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991.
Root tensile strength and root distribution of typical Mediterranean plant species and their contribution to soil shear strength 总被引:13,自引:0,他引:13
S. De Baets J. Poesen B. Reubens K. Wemans J. De Baerdemaeker B. Muys 《Plant and Soil》2008,305(1-2):207-226
In Mediterranean environments, gully erosion is responsible for large soil losses. It has since long been recognized that
slopes under vegetation are much more resistant to soil erosion processes compared to bare soils and improve slope stability.
Planting or preserving vegetation in areas vulnerable to erosion is therefore considered to be a very effective soil erosion
control measure. Re-vegetation strategies for erosion control rely in most cases on the effects of the above-ground biomass
in reducing water erosion rates, whereas the role of the below-ground biomass is often neglected or underestimated. While
the above-ground biomass can temporally disappear in semi-arid environments, roots may still be present underground and play
an important role in protecting the topsoil from being eroded. In order to evaluate the potential of plant species growing
in Mediterranean environments to prevent shallow mass movements on gully or terrace walls, the root reinforcement effect of
25 typical Mediterranean matorral species (i.e. shrubs, grasses herbs, small trees) was assessed, using the simple perpendicular
model of Wu et al. (Can Geotech J 16:19–33, 1979). As little information is available on Mediterranean plant root characteristics,
root distribution data were collected in SE-Spain and root tensile strength tests were conducted in the laboratory. The power
root tensile strength–root diameter relationships depend on plant species. The results show that the shrubs Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. have the strongest roots, followed by the grass Brachypodium retusum (Pers.) Beauv. The shrubs Nerium oleander L. and the grass Avenula bromoides (Gouan) H. Scholz have the weakest roots in tension. Root area ratio for the 0–0.1 m topsoil ranges from 0.08% for the grass
Piptatherum miliaceum (L.) Coss to 0.8% for the tree Tamarix canariensis Willd. The rush Juncus acutus L. provides the maximum soil reinforcement to the topsoil by its roots (i.e. 304 kPa). Grasses also increase soil shear strength
significantly (up to 244 kPa in the 0–0.1 m topsoil for Brachypodium retusum (Pers.) Beauv.). The shrubs Retama sphaerocarpa (L.) Boiss. and Anthyllis cytisoides L. are increasing soil shear strength to a large extent as well (up to 134 and 160 kPa respectively in the 0–0.10 m topsoil).
Whereas grasses and the rush Juncus acutus L. increase soil shear strength in the topsoil (0–0.10 m) to a large extent, the shrubs Anthyllis cytisoides (L.), Retama sphaerocarpa (L.) Boiss., Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. strongly reinforce the soil to a greater depth (0–0.5 m). As other studies reported that Wu’s model overestimates root
cohesion values, reported root cohesion values in this study are maximum values. Nevertheless, the calculated cohesion values
are used to rank species according to their potential to reinforce the soil. 相似文献
992.
分子进化生物学中序列分析方法的新进展 总被引:6,自引:0,他引:6
简要介绍了分子进化生物学中序列分析方法的最新进展,特别强调了似然比检验和贝叶斯推论在分子进化和系统发育假说检验中的重要性,并介绍了新方法的一些成功应用,同时还给出了一些重要的信息资源。 相似文献
993.
994.
恒定磁场对苦荞种子的生物学效应 总被引:1,自引:0,他引:1
本试验用不同剂量的恒定磁场处理苦荞种子,结果表明:适宜的磁场可有效地提高苦荞种子萌发期的发芽势、发芽率,降低种子浸出液的电导率。 相似文献
995.
The purpose of this study was to determine the prevalence rate ratio of squamous lesions in women with recent smears without endocervical component (ECC-) versus women having a smear with ECC+ and to estimate the true prevalence of these lesions in women with ECC- smears by addition of short-term follow-up results of negative ECC- smears. Results of initial smears in a 3-year period, as well as follow-up results of negative ECC- smears in the same period were retrieved. Women were categorized into two groups: having ECC- and ECC+ smears. The data were analysed for three outcome parameters, ASCUS or higher (ASCUS+), LSIL or higher (LSIL+) and HSIL or higher (HSIL+). Squamous abnormalities occurred far less frequently in women with initial ECC- than with ECC+ smears. Prevalence rate ratio (PRR) was 0.27 for ASCUS+, 0.39 for LSIL+ and 0.36 for HSIL+. Addition of follow-up results of negative ECC- smears, as a correction for false-negative ECC- smears, results in PRRs which are still significantly lower than 1, and most marked in subset HSIL+ (PRR = 0.60). We conclude that the true prevalence of squamous lesions in women with recent ECC- smears is significantly lower as compared with ECC+ smears. These findings lent support to the decision to abolish the repeat of ECC- smears in the Dutch population screening programme. 相似文献
996.
Harald Staiger Otto Tschritter Jürgen Machann Claus Thamer Andreas Fritsche Elke Maerker Fritz Schick Hans‐Ulrich Hring Michael Stumvoll 《Obesity (Silver Spring, Md.)》2003,11(3):368-376
Objective: We investigated whether serum concentrations of adiponectin are determined by body fat distribution and compared the findings with leptin. Research Methods and Procedures: Serum concentrations of adiponectin and leptin were measured by radioimmunoassay (n = 394) and analyzed for correlation with sex, age, and body fat distribution, i.e., waist‐to‐hip ratio, waist and hip circumference, and subcutaneous adipose tissue area of the lower leg as assessed by magnetic resonance imaging. Results: After adjusting for sex and percentage of body fat, adiponectin was negatively (r = ?0.17, p < 0.001) and leptin was positively (r = 0.22, p < 0.001) correlated with waist‐to‐hip ratio. Leptin, but not adiponectin, correlated with both waist (r = 0.49, p < 0.001) and hip circumference (r = 0.46, p < 0.001). Furthermore, leptin, but not adiponectin, correlated with the proportion of subcutaneous fat of the lower leg cross‐sectional area (r = 0.37, p < 0.001). Discussion: These data suggest that both adipocytokines are associated with central body fat distribution, and serum adiponectin concentrations are determined predominantly by the visceral fat compartment. 相似文献
997.
HyoMin Lee EunKyung Yoon MyungSil Hwang GunYoung Lee MooKi Hong JiSun Yang 《人类与生态风险评估》2003,9(7):1801-1812
The purpose of this study was to estimate the daily exposure to lead due to food ingestion, air inhalation, and soil ingestion in the Republic of Korea's general population, and to evaluate the level of risk associated with the current lead exposure level using the proportional daily dose (3–4 μg/kg body weight/day) corresponding to the Provisional Tolerable Weekly Intake (PTWI) suggested by the Joint FAO/WHO Expert Committee on Food Additives as the toxicological tolerance level. The estimation of the daily exposure to lead via three pathways including food, soil ingestion and air inhalation was conducted as a chronic exposure assessment. For the lead exposure assessment through dietary intake, 1,389 lead residue data for 45 commodities investigated by the Korea Food and Drug Administration during the period 1995–2000 were utilized (KFDA 1996, 1997, 1998). Six hundred seventy-two air monitoring data from 7 major cities during the period 1993–2000 and 4,500 soil residue data at 1,500 sites during the period 1999–2001 were considered for the lead exposure assessment involving air inhalation and soil ingestion, respectively. The total daily exposure to lead was estimated by combining dietary intake, inhaled amount and soil intake corresponding to the typical activity of the general population, which was treated as a group of adults with a body weight of 60 kg. For risk characterization, the daily exposure to lead was compared with the toxicological tolerance level. The level of risk due to lead exposure was calculated using the hazard ratio (HR). The dietary intake of lead was 9.71 × 10?4 mg/kg/day and the total daily exposure level, including air inhalation and soil ingestion, was 9.97 × 10?4 mg/kg/day. The exposure contributions of foods, air and soil induced from the percentage of each media to the total daily exposure were 97.4%, 2.1% and 0.5%, respectively. Of the different commodity groups, the highest contribution to the total exposure came from grain, which represented 47.7% of the total. Additional exposure to lead occurs in certain population groups due to the use of tobacco, alcoholic beverages, and the intake of other foods, all factors not considered in this study. Through the comparison of the daily exposure to lead with the tolerance level based on the PTWI, the hazard ratio was estimated as being 0.25–0.33. This value implies that no increase in blood lead level is to be expected in the general population at the current lead exposure levels. 相似文献
998.
Mingjun Liao Feihai Yu Minghua Song Shumin Zhang Jinzheng Zhang Ming Dong 《Acta Oecologica》2003,24(5-6):231-239
Clonal fragments of the stoloniferous herb Glechoma longituba were subjected to a complementary patchiness of light and soil nutrients including two spatially homogeneous treatments (SR–SR and IP–IP) and two spatially heterogeneous treatments (IP–SR and SR–IP). SR and IP indicate patches (shaded, rich) with low light intensity (shaded, S), high nutrient availability (rich, R) and patches (illuminated, poor) with high light intensity (illuminated, I) and low nutrient availability (poor, P), respectively. Plasticity of the species in root–shoot ratio, fitness-related traits (biomass, number of ramets and dry weight per ramet) and clonal morphological traits (length and specific length of stolon internodes, area and specific area of laminae, length and specific length of petioles) were experimentally examined. The aim is to understand adaptation of G. longituba to the environment with reciprocal patches of light and soil nutrients by plasticities both in root–shoot ratio and in (clonal) morphology. Our experiment revealed performance of the clonal fragments growing from patches with high light intensity and low soil nutrient availability into the adjacent opposite patches was increased in terms of the fitness-related characters. R/S ratio and clonal morphology were plastic. Meanwhile, the capture of light resource from the light-rich patches was enhanced while the capture of soil nutrients from either the nutrient-rich or the nutrient-poor patches was not. Analysis of cost and benefit disclosed positive effects of clonal integration on biomass production of ramets in the patches with low light intensity and high soil nutrient availability. These results suggest an existence of reciprocal translocation of assimilates and nutrients between the interconnected ramets. The reinforced performance of the clonal fragments seems to be related with specialization of clonal morphology in the species. 相似文献
999.
KENNETH A. BARRICK 《Austral ecology》2003,28(3):252-262
Abstract Trees growing along windy coasts often have canopies that are greatly reduced in size by the sculpting effects of wind and salt spray. Trees with environmentally reduced stature are called elfinwood (windswept shrub‐form or krummholz) and are ecologically important because they represent outposts growing at the limit of tree success. The purpose of this study was to assess if Banksia grandis elfinwood growing at Cape Leeuwin had a different nutrient status than normal low‐form (LF) trees growing nearby, and if nutrient deficiencies, toxicities and/or imbalances were among the limiting factors imposed on elfinwood. The concentrations of N, P, K, Ca, Mg, Na, Cl–, Fe, Mn, Zn, Cu, Mo and B were analysed for mature green foliage, immature foliage, foliage litter, flowers and soil. When the elfinwood and LF trees were compared, the foliar nutrient status was generally similar, except that elfinwood foliage had significantly higher mean concentrations of N, Zn and Cu, while LF trees had higher Fe and Mn contents. Many nutrients were conserved before leaves were shed in both elfinwood and LF trees, including N, P, K, Na, Cl–, Mn and Cu (LF trees also conserved Ca and Mg). However, elfinwood and LF tree‐litter contained significantly higher Fe concentrations than green foliage (elfinwood litter also had higher levels of Mg and B). It is tempting to suggest that the translocation of Fe into leaves before they were shed is a regulation mechanism to prevent Fe toxicity, or imbalance in the Fe : Mn ratio. Proteoid roots strongly acidify the soil to mobilize P, which also chemically reduces Fe+3 to plant‐available Fe+2. The increased supply of Fe+2 in the rhizosphere, caused by the action of proteoid roots, might tend to defeat self‐regulation of Fe uptake. It is possible that excess Fe accumulation in the plant might be regulated, in part, by exporting Fe into the leaves before they are shed. The nutrient status of B. grandis elfinwood is compared with mountain elfinwood of North America. The extreme habitat of coastal elfinwood provides many theoretical pathways for nutrient limitation, but B. grandis elfinwood at Cape Leeuwin does not appear to be nutrient deficient. 相似文献
1000.