to characterize the plant growth promoting traits of a fraction of culturable diazotrophs colonizing the genotypes CNPGL F06-3 and Cameroon. Methods   A total of 204 isolates were obtained from surface sterilized leaves, stems and roots after culturing on five different N-free semisolid media. These were then analyzed by BOX-PCR, and the 16S rRNA and nif H sequences of representative isolates were obtained. The functional ability of the isolates to reduce acetylene, produce indole and to solubilize phosphate was also determined. Results   The diazotrophic bacterial population varied from 10 2 up to 10 6 bacteria g −1 fresh tissues of both genotypes. The BOX-PCR analysis suggested a trend in the genetic diversity among the 204 diazotrophic strains colonizing the different genotypes and plant tissues. Sequencing of 16S rRNA fragments confirmed the presence of Azospirillum brasilense and Gluconacetobacter diazotrophicus and revealed for the first time the occurrence of G. liquefaciens, G. sacchari , Burkholderia silvatlantica , Klebsiella sp., Enterobacter cloacae and E. oryzae in elephant grass . Interestingly, several nif H sequences from isolates identified as G. liquefaciens and G. sacchari showed homologies with nif H sequences of Enterobacter species. The majority of the isolates (97%) produced indole compounds, 22% solubilized phosphate and 6.4% possessed both characteristics. Conclusions   The results showed the occurrence of novel diazotrophic bacterial species colonizing different tissues of both genotypes of elephant grass. In addition, the study revealed the presence of several bacteria with growth promoting traits, and highlighted their potential to be exploited as biofertilizers. Content Type Journal Article Category Regular Article Pages 1-16 DOI 10.1007/s11104-011-1082-6 Authors Sandy Sampaio Videira, Graduate student, Soil Sciences-UFRRJ/Embrapa Agrobiologia, Seropédica, RJ, Brazil Danilo Messias de Oliveira, Undergraduate student-UFRRJ/Embrapa Agrobiologia, Seropédica, RJ, Brazil Rafael Fiusa de Morais, Graduate student, Soil Sciences-UFRRJ/Embrapa Agrobiologia, Seropédica, RJ, Brazil Wardsson Lustrino Borges, Research scientist-Embrapa Amapá, Rodovia Juscelino Kubitscheck, Km5, 2600 Macapá, AP, Brazil Vera Lúcia Divan Baldani, Research Scientists-Embrapa Agrobiologia, BR 465, km 07, Seropédica, RJ CEP 23890-000, Brazil José Ivo Baldani, Research Scientists-Embrapa Agrobiologia, BR 465, km 07, Seropédica, RJ CEP 23890-000, Brazil Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Background and aims   Plant-bacterial interactions in the rhizosphere are important in mediating soil nutrient transformations. Plants supply carbon-rich substrates to rhizobacteria as root exudates and bacteria mobilise soil-bound phosphate for plant nutrition. This study aimed to probe the specificity of the plant effect on bacterial gene expression in P-starved rhizosphere conditions. Methods   DNA microarrays were employed to study gene expression in the rhizosphere of Lolium perenne grown under high and low phosphate regimes (330 μM vs. 3–6 μM phosphate). Root exudation under these regimes was also quantified. Phosphate-regulated gene expression of a panel of 22 genes was compared in rhizosphere, planktonic culture and during biofilm growth on an artificial root. Results   Plant growth and root exudation were affected by P-availability. P-limited conditions induced increased expression of bacterial genes of an aromatic degradation pathway ( catA ), heavy metal sensing ( PA2523 ), and membrane proteins ( glpM , crcB ), while genes involved in cell motility and amino acid uptake/ metabolism were downregulated. A crcB mutant was impaired in rhizosphere survival under low phosphate conditions, though glpM and catA mutants were not affected. Several of the genes studied were induced by phosphate limitation in all three lifestyles studied. Conclusions   Our results show the importance of the plant-microbe interaction in controlling the bacterial transcriptional response in a phosphate-limited rhizosphere. Content Type Journal Article Category Regular Article Pages 1-20 DOI 10.1007/s11104-011-1060-z Authors Agnieszka Zyśko, Faculty of Life Sciences, University of Manchester, Oxford Rd, Manchester, M13 9PT UK Hervé Sanguin, Faculty of Life Sciences, University of Manchester, Oxford Rd, Manchester, M13 9PT UK Andrew Hayes, Faculty of Life Sciences, University of Manchester, Oxford Rd, Manchester, M13 9PT UK Leanne Wardleworth, Faculty of Life Sciences, University of Manchester, Oxford Rd, Manchester, M13 9PT UK Leo A. H. Zeef, Faculty of Life Sciences, University of Manchester, Oxford Rd, Manchester, M13 9PT UK Allan Sim, The James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH Scotland, UK Eric Paterson, The James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH Scotland, UK Brajesh K. Singh, The James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH Scotland, UK Michael A. Kertesz, Faculty of Life Sciences, University of Manchester, Oxford Rd, Manchester, M13 9PT UK Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Background and aims   Under chronically elevated N deposition, N retention mainly occur at high soil C-to-N ratio. This may be mediated through soil microbes, such as ectomycorrhizal (EM) fungi, saprotrophic fungi and bacteria, and the aim of this study was to evaluate the relationship between soil microbes and forest floor C-to-N ratios. Methods   Soil samples from 33 Norway spruce ( Picea abies (L.) H. Karst) forests in Denmark and southern Sweden in a forest floor C-to-N ratio gradient (ranging from 14 to 35) were analysed regarding the content of phospholipid fatty acids (PLFAs) to estimate their soil microbial community composition and the relative biomasses of different microbial groups. The relation of EM biomass to total fungal biomass was estimated as the loss of the fungal PLFA 18:2ω6,9 during incubation of soils and the production of EM mycelia was estimated using fungal in-growth mesh bags. The soil microbial variables were correlated to forest floor C-to-N ratio, NO 3 - leaching, soil pH and stand age. Results   Fungal proportions of microbial biomass, EM to total fungi and EM mycelial production were all positively related to C-to-N ratio, while NO 3 - leaching was negatively related to C-to-N ratio. Conclusions   Both EM and saprotrophic fungi change with forest floor C-to-N ratios and appear to play a central role in N retention in forest soil. A better understanding of the mechanisms behind this process may be revealed if the role of recalcitrant fungal metabolites for N retention (and soil C sequestration) can be identified. Research along this line deserves further studies. Content Type Journal Article Category Regular Article Pages 1-12 DOI 10.1007/s11104-011-1081-7 Authors Lars Ola Nilsson, Danish Centre for Forest, Landscape and Planning, University of Copenhagen, Copenhagen, Denmark Håkan Wallander, Department of Biology, Microbial ecology group, Lund University, 223 62 Lund, Sweden Per Gundersen, Danish Centre for Forest, Landscape and Planning, University of Copenhagen, Copenhagen, Denmark Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Background and Aims   Rocket salad ( Eruca sativa Mills) is one of the major leafy vegetables produced worldwide and has been characterized as a rich source of chemoprotective glucosinolates (GSL). The relationship between N fertilization and the resulting plant biomass and N status with GSL quantity and quality in rocket leaves was examined. Methods   A pot experiment was conducted, applying ten different N-rates and destructive sampling was carried out 15, 30 and 45 days after transplanting (DAT). The Mitscherlich equation was used to establish NO 3 -N critical levels at each growth stage and as an indicator of N demand for relative maximum dry matter accumulation and glucosinolate content and composition was determined. Results   Glucosinolate content was significantly influenced by N rate, growth stage and their interaction. Different GSL types showed dissimilar responses to N fertilization: aliphatic GSLs were significantly reduced under increased N rates whereas indole GSL showed the reverse. Under excess N fertilization (〉1.04 g/plant), dry matter accumulation remained constant, NO 3 -N was significantly increased and total GSL content was significantly reduced, factors that could lead to an anticipated product quality decline. Conclusions   The application of the critical NO 3 -N level approach used to identify optimal N fertilization rates for plant growth could serve as means to obtain optimized GSL content in the edible plant parts. Content Type Journal Article Category Regular Article Pages 1-12 DOI 10.1007/s11104-011-1071-9 Authors Michalis Omirou, Department of Natural Resources and Agricultural Engineering, Laboratory of Soils and Agricultural Chemistry, Agricultural University of Athens, 75 Iera Odos Str., 11855 Athens, Greece Chara Papastefanou, cp FoodLab LTD, P.O.Box 28729, 2082 Nicosia, Cyprus Dimitra Katsarou, Department of Biochemistry and Biotechnology, University of Thessaly, Ploutonos 26 & Aeolou Str., Larisa, 41221 Greece Ioannis Papastylianou, Agricultural Research Institute, Ministry of Agriculture, Natural Resources and Environment, P.O.Box 22016, 1516 Nicosia, Cyprus Harold C. Passam, Department of Crop Science, Laboratory of Vegetable Production, Agricultural University of Athens, 75 Iera Odos Str., 11855 Athens, Greece Constantinos Ehaliotis, Department of Natural Resources and Agricultural Engineering, Laboratory of Soils and Agricultural Chemistry, Agricultural University of Athens, 75 Iera Odos Str., 11855 Athens, Greece Kalliope K. Papadopoulou, Department of Biochemistry and Biotechnology, University of Thessaly, Ploutonos 26 & Aeolou Str., Larisa, 41221 Greece Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Aims   We investigated the link between tree community composition and soil microbial community biomass and structure in central-eastern Spain. Methods   The effects of the forest stand composition on the soil organic matter dynamics and on the structure and activity of the soil microbial community have been determined using phospholipid fatty acid profiles and soil enzymatic activities. Results   The soil and litter N and C contents were higher in Pinus nigra Arn. ssp. salzmannii and Quercus ilex mixed forest stands (SBHO) and in long-term unmanaged Pinus nigra Arn. ssp. salzmannii forest stands (SBPC) than in pure Pinus nigra Arn. ssp. salzmannii forest stands (SBPA) and Pinus nigra Arn. ssp. salzmannii and Juniperus thurifera mixed forest stands (SBSJ). The bacterial biomass was significantly higher in SBSJ and SBPA than in SBPC and SBHO. The results show an uncoupling of the soil microbial biomass and its activity. pH is related to microbial biomass and its community structure under a Mediterranean humid climate. Conclusions   The tree species seem to affect the biomass of the soil microbial community and its structure. The pH, but not the C/N ratio, is a factor influencing the microbial dynamics, biomass, and community structure. Content Type Journal Article Category Regular Article Pages 1-12 DOI 10.1007/s11104-011-1072-8 Authors M. E. Lucas-Borja, Departamento de Ciencia y Tecnología Agroforestal y Genética, Universidad de Castilla La Mancha, Campus Universitario s/n, C.P. 02071 Albacete, Spain D. Candel, Departamento de Ciencia y Tecnología Agroforestal y Genética, Universidad de Castilla La Mancha, Campus Universitario s/n, C.P. 02071 Albacete, Spain K. Jindo, Centro de Edafología y Biologia Aplicada del Segura, C.S.I.C., Campus Universitario de Espinardo, Apartado de correos 164, C.P. 30100 Murcia, Spain J. L. Moreno, Centro de Edafología y Biologia Aplicada del Segura, C.S.I.C., Campus Universitario de Espinardo, Apartado de correos 164, C.P. 30100 Murcia, Spain M. Andrés, Departamento de Ciencia y Tecnología Agroforestal y Genética, Universidad de Castilla La Mancha, Campus Universitario s/n, C.P. 02071 Albacete, Spain F. Bastida, Centro de Edafología y Biologia Aplicada del Segura, C.S.I.C., Campus Universitario de Espinardo, Apartado de correos 164, C.P. 30100 Murcia, Spain Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Background and aims   We conducted a mesocosm study to investigate the extent to which the process of hydraulic redistribution of soil water by plant roots is affected by mycorrhizosphere disturbance. Methods   We used deuterium-labeled water to track the transfer of hydraulically lifted water (HLW) from well-hydrated donor oaks ( Quercus agrifolia Nee.) to drought-stressed receiver seedlings growing together in mycorrhizal or fungicide-treated mesocosms. We hypothesized that the transfer of HLW from donor to receiver plants would be enhanced in undisturbed (non-fungicide-treated) mesocosms where an intact mycorrhizal hyphal network was present. Results   Contrary to expectations, both upper soil and receiver seedlings contained significantly greater proportions of HLW in mesocosms where the abundance of mycorrhizal hyphal links between donor and receiver roots had been sharply reduced by fungicide application. Reduced soil hyphal density and viability likely hampered soil moisture retention properties in fungicide-treated mesocosms, thus leading to faster soil water depletion in upper compartments. The resulting steeper soil water potential gradient between taproot and upper compartments enhanced hydraulic redistribution in fungicide-treated mesocosms. Conclusions   Belowground disturbances that reduce soil hyphal density and viability in the mycorrhizosphere can alter the patterns of hydraulic redistribution by roots through effects on soil hydraulic properties. Content Type Journal Article Category Regular Article Pages 1-11 DOI 10.1007/s11104-011-1080-8 Authors José Ignacio Querejeta, Departamento de Conservación de Suelos y Aguas, Centro de Edafología y Biología Aplicada del Segura-Consejo Superior de Investigaciones Científicas (CEBAS-CSIC), Campus Universitario de Espinardo, 30100 Murcia, Spain Louise M. Egerton-Warburton, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL, USA Iván Prieto, Estación Experimental de Zonas Áridas-Consejo Superior de Investigaciones Científicas (EEZA-CSIC), La Cañada de San Urbano, Almería, Spain Rodrigo Vargas, Departamento de Biología de la Conservación, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada, Mexico Michael F. Allen, Center for Conservation Biology, University of California, Riverside, CA, USA Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Aims   In spite of the important role played by herbivory in plant community structure and the fact that it constitutes one of the most important ecological disturbance processes in the dynamics of both natural and anthropic systems, few studies have concentrated on the consequences of browsing on vegetation spatial patterns. The main objective of this study was to examine the role of domestic livestock pressure in the spatial distribution pattern and interspecific competition of two sand dune shrubs: Retama monosperma and the endangered species Thymus carnosus . Methods   We compared three areas featuring different intensities of livestock pressure. Two 25 × 25 m plots were established in each study area, and the crown heights, diameters and x, y coordinates of every individual in each plot were recorded. Results   Livestock activity produced a considerable effect, not only on plant cover and size (larger and higher crowns of both species in non herbivory plots) but also on spatial pattern. Whereas light herbivory lead to a random spatial pattern for both species, high herbivory resulted in a repulsion one. Conclusions   Under high and no livestock pressure, T. carnosus is displaced by R. monosperma , creating a repulsion point pattern distribution between the two species. However, when livestock disturbance was low, our data reveal relatively higher T. carnosus cover values than in the other livestock pressure scenarios, along with a random distribution pattern. Content Type Journal Article Category Regular Article Pages 1-11 DOI 10.1007/s11104-011-1066-6 Authors M. Zunzunegui, Universidad de Sevilla, Departamento de Biología Vegetal y Ecología, Apdo 1095, 41080 Sevilla, Spain M. P. Esquivias, Universidad de Sevilla, Departamento de Biología Vegetal y Ecología, Apdo 1095, 41080 Sevilla, Spain F. Oppo, Universidad de Sevilla, Departamento de Biología Vegetal y Ecología, Apdo 1095, 41080 Sevilla, Spain J. B. Gallego-Fernández, Universidad de Sevilla, Departamento de Biología Vegetal y Ecología, Apdo 1095, 41080 Sevilla, Spain Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Background and aims   Phenological variations in tropical forests are usually explained by climate. Nevertheless, considering that soil water availability and nutrient content also influence plant water status and metabolism, soil conditions may also be important in the regulation of plant reproductive and vegetative activities over time. We investigated whether phenological patterns and stem growth differ in trees growing in two types of soil that display contrasting water and nutrient availability, namely, Gleysol (moist and nutrient-poor) and Cambisol (drier and nutrient-rich). Methods   Phenological observations (flushing, leaf fall, flowering and fruiting) and stem diameter growth were recorded for 120 trees fitted with fixed dendrometer bands, at 15 days intervals, for 1 year. Two species of contrasting deciduousness were investigated: Senna multijuga (semi-deciduous) and Citharexylum myrianthum (deciduous). Results   Both species were seasonal in all phenophases, regardless of soil type. However, frequency, mean date and intensity of phenophases varied according to soil type. Girth increment of C. myrianthum was four times greater in Cambisol than in Gleysol, whereas the type of soil had no significant effect on that of S. multijuga . Conclusions   These results show that soil characteristics also play an important role in determining phenological patterns and growth and must be considered when analysing phenological patterns in tropical forests. Content Type Journal Article Category Regular Article Pages 1-13 DOI 10.1007/s11104-011-1063-9 Authors F. C. G. Cardoso, Laboratório de Ecologia Vegetal; Departamento de Botânica, SCB, Universidade Federal do Paraná, CP 19031, 81531-980 Curitiba, PR, Brazil R. Marques, Departamento de Solos e Engenharia Agrícola, Universidade Federal do Paraná, Curitiba, Brazil P. C. Botosso, Empresa Brasileira de Pesquisa Agropecuária, Embrapa Florestas, Colombo, Brazil M. C. M. Marques, Laboratório de Ecologia Vegetal; Departamento de Botânica, SCB, Universidade Federal do Paraná, CP 19031, 81531-980 Curitiba, PR, Brazil Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Background and aims   This study aimed to investigate the roles of silicon (Si) in ameliorating manganese (Mn) toxicity in two rice ( Oryza sativa L.) cultivars: i.e. cv. Xinxiangyou 640 (XXY), a Mn-sensitive cultivar and cv. Zhuliangyou 99 (ZLY), a Mn-tolerant cultivar. Methods   Plants were cultured in nutrient solution containing normal Mn (6.7 μM) or high Mn (2.0 mM), both with or without Si supply at 1.5 mM Si. Results   Plant growth was severely inhibited by high Mn in cv. XXY, but was enhanced by Si supply. In cv. XXY, Si-enhanced tolerance resulted from a restriction of Mn transport, whereas in cv. ZLY Mn uptake was depressed. In cv. XXY, high Mn significantly increased superoxide dismutase (SOD), catalase and ascorbate peroxidase activities but decreased non-protein thiols and glutathione concentrations, leading to accumulation of H 2 O 2 and malondialdehyde. The addition of Si significantly counteracted high Mn-elevated malondialdehyde and H 2 O 2 concentrations and enhanced plant growth. In cv. ZLY, high Mn considerably raised SOD activities and glutathione concentrations, thus leading to relatively low oxidative damage. Conclusions   Si-enhanced Mn tolerance was attributed mainly to restricted Mn transport in cv. XXY but to depressed Mn uptake in cv. ZLY. Silicon mainly influenced non-enzymatic antioxidants in these two rice cultivars under high Mn stress. Content Type Journal Article Category Regular Article Pages 1-13 DOI 10.1007/s11104-011-1076-4 Authors Ping Li, Ministry of Agriculture Key Laboratory of Crop Nutrition and Fertilization, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081 Peoples’ Republic of China Alin Song, Ministry of Agriculture Key Laboratory of Crop Nutrition and Fertilization, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081 Peoples’ Republic of China Zhaojun Li, Ministry of Agriculture Key Laboratory of Crop Nutrition and Fertilization, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081 Peoples’ Republic of China Fenliang Fan, Ministry of Agriculture Key Laboratory of Crop Nutrition and Fertilization, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081 Peoples’ Republic of China Yongchao Liang, Ministry of Agriculture Key Laboratory of Crop Nutrition and Fertilization, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081 Peoples’ Republic of China Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Aims   The high concentrations of Mn, Fe and Al in acid soils during waterlogging impair root and shoot growth more severely in intolerant than tolerant wheat genotypes. This study aims to establish whether this difference in vegetative growth and survival during waterlogging (1) is verifiable across a range of tolerant/intolerant genotypes and acid soils, and (2) results in improved recovery after cessation of waterlogging and enhanced grain yield. Methods   Wheat genotypes contrasting in their tolerance to ion toxicities were grown in four acid soils until 63DAS and maturity, with a 42-day waterlogging treatment imposed at 21 DAS. Results   The shoot Al, Mn and Fe concentrations increased by up to 5-, 3- and 9-fold respectively due to waterlogging in various soils. Compared to the intolerant lines, Al-, Mn- and Fe-tolerant genotypes maintained a relatively lower increase in shoot concentrations of Al (79 vs. 117%), Mn (90 vs. 101%) and Fe (171 vs. 252%) and demonstrated better waterlogging tolerance at the vegetative stage expressed in relative root (38% vs. 25%) and shoot (62% vs. 52%) growth. After cessation of waterlogging and the continued growth to maturity, tolerant genotypes maintained a relatively lower plant concentration of Al, Mn and Fe, but produced a higher above-ground biomass (74% vs. 56%) and most importantly demonstrated improved waterlogging tolerance (a relative grain yield of 78% vs. 54%) compared to intolerant genotypes. Maturity following waterlogging stress was delayed less in tolerant than intolerant genotypes (114 vs. 124%, respectively), which would reduce the potential yield loss where post-anthesis coincides with drought. Conclusions   The results confirm the validity of a novel approach of enhancing waterlogging tolerance of wheat genotypes grown in acid soil via increased tolerance to ion toxicities. Content Type Journal Article Category Regular Article Pages 1-11 DOI 10.1007/s11104-011-1073-7 Authors Hossein Khabaz-Saberi, Soil Science and Plant Nutrition, School of Earth and Environment, UWA Institute of Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia S. J. Barker, School of Plant Biology, Faculty of Natural and Agricultural Sciences and Centre for Legumes in Mediterranean Agriculture, UWA Institute of Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia Z. Rengel, Soil Science and Plant Nutrition, School of Earth and Environment, UWA Institute of Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X