Olive mill wastewater effects on the microbial communities as studied in the field of olive trees by analysis of fatty acid signatures

The aim of this work was to study the effects of spreading olive mill wastewater (OMW) on the soil surface of an olive grove on the soil microbial communities. Analyses of ester-linked fatty acid methyl esters (EL-FAME) were used to assess variations in the soil microbial community structure following land spreading of OMW. Our data provide evidence that agronomic application of OMW has important effects on soil microbial community. Bacteria were relatively more reduced by these treatments than fungi and actinomycetes as revealed by an increased index of fungal/bacterial FAME and actinomycetes/bacterial FAME. Specific FAME markers indicated a significant reduction in the Gram-positive bacteria. However, the relative proportion of the Gram-negative bacteria was not significantly different after agronomic application of OMW. The ratios of cyclopropyl/monoenoic precursors decreased and the total monounsaturated/total saturated fatty acids increased in the OMW amended soils, suggesting that the microbes inhabiting the control soil are more carbon limited than the OMW amended soils. The changes in the FAME pattern of the soil organisms possibly were related (i) to an altered substrate quantity, that is the availability of substrates after the treatments, (ii) the complex nature of OMW which also contains high molecular-mass recalcitrant polyphenols.     

Effect of different irrigation regimes on carbohydrate partitioning in leaves and wood of two table olive cultivars (Olea europaea L. cv. Meski and Picholine)

In this study, changes in carbohydrate composition were investigated at the end of the biological cycle of two important table olive cultivars ‘Meski’ and ‘Picholine’ grown in Tunisia under different irrigation regimes. A control treatment [100% crop evapotranspiration (ETc)] and a stress treatment (50% ETc) were considered. At the end of August, leaf water potential was measured and sugar compounds were determined in mature leaves and in the wood of fruit-bearing branches by gas chromatography. The leaf water potential increased with the stress treatment in both cultivars, but the increase was more pronounced with ‘Picholine’ than with ‘Meski’. Glucose, fructose, mannitol, sucrose, galactose and inositol were the main sugars found in the leaves and wood of olive trees. Glucose, fructose and mannitol accounted for 90% of the total soluble carbohydrate fraction. The fraction and amount of these sugars changed between cultivars and with irrigation treatment. In the control treatment, the leaves of Meski showed a high level of glucose (48%), fructose (19%) and mannitol (25%), while the leaves of Picholine showed amounts of 57, 15 and 17%, respectively. The restriction of irrigation water (50% ETc) induces an accumulation of glucose in the leaves and wood of ‘Meski’ and an accumulation of mannitol and glucose in the wood of ‘Picholine’, while the leaves showed only an increase in mannitol.     

Response to drought of two olive tree cultivars (cv Koroneki and Meski)

The effect of water deprivation on plant water status, photosynthetic gas exchange and fluorescence parameters in two different olive tree varieties (Olea europaea L. var. ‘koroneiki’, ‘Meski’) was studied. Two-year-old olive trees, grown in pots in greenhouse, were subjected to one of three drought treatments (i.e., mild, moderate and severe drought stress) and compared to control trees. Both the leaf water potential (Ψ_w) and the relative water content (RWC) of the two varieties decreased with increasing levels of drought stress. Koroneiki showed higher (less negative) values of Ψ_w and lower values of RWC than the Meski, particularly during severe drought stress.

Net photosynthetic assimilation and stomatal conductance declined with drought. This inactivation of photosynthetic activity was accompanied by changes in the fluorescence characteristics. The PSII maximal photochemical efficiency (F_v/F_m), the intrinsic efficiency of open PSII reaction centres (F_v′/F_m′), the photochemical efficiency of PSII (Φ_PSII) and the total electron flow (J_t) decreased during the development of drought stress.

The non-quenching photochimique (q_N) showed an increase in the response to water deficit. These observations are discussed in relation to the strategies developed to grow drought-resistant olive trees in arid areas.     

Change in soil properties and the soil microbial community following land spreading of olive mill wastewater affects olive trees key physiological parameters and the abundance of arbuscular mycorrhizal fungi

Olive mill wastewater (OMW) constitutes a major environmental problem for Mediterranean countries, where most of the world olive oil production takes place. The recycling of the OMW and its use as water for irrigation in agriculture, provided that its impact on soil and plant is established, is an attractive possibility for the Mediterranean countries. Investigations were performed on the influence of agronomic application of OMW (amount applied: 30, 60, 100 and 150 m³ ha^?1) in a field of olive trees on trees characters (photosynthesis, root-soluble carbohydrate and root colonisation), soil properties, and soil microbial community structure. Specific attention was paid to arbuscular mycorrhizal (AM) fungi. The soil fatty acid methyl ester (FAME) 16:1ω5 was used to quantify biomass of AM fungi and the root FAME 16:1ω5 analysis was used as index for the development of colonisation in the olive trees roots. A significant increase in organic C, C/N ratio, extractable phosphorus and exchangeable potassium was found after one year of agronomic application of OMW. The development of saprophytic fungi was significantly higher in the OMW amended soils, whereas the abundance of the soil FAME 16:1ω5, root FAME 16:1ω5, photosynthetic rates and the amount of the total root-soluble carbohydrate were decreased significantly after agronomic application of OMW. A principal component analysis (PCA) of the trees characteristics profiles showed discrimination between the nonirrigated and the OMW irrigated olive trees. These findings suggest that the altering functioning of arbuscular mycorrhizas should be considered as potential factors mediating olive trees responses to agronomic application of OMW when the OMW dose applied is higher than 30 m³ ha^?1. To our knowledge, this is the first report of alterations in the soil FAME 16:1ω5 and root FAME 16:1ω5 due to land spreading of OMW.