Phytoplasmas infecting sour cherry and lilac represent two distinct lineages having close evolutionary affinities with clover phyllody phytoplasma

Phytoplasmas infecting sour cherry and lilac in Lithuania were found to represent two lineages related to clover phyllody phytoplasma (CPh), a subgroup 16SrI-(R/S)C (formerly 16SrI-C) strain exhibiting rRNA interoperon sequence heterogeneity. 16S rDNAs amplified from the cherry bunchy leaf (ChBL) and lilac little leaf (LcLL) phytoplasmas were identical or nearly identical to those of operon rrnA and operon rrnB, respectively, of CPh. There was no evidence of 16S rRNA interoperon sequence heterogeneity in either LcLL or ChBL phytoplasma. Based on collective RFLP patterns of 16S rDNA, ChBL was classified in subgroup 16SrI-R, and LcLL was classified in new subgroup 16SrI-S. The ribosomal protein (rp) gene sequences from LcLL phytoplasma were identical to those of CPh, and strain LcLL was classified in rp subgroup rpI-C. By contrast, rp gene sequences from ChBL phytoplasma differed from those of subgroup rpI-C; based on RFLP patterns of rp gene sequences, ChBL was classified in new rp subgroup rpI-O. Single nucleotide polymorphisms (SNPs), designated here by a new SNP convention, marked members of rp subgroup rpI-C, and distinguished LcLL and CPh from ChBL and other non-rpI-C phytoplasmas in group 16SrI. The results raise questions concerning phytoplasma biodiversity assessment based on rRNA genes alone and encourage the supplemental use of a single copy gene in phytoplasma identification and classification, while drawing attention to a possible role of horizontal gene transfer in the evolutionary history of these lineages.     

Identification of metallic-smelling 1-octen-3-one and 1-nonen-3-one from solutions of ferrous sulfate

Taste threshold tests of ferrous sulfate (FeSO4) solutions have been confounded by the presence of putative odorants. To detect the presence of odorants released from these solutions solid-phase microextraction (SPME) was used to collect volatiles in the headspace above FeSO4 solutions. Gas chromatography-olfactometry of samples collected over three time periods (1, 5, and 16 h) and at two temperatures (22 and 37 degrees C) revealed the presence of several metallic-smelling odorants in the headspace. Using authentic standards, two of the odorants were conclusively identified as 1-octen-3-one and 1-nonen-3-one. Trace levels of other odorants were also detected, but dilution experiments indicated that 1-nonen-3-one was at least 10 times more potent than anything else released from the solutions. 1-Octen-3-one and 1-nonen-3-one are excellent candidates for the metallic odor responses often observed in threshold testing of solutions of FeSO4.     

Characterisation of endobacterial communities in ectomycorrhizas by DNA- and RNA-based molecular methods

The diversity of endobacteria associated with ectomycorrhizas of Suillus variegatus and Tomentellopsis submollis, in two Corsican pine (Pinus nigra) stands was analysed by cultivation-dependent and cultivation-independent molecular methods. Denaturing gradient gel electrophoresis (DGGE) analysis revealed the cultivable endobacterial communities associated with S. variegatus were similar within the same stand. The most abundant cultivable bacterial species belonged to the genera Pseudomonas and Burkholderia. Cultivation-independent molecular analysis indicated that the structure of the endobacterial communities in ectomycorrhizas was consistent across all samples regardless of ECM fungal species or the pine stand from which the samples were collected. However, comparison between rDNA- and rRNA-derived DGGE gels showed that metabolically active endobacterial species were not always detected in rDNA-based profiles. Clone libraries constructed from rRNA molecules indicated that Pseudomonas and Burkholderia spp. were metabolically active bacteria. As some of the most abundant cultivable bacteria, including Bacillus/Paenibacillus spp., were not detected in cultivation-independent DGGE profiles, a combination of cultivation-dependent and -independent approaches provided a more complete assessment of the diversity of endobacteria associated with ectomycorrhizas.     

Lakeshore diversity and rarity relationships along interacting disturbance gradients: catchment area, wave action and depth

Diversity patterns of riparian plant communities have been associated with disturbance. Populations of a diversity of Atlantic Coastal Plain plants occur as disjuncts on shores of large catchment area lakes in Nova Scotia. These lakeshore communities contain rare plants with local, national and global rankings. The populations of rare plants are dynamic and their management requires an understanding of the relationship between disturbance and the survival of rare plants. This present study measured (overwinter wooden dowel removal) and observed disturbance along gradients of catchment area (CA), exposure and depth. In three separate experiments ranging from the landscape to the lake, to the single shoreline level, disturbance was linked to lake CA, exposure and depth, respectively. At all scales, disturbance was positively associated with the presence of rare species. The pattern of rare species richness over the river system was complex; at the within-lake level, the frequency of rare species per site was greatest in the intermediate CA lake while the pool of rare species was greatest in the largest CA lake. The findings focus field efforts on wide, exposed shorelines of large CA lakes where new rare plants continue to be discovered. In addition, the discrepancy between highest frequency of rare plants on intermediate CA lakes and highest species pools of rarities on large CA lakes, reinforces the need for larger protected area systems for the most naturally disturbed ecosystems which often support populations having a high turnover rate but a low site to site frequency.     

Dry bean production with various tillage and residue management systems

Limited information is available on the influence of high surface residue tillag systems and the interaction of weed control methods, cultivar maturity, and phosphorus fertilizer placement on yield parameters of dry bean (Phaseolus vulgaris L.) A 3-year field study was conducted on a Fargo clay (fine, frigid, montmorillonitic Vertic Haplaquoll) to evaluate the influence of surface or deep band placed phosphorus fertilizer, tillage systems (PLOW, SWEEP, STRIP, NOTILL) and weed control methods on harvest plant populations, seed yield and seed weight of ‘Upland’ (early maturity) and ‘C-20’ (late maturity) dry bean cultivars. Yield variables were influenced by cultivar planted and climatic conditions. Zinc deficient plants and decreased yield were observed with the ‘C-20’ cultivar when grown on PLOW system plots where phosphorus fertilizer was surface applied. Zinc deficient plants were not present when the phosphorus fertilizer was deep banded or none was applied. No zinc deficient plants were observed on NOTILL, STRIP and SWEEP system plots. Both cultivars matured 7 to 10 days earlier with NOTILL, STRIP and SWEEP systems when compared with the PLOW system. Dry bean yields were reduced 180 to 310 kg ha⁻¹ by cultivation for weed control. Little difference in yields occurred among tillage systems when climatic conditions were normal. During a cool wet season, seed yields on PLOW system plots were 150 to 400 kg ha⁻¹ higher than on plots of systems with surface residue. Seed weight, although lower on the late maturity cultivar, was not greatly changed by tillage or weed control method. Results from this study indicate that dry beans can be successfully grown with small grain surface residue systems in northern climatic areas where growing degree days exceed 1200 and growing season precipitation does not exceed 400 mm. Further, deep band placement of phosphorus fertilizer is essential in dry bean rotations to eliminate potential zinc deficiency on soils low in zinc. Switching to a high residue management system may require a special cultivator design to eliminate yield loss due to pruning of shallow roots present with high surface residue.     

Assessment of C budget for grasslands and drylands of the world

Intergovernmental Panel on Climate Change (IPCC) estimates indicate that potential changes in seasonal rainfall and temperature patterns in central North America and the African Sahel will have a greater impact on biological response (such as plant production and biogeochemical cycling) and feedback to climate than changes in the overall amount of annual rainfall. Simulation of grassland and dryland ecosystem responses to climate and CO₂ changes demonstrates the sensitivity of plant productivity and soil C storage to projected changes in precipitation, temperature and atmospheric CO₂. Using three different land cover projections, changes in C levels in the grassland and dryland regions from 1800 to 1990 were estimated to be ?13.2, ?25.5 and ?14.7 Pg, i.e., a net source of C due to land cover removal resulting from cropland conversion. Projections into the future based on a double-CO₂ climate including climate-driven shifts in biome areas by the year 2040 resulted in a net sink of +5.6, +27.4 and +26.8 Pg, respectively, based upon sustainable grassland management. The increase in C storage resulted mainly from an increase in area for the warm grassland sub-biome, together with increased soil organic matter. Preliminary modeling estimates of soil C losses due to 50 yr of regressive land management in these grassland and dryland ecoregions result in a 11 Pg loss relative to current conditions, and a potential loss of 37 Pg during a 50 yr period relative to sustainable land-use practices, an average source of 0.7 Pg C yr^?1. Estimates of the cost of a 20 yr rehabilitation program are 5 to 8×10⁹ US$ yr^?1, for a C sequestering cost of approximately 10 US$ per tC.     

Do plant species encourage soil biota that specialise in the rapid decomposition of their litter?

Plants are often nutrient limited and soil organisms are important in mediating nutrient availability to plants. Thus, there may be a selective advantage to plants that alter the soil community in ways that enhance the decomposition of their litter and, hence, their ability to access nutrients. We incubated litter from three tree species (Fagus sylvatica, Acer pseudoplatanus and Picea sitchensis) in the presence of biota extracted from soil beneath a stand of each species to test the hypothesis that litter decomposes fastest in the presence of biota derived from soil where that species is locally abundant. We found that respiration rate, a measure of decomposer activity and carbon mineralisation, was affected by litter type and source of soil biota, whereas, mass loss was only affected by litter type. However, litter from each tree species did not decompose faster in the presence of indigenous soil biota. These findings, therefore, provide no support for the notion that woodland plants encourage the development of soil communities that rapidly decompose their litter.     

Restoring the capacity of spent mushroom compost to treat coal mine drainage by reducing the inflow rate: A microcosm experiment

Four volumes of spent mushroom compost were exposed to synthetic coal mine drainage (pH 3.5, 48 mg L^?1 Fe, 22 mg L^?1 Mn) under oxidizing conditions (Eh 300 to 400 mV) at a relatively high rate of flow. After 15 days, the compost lost its ability to elevate pH, to lower the redox potential, to lower outlet iron concentrations, and to lower manganese concentrations, with larger volumes retaining more Fe and H⁺, but less Mn. Estimated retention maxima per liter of spent mushroom compost were 281 μeq H⁺, 5.56 g Fe, and 0.15 g Mn. These values are similar to those reported elsewhere for peat. The ‘saturated’ compost was then mixed and exposed to mine water in order to eliminate ‘dead zones’ in the compost. Subsequently, the compost was re-exposed to synthetic mine water (pH 4.0, 60 mg L^?1 Fe, O mg L^?1 Mn) under a much lower flow rate and less oxidizing regime for a period of 114 days. Under the low flow regime, iron was first exported from the compost as reducing conditions were established, and then retained on a stable basis. In addition, Eh was lowered and pH was elevated by the compost. On a net basis, the capacity of the compost to retain iron was increased and apparently stable under the decreased flow conditions.