RESUMO
The forest floor is often considered the most important source of dissolved organic carbon (DOC) in forest soils, yet little is known about the relative contribution from different forest floor layers, understorey vegetation and deadwood. Here, we determine the carbon stocks and potential DOC production from forest materials: deadwood, ground vegetation, leaf litter, the fermentation layer and top mineral soil (Ah horizon), and further assess the impact of management. Our research is based on long-term monitoring plots in a temperate deciduous woodland, with one set of plots actively managed by thinning, understorey scrub and deadwood removal, and another set that were not managed in 23 years. We examined long-term data and a spatial survey of forest materials to estimate the relative carbon stocks and concentrations and fluxes of DOC released from these different pools. Long-term soil water monitoring revealed a large difference in median DOC concentrations between the unmanaged (43.8 mg L-1) and managed (18.4 mg L-1) sets of plots at 10 cm depth over six years, with the median DOC concentration over twice as high in the unmanaged plots. In our spatial survey, a significantly larger cumulative flux of DOC was released from the unmanaged than the managed site, with 295.5 and 230.3 g m-2, respectively. Whilst deadwood and leaf litter released the greatest amount of DOC per unit mass, when volume of the material was considered, leaf litter contributed most to DOC flux, with deadwood contributing least. Likewise, there were significant differences in the carbon stocks held by different forest materials that were dependent on site. Vegetation and the fermentation layer held more carbon in the managed site than unmanaged, whilst the opposite occurred in deadwood and the Ah horizon. These findings indicate that management affects the allocation of carbon stored and DOC released between different forest materials.
Assuntos
Carbono , Quercus , Ciclo do Carbono , Florestas , SoloRESUMO
The nonlinear optical technique of second harmonic generation has been used as an in situ probe of surface structure and symmetry at the electrode-electrolyte interface. Rotational anisotropy in the second harmonic (SH) signalprovides valuable information on the degree of structural order at the metal surface. For Ag(111), the observed patterns in the p-and s-polarized SH output agree with current theories and demonstrate that an ordered surface is present. These patterns change as the electrode is electrochemically roughened.
RESUMO
The ontogeny of hepatic metallothioneins (Mt) in fetal tissue as related to dietary and hepatic Zn was investigated. Sixty 6-month-old female rats were divided into two groups and given either double-distilled water or water containing 700 mug of Zn per milliliter. Dams from each group were killed on 16, 19, or 21 days of gestation, and maternal and fetal livers were removed. Mt content of the tissue was estimated by Piotrowski's Hg-saturation method. Results established the presence of an endogenous hepatic Mt in the fetal rat as early as 16 days of gestation. We further demonstrated a marked progressive increase in fetal Mt from Day 16 through gestation accompanied by a decrease in maternal hepatic Mt. It is suggested that Zn increased fetal Mt by inducing fetal synthesis, redistributing fetal Mt, or increasing Mt transport to the fetus, because both fetal and maternal hepatic Mt were increased. Fetal hepatic Mt concentration was several times greater than maternal Mt at corresponding stages of gestation. Mt may serve to either ensure adequate storage of Zn or Cu for fetal development or protect the fetus against metal toxicity, but the significance of these high endogenous levels of fetal Mt are not clear at this time.
