The olive tree: a paradigm for drought tolerance in Mediterranean climates

Olive trees (<i>Olea europaea</i> L.) are commonly grown in the Mediterranean basin where prolonged droughts may occur during the vegetative period. This species has developed a series of physiological mechanisms, that can be observed in several plants of the Mediterranean macchia, to tolerate drought stress and grow under adverse climatic conditions. These mechanisms have been investigated through an experimental campaign carried out over both irrigated and drought-stressed plants in order to comprehend the plant response under stressed conditions and its ability to recover. Experimental results show that olive plants subjected to water deficit lower the water content and water potentials of their tissues, establishing a particularly high potential gradient between leaves and roots, and stop canopy growth but not photosynthetic activity and transpiration. This allows the continuous production of assimilates as well as their accumulation in the various plant parts, so creating a higher root/leaf ratio if compared to well-watered plants. Active and passive osmotic adjustment due to the accumulation of carbohydrates (in particular mannitol and glucose), proline and other osmolytes have key roles in maintaining cell turgor and leaf activities. At severe drought-stress levels, the non-stomatal component of photosynthesis is inhibited and a light-dependent inactivation of the photosystem II occurs. Finally, the activities of some antioxidant enzymes involved in the scavenging of activated oxygen species and in other biochemical pathways increase during a period of drought. The present paper provides an overview of the driving mechanisms adopted by olive trees to face drought stress with the aim of better understanding plant-soil interactions

Characterization of microclimate and turbulent fluxes at a Mediterranean kiwi orchard covered with hail-protection net

Screens and covers are increasingly used to protect crops from pests and extreme meteorological events. Their use affects plant microclimate and physiological responses as well, but this is only partly understood, particularly when considering the interaction among the cover and the training system. This study focuses on the microclimatic effects of the use of a hail protection net and an horizontal (pergola) kiwifruit canopy. The system splits the orchard environment in three distinct layers, determining a shaded understory, a space comprised between the canopy and the net, and the atmosphere above the net. To accent the effects, we considered a high-water demanding crop-kiwifruit, in an environment characterized by high evaporative demand (Bernalda, southern Italy).Three full eddy covariance and radiative balance equipment were used to assess fluxes (carbon dioxide, water vapor, and sensible heat) in the three layers and monitor meteorological variables (air temperature and relative humidity, wind, upward and downward short and long wave radiation, carbon dioxide and water vapor concentrations). Data from a typical clear-sky summer day are considered in this paper.While the net strongly reduced wind speed, it had a modest impact on all other variables. Conversely, the tick canopy layer had a major impact on all variables, determining a highly shaded, cooler and more humid understory, with very light wind. Nevertheless, the combination of high relative humidity and presence of the net was able to reduce the net loss of longwave radiation from the canopy during night, mitigating its cooling under these conditions.The reduction in wind speed and the increase in incoming longwave radiation around the crop, observed at night time, indicate potential valuable mechanisms that may be exploited to decrease water needs and prevent late frosts in the context of climate change, where extreme climatic events are more frequent and crop water requirements continue to increase

Multifunctional peri-urban agriculture: Some ecosystem services of a sustainable olive grove

This study reports the influence of a sustainable management model which entails the recycling of urban wastewater and distribution by drip irrigation, recycling of polygenic carbon sources internal to the olive orchard (cover crops, pruning material) on yield, soil water holding capacity, soil biodiversity. Sustainable management practices were applied for a 15-year period in a 2-ha olive orchard located in an hilly peri-urban zone of southern Italy, where olive tree represents the dominant crop and has a key role inside the traditional landscape. A comparison between sustainable and conventional management (soil tillage, burning of the pruning residues, mineral fertilization, empirical irrigation) was carried out. This study suggests some guidelines of a sustainable management of peri-urban olive groves, with benefits to the whole agro-ecosystem stability and to the near town, recognizing the multifunctional role of agriculture that enhances the creation of synergies between urban and rural areas

Carbon isotope discrimination and water use efficiency in interspecific Prunus hybrids subjected to drought stress

In C3 plants, carbon isotope composition (δ13C) is influenced by isotopic effects during diffusion from the atmosphere to the chloroplasts and carboxylation reactions. This work aimed to demonstrate if δ13C of leaf soluble carbohydrates (δ13Cleaves) and of dry matter from new-growth shoots (δ13Cshoots) of Prunus plants subjected to a period of water deficit was related to water use efficiency (WUE). For this purpose, three interspecific Prunus hybrids rootstocks (6–5, 7-7 and G × N) were gradually subjected to drought and then rewatered. Soil water content (SWC) decreased from 26.1 to 9.4% after 70 days of water shortage, when plants reached values of predawn leaf water potential (LWP) ranging from −3.12 to −4.00 MPa. Gas exchange, particularly net photosynthetic and transpiration rates, differed among the three hybrids, leading to different values of WUE. After 70 days of drought, a significant δ13C increase of 5.86, 4.28 and 4.99‰ was observed in 6–5, 7-7 and G × N, respectively. Significant correlations between δ13C and other parameters (substomatal CO2/atmospheric CO2 ratio, stomatal conductance and stem water potential) were found in all hybrids. The rewatering phase caused a recovery of the physiological status of the plants. The isotope composition of δ13Cshoots was correlated with the average WUE measured during the whole experiment. δ13Cleaves and δ13Cshoots were positively related (r = 0.87; p < 0.001). The isotopic signature was a reliable screening tool to identify Prunus genotypes tolerant to drought stress. The results suggest the possibility of using δ13C as an integrated indicator of level of drought stress in plants subjected to prolonged stress conditions

Management options influence seasonal CO2 soil emissions in Mediterranean olive ecosystems

Field trials were conducted at traditional Mediterranean olive agro-ecosystems grown at two locations (Italy –IT, Greece –GR). Groves were managed for many years using sustainable (S, cover crops, compost application, mulching of pruning biomass) or conventional (C) practices (e.g., soil tillage, burning of pruning residuals). The IT grove was rainfed (RAIN) while the GR was irrigated (IRR). This study examined the seasonal variation of soil CO2 emission (Rs) to explore the effect of the management options (C, S) on Rs at both sites. The second aim was to test the hypothesis that the seasonal Rs is differentially modulated by soil temperature and moisture, namely that (i) soil moisture limits Rs when it is below the lower limit of the readily available water (RAWLLim) and (ii) soil temperature above a threshold (max_T) reduces Rs even if soil moisture is non limiting. On the whole-season basis, the mean Rs rate at the rainfed site was 2.17 ± 0.06 (SE) at CRAIN and 2.32 ± 0.06 μmol CO2 m−2 s–1 at SRAIN plot, while at the irrigated site Rs was about 3.64 ± 0.11 (CIRR) and 4.05 ± 0.15 μmol CO2 m−2 s–1 (SIRR). The seasonal oscillation of Rs was consistent across locations and partitionable in three periods according to DOY (Day of Year) interval: Phase I (DOY 20–103 –GR; 20–118 -IT), Phase II (DOY 141÷257, GR; 142–257, IT) and Phase III (DOY 291–357, GR; 286–350, -IT). Pooling all the Rs data across sites and managements, max_T was ∼ 20 °C discriminating a differential response of Rs when soil moisture was < or > RAWLLim. These differential modulations exerted by temperature and moisture were integrated into a conditional model developed with a repeated random subsampling cross-validation procedure to effectively (R2 = 0.84) predict Rs. This paper mechanistically describes the interaction of the environment (soil moisture and temperature) and the management options (S, C) under various moisture conditions on Rs and would support carbon flux accounting procedures (e.g., regulating ecosystem services) tailored to the estimation of sink/source capability of traditional olive agro-ecosystem within environmental-friendly agricultural domains

Effects of post-harvest regulated deficit irrigation on carbohydrate and nitrogen partitioning, yield quality and vegetative growth of peach trees

Abstract The aim of the present work was to evaluate the effects of regulated deficit irrigation (RDI) applied in the post-harvest stage of peach trees. The 3-year trial was carried out in Italy (N 40°20¢, E 16°48¢) on mature peach plants (cv ''Springcrest'') trained to transverse Y. From bud break to harvest, irrigation was carried out by applying 100% ET c , while from harvest to early autumn, plants were separated into three groups and subjected to different irrigation treatments (100, 57 and 34% ET c ). The decrease in soil water content caused a reduction in the values of tissue water potential and gas exchange both in 57% ET c and 34% ET c treatments. RDI determined the reduction in the growth of waterspouts and lateral shoots but did not influence the growth of fruiting shoots. During the trial, no significant reductions in crop yield and quality were observed in the 57% ET c treatment, whereas about 1,100, 1,800 and 2,500 m 3 ha -1 of water were saved in the first, the second and the third year, respectively. In the second year of the trial, the use of RDI in the post-harvest stage determined carbohydrate and nitrogen accumulation in roots, branches, shoots and floral buds. The results demonstrate that, under scarce water supply conditions, a clear benefit can be obtained through the use of RDI during the post-harvest stage. This confirms the possibility to reduce the irrigation water by applying RDI during phenological stages less sensitive to water deficit without negatively affecting peach growth and yield

Moria del kiwi: alterazione della struttura anatomica e morfologica delle radici di actinidia sottoposte a condizioni di asfissia del suolo

produzione negli ultimi anni a causa della diffusione della sindrome del declino dell’actinidia (KVDS/moria). Sintomi simili al KVDS sono stati osservati in diversi ambienti e vengono spesso associati a ristagno idrico e asfissia radicale, con conseguente marciume radicale. Nell'ambito del progetto Zespri “Water and soil management of G3 in Italy”, nel 2020 è stata avviata la sperimentazione in actinidieti colpiti da moria a Latina (Lazio, - ET0 732 mm) al fine di indagare sulle possibili cause e suggerire delle soluzioni per contrastare questa fisiopatia. Sono stati raccolti campioni di radici da piante sane e confrontati con campioni raccolti da piante affette da KVDS. Per l’analisi microscopica, le radici sono state fissate in formalina al 10%, disidratate e incluse in paraffina. Ogni singolo campione è stato sezionato in sezioni dello spessore di 5 μm e colorate con diverse metodiche. Macroscopicamente, le radici affette da KVDS sono risultate marcescenti, mostrando una perdita di rizoderma e parenchima corticale. L’analisi microscopica ha rilevato danneggiamenti del sistema radicale con rottura e decomposizione tissutale, sfaldamento di rizoderma, area corticale con evidente perdita di turgore cellulare, disfacimento iniziale della stele ed evidente distacco della corteccia dai tessuti conduttori centrali. Nel campione di controllo, le radici hanno presentato un rizoderma con spessore di 13 μm e una dimensione media di cellule del parenchima di 44,5 μm, a differenza del campione KVDS, in cui lo spessore del rizoderma, quasi assente, è stato di 8,3 μm e la dimensione media delle cellule di 34,7 μm. Dall’analisi dei gas tellurici è emerso che, conseguentemente all'insorgenza del ristagno idrico nel suolo, nei suoli attorno alle piante colpite da KVDS, il potenziale redox, parametro inversamente correlato alla concentrazione di ossigeno, è risultato essere significativamente più basso (+331 vs. +368 mV; media 0-90 cm di profondità), mentre sono state riscontrate concentrazioni più elevate di CO2 (7467 vs. 5870 ppm; media 0-90 cm di profondità), un indicatore di condizioni anossiche del suolo. Per migliorare le qualità fisica del suolo e assicurare una crescita ottimale delle radici di actinidia, sarà applicata una gestione innovativa del suolo volta ad aumentarne la sostanza organica e ridurre la compattazione, facilitando il movimento orizzontale e verticale dell'acqua nel terreno per fornire alle radici di actinidia l'ossigeno necessario per mitigare gli effetti di microrganismi potenzialmente patogeni, molti dei quali proliferano in ambienti anaerobi. Sarà, infine, ottimizzata la gestione della chioma e dell’apparato radicale per bilanciare il rapporto tra radici e foglie e migliorare la capacità delle piante di riprendersi da questo declino fisiologico

Phenolic compounds in young developing kiwifruit in relation to light exposure: Implications for fruit calcium accumulation

The interaction between light availability and the biosynthesis of phenolic compounds in fruit of kiwifruit (Actinidia deliciosa var. deliciosa, C.F. Liang et A. R. Ferguson) was investigated. Fruits were exposed either to natural light or were artificially shaded while growing on mature vines and were analysed weekly during the first 11 weeks of development. Phenols were identified and quantified by using High Performance Liquid Chromatography (HPLC). Results showed that the predominant phenolic compounds were hydroxycinnamic acids (HCAs), flavonols and the flavan 3-ol epicatechin. Calcium (Ca2+), the main mineral nutrient involved in fruit quality was also determined. Light significantly increased the accumulation of both phenols and Ca2+ into the fruit. This work expands the list of known phenolics in kiwifruit and provides a possible explanation for the seasonal pattern of Ca2+ import into the fruit. Results on light–phenol interaction being apparently beneficial for fruit Ca2+ accumulation, suggest that accurate canopy management could enhance fruit quality