Inflorescence and seed production in festuca pratensis var. apennina (2n\t=28)

Summary Plants of tetraploid Festuca pratensis var. apennina (2n=28) collected from Switserland and Northern Italy produced few inflorescences when grown in the field and under glasshouse conditions. The effects of winter and spring treatments upon reproductive growth were investigated and it was concluded that exposure to low winter temperatures and the control of tiller density in the spring were two important factors controlling the production of inflorescences. A procedure for the production of seed is suggested which will allow breeders to obtain efficient multiplication of collected plant material.     

Carbohydrate dynamics in particle-size fractions of sandy spodosols following forest conversion to maize cropping

In southwest France, much of the forested land on sandy spodosols has been converted to continuous maize cropping in the last few decades. To evaluate the impacts of this change on soil organic matter properties, we compared total organic C and neutral and amino sugars content in whole soil and particle size separates of two forested, and five related sites that had been either clear-cut for 12 and 18 mo, or cultivated to maize for 4-22 yr. Soil carbohydrates accounted for 4-7% of the total organic C across all sites. Soil organic C contents of clear-cut and cultivated sites were only 57-79% of the average value measured in forested sites. Accordingly, carbohydrate content of clear-cut and cultivated sites were only 35-66% of the value in forested sites. Ordering the sites in a chronosequence indicated that both total organic C and carbohydrate contents decreased with an increase in time elapsed since clear-cutting and maize cultivation. The only exception was a partial recovery of carbohydrate content in the site that had been under continuous maize for 22 yr. The clay+silt fraction (0-50 μm) was enriched in carbohydrates, mainly of microbial origin, whereas the sand size fractions (50-200 and 200-2000 μm) contained fewer carbohydrates which were mainly of plant origin. Monosaccharide analysis of particle size separates revealed significant differences in carbohydrate composition between sites. Relative to forested sites, the coarse and fine sand fractions in clear-cut and cultivated sites were depleted in carbohydrates and were relatively enriched in plant-derived carbohydrates. Carbohydrate content of the clay+silt fraction drastically decreased upon clear-cutting. Amino sugar content was consistently lower in clear-cut and cultivated sites than in forested sites, indicating that microbial populations were negatively affected by clear-cutting and cultivation. The fungal population appeared more sensitive than bacteria to these land-use changes as indicated by a greater decline in glucosamine than in muramic acid contents.     

Fumarolic activity in marie byrd land, antarctica

Ice towers, probably formed by recent fumarolic activity, have been found around the summit calderas of two volcanoes in Marie Byrd Land. These active (?) volcanoes lie within a broad belt of Mesozoic intrusion and late Cenozoic extrusion that appears to be part of the circum-Pacific orogenic province.     

Evaluation of the intrinsic competitiveness and saprophytic competence of Rhizobium tropici IIB strains

Inoculation of beans (Phaseolus vulgaris L.) with strains of R. tropici IIB and R. etli resulted in the disappearance of the R. tropici IIB stains from the nodule population and their replacement by other (non R. tropici IIB) bean symbionts (Vlassak et al. 1996). Coinoculation studies in monoxenic conditions and in soil core microcosms with plants harvested at two different growth stages indicated that the inoculated R. tropici IIB strains CIAT899 and F98.5 possess a good intrinsic competitiveness which declines, however, at a later plant growth stage and in soil conditions. The poor saprophytic competence of R. tropici IIB strain CIAT899 was further demonstrated by its poor survival in soil core microcosms after bean harvest. Strains were isolated from the field plots with a 3-year bean-planting history, characterized and evaluated for their competitiveness against R. tropici IIB strain CIAT899. Isolates from field plots, which had been repeatedly inoculated with R. tropici IIB strain CIAT899, showed a higher nodule occupancy compared to R. tropici IIB strain CIAT899, and this higher competitiveness exhibited by the field isolates might be an additional reason for the poor performance of R. tropici IIB strain CIAT899 in the field study. Plots with and without a history of bean production revealed after 3-year bean cultivation an almost totally different population that also significantly differed in competitiveness. Received: 12 February 1996