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Leaf and soil samples were taken and analyzed from two mature biological olive groves (Olea europaea L., cv. 'Chondrolia Chalkidikis'), in Thessaloniki, Macedonia, Northern Greece, in order to determine the correlations between soil exchangeable cations and foliar calcium (Ca), magnesium (Mg) and potassium (K) concentrations, and the interrelations among leaf nutrients. Τhe nutritional requirements of trees for both biological groves were exclusively based on patent kali supply and nutrient recycling (via pruning material and weed cut recycling). Foliar K, Ca and Mg were positively correlated with soil exchangeable K, Ca and Mg, in the 40-60 cm layer, then in the 20-40 cm layer. Synergistic uptake mechanisms among Ca2+, Mg2+ and K+ probably exist. Leaf N was negatively correlated with foliar K, and positively with leaf Ca, Mg and manganese (Mn). Foliar P was negatively correlated with leaf Ca, Mg and Mn, while foliar Ca was positively correlated with leaf Mg and Mn. Foliar Mg was positively related with leaf Mn. High phosphorus (P) may decrease leaf Ca, Mg and Mn. Enhanced Ca may increase leaf Mg and Mn, while high Mg may also enhance foliar Mn. Finally, based on the determination of foliar nutrient concentrations, the nutritional requirements of olive trees in Ca, Mg, K, P, Fe, Zn were sufficiently (or over-sufficiently) satisfied. However, additional organic fertilization is needed, in order to achieve optimum levels of N, B and Mn (since their foliar concentrations were slightly insufficient). The correlations between leaf and soil exchangeable Ca, Mg and K, as well as among foliar nutrients should be taken into consideration, in order to achieve successful organic fertilization for mature biological olive groves, and to avoid nutritional imbalances and disorders. [ABSTRACT FROM AUTHOR]

Background: A floating system is a suitable low-cost hydroponic method for growing baby leaf vegetables. Among other, an important characteristic of the system is the use of large volume of nutrient solution which is characterized by high heat capacity. The aim of this study was to evaluate the effect of different root-zone temperatures on baby leaves of lettuce and rocket plants grown in a floating system under mild (spring) or extreme environmental conditions (summer and winter)., Results: Root-zone temperature was recorded in two tanks, one powered by a photovoltaic system and one where root-zone temperature was not controlled - this was used as a control tank. Photosynthetic parameters, yield, nutritional quality, and mineral composition were determined. In both baby leaf vegetables, during extreme weather conditions, yield was higher in the tanks with controlled root-zone temperature conditions than the control (+18.9% for rocket, and + 31.4% for baby lettuce), while quality parameters and chemical composition were not significantly affected. Stomatal conductance and net photosynthesis values were positively affected only during summer. On the other hand, control of root-zone temperature under mild weather conditions had no significant effect on baby lettuce and rocket., Conclusion: Control of the root-zone temperature could be a useful tool to improve productivity for baby lettuce and rocket crops cultivated in floating systems under extreme weather conditions. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

The olive tree ( Olea europaea L.) is an emblematic, long-living fruit tree species of profound economic and environmental importance. This study is a literature review of articles published during the last 10 years about the role of beneficial microbes [Arbuscular Mycorrhizal Fungi (AMF), Plant Growth Promoting Rhizobacteria (PGPR), Plant Growth Promoting Fungi (PGPF), and Endophytes] on olive tree plant growth and productivity, pathogen control, and alleviation from abiotic stress. The majority of the studies examined the AMF effect using mostly Rhizophagus irregularis and Glomus mosseae species. These AMF species stimulate the root growth improving the resistance of olive plants to environmental and transplantation stresses. Among the PGPR, the nitrogen-fixing bacteria Azospirillum sp. and potassium- and phosphorous-solubilizing Bacillus sp. species were studied extensively. These PGPR species were combined with proper cultural practices and improved considerably olive plant's growth. The endophytic bacterial species Pseudomonas fluorescens and Bacillus sp., as well as the fungal species Trichoderma sp. were identified as the most effective biocontrol agents against olive tree diseases (e.g., Verticillium wilt, root rot, and anthracnose).

Background: The time course of polyphenol oxidase (PPO) activity in the leaves of two olive cultivars (Picual and FS-17) irrigated with nutrient solutions differing in Mn concentration (0, 2 and 1280 micromol L(-1)) was studied under hydroponic conditions to determine whether PPO activity could be used as an early criterion of Mn status of olive plants, and to elucidate whether genotypic differences exist between the two olive cultivars studied, concerning the effect of Mn concentration on PPO activity., Results: In all the Mn treatments, PPO activity was greater in Picual than in FS-17. Under excess Mn (1280 micromol L(-1)), PPO activity gradually increased with time, starting from day 30 of the experiment in both cultivars, and this increase preceded the appearance of Mn toxicity symptoms. In contrast, in the other two Mn treatments (0 and 2 micromol L(-1)) PPO activity increased and afterwards decreased during the experiment, but the trend was not clear. In the 1280 micromol L(-1) treatment, PPO activity linearly increased (R = 0.8836 for Picual and 0.943 for FS-17) with the increase of Mn concentration in the leaves of both cultivars. In the 1280 micromol L(-1) Mn treatment, PPO activity was negatively related with Fe and Zn concentrations in the leaves, and positively in the 0 and 2 micromol L(-1) Mn treatments with the Ca, Mg and K concentrations., Conclusion: From the differential time course of PPO activity in the three Mn treatments (0, 2 and 1280 micromol L(-1)), it is concluded that periodic measurements of PPO activity in the leaves of the olive cultivars Picual and FS-17 can be used for the early detection of Mn toxicity (before the appearance of symptoms).