科尔沁沙地4种植物抗旱性的比较研究

对科尔沁沙地小叶锦鸡儿,紫穗槐,差巴嘎蒿和胡枝子4种植物的若干水分生理生态指标进行了测定。结果表明,小叶锦鸡儿具有低水势,高水力和束缚水／自由水比及水分利用效率,抗旱性强;紫穗槐的各项指标与小叶锦鸡儿相反,抗旱性最差;差巴嘎蒿虽然水势较高,但它的持水力高,束缚水／自由水比和水分利用效率都较高,抗旱性也较强,但次于小叶锦鸡儿;胡枝子的水势和持水力较低,束缚水／自由水比及水分利用效率一般,它的抗旱性强于紫穗槐,但比差巴嘎蒿差。     

Effect of Agricultural Management on Nematode Communities in a Mediterranean Agroecosystem

The effects of agricultural management on the soil nematode community were investigated in a field study at depths of 0 to 10 cm and 10 to 20 cm during a peanut (Arachis hypogaea) growing season in Israel. Nineteen nematode families and 23 genera were observed. Rhabditidae, Cephalobus, Eucephalobus, Aphelenchus, Aphelenchoides, Tetylenchus, Tylenchus, Dorylaimus, and Discolaimus were the dominant family and genera. Ecological measures of soil nematode community structure, diversity, and maturity indices were assessed and compared between the managed (by fertilization, irrigation, and pesticide application) and unmanaged fields. The total number of nematodes at a 10-cm depth during peanut-sowing, mid-season, and harvest periods was higher in the treated (managed) plot than in the control (unmanaged) plot. Bacterivores and fungivores were the most abundant trophic groups in both plots and both depths. The relative abundance of each group averaged 60.8 to 67.3% and 11.5 to 19.6% of the nematode community, respectively. Plant parasites and omnivores-predators at the 0 to 10-cm depth were much less abundant than any other two groups in our experimental plots. During the growing season, except the harvest period, populations of plant parasites and omnivores-predators at the 10 to 20-cm depth were lower in the treated plot than in the control plot. Maturity index (MI), plant-parasite index (PPI), and ratio of fungivores and bacterivores to plant parasites (WI) were found to be more sensitive indicators than other ecological indices for assessing the response of nematode communities to agricultural management in an Israeli agroecosystem.     

Mineral nutrition and growth of tropical maize as affected by soil acidity

Soil constraints linked to low pH reduce grain yield in about 10% of the maize growing area in tropical developing countries. The aim of this research was to elucidate the reasons for this maize yield reduction on an oxisol of Guadeloupe. The field experiment had two treatments: the native non-limed soil (NLI, pH 4.5, 2.1 cmol Al kg^–1, corresponding to 20% Al saturation), and the same soil limed 6 years prior to the experiment (LI, pH 5.3, 0 cmol Al kg^–1). The soils were fertilized with P and N. The above-ground biomass, root biomass at flowering, grain yield and yield components, leaf area index (LAI), light interception, radiation-use-efficiency (RUE), P and N uptake, soil water storage, and soil mineral N were measured during the maize cycle. The allometric relationships between shoot N concentration, LAI and above-ground biomass in LI were similar to those reported for maize cropped in temperate regions, indicating that these relationships are also useful to describe maize growth on tropical soils without Al toxicity. In NLI, soil acidity severely affected leaf appearance, leaf size and consequently the LAI, which was reduced by 60% at flowering, although the RUE was not affected. Therefore, the reduction in the above-ground biomass (30% at flowering) and grain yield (47%) were due to the lower LAI and light interception. At flowering, the root/shoot ratio was 0.25 in NLI and 0.17 in LI, and the root biomass in NLI was reduced by 64% compared to LI. Nitrogen uptake was also reduced in NLI in spite of high soil N availability. Nevertheless, shoot N concentration vs aboveground biomass showed a typical decline in both treatments. In NLI, the shoot P concentration vs above-ground biomass relationship showed an increase in the early stages, indicating that P uptake and root-shoot competition for the absorbed P in the early plant stages controlled the establishment and the development of the leaf area.     

Seasonal patterns in water use and leaf turnover of different plant functional types in a species-rich woodland,south-western Australia

Woodlands in south-western Australia are evergreen and transpire throughout the year despite the long, hot and dry summers of the Mediterranean climate. Results from a case study in a species-rich Banksia woodland are used to discuss the ecological and physiological properties that appear to be essential features of this and similar communities. Tree, shrub and perennial herbaceous species with long-lived leaves dominate the community, whereas winter-green herbaceous species with short-lived leaves constitute a minor group. The total leaf area index is therefore reasonably constant in all seasons. Leaf area index is low and canopies are open, causing good coupling between the vegetation and the atmosphere, and making stomatal control an effective regulator of transpiration. Mean maximum (winter) stomatal conductances were high at approximately 300 mmol m^–2 s^–1. Deep-rootedness allows the dominant species to access soil moisture throughout the unsaturated zone, and down to the capillary fringe of the saturated zone. Shrubs and herbs with shallow roots experience greater drought stress during summer. Rates of community evapotranspiration are limited by leaf area index in the wet season, and further reduced by stomatal closure in the dry season. Deep-rooted plants appear to decrease their stomatal conductance before the development of severe drought stress. Such conservative behaviour, possibly related to plant hydraulic constraints, is a contributing factor to the limited seasonality in community water use.     

Catalogue of Human Tissue Optical Properties at Terahertz Frequencies

Recently published studies suggest thatterahertz pulsed imaging will have applications inmedicine and biology, but there iscurrently very little information about the opticalproperties of human tissue at terahertzfrequencies. Such information would be useful forpredicting the feasibility of proposedapplications, optimising acquisition protocols,providing information about variability ofhealthy tissue and supplying data for studies of theinteraction mechanisms. Research ethicscommittee approval was obtained, andmeasurements made from samples of freshlyexcised human tissue, using a broadbandterahertz pulsed imaging system comprisingfrequencies approximately 0.5 to 2.5 THz.Refractive index and linear absorptioncoefficient were found. Reproducibility wasdetermined using blood from one volunteer,which was drawn and measured on consecutivedays. Skin, adipose tissue, striatedmuscle, vein and nerve were measured (to date, from oneindividual). Water had a higher refractiveindex (2.04 ± 0.07) than any tissue.The linear absorption coefficient was higher formuscle than adipose tissue, as expectedfrom the higher hydration of muscle. As these samples camefrom a single subject, there is currentlyinsufficient statistical power to draw firmconclusions, but results suggest that in vivo clinical imaging will be feasible in certainapplications.