Measurements of water oxygen isotopic composition were conducted in the 2003 growing season for a montane larch (Larix sibirica Ledeb.) forest in northern Mongolia, a transitional area from the south Siberian taiga to the Asian steppe. Oxygen isotopic
composition of foliar water and its daily variability were found to be sensitive to atmospheric evaporative demand. During
most of the growing season, water sources used by larch trees were from the upper 30-cm surface layer of the soil when precipitation
input was large, and were from the deeper layer when the water supply at the upper soil layer was limited. The Keeling plot
method suggested that the forest returned soil water to the atmosphere predominantly by means of canopy transpiration during
the peak growth period (in August). 相似文献
The purpose of this study was to develop a buccal paclitaxel delivery system using the thermosensitive polymer Pluronic F127 (PF127) and the mucoadhesive polymer polyethylene oxide (PEO). The anticancer agent paclitaxel is usually used to treat ovarian, breast, and non-small-cell lung cancer. To improve its aqueous solubility, paclitaxel was incorporated into an inclusion complex with (2,6-di-O-methyl)-β-cyclodextrin (DMβCD). The formation of the paclitaxel inclusion complex was evaluated using various techniques, including x-ray diffractometry (XRD), Fourier-transform infrared (FT-IR) spectrophotometry, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Hydrogels were prepared using a cold method. Concentrations of 18, 20, and 23% (w/v) PF127 were dissolved in distilled water including paclitaxel and stored overnight in a refrigerator at 4°C. PEO was added at concentrations of 0.1, 0.2, 0.4, 0.8, and 1% (w/v). Each formulation included paclitaxel (0.5 mg/mL). The sol-gel transition temperature of the hydrogels was measured using the tube-inverting method. Drug release from the hydrogels was measured using a Franz diffusion cell containing pH 7.4 phosphate-buffered solution (PBS) buffer at 37°C. The cytotoxicity of each formulation was measured using the MTT assay with a human oral cancer cell (KB cell). The sol-gel transition temperature of the hydrogel decreased when PF127 was present and varied according to the presence of mucoadhesive polymers. The in vitro release was sustained and the release rate was slowed by the addition of the mucoadhesive polymer. The cytotoxicity of the blank formulation was low, although the drug-loaded hydrogel showed acceptable cytotoxicity. The results of our study suggest that the combination of a PF 127-based mucoadhesive hydrogel formulation and inclusion complexes improves the in vitro release and cytotoxic effect of paclitaxel. 相似文献
This paper reports the temporal variation (2002–2004) in foliar δ13C values, which are indicative of long-term integrated photosynthetic and water use characteristics, of Siberian larch (Larix sibirica Ledeb.) trees in a montane forest at Mongonmorit, NE Mongolia. At the stand, the δ13C value for understory shaded leaves was more negative by 2‰ on average than that for sunlit leaves sampled concurrently from
open and sun-exposed environments in a forest gap. The δ13C value of both sunlit and shaded leaves showed pronounced intra- but relatively small inter-seasonal variations. The δ13C value was more positive for juvenile than mature leaves. We conjecture that juvenile leaves may derive carbon reserves in
woody tissues (e.g., stems). Regardless of leaf habitats, the δ13C value was also affected by insect herbivores occurred in mid summer of 2003, being more negative in newly emerging leaves
from the twigs after defoliation than in non-defoliated mature leaves. This pattern seems to contrast with that for the juvenile
leaves in the early growing season. We surmise that the newly emerging leaves used stored organic carbon that was depleted
due to fractionation during remobilization and translocation for leaf regrowth. There was also intra- and inter-seasonal variation
in the foliar N concentrations and C:N ratios. A good positive (negative) correlation between the foliar δ13C values and N concentrations (C:N ratios) was also observed for both sunlit and shaded leaves, suggesting that the relationship
between water and nitrogen use is a crucial factor affecting the plant carbon–water relationship in this mid latitude forest
with a cold semiarid climate. Our isotopic data demonstrate that the larches in NE Mongolia exhibits relatively higher water
use efficiency with a distinct within-season variability. 相似文献
Human-induced ecological and climatic changes have led to the decline and even local extinction of many formerly widely distributed temperate and cold-adapted species. Determining the exact causes of this decline remains difficult. Bryodemella tuberculata was a widely distributed orthopteran species before the mid-19th century. Since then, many European populations have suffered drastic declines and are now considered extinct or critically endangered. We used ecological niche modelling based on a large dataset of extant and extinct occurrence data to investigate whether poor climatic suitability in the periphery of its global range was a possible cause of the local extinction of the European populations of B. tuberculata. We also used population genetics based on the COI marker to estimate and compare the genetic diversity of extant populations. We found that Europe still provides highly suitable habitats close to the climatic optimum, contradicting the assumption of climate change as major driver of this decline. Instead, changes in land-cover and other anthropogenic modifications of the habitats at the local scale seem to be the major reasons for local extinctions. Genetic analysis suggests Central Asia as center of diversity with a stable population size, whereas the effective sizes of the remaining European populations are decreasing. We found European genetic lineages nested within Central Asian lineages, suggesting a Central Asian source distribution area. Our results suggest that the declining European populations represent relics of a formerly wider distribution, which was fragmented by changes in land-use. These relics are now threatened by limited connectivity and small effective population sizes. Specific conservation actions, such as the restoration of former or potential new habitats, and translocation of individuals from extant populations to these restored sites may help slow, stall, or even revert the extinction process.
The regression tree method is used to upscale evapotranspiration (ET) measurements at eddy-covariance (EC) towers to the grassland ecosystems over the Dryland East Asia (DEA). The regression tree model was driven by satellite and meteorology datasets, and explained 82% and 76% of the variations of ET observations in the calibration and validation datasets, respectively. The annual ET estimates ranged from 222.6 to 269.1 mm yr−1 over the DEA region with an average of 245.8 mm yr−1 from 1982 through 2009. Ecosystem ET showed decreased trends over 61% of the DEA region during this period, especially in most regions of Mongolia and eastern Inner Mongolia due to decreased precipitation. The increased ET occurred primarily in the western and southern DEA region. Over the entire study area, water balance (the difference between precipitation and ecosystem ET) decreased substantially during the summer and growing season. Precipitation reduction was an important cause for the severe water deficits. The drying trend occurring in the grassland ecosystems of the DEA region can exert profound impacts on a variety of terrestrial ecosystem processes and functions. 相似文献
Steppe desertification due to vehicle travel is a severe environmental issue in Mongolia. We studied natural vegetation recovery
on abandoned vehicle tracks in the central Mongolia steppe through vegetation surveys and stable isotopic techniques. The
following issues were addressed: (i) invasion of pioneering plant species, (ii) alteration of soil surface features, and (iii)
contribution of revegetated plants to soil organic matter (SOM). The pioneering plant species that firstly invaded the abandoned
tracks are those that could germinate, root and survive in the compacted track surface.Salsola collina is one of these candidate plants. Due to revegetation, soil surface hardness was reduced. With the improvement of surface
microenvironmental conditions, other plants began to colonize and establish; concomitantly species richness and species diversity
increased. Carbon isotope ratios of SOM at the top surface layer indicated that C4-derived carbon contributed more to SOM in the early phase of recovery and decreased with further recovery 相似文献