Deep infiltration through a sandy alluvial fan in semiarid Niger inferred from electrical conductivity survey,vadose zone chemistry and hydrological modelling

In semiarid southwestern Niger, most of the groundwater recharge is indirect and occurs through endoreic ponds. Elsewhere in the landscape, there is no evidence of deep infiltration, with a possible exception for gullies and alluvial fans on sandy slopes. In order to verify this hypothesis, a detailed geophysical and geochemical survey was conducted on a large, representative mid-slope fan (6 ha). At this site, distributed hydrological modelling conducted over the encompassing endoreic catchment (190 ha) showed high losses of runoff water by infiltration. Electromagnetic mapping and 2-D electrical imaging survey were used to investigate the 35 m deep vadose zone; in addition, 8 boreholes were drilled following the geophysical survey to constrain the interpretation. Variations in apparent electrical conductivity measured in boreholes appear to be mainly linked with changes in the soil solution mineralization. An extrapolation throughout the area shows that apparent electrical conductivity of the ground is systematically lower below channels; this suggests localised leaching through the unsaturated zone. A physically-based, 2-D distributed hydrologic model was used to estimate the amount of surface water loss by infiltration for the 1992–2002 period. Depending on year, infiltrated volumes range from 1000 to 24 000 m³. This represents between 5% and 16% of the runoff that reaches the final outlet of the basin, an endoreic valley bottom pond where recharge to the aquifer has been shown to occur. Because leaching of the vadose zone is observed down to a depth of 10 m below channels, episodic groundwater recharge through sandy mid-slope fans is highly probable during rainy years.     

森林土壤肥力概述

森林土壤肥力以维持和恢复自然肥力为主,人工施肥为输。概述了森林与土壤的关系,维持和提高森林土壤肥力的途径,对提高森林土壤肥力及其生态、经济效益具有重要的指导意义。     

Predicting the vertical location of branches along Atlas cedar stem (Cedrus atlantica Manetti) in relation to annual shoot length

A model for the vertical location of whorl and interwhorl branches was constructed for Atlas cedar (Cedrus atlantica Manetti). The vertical location of branches in the crown partly governs their further growth and mortality from which depend (i) the stem growth and form and (ii) the quality of lumber and veneer, including wood knots. The modeling method, based on an architectural approach, reveals branching patterns. Each annual shoot was considered as a sequence of successive positions, unbranched or branched with two types of branch: short or long shoot. Branching sequences were analyzed using hidden semi-Markov chains. A wide range of annual shoot lengths was sampled in order to determine the relationships between sequence length and the characteristics of every zone identified (frequency of every type of axillary production, probability of zone occurrence and probability of transition to the following zone). The model predicts branch vertical position which can be used as inputs for branch diameter and mortality models.     

基于杂交小波变换的农产品图像去噪算法

针对现有图像去噪方法去噪效果不明显、易丢失细节特征等缺陷,提出了一种基于杂交小波变换的农产品图像去噪算法。该方法综合了小波去噪能较好保留图像细节特征和Wiener滤波器可得到最优解的优势,分别以经小波变换、Wiener滤波处理后的图像作为杂交小波变换初始种群的父本和母本,并以最大类间方差作为适应度函数来评价个体的优劣,通过杂交和变异操作实现基因重组,提取出小波变换与Wiener滤波在图像去噪中的优势基因;经过有限次的杂交代数最终得到兼有父本和母本优势的子代图像。试验中用红枣和小麦图像对算法进行测试,去噪后红枣和小麦的图像峰值信噪比（PSNR）分别为178.44和183.24,好于邻域平均法（176.76和175.16）、中值滤波法（174.79和173.13）、维纳滤波（172.75和173.48）和高斯滤波（167.50和165.60）等常规去噪方法,并且在视觉效果上同时兼有噪声低和边缘清晰等优点,表明该方法用于农产品图像去噪是有效的、可行的。     

Evidence for an extracellular acid proteolytic activity secreted by living cells of Saccharomyces cerevisiae PlR1: impact on grape proteins

In this work, Saccharomyces cerevisiae PlR1, a strain isolated from Pinot noir grapes in the Champagne area, was shown to secrete an acid proteolytic activity against bovine serum albumin. This proteolytic activity was detectable in cell-free culture supernatants at the beginning of the exponential growth phase and increased with yeast growth. Using a zymography method, only one protease band with a molecular mass of 72 kDa was observed. This extracellular proteolytic activity was detected in the pH range from 2 to 4 with a maximal value at pH 2.5 and 38 °C and was completely inhibited by pepstatin A. The secretion of this protease did not need any protein inducer and seemed to be insensitive to nitrogen catabolic repression. S. cerevisiae PlR1 was also able to secrete this proteolytic activity during alcoholic fermentation, and it was found to be active against grape proteins, with a molecular mass around 25 kDa, at optimal conditions of 38 °C, pH 3.5.     

Growth and morphology of three forest understorey species (Calluna vulgaris, Molinia caerulea and Pteridium aquilinum) according to light availability

Calluna vulgaris, Molinia caerulea and Pteridium aquilinum are three forest understorey species that compete with tree seedlings for environmental resources. Forest managers therefore seek to control their growth, which is driven in part by the light available in the forest understorey.An experiment was set up in a nursery in which the three understorey species C. vulgaris, M. caerulea and P. aquilinum were planted at six light levels (6, 11, 22, 36, 48 and 100% of full sunlight) replicated in three blocks. The different light levels other than 100% were obtained using neutral shading nets. The response of the three species to light availability was estimated after two growing seasons by their cover and height, their morphology, assessed by the foliar tuft height-to-width ratio for C. vulgaris and M. caerulea and by the frond height-to-length ratio for P. aquilinum, and their functional acclimation, assessed by a leaf trait (leaf mass on an area basis, LMA).Vegetation cover changed with light availability following a bell-shaped curve. By contrast, vegetation height remained approximately the same, irrespective of the light treatment, except for P. aquilinum, which grew higher than the other two species at medium and high light levels. As a consequence, vegetation individuals were more spindly in a dark environment. From the lowest light treatment, P. aquilinum cover was high (75%) and intercepted a larger proportion of the light than the other two species. This species thus proved the most competitive for light.All three species showed a notable acclimation to light availability by their LMA, though in different ways. The LMA of C. vulgaris decreased in shaded conditions by an increase in leaf area, whereas decrease in LMA for P. aquilinum was due to a decrease in leaf mass. For M. caerulea, the LMA remained stable whatever the light conditions by a simultaneous increase in both leaf mass and leaf area in shaded conditions.Consequently, the in-forest development of C. vulgaris and M. caerulea could be managed through small adult canopy thinnings, as both species grew well from light levels above 20%. Conversely, it seems unrealistic to manage P. aquilinum in this way as its development was almost maximal even at very low light levels.     

Identification of novel DNA fragments and partial sequence of a genomic island specific of Brucella pinnipedialis

Since the 1990s, Brucella strains have been isolated from a wide variety of marine mammals and were recently recognized as two different species, i.e. Brucella pinnipedialis for pinniped isolates and Brucella ceti for cetacean isolates. The aim of this study was to identify specific DNA fragments of marine mammal Brucella strains using a previously described infrequent restriction site-PCR (IRS-PCR) method but with three new couples of restriction enzymes applied on a larger panel of marine mammal Brucella isolates (n=74) and one human isolate from New Zealand likely from marine mammal origin. This study revealed five DNA fragments specific of Brucella strains isolated from marine mammals. Among them two new DNA fragments were specific of B. pinnipedialis but were not detected in hooded seal isolates. DNA fragment I identified in the previous IRS-PCR study and fragment VI of this study were located on a cloned and sequenced 6kb SacI fragment. Its nucleotide sequence revealed that it is likely part of a putative genomic island. Sequence analysis showed that it carries four ORFs coding for putative metabolic functions. Although hooded seal isolates are classified within B. pinnipedialis it was shown in this study that they do not carry this genomic island and this raises the question about their evolutionary history within B. pinnipedialis.     

Root elongation in tropical Eucalyptus plantations: effect of soil water content

? Sustainability of Eucalyptus plantations is often questioned in resource-limited environments, especially in areas characterized by soils with poor nutrient and water holding capacities. Yet, field-based observations of fine root dynamics in relation with the seasonality of rainfall are lacking.

? This study was undertaken on two Eucalyptus stands planted in the Kouilou Region (south-western Congo), which is characterized by a four-month-long dry season. Fine root (less than 2 mm in diameter) dynamics were studied using rhizotron observations of root elongation in the field.

? Fine root elongation rates displayed a seasonal variation in the two stands, with higher elongation rates during the rainy season than during the dry season. Positive and significant correlations were found between fine root elongation rates and soil water content at all depths, but a better correlation was found with soil water content in the deep soil horizon than in the superficial horizons.

? These results suggest that the temporal variations in fine root elongation were related to the seasonality of rainfall, and they were probably associated with seasonal changes in tree water status, carbon assimilation and belowground allocation.

     

Dry-heating makes hen egg white lysozyme an efficient foaming agent and enables its bulk aggregation

Dry-heating is considered to be one of the most promising approaches to improving the functionality of food proteins. It has been shown that even if only minor structural modifications occur during dry-heating, the foaming properties of proteins are highly improved. With the recent results obtained in the field of foam stabilization by nanoparticles or protein aggregates in mind, a study was undertaken on the impact of dry-heating of lysozyme, used as a model protein, on its foaming properties. This work highlighted the fact that dry-heated hen egg white lysozyme simultaneously exhibited enhanced foaming properties and aggregation capacity. Although the conditions that favored bulk aggregation (high ionic strength, pH, treatment duration, and protein concentration) also favored foaming properties, the large bulk aggregates were not essential to obtain the best functionality. It is envisaged that heat-treated lysozyme may self-associate at the air/water interface, stabilizing air bubbles.