Photosynthetic responses to phosphorus nutrition in two-year-old maritime pine seedlings

We analyzed processes limiting photosynthesis in two-year-old, container-grown Pinus pinaster Ait. seedlings subjected to phosphorus (P) deficiency. After withholding P for 3 months, seedlings were supplied P at four relative addition rates (0, 0.005, 0.01 and 0.02 day(-1)) in a nutrient recycling system. At Weeks 12 and 22, responses of photosynthesis to CO(2) and irradiance were measured and the following parameters derived: maximal velocity of carboxylation by Rubisco, V(m); apparent quantum efficiency of electron transport, alpha maximal electron transport rate, J(m); stomatal conductance and relative stomatal limitation of photosynthesis. At Week 22, these measurements were combined with concurrent measurements of chlorophyll fluorescence to determine the quantum yield of PSII, and a theoretical partitioning of total light-driven linear electron flow between fractions used to regenerate carboxylated and oxygenated RuBP. After 12 weeks of treatment, needle P concentrations ranged from 0.04 to 0.15 x 10(-2) g g(DW) (-1), and then remained constant until Week 22. Values of J(m), alpha and V(m) increased with increasing needle P concentration (from 30 to 133 &mgr;mol m(-2) s(-1), 0.02 to 0.25 mol mol(-1) and 13 to 78 &mgr;mol CO(2) m(-2) s(-1) at the lowest and highest needle P concentrations, respectively). Under ambient conditions, net assimilation rates in P-deficient seedlings were limited by V(m) under saturating irradiance, and by J(m) under limiting irradiance, but not by triose-P regeneration. There was no detectable change in the partitioning of total light-driven linear electron flow between the fractions used for carboxylation and oxygenation. Predawn photochemical efficiency of PSII was significantly reduced in seedlings with low P concentrations. Although stomatal conductance tended to decrease with decreasing needle P concentration, relative stomatal limitation was not significantly affected. At Week 22, there was an attenuation of the effects of P nutrition on V(m) and an increase in alpha and J(m) that was probably related to cessation of growth and the seasonal decline in natural irradiance.     

Improving fruit quality,nutritional value and yield of Zaghloul dates by the application of organic and/or mineral fertilizers

A field study was carried out during the years 2007 and 2008 on 30-year old Zaghloul cultivar growing in clay soil. Mineral fertilization sources: N, ammonium nitrate or NPK, ammonium nitrate + calcium superphosphate + potassium sulphate, and organic sources: chicken manure (CM), cow dung (CD) and composted domestic refuse (CDR) were applied either alone or in combinations in order to study their influence on the yield and fruit physical and chemical quality characteristics. The results revealed that applying organic manure alone or in combination with mineral NPK increased palm yield as compared to mineral fertilization alone (NPK or N). In general, fruit weight, flesh weight, length, diameter and dry weight were increased, while fruit moisture content decreased by the application of organic manures either alone or in combination with mineral NPK as compared to the mineral N. Higher fruit TSS and total sugars content were obtained by the application of organic manures alone or in combination with mineral NPK as compared with mineral fertilization alone (NPK or N). Overall values of fruit minerals content did not differ among the different treatments. Organic manures fertilization (especially CM and CD) resulted in decreasing fruit lead, cadmium, nitrate and nitrite contents more than mineral fertilization. In general, the application of organic manures either alone or in combinations with mineral NPK did not differ from each other in their effect on yield and fruit quality.     

Development of cork oak (Quercus suber L.) seedlings in response to tree shelters and mulching in northwestern Tunisia

The need for reforestation in cork oak (Quercus suber L.) areas is challenged by difficulties. Principal among these is herbivory of young plants, vegetative competition, and slow growth rates of cork oak seedlings. We evaluated the early development of cork oak seedlings treated using tree shelters and mulching in northwestern Tunisia. We tested three tree shelter treatments (non-vented, vented, and control) to shield seedlings from animal damage and five mulch types to control competing vegetation (Italian Stone Pine, Lentisk, combination of Italian Stone Pine and Lentisk (organic mulches), gravel (inorganic mulch) and no mulch). At the end of the two-year experiment, sheltered seedlings were 89-99% taller than unshelteredseedlings and had higher numbers and lengths of shoot growth flushes. In contrast, both stem diameter growth and dry weight biomass (from samples extracted after two years) were significantly reduced inside tree shelters. Root-to-shoot ratio was not significantly different in sheltered vs. unsheltered seedlings, suggesting that tree shelters do not adversely affect this parameter. Mulching alone did not favour growth, but could be beneficial when combined with tree shelters. The combination of vented tree shelters and gravel mulch was the most effective treatment for promoting diameter, height and stem volume growth.     

Phenotypic responses of the wild wheat relative Aegilops geniculata Roth and wheat (Triticum durum Desf.) to experimentally imposed salt stress

In order to study the salt effect on the wild wheat and durum wheat, three accessions of Aegilops geniculata L. from Ain zana, Zaghouan, and Sbitla and one variety of wheat (Triticum durum L.) have been grown in the INRAT green house and treated with different salt concentrations. The morphological, phenological and yield characters have been measured for each plant and analyzed using SAS software. This study has shown a high degree of variation of these characters mainly related to geographical origin. It was observed also that Sbitla accession was less affected by the imposed salt stress than all the others while Ain zana was the most affected one.     

Genetic diversity in Tunisian olive accessions and their relatedness with other Mediterranean olive genotypes

Eighty-four olive accessions obtained from the National Conservatory of Boughrara-Sfax (Tunisia), previously evaluated for morphological traits, were analysed with 47 random amplified polymorphic DNA (RAPD) markers. They were compared with other olive genotypes originated from Eastern or Western Mediterranean. The highest and lowest similarities between genotypes, estimated by simple matching algorithm, were 0.98 and 0.40, respectively. A dendrogram based on Ward's method and a factorial correspondence analysis (FCA) showed that most of Tunisian accessions are closely related to olive genotypes originating from the Eastern Mediterranean and some are clustering with genotypes originated from the Western Mediterranean. These findings suggested multiple and complex origin of Tunisian olive. A comparative study between a previous morphological analysis and current RAPD assay was carried out and discussed.     

Characteristics and mineralogy of desert alluvial soils: Wadi Zegrir,Northern Sahara of Algeria

Few studies on the characteristics and mineralogical trends of the soils in the Sahara Desert have been reported in the literature. This work aims at studying the morphology, the classification, and the mineralogy of desert alluvial soils of the Mzab region in the Northern Sahara, Algeria. Morphological and analytical studies carried out on fourteen pedons of wadi Zegrir over a range of elevations (250–850?m) indicate that the soils are sandy to silty clay, nonsaline (electrical conductivity, EC?相似文献   

Cadmium Accumulation and Tolerance of Two Salix Genotypes Hydroponically Grown in Presence of Cadmium

Abstract

In general, according to previous studies, pioneer species do not require arbuscular mycorrhizal fungi (AMF) to increase their growth and survival in tropical systems. The aim of this study was to determine the dependence response to AMF of Heliocarpus appendiculatus, a pioneer species, at different phosphorus (P) levels. In a greenhouse experiment, H. appendiculatus seedlings were grown in pots with a sterile vermiculite-sand mixture (1:1). Two sets of pots were set up: One set was inoculated (150 spores per pot) with indigenous AMF from a tropical rain forest at “Los Tuxtlas” (Veracruz, Mexico); the other set was not inoculated. To each set, 0, 0.02, 0.2, and 2 g L^?1P was added. All pots were watered with 250 mL of nutrient solution. Mycorrhizal plants showed a higher total dry weight and relative growth rate in 0.02 g L^?1P concentration, while nonmycorrhizal plants responded positively at 0.2 g L^?1P; a decrease in plant responses at higher P levels was observed in both treatments. H. appendiculatus showed to have higher relative dependence at lower P concentration (≈50%). As levels of P increased, mycorrhizal colonization decreased. Successful growth of pioneer species during succession process may be improved if there is AMF content in soils, prior to disturbance.     

Measuring reactive metal in soil: a comparison of multi‐element isotopic dilution and chemical extraction

The isotopically exchangeable metal pool (E‐value) of zinc (Zn), cadmium (Cd) and lead (Pb) were simultaneously measured, using stable isotope dilution, in soils contaminated by Pb/Zn mining activities and varying in properties likely to affect metal reactivity, including pH, organic matter content, metal concentration and land use. E‐values were compared with single and sequential extraction schemes. Results showed a wide range of metal reactivity (approximately 1–100% of total) depending on the extent of contamination and on the prevailing soil conditions. Across the range of soils, the E‐values showed no consistent correspondence to any single chemical extraction procedure (EDTA, DTPA and HNO₃) although there was reasonable agreement with the extractants 0.05 m EDTA and 0.43 m HNO₃ in acidic organic soils. Extraction with 0.005 m DTPA substantially under‐estimated the isotopically exchangeable metal content. E‐values corresponded reasonably well with the exchangeable metal (fraction 1 (F1) of the sequential extraction procedure) in calcareous soils but relatively poorly and inconsistently with F1–F2, F1–F3 or F1–F4 in acidic‐neutral soils. Operational aspects associated with determination of multi‐element E‐values are discussed.     

Essential oil composition of Hypericum perfoliatum L. and Hypericum tomentosum L. growing wild in Tunisia

The essential oils obtained by hydrodistillation from the aerial parts of Tunisian native Hypericum perfoliatum L. (sect. Drosocarpium Spach.) and Hypericum tomentosum (sect. Adenosepalum Spach.) were analyzed by GC and GC–MS. Thirty-two compounds were identified in the essential oils of H. perfoliatum with α-pinene (13.1%), allo-aromadendrene (11.4%), germacrene-D (10.6%), n-octane (7.3%), α-selinene (6.5%) and β-selinene (5.5%) as main constituents. Sixty-seven components were identified in the oil of H. tomentosum with menthone (17.0%), n-octane (9.9%), β-caryophyllene (5.3%), α-pinene (5.2%), lauric acid (4.1%) and β-pinene (3.7%) as the most abundant components. Both oils were characterized by the presence of many components which could have numerous applications in food, pharmaceutical and perfume industries.