Ecophysiological aspects and photosynthetic pathways in 105 plants species in saline and arid environments of Tunisia

In Tunisian arid regions, plant life forms, ecotypes, physiological types and photosynthetic pathways （03, 04 or CAM） remain unclear. Understanding the characters of these plant species could be important for land restoration. A literature survey was conducted for 105 plants species in arid regions of Tunisia. These plant species belong to several ecotypes： halophytes, xerophytes, gypsophytes, psamophytes, xero-halophytes, gypso-halophytes, psamo-halophytes, psamo-xerophytes, xero-gypsophytes and hygro-halophytes. The variation of photosynthetic pathway types in the 105 studied species shows that 56.2% were C3, 41.0% were C4, 1.9% were CAM and 1.0% were C3-CAM. The C3 pathway was more abundant in the halophytes, whereas the C4 one was more common in the xerophytes, gypsophytes, gyp- so-halophytes and psamo-halophytes. The ratio of C3 to C4 species （C3/C4 ratio） was 0.2 in the psamo-halophytes, 0.8 in the gypso-halophytes, 1.1 in the xerophytes, 1.6 in the xero-halophytes, 1.8 in the hygrohalophytes, 2.0 in the psamo- phytes and 3.8 in the halophytes. The annuals were mainly C3 plants whereas most of perennials were C4 ones. The C3/C4 ratio was 1.3 in succulent species and 1.4 in non-succulent species. Thus, succulence seems not to affect the distribution of C3 and C4 pathways within the studied plants. This investigation shows high percentages of C4 plants occurred in Tuni- sian arid regions. However, there were significant differences in their abundance among ecotypes. Basing on C3/C4 ratio, we can find that the abundance of the C4 pathway was in the following order： psamo-halophytes, gypso-halophytes, xe- rophytes, xero-halophytes, hygro-halophytes, psamophytes and halophytes. In Tunisian arid regions, C4 species were most abundant in xerophytes and less abundant in halophytes. In the Chenopodiaceae the number of C3 plants was 13 and the number of C4 species was 20 and in the Poaceae the number of C3 was 23 and the number of C4 was 19 species. Thus, the most C4 proportion was in the Chenopodiaceae a     

Phenology and Yield Efficiency of Early,Mid-, and Late-Maturing Cultivars of Peach in Irrigated Orchards under Mediterranean Climate

Productivity of peach cultivars with different ripening seasons was studied under the growers’ conventional conditions of Tunisia. Experiments were performed in northern Tunisia (36° 41? N, 10° 15? E). Performances of Flordastar, Royal Glory, and Carnival as respectively early, mid-season, and late ripening cultivars were evaluated under the grower’s conventional irrigation programs. Fruit growth, yield, water supply, and water productivity were determined through four years. For the three cultivars, Flordastar, Royal Glory, and Carnival, fruit maturity was achieved at 650, 1100, and 2200 GDD, respectively. Average yields were 17.4, 29.8, and 41.1 t ha^–1 and mean values of water productivity were 1.9, 3.1, and 3.6 kg fresh yield m^–3 for early, mid-season, and late cultivars, respectively. Results of agronomic performances evaluation at the farm scale provided a reference on the behavior of early, mid-season, and late cultivars of peach in irrigated orchards in semi-arid conditions.     

Water balance of the olive tree–annual crop association: A modeling approach

Water transfers within mixed crops systems are complicated to understand due to the large number of complex interactions between the various components. Standard techniques fail to provide the proper assessment of the components of the water balance. Experiments and modeling developments are used to understand the dynamics of water transfers within the association of olive trees with annual crops under irrigation in Central Tunisia. The whole system is represented by a unit area made up of three components: a plot with the annual crop, a plot with the olive tree and a plot of bare soil. The modeling approach is based on the concept of reservoir. The model works on a daily time step and accounts for the lateral transfers of water occurring between the components of the system: (i) the water uptake by the roots of olive trees; (ii) the physical flow of water between the irrigated plot and the non-irrigated ones. A field experiment was carried out during 2 years (2002, 2003) and three crop cycles (spring potato, spring pea and autumn potato) in order to calibrate the model and test its validity. Olive tree transpiration was estimated from sap flow measurements and soil moisture in the different compartments was measured by neutron probe technique. The experimental data compare fairly well with the model outputs. The first purpose of the model is to understand the functioning of the olive tree–annual crop association from a water standpoint, but it can be easily extended to other intercropping systems mixing perennial vegetation with annual crops or used as a management tool. The estimates of the water extracted by the olive trees in each reservoir appear to be much more significant than those of the water physically transferred between reservoirs.     

Salinity and Temperature Effects on the Lipid Composition of Mullet Sea Fry (Mugil cephalus, Linne, 1758)

A large part of the extensive aquaculture in Tunisia was based on the transfer of mullet fry from the marine coastal areas to the continental fresh water lakes, the aim of this work is the monitoring of the changes made in the lipid composition of Mugil cephalus fry according to salinity and temperature acclimation. Fish acclimated to 14 °C and 0.5 psu salinity, contained 55% less total fatty acid than those acclimated to the seawater at the same temperature. Low salinity induces an increase in the percentage of some polyunsaturated fatty acid such as the 22:5 (n-3), the 22:6 (n-3) and the 20:4 (n-6), as a result of change in the level of triacylglycerol content or the activation in the synthesis of those fatty acids. The transition of the acclimation temperature from 26 to 14 °C in seawater is followed by a 215% increase in the amount of total fatty acids in the fourth week of acclimation. The total fatty acid levels of all fish at 1 week were higher than most values at 4 weeks. There was an increase of polyunsaturated fatty acids percentages due to the decrease of the temperature at the low salinity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Water relations of olive trees cultivated under deficit irrigation regimes

The experiment was carried out at the Experimental Field ‘Taoues’, southern Tunisia (34°N, 10°E) to examine the effect of irrigation schedules on water relations for young olive trees, cultivars Chétoui, Chemlali, Coratina, Picholine and Manzanille. Plants were cultivated at 7 m × 7 m spacing and drip irrigated from April to September. Irrigation amounts (IA) of 20%ET_c, 50%ET_c and 100%ET_c were applied, where ET_c is the FAO crop evapotranspiration. The effect of IA on midday leaf water potential (Ψ_leaf), stomatal resistance (R_s) and conductance (g_s), soil (H_v) and relative leaf (RWC) water contents was studied. Results showed that a further increase in IA was not systematically followed by an increase of water potential, production and WUE values. Some controversial responses were observed following to a variety with large seasonal variations. At the beginning of the growing season, differences between treatments were not very important because soil water content was still high enough to prevent important changes in Ψ_leaf values. The most stressed trees showed potentials of −1.53 MPa for Picholine cv. and ranging between −2.30 MPa and −2.10 MPa for the other varieties depending on IA. The less stressed trees provided potentials of −0.97 MPa for Picholine cv. and varying between −1.63 MPa and −2.13 MPa for cultivars Coratina, Manzanille, Chétoui and Chemlali. Then, as the season progresses, and when IA was increased from 20%ET_c to 50%ET_c, Ψ_leaf values decreased significantly for cultivars Chemlali (−3.05 MPa), Coratina (−3.75 MPa), Manzanille (−3.0 MPa) and Chétoui (−3.5 MPa). At 100%ET_c, Manzanille and Picholine cultivars show better water status with respective potentials of −2.7 MPa and −2.6 MPa. Stomatal resistance monitoring showed maximums at midday for all cultivars with pick value of 4.45 s/cm recorded for Chétoui cultivar irrigated at 50% ET_c. The most important variations were recorded for cultivar Chemlali which seem to be the ablest to regulate stomata aperture. Close coordination between Ψ_leaf and g_s and Ψ_leaf and RWC measurements was found. But, the response varied following to treatment. At low irrigation levels (20%ET_c and 50%ET_c), g_s was found to be linearly and positively correlated to Ψ_leaf. It increased linearly and positively with increasing values of Ψ_leaf (r of 0.84 and 0.96, respectively). At 100%ET_c, Ψ_leaf is found to be correlated to g_s following to a polynomial function with an optimum g_s value of 450 mmol/m²/s and Ψ_leaf of about −2.5 MPa.     

Aetiological factors and perception of anaemia in Tunisian women of reproductive age

OBJECTIVES: To identify aetiological factors in anaemia and to explore knowledge, perceptions and attitudes towards anaemia. DESIGN: Two cross-sectional surveys and sixteen focus group discussions. SETTING: The two regions with the highest prevalence of anaemia in Tunisia, Greater Tunis (GT) and the South West (SW). SUBJECTS: Two representative samples of 687 (GT) and 729 (SW) women of reproductive age; 108 women were included in focus group discussions. RESULTS: Among anaemic women, 63.4% in the GT region and 80.2% in the SW displayed iron deficiency (ID). Genetic haemoglobinopathies accounted for 10.0% and 3.6% of the cases of anaemia in the two regions, respectively. After adjustment for confounders, the major factors for iron-deficiency anaemia were low dietary Fe intake (OR = 5.0, 95% CI 3.0, 8.4), drinking tea after eating (OR = 3.4, 95% CI 2.0, 5.7) and pica (OR = 2.1, 95% CI 1.1, 3.9). Most of the women related anaemia to the following causes: malnutrition, lack of hygiene, and their heavy workload and responsibilities in the household. Many women connected anaemia with hypotension. Few established a relationship between ID and anaemia. They had confidence in their doctor for treatment, but many complained they were not given sufficient information. Low dietary Fe intake, inappropriate food practices and inadequate perceptions contribute to the aetiology of anaemia in women. CONCLUSIONS: These results point out to the need for a strategy combining food fortification, Fe supplementation for pregnant women, nutritional education for the general public and at-risk specific target groups, and training of health professionals.     

Functional relationships between leaf structure and photosynthetic traits as modulated by irradiance and nutrient availability in a sclerophyllous and a non-sclerophyllous mediterranean oak species

Plasticity of structural and physiological leaf traits elicited by irradiance and soil nutrients was investigated in two sympatric mediterranean oaks: a sclerophyllous (Quercus suber L.) and a non-sclerophyllous species (Q. canariensis Willd.). Seedlings were grown for 2 years in pots in a 2-way crossed factors design. Leaf mass-to-area ratio (LMA) and nitrogen were recorded, and photosynthetic capacity (i.e. the apparent maximal carboxylation rate by rubisco, V _cmax) was derived from response curves of net CO₂ assimilation (A) versus intercellular CO₂ mol fraction (C _i). Structural equation modelling was applied to the data for disentangling the complex correlation structure between variables. The two species differed significantly in photosynthetic nitrogen use efficiency (PNUE). They displayed the expected responses to irradiance, with large increases in LMA, V _cmax and nitrogen per unit leaf area and decreases in mass-based nitrogen content. Nutrient availability modulated severely leaf N content (mass- and area-based) and mass-based maximal carboxylation rate, but not the plastic response of all these parameters to irradiance. Irradiance primarily modulated leaf structure (LMA), and secondarily nitrogen content, while nutrient availability modulated directly nitrogen content. Nitrogen content in turn had a severe impact on mass-based photosynthetic capacity. It is concluded that in young trees solely leaf structure displayed irradiance-elicited plasticity. This plasticity was not modulated by nutrient availability and was similar in a sclerophyllous and a non-sclerophyllous species.     

Sap flow measurements in young olive trees (Olea europaea L.) cv. Chétoui under Tunisian conditions

Measurements of sap flux were carried out from May 2003 to March 2004 on 6 year-old irrigated olive trees of cultivar Chétoui cultivated at 6 m × 6 m spacing in Mornag (36.5°N, 10.2°E), Northern Tunisia. The aim of the research is to evaluate the sap flux technique for its applicability with young olive trees and to estimate their water consumption under field conditions. Three thermal sensors were implanted in the trunk of three olive trees following to North (N), South-East (SE) and South-West (SW) directions. Data were analyzed following to the procedure of Do and Rocheteau (2002b) that derives from Granier (1985). In this paper, data on probe calibration, wood conductive section estimation and sap flux spatial-variability are presented and discussed. Relationships between sap flux measurements, climate and soil water status have been investigated. Results show that sap flux values vary with sensor position, soil water content and climate demand. Good agreements between sap fluxes and global radiation and reference evapotranspiration measurements were observed. Some variations were recorded under water shortage conditions. Maximum and minimum daily fluxes of 4.5 l and 41.0 l per tree were found in February 2003 and in August 2003, respectively. Maximum transpiration represented only 53% of the crop evapotranspiration as determined by the F.A.O. method.