97 research outputs found
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Novel characteristics (Intra and Ex planta) of indigenous serogroups of rhizobium meliloti
This thesis presents novel findings regarding
symbiotic, physiological, and antigenic characteristics of
representatives from an indigenous soil-borne population
of Rhizobium meliloti. Nodules were sampled from 'Vernal',
'Anchor', and 'Saranac' alfalfa, and the isolates analyzed
serologically. Rhizobium meliloti serogroup 31 was
identified as a dominant nodule occupant, with a greater
and more consistent nodule occupancy rate on Vernal (60%)
compared to Anchor (24%) or Saranac (36%). The symbiotic
effectiveness of the parent isolate of serogroup 31 was
evaluated on each cultivar over four harvests in a
greenhouse study. Only inoculated Vernal responded with an
increase in shoot dry weight and N₂ assimilated relative
to N supplemented plants between harvests two and three.
Field isolates of serogroup 31 from nodules on Vernal produced homogeneous, effective responses on Vernal and
Anchor. In contrast, serogroup 31 isolates from Anchor
nodules were heterogeneous in effectiveness on the parent
host, with poorly effective isolates shown to be
substantially more effective on Vernal.
Isolates of Rhizobium meliloti serogroups 31 and 17
were grown in yeast extract mannitol broth (YEM)
containing NaCl or polyethylene glycol (PEG). At water
potentials below -0.5 MPa imposed by PEG, strain 31 had a
lower specific growth rate than strain 17 which was
accompanied by irregular cell morphology. In contrast,
neither strain was affected significantly over the range
of water potentials created by NaCl. Upshock of water
stressed cells (-1.0 MPa PEG) into normal YEM (-0.15 MPa)
resulted in a faster recovery of growth by strain 31 than
strain 17. Strain 31 also required significantly fewer
days to nodulate alfalfa compared with strain 17 when
transferred from YEM at -1.0 MPa PEG onto the roots of
alfalfa seedlings in plant growth medium (-0.1 MPa).
Supplemental calcium (O.lmM) reduced the differences
between strains in their response to water stress.
Several novel phenomena were shown to hinder the
production of fluorescent antibody conjugates specific to
serogroup 31. An indirect fluorescent methodology, using
the biotin-avidin system, was developed to successfully
detect and specifically discriminate members of serogroup 31 from other strains of R. meliloti. Using this
technique, members of serogroup 31 were found to comprise
17% of the total R. meliloti population in soil samples
with a recent history of alfalfa cultivation
Fuel Reduction Practices and Their Effects on Soil Quality
Soils sustain our terrestrial ecosystems, help fuel plant growth, and govern key ecosystem services such as the storage and provision of clean water, degradation of toxic compounds, and regulation of atmospheric gases. Preserving the integrity of soil thus is an earnest responsibility of land stewardship in the United States. This report provides a synthesis of soil chemical, biological, and physical responses to various prescribed fire and mechanical thinning practices and offers practical considerations for use in fuel reduction planning. A wide range of current topics, identified in a nationwide survey of natural resource managers, is discussed in detail: (1) ecological consequences of prescribed fire on soil heating, water repellency, and soil nitrogen release; (2) whole tree harvesting and nutrient removal; (3) soil compaction; (4) masticated fuel beds; (5) pile burning; (6) cumulative effects of fire and thinning; (7) coarse woody debris; and (8) soil in a changing climate. We submit that with thoughtful planning and implementation, reducing fuels while proactively managing our soils can be complementary outcomes
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Soil carbon sequestration and changes in fungal and bacterial biomass following incorporation of forest residues.
Sequestering carbon (C) in forest soils can benefit site fertility and help offset greenhouse gas emissions. However, identifying soil conditions and forest management practices which best promote C accumulation remains a challenging task. We tested whether soil incorporation of masticated woody residues alters short-term C storage at forested sites in western and southeastern USA. Our hypothesis was that woody residues would preferentially stimulate soil fungal biomass, resulting in improved C use efficiency and greater soil C storage. Harvest slash at loblolly pine sites in South Carolina was masticated (chipped) and either (1) retained on the soil surface, (2) tilled to a soil depth of 40 cm, or (3) tilled using at least twice the mass of organics. At comparative sites in California, live woody fuels in ponderosa pine stands were (1) masticated and surface applied, (2) masticated and tilled, or (3) left untreated. Sites with clayey and sandy soils were compared in each region, with residue additions ranging from 20 to 207 Mg ha_1. Total and active fungal biomass were not strongly affected by residue incorporation despite the high input of organics. Limited response was also found for total and active bacterial biomass. As a consequence, fungal:bacterial (F:B) biomass ratios were similar among treatments at each site. Total soil C was elevated at one California site following residue incorporation, yet was significantly lower compared to surface-applied residues at both loblolly pine sites, presumably due to the oxidative effects of tilling on soil organic matter. The findings demonstrated an inconsequential effect of residue incorporation on fungal and bacterial biomass and suggest a limited potential of such practices to enhance long-term soil C storage in these forests
Soil carbon sequestration and changes in fungal and bacterial biomass following incorporation of forest residues
Towards Equitable, Diverse, and Inclusive science collaborations: The Multimessenger Diversity Network
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