Mohamed Braham

Nondestructive determination of nitrogen and chlorophyll content in olive tree leaves and the relation with photosynthesis and fluorescence parameters

For Tunisian olive tree orchards, nitrogen deficiency is an important nutritional problem, in addition to the availability of water. Establishment of relationships between nutrients such as nitrogen and ecophysiological parameters is a promising method to manage fertilisation at orchard level. Therefore, a nitrogen stress experiment with one-year-old olive trees (Olea europaea L. ‘Koroneiki’ and ‘Meski’) was conducted with trees respectively subjected to four nitrogen supply regimes (23.96 meq l−1, 9.58 meq l−1, 4.79 meq l−1 and 0 meq l−1 NO3−1).The current paper focuses on the use of the SPAD-502 portable chlorophyll (Chl) meter, a nondestructive method for fertilisation management under nitrogen stress conditions of olive trees. Maximum net photosynthetic assimilation rates, chlorophyll fluorescence parameters and the SPAD Chl index were therefore measured simultaneously and the Chl and nitrogen content of the leaves were analysed. Significant correlations were established in the olive tree leaves between SPAD-502 readings on the one hand and Chl content, nitrogen content, photosynthetic assimilation rate, and Chl fluorescence parameters (ΦPSII and ETR) on the other hand.

Nutrient Stress, Ecophysiological, and Metabolic Aspects of Olive Tree Cultivars

ABSTRACT This research, aimed at evaluating stress on the olive tree, utilized cultivars ‘Meski’ and ‘Chetoui’ in regards to the removal of major elements such as nitrogen (N), phosphorus (P), magnesium (Mg), and potassium (K). The experiment was conducted under greenhouse conditions in hydroponics culture. Measurements of leaf area showed a non-substantial and weak effect due to phosphorus, potassium, or magnesium deficiency compared to nitrogen. The growth analysis of dry matter showed an early depressive effect of nitrogen deficiency and a similar, but less important effect concerning phosphorus. The induced nutritional stresses showed an important increase in stomata resistance, caused primarily by nitrogen or potassium deficiency, accompanied by a reduction of chlorophyll concentration, which resulted from the removal of phosphorus, magnesium, and mainly nitrogen supply. Remarkable starch synthesis and storage was also revealed following nitrogen deficiency, but it was very weak after the suppression of magnesium, which may provoke a weakening of growth and development of these plants.

Fruit thinning affects photosynthetic activity, carbohydrate levels, and shoot and fruit development of olive trees grown under semiarid conditions

Olive (Olea europaea L.) production is marked by annual oscillations as trees alternate from high to low crop loads in successive years. Gas exchanges and carbohydrate content of leaves and fruits in olive tree (O. europaea cv. Besbassi) were monitored at pit hardening and fruit ripening. After fruit set, three crop loads were applied (100%, 50% and 25% of the initial fruit load) by manual thinning. Severe fruit thinning reduced photosynthesis, stomatal conductance and intercellular CO2 concentration. Crop load had no significant effect on chlorophyll fluorescence parameters. The reduction of 75% of the initial crop load favoured the accumulation of starch in leaves and soluble sugars in leaves and fruits. The reduction in initial fruit load had a significant positive effect on the current years shoot elongation and on inflorescence number the following spring. To increase the fruit size, a strong thinning (75%) was necessary, which coincided with the highest shoot vigour. Moderate thinning (50%) hardly affected leaf carbohydrate content and fruit size, but photosynthetic capacity was only limited at fruit ripening.

Effects of Nitrogen Deficiency on Leaf Chlorophyll Fluorescence Parameters in Two Olive Tree Cultivars ‘Meski’ and ‘Koroneiki’

Effects of nitrogen (N) deficiency on photosynthetic carbon dioxide (CO2) assimilation, photosystem II (PSII) photochemistry and photoinhibition were investigated in young trees of two olive cultivars ‘Meski’ and ‘Koroneiki’ grown in a greenhouse under controlled conditions. The trees were subjected to four different levels of N supply. N deficient trees had a significantly smaller CO2 assimilatory capacity, but showed little changes in maximum quantum efficiency of PSII photochemistry. However, modifications in PSII photochemistry induced by N deficiency were observed. This was reflected in decreases in quantum yield of PSII electron transport (ΦPSII) and efficiency of excitation energy capture by open PSII reaction centres (Fv’/Fm’) and in an increase in non-photochemical quenching (NPQ). These results suggest that modifications in PSII photochemistry might be a mechanism to down-regulate photosynthetic electron transport so that production of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). would be in equilibrium with the decreased demand in the Calvin cycle in the N deficient trees. Therefore, both CO2 assimilation rate and total electron flow (Jt) with its compound electron flows devoted to either carboxylation (Jc) or oxygenation (Jo) can be considered as useful tools to assess the N nutrition status of the trees. Clear relationships were found between Amax and the nitrogen nutrition index (NNI) on the one hand, and between Jt and NNI on the other hand. The results demonstrate that ‘Meski’ is more efficient than ‘Koroneiki’ when subjected to N deficiency.

Ecophysiological, Nutritive and Growth Responses of Two Olive Tree Cultivars (Olea Europaea L. ‘Chemlali’ and ‘Koroneiki’) Under Salt Stress

Tunisia’s olive resources are estimated at over 83 million of olive trees, grown on 1.83 million ha. Despite the immense potential for olive production, Tunisia is known as an underprivileged country in water resource and water scarcity is evident in certain regions. In the long-term, this situation could become more and more exacerbated, considering the increased risk of aridity. Plants grown in these regions are often exposed to a long period of drought and harsh environmental conditions, which affects plant growth and, hence, agricultural development. In order to increase productivity of olive trees the intensification of the olive tree sector in Tunisia is a necessity. The irrigated olive orchards in Tunisia cover about 75000 ha in 2016.

Methods to Estimate Water Use Efficiency (WUE) of Two Olive Tree Cultivars ( Olea europaea L. cv Koroneiki and Chemlali) Under Water Restriction Conditions

Nowadays, due to climate change conditions, water scarcity in the Mediterranean basin is the major problem. Increasing water productivity is crucial to improve the sustainable development of olive tree, the most prominent crop in the Mediterranean basin. Chemlali plants valorizes better low quantities of water (T50%) rather than high quantities (T100%). Chemlali T50% plants increase their plant water use efficiency by 20% compared to T100% plants. Chemlali cultivar had a better capability to cope with low quantity of water and the combination Chemlali-T50% Available Water Content (AWC) water treatment was the most efficient.

Effects of two drip-irrigation regimes on sap flow, water potential and leaf photosynthetic activity of mature olive trees

We evaluated the potential of sap flow values estimated from records with the heat dissipation method for irrigation in an olive orchard (Olea europaea L, cv. Meski) near Enfidha, Tunisia. Trees were cultivated at 7 × 7 m spacing. Two drip irrigation treatments were imposed using the sap flow and the FAO methods. The two treatments were irrigated by 100% of crop evaptranspiration (ETc). T1: ETc measured by the sap flow method and T2: ETc estimated by the FAO method. Sap flow, leaf and stem water potentials, leaf photosynthetic activity, stomatal conductance and transpiration rate were recorded in representative trees from both treatments, during the full irrigation season from April to August. Results showed that the irrigation dose calculated from T2, based on FAO method compared to the T1, based on sap flow decreased by about 25%. Under T1 irrigation scheduling strategy, the daily transpiration decreased by 20% and consequently the water potentials were decreased significantly. Infect, olive trees under T1 were moderately stressed and subsequently leaf gas exchange parameters were affected by about 15%.