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  • 1
    Language: English
    In: Plant and Soil, 2011, Vol.339(1), pp.231-245
    Description: Diversity in phosphorus (P) acquisition strategies was assessed among three species of arbuscular mycorrhizal fungi (AMF) isolated from a single field in Switzerland. Medicago truncatula was used as a test plant. It was grown in a compartmented system with root and root-free zones separated by a fine mesh. Dual radioisotope labeling ( 32 P and 33 P) was employed in the root-free zone as follows: 33 P labeling determined hyphal P uptake from different distances from roots over the entire growth period, whereas 32 P labeling investigated hyphal P uptake close to the roots over the 48 hours immediately prior to harvest. Glomus intraradices , Glomus claroideum and Gigaspora margarita were able to take up and deliver P to the plants from maximal distances of 10, 6 and 1 cm from the roots, respectively. Glomus intraradices most rapidly colonized the available substrate and transported significant amounts of P towards the roots, but provided the same growth benefit as compared to Glomus claroideum , whose mycelium was less efficient in soil exploration and in P uptake and delivery to the roots. These differences are probably related to different carbon requirements by these different Glomus species. Gigaspora margarita provided low P benefits to the plants and formed dense mycelium networks close to the roots where P was probably transiently immobilized. Numerical modeling identified possible mechanisms underlying the observed differences in patterns of mycelium growth. High external hyphal production at the root-fungus interface together with rapid hyphal turnover were pointed out as important factors governing hyphal network development by Gigaspora , whereas nonlinearity in apical branching and hyphal anastomoses were key features for G. intraradices and G. claroideum , respectively.
    Keywords: Arbuscular mycorrhiza ; Extraradical mycelium ; Functional diversity ; Hyphal growth model ; Medicago truncatula ; Phosphorus
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 2
    Language: English
    In: Plant and Soil, 2014, Vol.377(1), pp.439-456
    Description: Aims Phosphorus resources have to be managed sustainably and therefore the recycling of P from waste streams is essential. A thermo-chemical recycling process has been developed to produce a P fertilizer from sewage sludge ash (SSA) but its plant availability is unknown. Methods Two SSA products prepared with either Ca[Cl.sub.2] (SSACa) or Mg[Cl.sub.2] (SSAMg) as chemical reactant during the thermal treatment were mixed with three soils previously labeled with [sup.33]P. Reference treatments with water-soluble P added at equal amounts of total P were included. The transfer of P from SSACa and SSAMg to Lolium multiflorum or P pools of sequentially extracted soil-fertilizer incubations were quantified. Results The shoot P uptake from SSAMg was higher than from SSACa. For SSAMg the relative effectiveness compared to a water-soluble P fertilizer was 88 % on an acidic and 71 % on a neutral soil but only 4 % on an alkaline soil. The proportion of P derived from the fertilizer in the plant and in the first two extraction pools of soil-fertilizer incubations were strongly correlated, suggesting that it is sufficient to conduct an incubation study to obtain robust information on plant P availability. Conclusions We conclude that under acidic to neutral conditions SSAMg presents an appropriate alternative to conventional P fertilizers and the dissolution of P from SSAMg seems to be governed by protons and cations in the soil solution. Keywords Sewage sludge ash * [sup.33]P labeling * Recycling fertilizer * Radioisotopes * Italian ryegrass * Sequential extraction
    Keywords: Sewage sludge ash ; P labeling ; Recycling fertilizer ; Radioisotopes ; Italian ryegrass ; Sequential extraction
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 3
    Language: English
    In: Plant and Soil, 2011, Vol.341(1), pp.179-192
    Description: The integration of multipurpose legumes into low-input tropical agricultural systems is needed because they are a nitrogen (N) input through symbiotic fixation. The drought-tolerant cover legume canavalia ( Canavalia brasiliensis ) has been introduced for use either as forage or as a green manure into the crop-livestock system of the Nicaraguan hillsides. To evaluate its impact on the subsequent maize crop, an in-depth study on N dynamics in the soil-plant system was conducted. Microplots were installed in a 6-year old field experiment with maize-canavalia rotation. Direct and indirect 15 N-labelling techniques were used to determine N uptake by maize from canavalia residues and canavalia-fed cows’ manure compared to mineral fertilizer. Litter bags were used to determine the N release from canavalia residues. The incorporation of N from the amendment into different soil N pools (total N, mineral N, microbial biomass) was followed during the maize cropping season. Maize took up an average of 13.3 g N m −2 , within which 1.0 g N m −2 was from canavalia residues and 2.6 g N m −2 was from mineral fertilizer, corresponding to an amendment N recovery of 12% and 32%, respectively. Recoveries in maize would probably be higher at a site with lower soil available N content. Most of the amendment N remained in the soil. Mineral N and microbial N were composed mainly of N derived from the soil. Combined total 15 N recovery in maize and soil at harvest was highest for the canavalia residue treatment with 98% recovery, followed by the mineral fertilizer treatment with 83% recovery. Despite similar initial enrichment of soil microbial and mineral N pools, the indirect labelling technique failed to assess the N fertilizer value of mineral and organic amendments due to a high N mineralization from the soil organic matter.
    Keywords: Canavalia brasiliensis ; N ; Indirect and direct labelling techniques ; Microplot study ; Organic amendments
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 4
    Language: English
    In: Journal of Cleaner Production, 01 March 2015, Vol.90, pp.104-113
    Description: In this study, we used LCA to test the influence of practicing low-input farming, on-farm processing and direct distribution on the environmental impact of bread consumption. Primary data were collected from four commercially active producers (two in France, one in Italy and one in Portugal) who cultivate cereals under low levels of inputs, process grains on farm and distribute their products directly to end consumers. Environmental impacts of products were compared to equivalents from supermarkets, characterised by higher rates of applied inputs at the agricultural stage, industrial processing and centralised distribution. The scope of LCA was from cradle to the consumer. The study revealed a high variability of results between individual cases. At the agricultural stage, products from a low-input cropping system integrated with livestock production in France and from a small-scale labour intensive production in Portugal showed similar or better performance on most impact categories to those from high-input agriculture, while horse farming in France and a stockless cultivation of ancient wheat cultivars in Italy revealed mostly higher environmental burdens. Decentralised processing and distribution in France had similar or slightly higher impacts to conventional supply chains, while Italian and Portuguese cases revealed clearly higher environmental burdens for most impact categories. Results demonstrate that while there might be a positive relationship between the scale and eco-efficiency of processing and distribution, the level of agricultural inputs, yields and transport distances cannot be used as proxies of environmental performance. Products of low-input systems can have much higher, similar or lower impacts to their high-input counterparts due to the influence of site conditions and the management. More research assessing the effectiveness of context-specific management systems is needed as oppose to the generic comparisons between labelling schemes (i.e. organic and conventional farming).
    Keywords: Low-Input Agriculture ; Bread ; Life Cycle Assessment ; Agro-Ecology ; Alternative Food Networks ; Engineering
    ISSN: 0959-6526
    E-ISSN: 1879-1786
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  • 5
    Language: English
    In: Plant and Soil, 2010, Vol.334(1), pp.391-407
    Description: Organic farming largely depends on animal manure as a source of phosphorus (P) and the recycling of animal manure globally is becoming increasingly important. In a pot experiment, using radioactive P labeling techniques, we studied ryegrass uptake of P applied with animal manure and water soluble mineral fertilizer to soils that had been cropped for 22 years according to organic or conventional farming practices. The soils differed in P status and microbial activity. Labeling soil-available P also allowed assessing the uptake from residual P that remained in the soils because of their different fertilization histories. On each soil, recovery of fresh manure P in four harvests of ryegrass shoots was lower than recovery of mineral P. It ranged from 24% to 35% for manure P and from 37% to 43% for mineral P. Recovery of fresh manure P was affected by soil-available P contents. It was lower at a higher available P in a conventional soil. Different levels in microbial activity among soils were of lesser importance for the recovery of fresh manure P in plants. The recovery of residual P ranged from 9% to 15%. Residual P contained in organic cropped soils contributed less to P nutrition of ryegrass than the residual P contained in conventional cropped soils, probably due to their lower residual P contents being composed of stable P forms. The indirect isotope dilution technique is useful in assessing manure P uptake by plants, but attention must be given to added P interactions, i.e., the potential impact of organic amendments on P uptake from non-labeled soil and residual P.
    Keywords: Phosphorus ; Animal manure ; Residual phosphorus ; Isotope techniques ; Phosphorus uptake ; Organic and conventional farming
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 6
    Language: English
    In: Plant and Soil, 2010, Vol.328(1), pp.155-164
    Description: Brachiaria forage grasses are widely used for livestock production in the tropics. Signalgrass ( Brachiaria decumbens cv. Basilisk, CIAT 606) is better adapted to low phosphorus (P) soils than ruzigrass ( B. ruziziensis cv. Kennedy, CIAT 654), but the physiological basis of differences in low-P adaptation is unknown. We characterized morphological and physiological responses of signalgrass and ruzigrass to low P supply by growing both grasses for 30 days in nutrient solution with two levels of P supply using the hydroxyapatite pouch system. Ruzigrass produced more biomass at both levels of P supply whilst signalgrass appears to be a slower-growing grass. Both grasses increased biomass allocation to roots and had higher root acid phosphatase and phytase activities at low P supply. At low P supply, ruzigrass showed greater morphological plasticity as its leaf mass density and lateral root fraction increased. For signalgrass, morphological traits that are not responsive to variation in P supply might confer long-term ecological advantages contributing to its superior field persistence: greater shoot tissue mass density (dry matter content) might lower nutrient requirements while maintenance of lateral root growth might be important for nutrient acquisition in patchy soils. Physiological plasticity in nutrient partitioning between root classes was also evident for signalgrass as main roots had higher nutrient concentrations at high P supply. Our results highlight the importance of analyzing morphological and physiological trait profiles and determining the role of phenotypic plasticity to characterize differences in low-P adaptation between Brachiaria genotypes.
    Keywords: Adaptation ; Growth rate ; Lateral roots ; Phosphorus ; Plasticity ; Tissue mass density
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 7
    Language: English
    In: Applied Microbiology and Biotechnology, 2018, Vol.102(12), pp.5265-5278
    Description: Cowpea N 2 fixation and yield can be enhanced by selecting competitive and efficient indigenous rhizobia. Strains from contrasting agro-ecologies of Kilifi and Mbeere (Kenya) were screened. Two pot experiments were established consisting of 13 Bradyrhizobium strains; experiment 1 (11 Mbeere + CBA + BK1 from Burkina Faso), experiment 2 (12 Kilifi + CBA). Symbiotic effectiveness was assessed (shoot biomass, SPAD index and N uptake). Nodule occupancy of 13 simultaneously co-inoculated strains in each experiment was analyzed by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) to assess competitiveness. Strains varied in effectiveness and competitiveness. The four most efficient strains were further evaluated in a field trial in Mbeere during the 2014 short rains. Strains from bacteroids of cowpea nodules from pot and field experiments were accurately identified as Bradyrhizobium by MALDI-TOF based on the SARAMIS™ database. In the field, abundant indigenous populations 7.10 × 10 3 rhizobia g −1 soil, outcompeted introduced strains. As revealed by MALDI-TOF, indigenous strains clustered into six distinct groups (I, II, III, IV, V and VI), group III were most abundant occupying 80% of nodules analyzed. MALDI-TOF was rapid, affordable and reliable to identify Bradyrhizobium strains directly from nodule suspensions in competition pot assays and in the field with abundant indigenous strains thus, its suitability for future competition assays. Evaluating strain competitiveness and then symbiotic efficacy is proposed in bioprospecting for potential cowpea inoculant strains.
    Keywords: Bradyrhizobium ; Cowpea ; Symbiotic effectiveness ; Nodule occupancy ; Protein profile ; Bacteroid
    ISSN: 0175-7598
    E-ISSN: 1432-0614
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  • 8
    Language: English
    In: Plant and Soil, 2016, Vol.408(1), pp.15-30
    Description: Background and Aims Soil microbial communities contribute to organic phosphorus cycling in a variety of ways, including secretion of the PhoD alkaline phosphatase. We sampled a long-term grassland fertilization trial in Switzerland characterized by a natural pH gradient. We examined the effects of phosphate depletion and pH on total and active microbial community structures and on the structure and composition of the total and active phoD-harboring community. Methods Archaeal, bacterial and fungal communities were investigated using T-RFLP and phoD-harboring members of these communities were identified by 454-sequencing. Results Phosphate depletion decreased total, resin-extractable and organic phosphorus and changed the structure of all active microbial communities, and of the total archaeal and phoD-harboring communities. Organic carbon, nitrogen and phosphorus increased with pH, and the structures of all total and active microbial communities except the total fungal community differed between the two pH levels. phoD-harboring members were affiliated to Actinomycetales, Bacilliales, Gloeobacterales, Planctomycetales and Rhizobiales. Conclusions Our results suggest that pH and associated soil factors are important determinants of microbial and phoD-harboring community structures. These associated factors include organic carbon and total nitrogen, and to a lesser degree phosphorus status, and active communities are more responsive than total communities. Key players in organic P mineralization are affiliated to phyla that are known to be important in organic matter decomposition.
    Keywords: 454-sequencing ; Grassland ; Alkaline phosphatase ; DNA ; RNA ; T-RFLP
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 9
    Language: French
    In: Comptes Rendus de l'Académie d'Agriculture de France, 2012, Vol.98(4), pp.29-37
    Description: Le phosphore (P) est un des 29 éléments strictement indispensables au vivant. Il est à la fois irremplaçable et non renouvelable à l’échelle humaine. Dans les volumes de sol exploités par les racines il est presque un élément trace, puisque...
    Keywords: Life Sciences ; Agriculture
    ISSN: 0989-6988
    Source: Hyper Article en Ligne (CCSd)
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  • 10
    Language: English
    In: Plant and Soil, 2005, Vol.276(1), pp.163-176
    Description: Diversity in phosphorus (P) acquisition strategies was assessed among eight isolates of arbuscular mycorrhizal fungi (AMF) belonging to three Glomus species, all obtained from the same field site. Maize ( Zea mays L. cv. Corso) was used as a test plant. Compartmented cultivation containers coupled with 33 P radioisotope labeling of soil P were employed to estimate (1) the distance from the roots that AMF were able to acquire soil P from, (2) the rate of soil colonization, (3) the efficiency of uptake of soil P by AMF, (4) benefits provided to maize in terms of P acquisition and growth. Glomus mosseae and G. intraradices took up P 10 cm from roots, whereas G. claroideum only up to 6 cm from the roots. G. mosseae most rapidly colonized the available soil volume and transported significant amounts of P to maize from a distance, but provided no net P uptake benefit to the plants. On the other hand, both G. intraradices and three out of four G. claroideum isolates significantly improved net P uptake by maize. These effects seem to be related to variability between and to a limited extent also within AMF species, in mycelium development, efficiency of hyphal P uptake and effects on plant P acquisition via the root pathway. In spite of absence of maize growth responses to inoculation with any of the AMF isolates, this study indicates remarkable functional diversity in the underground component of the studied field site.
    Keywords: compartmented containers ; functional diversity ; Glomus ; radioisotope labeling
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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