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

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