Consequences Of Cultivation Research Articles

Impact of marine influence and cultivation on the diatom flora of Thiaroye Pond, Dakar, Senegal

During a limnological and palaeolimnological study of the western part of the Great Coast of Senegal, an analysis of diatoms was carried out in Thiaroye Pond in the suburbs of Dakar. Current diatom flora in the water and on floating plants, and subfossil flora in two cores were sampled in 1996 and 2003. A total of 104 species and varieties, belonging to 38 genera were identified, 61 in the current environment and 87 from the cores. The genera most represented were Nitzschia (16 species), Eunotia (9 species), Amphora and Pinnularia (7 species each). The most frequently and regularly observed freshwater species were Cyclotella meneghiniana, Diadesmis confervacea, Eunotia pectinalis and Nitzschia amphibia, with marine to brackish-water forms occasionally being present. The proximity of the pond to the Atlantic Ocean had a dual effect on the diatom assemblage. Marine to brackish-water diatoms were transferred by wind and birds, and salinity increased over time, due to the rising level of saline groundwater. The alkalinity of the pond increased over time, due to the progressive destruction of the natural vegetation of the pond as a consequence of cultivation.

Artificial regeneration with Quercus ilex L. and Quercus suber L. by direct seeding and planting in southern Spain

The limited ability of Quercus species to regenerate naturally in Mediterranean forests has led to the development of various artificial regeneration methods; however, there is no general consensus as to what specific method is the best one for this purpose. In this work, we assessed morphology, growth and survival of two Quercus species (Quercus ilex ssp. ballota and Quercus suber) using two different methods of artificial regeneration (viz. direct seeding and planting) and two seedling ages (1-year-old seedlings and 3-year-old seedlings) in southern Spain. The 1-year-old seedlings of both species were found to exhibit the highest survival percentages and direct-seeded plants intermediate survival values. For direct-seeded plants, seed mass was found to have a significantly positive effect on the establishment success in both species. No clear-cut trend in survival was detected in the 3-year-old seedlings. The survival of the 3-year-old Q. suber seedlings and the direct-seeded plants was similar, but not in Q. ilex, where the survival of the 3-year-old seedlings was the lowest. The latter result may have been a consequence of cultivation in smaller containers leading to root deformation and limiting plant access to water. Differences in survival could not be ascribed to morphological and growth variables or stomatal conductance. Based on the results, all three artificial regeneration methods can be similarly effective provided appropriate nursery cultivation conditions are used and seeds are protected against predators, the best choice in each case being dictated by the particular restoration goals.

Long-term effects of farmyard manure and sewage sludge on some soil biochemical characteristics

Changes in some soil biochemical properties were investigated following repeated applications of aerobically digested sewage sludge (SS) under field conditions over 12 years, and compared with those of an adjacent soil cultivated and amended with 5 t ha–1 year–1 (dry weight) farmyard manure (FYM) for at least 40 years, as well as with those of an adjacent uncultivated soil, in order to ascertain changes in soil quality. A short-term aerobic incubation was used to determine the potential of the samples to mineralize the organic C supplied. Results indicated that cultivation caused a reduction in total, humified and potentially mineralizable organic C, total N, light-fraction (LF) C, total and water-soluble carbohydrates, phenolic compounds, cation-exchange capacity (CEC), microbial biomass C, specific respiration, hydrolytic and urease activities, and an increase in the heavy metal content. Total and water-soluble carbohydrates and phenolic compounds expressed as a percentage of total organic C (TOC) were similar in the differently managed plots. Of the two amendments, FYM treatments showed higher amounts of TOC and N, LF-C, total and water-soluble carbohydrates, phenolic substances, CEC, specific respiration of biomass, hydrolytic and urease activities, similar amounts and characteristics of humified organic matter and lower concentrations of Cu, Zn and Cr. Both FYM and SS were inadequate treatments for the restoration of soil organic matter lost as a consequence of cultivation.

Soil, Landscape, and Erosion Relationships in a Northwest Illinois Watershed

AbstractThe purpose of this study was to establish the relationship between soil taxonomic description, landscape form and position, and erosion in northwest Illinois. The study area consists of a first‐order drainage basin about 10 ha in size. The hillslopes have mean gradients of 6 to 10% with overland flow the primary contributor to erosion. A detailed geomorphic map of the watershed was constructed on a 1‐m topographic survey base map. Map units were delineated based on slope shape, gradient, and USDA erosion class. Erosion classes were determined for the transect pedons by comparison with two uneroded and uncultivated pedons in area cemeteries with similar slope gradient, slope shape, slope length, and landscape positions. The A horizon thickness and organic C content decreased and clay content increased as a consequence of cultivation and erosion. Transect data for all hillslope geomorphic units showed the erosion classes near the shoulder to be either slightly or moderately eroded. The lower backslopes and upper footslopes, just above the sediment basin, were either severely or very severely eroded, suggesting slope length to be the dominant factor affecting erosion. The geomorphic units with concave across‐slope shapes were found to be less eroded than those with convex across‐slope shapes. All cultivated pedons failed to meet the criteria for Mollisols, which was the taxonomic placement of the uncultivated pedons. Erosion phase, landscape segment, slope shape, slope gradient, and slope length affected the taxonomic placement of the cultivated hill‐slope soils when compared with uncultivated sites.

Genetic regulation of class I major histocompatibility complex (MHC) antigen induction on astrocytes.

Neural cells, indluding astrocytes, normally do not express detectable levels of class I major histocompatibility complex (MHC) molecules, unlike cells of most tissues. However, upon cultivation in vitro, astrocytes begin to express class I molecules, increasing with time after plating. This spontaneous expression was examined in the present study to characterize inducible expression on astrocytes among various strains of mice. Inducible expression, either as a consequence of cultivation or standard γ-interferon treatment, differed markedly among the strains examined. Analysis of congenic strains on a C57BL/10 (B10) background showed that expression was controlled by genes within the MHC locus. Examination of additional congeneic animals with various recombinations within the MHC showed that high or low expression of MHC molecules correlates with the presence of particular MHC class I genes. In general, H-2a and H-2d class I products are expressed much higher on astrocytes than H-2b and H-2s products. This difference in expression is not seen on spleen cells indicating tissue specificity. Moreover, levels of expression at the cell surface are reflected by the steady-state level of RNA message within astrocytes of the different strains.

Distribution of potassium forms in virgin and cultivated soils of the U.S.A.

The potassium status of virgin soil profiles and their cultivated analogues is compared. Eight agriculturally important soil series, representative of various U.S. Land Resource Areas, cultivated for 16–72 years, were studied to ascertain if relative pool sizes or soil K fertility are being changed by cultivation and associated fertilizer K application. Little change in total or non-NH 4-exchangeable K contents was observed with cultivation. Increases NH 4-exchangeable (20% increase) and HNO 3-extractable K contents (13% increase) of surface soils (0–15 cm) compared to virgin analogues (166 and 692 mg kg −1, respectively), however, were observed when averaged across the six cultivated soils receiving fertilizer K. In contrast, both NH 4-exchangeable and HNO 3-extractable K contents of the two unfertilized cultivated soils, decreased 5 and 3%, respectively. Prior heating at 450° C increased NH 4-exchangeable K an average 315 in the surface 15 cm of cultivated compared to virgin soils. Changes in the contents of K forms in surface soils were greater than in deeper horizons, with little change observed below 45 cm as a consequence of cultivation. Relative to N and P, cultivation had less effect on soil K status, due to large native soil K reserves. In fact, the average NH 4-exchangeable K contents of all the cultivated surface soils (208 mg kg −1) were greater than the average calculated minimum NH 4-exchangeable K values (80 mg kg −1). Even after extended periods of cropping, native soil K reserves were large enough to supply most plant needs. On the basis of minimum exchangeable K values, further cropping of these soils should not result in any immediate plant K stress.