Effects of water stress on growth phenology photosynthesis and leaf water potential in Stipagrostis ciliata (Desf.) De Winter in North Africa

Stipagrostis ciliata (Desf.) De Winter is a pastoral C₄ grass grown in arid regions. This research work focused on assessing the growth of S. ciliata accessions derived from two different climate regions (a wet arid region in the Bou Hedma National Park in the central and southern part of Tunisia (coded as WA), and a dry arid region from the Matmata Mountain in the south of Tunisia (coded as DA)) under water stress conditions. Specifically, the study aimed to investigate the phenological and physiological responses of potted S. ciliata seedlings under different water treatments: T₁ (200 mm/a), T₂ (150 mm/a), T₃ (100 mm/a) and T₄ (50 mm/a). Growth phenology, net photosynthesis (P_n), stomatal conductance (g_s), midday leaf water potential (Ψ_md), predawn leaf water potential (Ψ_pd), soil water content (SWC) and soil water potential (Ψ_s) were observed during the water stress cycle (from December 2016 to November 2017). The obtained results showed that the highest growth potential of the two accessions (WA and DA) was recorded under treatment T₁. The two accessions responded differently and significantly to water stress. Photosynthetic parameters, such as P_n and g_s, decreased sharply under treatments T₂, T₃ and T₄ compared to treatment T₁. The higher water stress increased the R/S ratio (the ratio of root dry biomass to shoot dry biomass), with values of 1.29 and 2.74 under treatment T₄ for accessions WA and DA, respectively. Principal component analysis (PCA) was applied, and the separation of S. ciliata accessions on the first two axes of PCA (PC1 and PC2) suggested that accession DA was detected in the negative extremity of PC1 and PC2 under treatments T₁ and T₂. This accession was characterized by a high number of spikes. For treatments T₃ and T₄, both accessions were detected in the negative extremity of PC1 and PC2. They were characterized by a high root dry biomass. Therefore, S. ciliata accessions responded to water stress by displaying significant changes in their behaviours. Accession WA from the Bou Hedma National Park (wet arid region) showed higher drought tolerance than accession DA from the Matmata Mountain (dry arid region). S. ciliata exhibits a significant adaptation capacity for water limitation and may be an important species for ecosystem restoration.     

Ultrasonographic screening for cystic echinococcosis in sheep in Tunisia

Sheep from the areas of Fondouk-Jeddid, Bir Mchergua and El Fahs, located in the Northeast of Tunisia, were examined by ultrasonography between 2001 and 2004 in order to assess their infection with Echinococcus granulosus, the agent of hydatid disease, and to evaluate this method as an efficient aire for hydatid cysts. A total of 1039 sheep, aged between 1 and 14 years was examined. The highest prevalence was found in sheep aged more than 8 years. The least infected animals were aged between 1 and 2 years. All hydatid cysts detected by ultrasound were located in the liver. In all age-groups, the dead cysts were more numerous than viable cysts. Eighteen positive sheep were autopsied and a comparison between ultrasound and autopsy results was performed. The results showed a prevalence of about 40% for the three areas. Ultrasonography allowed the cysts, deep or superficial to localize in the central or left part in relation to the caudal vena cava of the animals. Consequently, all the cysts were not detected with this technique. This work shows that ultrasonography confirms the importance of ovine hydatid cyst in Tunisia and that its use as a mass screening approach for cystic echinococcosis in sheep could be helpful for the monitoring of this disease in a hydatid control program without great stress for the animals.     

Causal processes of soil salinization in Tunisia,Spain and Hungary

Soil salinization arises due to the build up of soluble salts at or near the soil surface. Salts accumulate by primary and secondary processes that alter the soils physicochemical properties and lead to direct and indirect soil degradation. Results are presented here from the study of three contrasting salt‐affected landscapes. The Chott el Fedjadj, Tunisia, is a naturally salt‐affected basin containing saline sediments deposited during a marine incursion. The endoreic conditions lead to salt recirculation, concentration and reprecipitation. In the Guadalentin Valley, Spain, increased irrigated agriculture has led to aquifer overexploitation releasing gas and salts. Irrigating with the resultant contaminated groundwater has induced soil salinization. The salt accumulation and translocation is dictated predominantly by irrigation method, water quality and quantity. Hungary has the largest expanse of naturally salt‐affected soil in Europe, with the dominant soil type being solonetz. In Hungary the type of salt‐affected soil development is related to the salts present, hydraulic properties of the soil and depth and quality of the watertable. In Tunisia a catenary relationship of increased water and soil salinity towards the centre of the chott is found, whereas in Spain the highest salinities were found under flood irrigation with the valley displaying a complex spatial distribution of soil salinity. The sediment distribution in Hungary dictates that solonchak soils are found mostly in the Danube–Tisza interfluve and solonetz soils in the Tisza floodplain, with localized variations in soil type related to watertable characteristics. Copyright © 2001 John Wiley & Sons, Ltd.     

Diversity of pomegranate (Punica granatum L.) germplasm in Tunisia

Thirty pomegranate (Punica granatum L.) accessions were studied to determine the overall degree of polymorphism and to detect similarities among genotypes. PCA and cluster analysis showed a considerable phenotypic and genetic diversity in the local pomegranate germplasm. Some polyclonal varieties were identified and cases of homonymy were detected. The geographic origin was not a determinant criterion for cultivars clustering. Parameters with high discriminating values were those related to fruit size and color and juice characteristics. Factors affecting pomegranate germplasm diversity are discussed.     

Genetic diversity in wild Tunisian populations of Mentha pulegium L. (Lamiaceae)

The allozyme variation of 15 Tunisian wild populations of Mentha pulegium L. threatened by human activities (clearing, hard-grazing, ploughing, traditional uses) was surveyed by the analysis of 14 isozyme loci using horizontal gel starch electrophoresis. The species exhibited a high level of genetic variation within populations (the mean Ap = 2.20, P = 72%, Ho = 0.349 and He = 0.229), which indicates a predominately outcrossing mating system and the recruitment of new genotypes via dispersal seeds. The genetic structure analysis of the populations using F statistics indicates no inbreeding, and showed an excess of heterozygosity for few loci. The moderate differentiation of populations (F_ST = 0.110) and the low rate of gene flow between them (Nm = 2.02) might been caused by recent isolation of the populations through biotope disturbances. The value of Nei's genetic identity varied from 0.839 to 0.999 reflecting a relatively low genetic divergence between populations. Cluster analysis using UPGMA method and Nei's genetic identity values, showed that populations geographically close didn't always cluster together. However, populations within the same bioclimatic stage generally subclustered together indicating that differentiation between bioclimatic regions occurred.     

Promoting the adoption of natural resource management technology in arid and semi-arid areas: Modelling the impact of spineless cactus in alley cropping in Central Tunisia

The arid and semi-arid areas of North Africa are becoming deserts. Most of the research and development projects in these areas aim at developing alternative technologies to reduce land degradation and favour sustainable economic activities. The ‘spineless cactus-alley cropping system’ is an interesting alternative in the low rainfall areas of North Africa. This system limits land degradation by the use of perennial crops, produces cheap and drought resistant sources of feed, and favours biomass production in the inter spaces. The important question is how to promote the adoption of this technology. A bio-economic model has been developed to identify the conditions of development of the ‘spineless cactus-alley cropping system’ in an agro-pastoral community of Central Tunisia. Scenarios relating to different types of institutional support, either monetary or informational, were analysed. The results revealed larger cash flow, more livestock and less cereal cultivation on marginal land. Adoption of the technology is clearly favoured by public financial support and also largely by transmission of information on the expected yield of the system. The findings suggest that extension services play a crucial role in creating awareness among farmers of the impact of technology in terms of yields and income diversification.     

MAPPING LINEAR EROSION FEATURES USING HIGH AND VERY HIGH RESOLUTION SATELLITE IMAGERY

Mapping and monitoring linear erosion features (LEFs) over large areas is fundamental for a better understanding of the main erosion processes and for planning suitable protection measures. The advent of very high‐resolution satellite imagery has expanded the range of satellite LEF identification to moderate‐size elements. After determining the relationship between satellite imagery resolution and the ability to detect LEFs, we discuss a highly automated method for extracting such LEFs from a very high spatial resolution image (0.61 m resolution). The method is based on a two‐stage strategy: (1) extraction of all linear features visible on the satellite image using filters and photo‐interpretation; (2) filtering these linear features according to geometric criteria (e.g. orientation relative to slope, sinuosity, position in landscape, etc.) so as to retain only those relative to linear erosion. A series of three images with increasing spatial resolution (10.5 and 0.61 m) was prepared for an area on the Cap Bon peninsula (Tunisia). This predominantly agricultural area has a high density of LEFs with very varied geometric characteristics. The area's problems are both onsite for the agriculture itself, and offsite with the silting up of hillside reservoirs. Respectively 22 per cent, 37 per cent and 73 per cent of the site's LEFs, with respective average widths of 2.8, 3.0 and 2.2 m, are visible on the 10, 5 and 0.61 m resolution images. Gully identification should help to identify the most threatened areas to help land use planning and management or to validate erosion models whether at regional or local (drainage basin) scale. Copyright © 2011 John Wiley & Sons, Ltd.     

Phosphorus sorption kinetics in different types of alkaline soils

This study investigated phosphorus sorption kinetics of three different soils from three sites within the Sahel region of Tunisia; iso-humic soils from Chott-Mariem site, calcic-magnesic soils from Enfidha site and saline-sodic soils from Kondar site. Soils from all sites were sampled (0–25 cm) and analysed for their physico-chemical proprieties. In previous works, we determined the adsorption efficiency of these different soils. In this study, we focused on the influence of contact time on phosphorus adsorption by the different soils. The analytic data were approached from the following kinetics models: pseudo-first-order, pseudo- second-order and Elovich model. The second order model was shown to be the best fit for describing phosphorus adsorption by each soil sample, as seen from the correlation coefficient R² which ranged from 0.68 to 0.96 for the pseudo-first-order model, 0.91 to 0.99 for pseudo-second-order model and 0.84 to 0.94 for Elovich model.