分布式模型在流域蒸散模拟中的应用与验证

根据四川杂谷脑河流域上游地区1989～2000年气象站常规观测数据,应用分布式模型方法,考虑流域的空间异质性及时空变异性,选择离散单元格尺度为500 m,时间步长为1 d,采用Penman-Monteith公式的改进形式,估算流域多年平均潜在蒸散量的时空分布;结合流域下垫面特点,估算逐日实际蒸散量的时空分布;并将模型模拟的多年平均值与研究区同期水量平衡法计算结果相比,相对误差为+3.47%且时空分布合理.为流域分布式降雨-径流模型提供了可靠的实际蒸散量模拟方法.     

羊草群落的水分利用

羊草(Leymus chinensis (Trin.)Tzvel.)群落的土壤水分具有明显的成层性:0～40 cm是根系集中分布层,受降水和蒸散的直接影响,称为蒸散与降水相互作用层;40～120 cm贮水变化滞后于根系层贮水和群落蒸散的季节变化,称为主要贮水层;120 cm以下称为水分相对稳定/平衡层.1996年属平水年,生长季末土壤水盈余18 mm;1998年属丰水年,在连续强降雨时发生渗漏,生长季末土壤水亏缺15 mm.蒸腾-蒸散比(T/ET)不仅反映群落的繁茂和活力,而且反映植物对环境水资源的利用状况.1998年8月T/E7值较小(0.5),6月达0.7,7月受降水少影响而有所降低(0.6),8月水分利用效率达到最大(0.9),9月降到0.6.水分利用效率(WUE)在良好的水分条件下(1998年),主要受植物自身生长速度的限制,其季节变化与生长大周期吻合.深入分析WUE和T/E的内涵,提出蒸散效率(ETE)的概念,能更好地反映植物对环境水资源利用的状况或程度,具有实际意义.     

拉格朗日逆分析在森林蒸散模拟中的应用

以长白山阔叶红松林为研究对象,根据Raupach提出的LocalizedNearField(LNF)理论为依据,耦合垂直速度标准差σ_w(z)和拉格朗日时间尺度T_L(z),建立林冠内水汽源汇强度和平均浓度廓线之间的关系;利用拉格朗日逆分析法(inverseLagrangiandispersionanalysis,IL)提出了通过林冠水汽浓度梯度计算林冠内的水汽源汇强度进而推算森林蒸散的方法.最终得到的结果与开路涡动相关系统的观测数据比较显示,对于白天水汽累积通量的模拟精度达到87.3%;IL模拟值高于EC实测值,大约高出15%～25%;林冠白天水汽通量远大于夜间,占日水汽总通量的70%以上.6～8月的水汽白天累积总通量高于5月和9月.     

信阳市干旱成因及其防御对策

信阳市发生的干旱主要有伏旱、秋旱和冬旱3种类型,且夏季发生干旱的频率远高于其它季节。干旱的成因除季风环流、地形地貌、地下水资源因素外,还有水利排灌设施不健全、农业生产结构与作物布局不合理、工业生产规模扩张等社会经济因素。本文在利用Pa法分级统计旱灾发生频次、总结旱灾发生规律的基础上,提出了有针对性的防御对策。     

Response of wheat seedlings to short-term drought stress with particular respect to nitrate utilization

Abstract. The effect of short-term changes in the water potential (from 0 to – 2.5 MPa) by addition of PEG 4000 to the nutrient solution was investigated with respect to nitrate uptake and reduction in 3-week-old wheat plants ( Triticum aestivum , cv Fidel). Plants were harvested at the end of 12-h treatments in the dark. The water potential of the mature leaves was similar to that of the medium down to – 0.8 MPa and was maintained at this level even though the external water potential was much lower. The medium water potential of 0.8 was a threshold level below which elongation of the youngest leaf was inhibited. Increase of the PEG concentration in the medium brought about a decrease of evapotranspiration and enhancement of nitrate uptake. No difference in the rate of nitrate reduction was observed, although the in vitro nitrate reductase activity was lowered. Nitrate accumulation in the shoot was ascribed both to the stimulation of net uptake from the medium, and to the mobilization and translocation of nitrate from the root. It is suggested that increase in the storage pool of nitrate in shoots was related to the role of NO₃⁻ as an osmoticum.     

A modification for increasing the sensitivity of the casein-agar plate assay: a simple semiquantitative assay for thermophilic and mesophilic proteases

A casein-agar plate assay was used for the quantitative determination of both mesophilic and thermophilic proteases. Because many proteases are thermostable, assay at higher temperatures is possible. The sensitivity of the plate assay increased with temperature, the optimum assay temperature depending on the thermostability of the enzyme (e.g. Thermus protease, 75 degrees C; thermolysin, 65 degrees C; trypsin, 65 degrees C; alpha-chymotrypsin, 45 degrees C). A positive correlation was observed between incubation temperature and the density of the para-casein precipitate, increasing the accuracy of diameter measurement. Using this modified method, thermostable proteases could be assayed at levels well below the limits of detection of other methods (e.g. 40 pg of thermolysin and 300 pg of trypsin detectable at 65 degrees C, a 16-fold increase in the sensitivity for trypsin compared with a conventional plate assay (Fossum, K. (1970) Acta Pathol. Microbiol. Scand. Sect. B 78, 350-361)). The sensitivity of the plate assay could be further increased by the inclusion of some detergents and chaotropic agents in the gel.     

Plant species richness–environment relationships across the Subantarctic–Patagonian transition zone

Aim To evaluate the relative importance of climate, productivity, environmental heterogeneity, biotic associations and habitat use by cattle to account for the species richness of trees, shrubs and herbs across the Subantarctic–Patagonian transition. Location An area of c. 150 × 150 km, within the transition zone between the Subantarctic and Patagonian subregions on the eastern slope of the Andes (c. 39–42° S, 70–72° W). Methods All vascular plants found at each one of 50 (10 × 10 m) sampling plots were counted to estimate the local tree, shrub and herb species richness. Path analysis was used to evaluate the relationship between the richness of the three life‐forms and plant cover, dried litter biomass, mean annual temperature, annual precipitation, daily temperature range, substrate heterogeneity and number of faecal pats. Principal coordinates of neighbour matrices was used to model the spatial autocorrelation of the data. Results Total plant species richness showed a unimodal pattern of spatial variation across the transition. Richness responded positively to indirect effects of precipitation mediated through plant cover, but there was a negative overall effect of precipitation on richness towards the west of the transition, most strongly for trees. An increase in substrate heterogeneity promoted a local increase in herb and shrub richness; the richness of trees increased in sites with steeper slopes. Canopy closure had a direct negative impact on herb richness; it also increased the local accumulation of litter, which negatively affected shrub and herb richness. The impact of habitat use by cattle negatively affected herb richness in areas to the east of the biogeographical transition. Main conclusions We suggest that the importance of indirect climatic effects mediated by vegetation cover can account for species richness patterns across this transition, most strongly for woody species, which supports the productivity hypothesis. The southern temperate forests towards the west may represent a deviation from the predictions of the water–energy dynamics hypothesis. Dissimilar spatial patterns of variation in the richness of woody and herbaceous species, and their different responses to climatic and heterogeneity variables across the transition, suggest that plant life‐form influences the plant species richness–environment relationships.     

Evaluation of mutagenic and genotoxic activities of lobeline and its modulation on genomic instability induced by ethanol

Aim

Lobeline is a natural alkaloid derived from Lobelia inflata that has been investigated as a clinical candidate for the treatment of alcoholism. In a pre-clinical trial, lobeline decreased the preference for and consumption of ethanol, due to the modulation of the nicotinic acetylcholine receptor. However, the interaction between lobeline and ethanol is poorly known and thus there are safety concerns.The present study was conducted to evaluate the mutagenic and genotoxic effects of lobeline and assess its modulation of ethanol-induced toxicological effects.

Main methods

CF-1 male mice were divided into five groups. Groups received an intraperitoneal injection of saline solution, lobeline (5 or 10 mg/kg), ethanol (2.5 g/kg), or lobeline plus ethanol, once a day for three consecutive days. Genotoxicity was evaluated in peripheral blood using the alkaline comet assay. The mutagenicity was evaluated using both Salmonella/microsome assay in TA1535, TA97a, TA98, TA100, and TA102 Salmonella typhimurium strains and the micronucleus test in bone marrow. Possible liver and kidney injuries were evaluated using biochemical analysis.

Key findings

Lobeline did not show genotoxic or mutagenic effects and did not increase the ethanol-induced genotoxic effects in blood. Lobeline also protected blood cells against oxidative damage induced by hydrogen peroxide. Biochemical parameters were not altered, indicating no liver or kidney injuries or alterations in lipid and carbohydrate metabolisms.

Significance

These findings suggest that lobeline does not induce gene or chromosomal mutations, and that this lack of genetic toxicity is maintained in the presence of ethanol, providing further evidence of the safety of this drug to treat alcohol dependence.     

Global deletion of lipocalin 2 does not reverse high-fat diet-induced obesity resistance in stearoyl-CoA desaturase-1 skin-specific knockout mice

Over the past century, obesity has developed into a paramount health issue that affects millions of people worldwide. Obese individuals have an increased risk to develop other metabolic disorders, such as insulin resistance and atherosclerosis, among others. Previously we determined that mice lacking stearoyl-CoA desaturase-1 (SCD1) enzyme specifically in the skin (SKO) were lean and protected from high-fat diet induced adiposity. Additionally, lipocalin 2 (Lcn2) mRNA was found to be 27-fold higher in the skin of SKO mice compared to control mice. Given reports suggesting that Lcn2 plays a role in protection against diet-induced weight gain, adiposity and insulin resistance, we hypothesized that deletion of Lcn2 alongside the skin-specific SCD1 deficiency would diminish the obesity resistance observed in SKO mice. To test this, we developed mice lacking SCD1 expression in the skin and also lacking Lcn2 expression globally and surprisingly, these mice did not gain significantly more weight than the SKO mice under high-fat diet conditions. Therefore, we conclude that Lcn2 does not mediate the protection against high-fat diet-induced adiposity observed in SKO mice.     

Impacts of Vegetation and Precipitation on Throughfall Heterogeneity in a Tropical Pre‐Montane Transitional Cloud Forest

Precipitation throughfall (TF) plays an important role in the water balance of tropical forests. This study used 164 gauges to quantify precipitation and TF variability in a tropical pre‐montane transitional cloud forest on the Caribbean slope of the Cordillera Tilarán, Costa Rica, to identify the ecological and meteorological drivers of this variability. Daily TF measurements were taken from 28 June to 17 July 2012 and 12 June to 16 July 2013, for a total of 39 precipitation events. The total mean TF was 87.9 percent and TF at individual gauges ranged from 22.7 percent to 245.7 percent. Leaf area index (LAI) was calculated above each gauge using hemispheric photography for a mean study‐site LAI of 7.7. There was no statistically significant relationship between LAI and TF. However, the amount of TF was positively correlated with precipitation intensity, while the variability of TF was negatively correlated with precipitation intensity. Our calculations indicate that at least 61 gauges are required to obtain mean TF estimates with less than 5 percent error. This study demonstrates that TF is highly spatially heterogeneous due to multiple compounding effects.