The role of arbuscular mycorrhiza in legume symbiotic performance

April 18, 2010 By biotech-source.com Leave a Comment

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This digital document is a journal article from Soil Biology and Biochemistry, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
Legumes may respond to non-rhizobial inoculants such as arbuscular mycorrhizal (AM) fungi either through an effect on plant growth or, in addition, through an effect on the function of the legume-Rhizobium symbiosis. We have examined the literature where the application of ^1^5N isotope dilution methodology permits the effect of indigenous AM and AM inoculants to be quantitatively separated into plant-growth-mediated and biological N”2 fixation (BNF)-mediated components. These studies clearly demonstrate the beneficial effects that both indigenous and inoculated AM have on legume growth, N uptake and the proportional dependence of the legume on atmospheric N”2. While the published data allow an assessment of various biological, edaphic and environmental factors that affect the response of various legumes to AM inoculation, they also highlight the paucity of quantitative field data and the lack of understanding of the interaction of legume genotype with AM species with respect to legume symbiotic performance.

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Exploring the mechanisms behind elevated microbial activity after wood ash application

April 18, 2010 By biotech-source.com Leave a Comment

Product Description
This digital document is a journal article from Soil Biology and Biochemistry, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
Wood ash fertilization increases the pH and concentration of dissolved organic carbon (DOC) in the soil solution and enhances the activity of soil microorganisms. However, it is unknown whether DOC or pH is primarily responsible for the increase in microbial activity. We designed an experiment to separate the effects of DOC and/or pH on soil microbial activity using suspensions of humus extracts and bacteria that had not previously been exposed to wood ash fertilization. After a 3-week incubation, DOC extracts were obtained from control (DOC”C) and ash (DOC”A) treatments with carbon concentrations of 9.1 and 32.5mg Cl^-^1, respectively. These extracts were supplied to bacterial suspensions at concentrations of 0 and 5mg Cl^-^1. We controlled for pH by matching adjustments, i.e. the original pH of the DOC”C extract was 4.5 and its adjusted pH was 6.9, whereas the DOC”A extract was pH 6.9 originally and pH 4.5 adjusted. The relative bacterial growth rate (RBGR), as measured by ^3H-thymidine incorporation, increased in suspensions of 5mg Cl^-^1 DOC as compared to control suspensions of 0mg Cl^-^1. At pH 6.9, RBGR was higher for both DOC extracts than at pH 4.5. These results suggest that both DOC and pH influence microbial activity. As the growth rate at pH 6.9 with DOC”A was higher than with DOC”C, the quality of the DOC extract must also play a role since the carbon concentration was controlled for. The decrease in relative abundance of hydrophobic and hydrophilic acids in DOC”A compared to DOC”C indicates a quality shift. As measured by DGGE banding patterns, the bacterial community structure changed over the course of the 24-h experiment in the following three trials, all of which received 5mg Cl^-^1: DOC”C at pH 6.9 and DOC”A at pH 4.5 and 6.9. These results demonstrate that both the DOC origin (control vs. ash) and the pH influence a subset of the bacterial community.

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Gross nitrogen mineralization rates still high 14 years after

April 18, 2010 By biotech-source.com Leave a Comment

Product Description
This digital document is a journal article from Soil Biology and Biochemistry, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
Significant areas of temperate forests in Central Europe, NE America and E Asia receive high amounts of N deposition. According to the few studies available, suspension of the N load leads to reductions in both inorganic soil N and leaching of N within a few years. We report that, surprisingly, N is still mineralized at high rates 14yr after suspension of a previous N-load of >100kg N/hayr for 20yr. In this treatment, gross N mineralization rates exceeded those in control plots by a factor 3, but equaled those in still on-going (34yr of) treatments with 30 and 60kg N/hayr, in which levels of extractable NH”4^+ were up to 10 times higher.

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Soil microbial metabolism and nutrient status in a Mediterranean area as affected by plant cover

April 18, 2010 By biotech-source.com Leave a Comment

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This digital document is a journal article from Soil Biology and Biochemistry, published by Elsevier in 2004. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

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The Mediterranean area of Southern Italy is characterized by different natural plant covers that mainly reflect different successional stages (i.e. low maquis, high maquis, Quercus ilex wood) and managed areas with introduced plant species (such as Pinus species). Soil properties could be affected by plant cover types as well as by plant species. Our objective was to determine the relationships of plant cover types and plant species with the chemical and biological characteristics of the soil. In four neighbouring areas with different plant cover types (low maquis, pure high maquis, high maquis with pines and pinewood, with pines planted by foresters in both cases), soil samples were collected under different plant species in order to evaluate the effect of plant cover types and plant species on soil properties. Soil samples were analyzed for nutrient content, microbial biomass, soil potential respiration and enzymatic activity (phosphatase, arylsulphatase, @b-glucosidase and hydrolase activities) as well as for pH, water holding capacity (WHC) and cation exchange capacity (CEC). Application of cluster analysis and principal component analysis to the data revealed that the plant cover type was the key factor influencing soil properties more than plant species. In fact, the largest differences were observed between pure high maquis soils and all other soils, with pure high maquis soils generally showing the highest values of WHC, CEC, nutrient content, organic and microbial C, soil respiration, phosphatase, arylsulphatase and @b-glucosidase activities. The significantly lower values of these variables in the low maquis relative to the pure high maquis probably reflect the effect of ecological succession on soil. The high maquis with pine, differing from the pure high maquis only for the presence or absence of pine, showed values of soil physical, chemical and biological characteristics similar to those found in the low maquis, thus suggesting that the presence of pine retards soil development.

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Birch invasion of heather moorland increases nematode diversity and trophic complexity

April 18, 2010 By biotech-source.com Leave a Comment

Product Description
This digital document is a journal article from Soil Biology and Biochemistry, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
To determine whether successional changes in plant communities may influence belowground community structure, we quantified nematode abundance, trophic structure and diversity along two separate chronosequences from heather moorland to birch woodland in the Scottish uplands. Tree invasion markedly altered plant community composition, and hence litter inputs, both directly, and indirectly through changes in understorey species. In turn, these changes in detrital inputs were reflected in consistent changes in nematode community structure. Nematode abundance increased from moorland to birch woodland, with moorland soils being dominated by a few taxa, notably root-hair and fungal feeders, compared to the more diverse composition of the birch woodland soils. Trophic structure was altered through an increase in the abundance of bacterial feeding relative to fungal-feeding nematodes, and an increase in the abundance of predatory nematodes. The increase in predators during the succession from moorland to woodland was associated with an increase in soil pH, highlighting that not only changes in the plant community, but also changes in soil properties associated with tree invasion may influence soil nematodes. Nematode diversity increased from moorland to birch woodland, with nematode richness being positively related to both plant species richness and soil pH. These results suggest that trees may control soil community structure through the manipulation of resources and the soil physico-chemical environment, promoting greater nematode diversity and trophic complexity.

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