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Earthworms are “ecosystem engineers” that improve soil water and nutrient content, soil macroporosity, and aeration, and provide suitable habitats for microbial populations. This study aimed at defining if the presence of epigeic earthworms (Eisenia sp.) affected the growth and development of two plant species (Brassica oleracea and Vicia faba) via the modifications of soil chemico-physical properties. A mesocosm experiment, in which plants were grown outdoors for 4 months with or without earthworms, was performed. The two plant species were selected based on their different habitus and root architecture and morphology. Soil macroporosity (Msoil) and water holding capacity (WHCsoil) were determined. Earthworm-driven bioturbation (Bsoil) was measured by filling mesh bags with artificial soil. Earthworm abundance and biomass, together with plant morphometric parameters (root and leaf morphology by imaging and microscope techniques), were measured at the end of the trial. The presence of earthworms increased Msoil (on average +16%) and WHCsoil (on average +9%) and this was accompanied by a remarkable degree of Bsoil. In most of the cases, earthworms enhanced plant growth in the two plant species studied, with a significant positive influence on the majority of the shoot and root traits. A significant increase of stomatal density (on average +24%) occurred in the leaves of both the plant species in the presence of earthworms. Our results confirmed the hypothesis that bioturbation by Eisenia sp. had a significant positive effect on plant growth, independently from the plant species cultivated, and that these growth-promoting effects were mediated by changes in soil chemico-physical parameters. By taking into account the essential role of earthworms in maintaining healthy soils and the vegetation they support, soils can become more resilient against environmental perturbations and climate change.

Background: Drought, N deficiency and herbivory are considered the most important stressors caused by climate change in the agro- and eco-systems and varied in space and time shaping a highly dynamic and heterogeneous stressful environments. This study aims to evaluate the to-mato morpho-physiological and metabolic responses to combined abiotic and herbivory at dif-ferent within-plant spatial levels and temporal scales. Methods: Leaf-level morphological, gas exchange traits and VOC profiles were measured in to-mato plants exposed to N deficiency and drought, T. absoluta larvae and their combination. Ad-ditive, synergistic or antagonistic effects of the single stress when combined were also evaluat-ed. Morpho-physiological traits and VOC profile were also measured on leaves located at three different positions along the shoot axes. Results: The combination of the abiotic and biotic stress has been more harmful than single stress with antagonistic and synergistic but non-additive effects for the morpho-physiological and VOC tomato responses, respectively. Combined stress also determined a high within-plant phenotypic plasticity of the morpho-physiological responses. Conclusions: These results suggest that the combined stress in tomato determined a “new stress state” and a higher within-plant phenotypic plasticity which could permit an efficient use of the growth and defence resources in the heterogeneous and multiple stressful environmental condi-tions.

Understanding how changes of any origin interact with the structure and survival of entire populations is very important for the protection and conservation of threatened, rare and/or endemic species. In this study, structure and population dynamics of Salvia ceratophylloides Ard., a precious endemic species, belonging to the subgenus Sclarea (Moench) Benth., section Plethiosphace Benth. (Lamiaceae) exclusive to the suburban environments of Reggio Calabria (Southern Italy), was analysed. Interactions between this species and its different growth habitats were examined. Moreover, the disturbance factors which directly affect the demographic viability of the species, influencing its growth, reproduction and distribution in its distribution area were identified. From 2019 to 2021, a census by counting individuals of all the known stations, recorded according to a specific protocol, was carried out. The recorded data were statistically analysed and compared with those of the phytosociological surveys carried out using the Braun-Blanquet method and summarised in phytosociological classes, in accordance with the hierarchical floristic classification system of vascular plant communities, accepted at national and European levels. The structure of the different populations was also related to the different threat factors that afflict S. ceratophylloides. It was observed that the most structured populations of S. ceratophylloides were found in natural and semi-natural environments where the anthropogenic disturbance was minor, while populations with an irregular structure were found in sites exposed to disturbances of various origins. The different phytosociological classes do not interact directly on population structure. The most important factors affecting structure and distribution are disturbances of various origins, in particular anthropogenic and phytosanitary disturbances. In order to keep populations balanced and stable over time, it would be useful to adopt conservation measures for the species and the habitat in which they live, with practical solutions for the following: (a) to limit infestations by insects that parasitize stems and seeds; (b) to prevent mowing, fires, grazing and the introduction of invasive alien species.

The investigation of the adaptive strategies of wild plant species to extreme environments is a challenging issue, which favors the identification of new traits for plant resilience. We investigated different traits which characterize the root-soil interaction of Parietaria judaica, a wild plant species commonly known as “Pellitory-of-the-wall”. P. judaica adopts the acidification-reduction strategy (Strategy I) for iron (Fe) acquisition from soil, and it can complete its life cycle in highly calcareous environments without any symptoms of chlorosis. In a field-to-lab approach, the microbiome associated with P. judaica roots was analyzed in spontaneous plants harvested from an urban environment consisting in an extremely calcareous habitat. Also, the phenolics and carboxylates content and root plasticity and exudation were analyzed in P. judaica plants grown under three different controlled conditions mimicking the effect of calcareous environments on Fe availability: results show that P. judaica differentially modulates root plasticity under different Fe availability-impaired conditions, and that it induces, to a high extent, the exudation of caffeoylquinic acid derivatives under calcareous conditions, positively impacting Fe solubility.

Salvia ceratophylloides (Ard.) is an endemic, rare, threatened plant species recently rediscovered in very few individuals in two different sites of South Italy. The study of within-plant variation more than among-plant one is fundamental to understand the plant adaptation to the local conditions, especially in rare species, and consequently to preserve plant biodiversity. Here, we reported the variation of the morpho-ecophysiological and metabolic traits between the sessile and petiolate leaf of S. ceratophylloides plants in two different sites for understanding the adaptation strategies for surviving in these habitats. The S. ceratophylloides individuals exhibited different net photosynthetic rate, maximum quantum yield, light intensity for the saturation of the photosynthetic machinery, stomatal conductance, transpiration rate, leaf area, fractal dimension and some VOCs between the different leaf types. This within-plant morpho-physiological and metabolic variation was depended on the site. These results provide empirical evidence of sharply within-plant variation of the morpho-physiological traits and VOCs profiles in S. ceratophylloides which could be because of adaptation to the local conditions.

Fine root-soil interactions fundamentally affect the terrestrial carbon (C) cycle and thereby ecosystem feedbacks to climate change [...]

Many fruit tree species develop symbioses relationships with mycorrhizal fungi by which they improve their efficiency in water and nutrient uptake and, in turn, increase their vegetative growth and productivity, particularly under stressful environments. These benefits origin from the effects that mycorrhizal determined on the root architecture, morphology and physiology. Usually, few attentions has been devoted to the tree root structure and function, especially, in fig plants during their growth phase in the nursery. Recently, several root traits or phenes have been reported as fundamental for the root functions such as the root length ratio (plant’s potential for the exploitation of soil resources); root mass ratio (allocation traits); the root fineness and tissue density (structural traits); the root very fine, fine and coarse (functional traits). Aim of the study was to test the effects of an arbuscular mycorrhizal fungi (AMF) on the root architecture traits of self-rooted cuttings of two fig (Ficus carica L.) cultivars: Dottato and Natalese. The root architecture traits were evaluated by image analysis system (WinRHIZO). Single root traits and rooting architecture models were statistically tested by univariate and multivariate analysis, respectively. This study confirmed that also the Ficus carica was positively responsiveness to the mycorrhizal inoculation but with cultivar-dependent patterns. Further, the fig with coarse root architecture is more responsive to the fungi inoculation and the AMF induced different root architecture models in Natalese and Dottato suggesting diverse root strategies for exploiting the soil resources.

Plants are continually exposed to multiple stresses, which co-occur in nature, and the net effects are frequently more nonadditive (i.e., synergistic or antagonistic), suggesting &ldquo, unique&rdquo, responses with respect to that of the individual stress. Further, plant stress responses are not uniform, showing a high spatial and temporal variability among and along the different organs. In this respect, the present work investigated the morphological responses of different root types (seminal, seminal lateral, primary and primary lateral) of maize plants exposed to single (drought and heat) and combined stress (drought + heat). Data were evaluated by a specific root image analysis system (WinRHIZO) and analyzed by uni- and multivariate statistical analyses. The results indicated that primary roots and their laterals were the types more sensitive to the single and combined stresses, while the seminal laterals specifically responded to the combined only. Further, antagonistic and synergistic effects were observed for the specific traits in the primary and their laterals and in the seminal lateral roots in response to the combined stress. These results suggested that the maize root system modified specific root types and traits to deal with different stressful environmental conditions, highlighting that the adaptation strategy to the combined stress may be different from that of the individual ones. The knowledge of &ldquo, unique or shared&rdquo, responses of plants to multiple stress can be utilized to develop varieties with broad-spectrum stress tolerance.

This study assesses the reliability of a non-destructive method for determining the in situ distribution of tree coarse roots within a scaled distance 6-fold the DBH by comparing the results with the actual 3D root architecture revealed by invasive methods. The root architecture of 22-year-old olive trees was determined non-destructively with a Root Detector device (Fakopp Enterprise Bt) using sonic speed and directly by a 3D digitizer (Fastrak, Polhemus) after soil removal. The radial and vertical distributions of the coarse root biomass and diameter in the soil as determined by the 3D digitizer were correlated with the root map detected by sonic speed. A highly significant correlation was observed between the coarse root biomass distribution and the sonic speed within 30 cm of soil depth, but this correlation decreased with increasing distance from the trunk, up to 120 cm. No correlations were observed between sonic speed and root diameter. The Root Detector was able to map the coarse roots of the olive tree in the soil environment, but only under certain conditions. First, root detection was more efficient within 30 cm of soil depth, provided that more than 35% of the total biomass of lateral roots occurs within this depth range. Second, the distance of 120 cm from the trunk, scaled as 6-fold the DBH, may be considered the threshold over which the sonic speed and the detection of roots markedly decreased. Third, Root Detector technology is unable to detect root size in terms of geometric parameters such as root diameter.

This study was aimed to investigate the effects of two different concentrations of NaCl on germination traits of seeds of four sugar beet (Beta vulgaris L.) hybrids, including a commercial variety. The seeds were sown in Petri dishes with two levels of NaCl (60 and 180 mM) and the control (0 mM NaCl). Germination and water content and electrical conductivity, as a result of solute leakage from seeds, were analyzed through linear and nonlinear equations. Results showed that the commercial variety germination seemed to be more sensitive to a moderate salt concentration (60 mM NaCl) which, conversely, was not detrimental to water uptake and germination rate in the other hybrids. Adverse effects were more evident at higher salt level (180 mM NaCl), although to a different extent, in all hybrids and for most of the parameters evaluated. This study demonstrated that salinity could induce numerous disorders in sugar beet seeds during the germination process, the seriousness of which depended on both the salt level and genotype.

In the biosynthesis of terpenoids, the ample catalytic versatility of terpene synthases (TPS) allows the formation of thousands of different molecules. A steadily increasing number of sequenced plant genomes invariably show that the TPS gene family is medium to large in size, comprising from 30 to 100 functional members. In conifers, TPSs belonging to the gymnosperm-specific TPS-d subfamily produce a complex mixture of mono-, sesqui-, and diterpenoid specialized metabolites, which are found in volatile emissions and oleoresin secretions. Such substances are involved in the defence against pathogens and herbivores and can help to protect against abiotic stress. Oleoresin terpenoids can be also profitably used in a number of different fields, from traditional and modern medicine to fine chemicals, fragrances, and flavours, and, in the last years, in biorefinery too. In the present work, after summarizing the current views on the biosynthesis and biological functions of terpenoids, recent advances on the evolution and functional diversification of plant TPSs are reviewed, with a focus on gymnosperms. In such context, an extensive characterization and phylogeny of all the known TPSs from different Pinus species is reported, which, for such genus, can be seen as the first effort to explore the evolutionary history of the large family of TPS genes involved in specialized metabolism. Finally, an approach is described in which the phylogeny of TPSs in Pinus spp. has been exploited to isolate for the first time mono-TPS sequences from Pinus nigra subsp. laricio, an ecologically important endemic pine in the Mediterranean area.

Rhizosphere microbiomes are influenced by abiotic stresses, but we know a little about their response to combinations of stresses. In this study we tested: (i) if drought and heat stress influence the maize rhizosphere microbial community; (ii) if the combination of drought and heat has a different outcome compared to a single stress; (iii) if rhizosphere microbiota clusters according to root class and root zone. We setup a microcosm system using maize as model plant. We exposed plants to drought, heat stress and their combination, and used 16S amplicon-sequencing to reconstruct bacterial communities of different root classes (crown and primary) and root zones (apical, sub-apical and basal). We found both drought and heat affect the structure of rhizosphere bacterial communities. The combination of these stressors also influenced the structure of rhizosphere microbial communities, but this effect did not differ compared to the single stresses. Interestingly, we found differences in microbial communities inhabiting the rhizosphere of crown and primary roots in the control treatment, but this difference disappeared once stresses were applied. Stress also lead to an increased abundance of beneficial organisms.

Biochar produced from pellet obtained from grapevine (GV) and sunflower husk (SFH) at different temperature (400 and 500 °C) were studied by pyrolysis batch reactor. Chemical and physical evolution of biomass under pyrolysis conditions was determined and products characterization was evaluated, including main organic components in gaseous stream. The Biochar is a “porous carbonaceous solid” produced by thermochemical conversion of organic materials in an oxygen depleted atmosphere, which has physiochemical properties suitable for the safe and long-term storage of carbon in the environment and, potentially, soil improvement. Results have shown a decrease in yield as an increase in temperature. The objective of this work is to improve the acknowledgment for the alternative use of the biochar gained from agro-forestry biomass residuals grapevine and sunflower husks by means of modern chemical and physical characterization tools.

Roots encounter cinnamic acid and its hydroxylated derivatives that are commonly found in soils. However, root systems consist of different root types with different morphological and physiological characteristics. Very little is known about the responses and adaptation mechanisms of the root types to cinnamic acid and its hydroxylated derivatives. In this study, the morphological and physiological responses of different maize root types exposed to different concentrations of t-cinnamic, ferulic, caffeic or p-coumaric acids were investigated. The results showed that the effects of allelochemicals were dependent on concentration, chemical structure, root type and process considered. In particular, t-cinnamic acid was characterized by higher allelopathic activity when compared with its derivatives, where a hydroxyl or methyl groups were present in aromatic ring. Among root types it was possible to delineate the following tolerance hierarchy: primary > seminal > nodal > lateral of the primary = lateral of the seminal roots. Moreover, primary and seminal roots showed a different strategy to cope the chemical stress by either increasing or decreasing specific root length. Finally, an electrophysiological approach identified an involvement of proton pump activity and consequently a decrease in nitrate uptake.

Common bean (Phaseolus vulgaris) is cultivated throughout Latin America and Africa, and for the European community, in Italy and Spain, areas are mainly subjected to drought stress which is predict to worsen by regional climatic models. The aims of this work were to identify the drought-tolerant and drought-sensitive bean landraces using drought tolerance and phenotypic plasticity indexes and to dissect the root morphological and 2D-architecture traits related to drought tolerance. Thirty-one landraces from diverse gene pools and areas of the Calabria region (South Italy), with different habits and morphological traits, were screened for drought tolerance in a hydroponic system. Root phenotyping was conducted by image analysis. Drought tolerance screening identified two landraces as drought tolerant and sensitive, respectively. Under drought stress, the drought-tolerant landrace exhibited several interesting root traits such as a higher root length, surface area and, above all, the fineness of the whole root systems and, with emphasis, of the higher order roots. Drought stress induced plastic root responses in both bean landraces but with contrasting patterns. The drought-tolerant landrace exhibited a dimorphic-rooted strategy, which could be included in future utility for bean breeding programmes in drought-prone environments.

The in situ 3D root architecture of Olea europea was described by a semi-automatic 3D digitizing approach, which permitted the estimation of the biomass and carbon content of coarse roots in the soil environment. Coarse roots, the skeleton of the root system, are of primary importance for soil exploration and plant anchorage and only recently have been recognized as playing a major role in “long-term” carbon sequestration. Despite this role, the 3D architecture of coarse roots represents a gap in knowledge on the biomass and carbon allocation within the root system and, consequently, below-ground carbon sequestration capacity. Using a semi-automatic 3D digitizing approach (3 Space Fastrak plus Long Ranger), the 3D distribution in the soil environment of coarse root biomass and C content and how these parameters were affected by manual and mechanical (trunk shaker) harvesting methods were quantified in a high-density olive orchard. The below-ground C content at stand level was estimated to be 11.93 Mg C ha−1 and distributed at deeper soil layers (45–60 cm) in the form of first- and second-order branching roots. The present study also revealed that the mechanical harvesting method significantly increased both the angle of growth (0° = vertically downwards) of first-order lateral roots and the stump biomass, but neither the biomass allocation nor the C content was increased within the first three branching orders.

Coumarin is one of the simplest plant secondary metabolites, widely distributed in the plant kingdom, affecting root form and function, including anatomy, morphology and nutrient uptake. Although, some plant responses to coumarin have been described, comprehensive knowledge of the physiological and molecular mechanisms is lacking. Maize seedlings exposed to different coumarin concentrations, alone or in combination with 200 μm nitrate (NO3- ), were analysed, through a physiological and molecular approach, to elucidate action of coumarin on net NO3- uptake rate (NNUR). In detail, the time course of NNUR, plasma membrane (PM) H+ -ATPase activity, proton pumping and related gene expression (ZmNPF6.3, ZmNRT2.1, ZmNAR2.1, ZmHA3 and ZmHA4) were evaluated. Coumarin alone did not affect nitrate uptake, PM H+ -ATPase activity or transcript levels of ZmNRT2.1 and ZmHA3. In contrast, coumarin alone increased ZmNPF6.3, ZmNAR2.1 and ZmHA4 expression in response to abiotic stress. When coumarin and NO3- were concurrently added to the nutrient solution, a significant increase in the NNUR, PM H+ -ATPase activity, together with ZmNAR2.1:ZmNRT2.1 and ZmHA4 expression was observed, suggesting that coumarin affected the inducible component of the high affinity transport system (iHATS), and this effect appeared to be mediated by nitrate. Moreover, results with vanadate, an inhibitor of the PM H+ -ATPase, suggested that this enzyme could be the main target of coumarin. Surprisingly, coumarin did not affect PM H+ -ATPase activity by direct contact with plasma membrane vesicles isolated from maize roots, indicating its possible elicitor role in gene transcription.

The identification of morpho-physiological traits related to drought tolerance and high yield potential is a challenge when selecting sugar beet genotypes with greater tolerance to water stress. In this paper, root morphological parameters, antioxidant systems, leaf relative water content (RWC) and H+-ATPase activity as key morpho-physiological traits involved in drought tolerance/susceptibility of sugar beet were studied. Genotypes showing a different drought tolerance index (DTI) but a similar yield potential, under moderate (−0.6 Mpa) and severe (−1.2 MPa) water stress, were selected and their morpho-physiological traits were investigated. The results showed a wide genetic variation in morpho-physiological parameters which demonstrated the different adaptive strategies under moderate and severe drought conditions in sugar beet. In particular, an efficient antioxidant system and redox signalling made some sugar beet genotypes more tolerant to drought stress. The alternative strategy of other genotypes was the reduction of root tissue density, which produced a less dense root system improving the axial hydraulic conductivity. These results could be considered as interesting challenge for a better understanding of the drought tolerance mechanisms in sugar beet.

Eighty-seven Phaseolus vulgaris landraces, still cultivated in Calabria (Italy), were investigated in order to study the patterns of common bean genetic diversity in this region, to better understand the evolutionary development of beans in Europe and to properly manage these genetic resources. Four American accessions and five Italian varieties were also included. Different markers, such as 12 microsatellites, seed traits, phaseolins and 100-seed weight were combined with different statistical approaches. For each microsatellite, expected (H e ) and observed (H o ) heterozygosities, polymorphism information content (PIC), probability of identity (PI) and homozygosity were calculated. Furthermore, in Calabrian group of bean landraces, total (N a ) and private (N pa ) number of alleles, observed (H o ), expected heterozygosities (H e ) and allelic richness (AR) were calculated. Genetic distances among landraces were estimated using Nei’s coefficient and a cluster analysis using the UPGMA algorithm was performed. The results clearly indicated that: (1) Calabrian germplasm showed a high level of diversity (H e = 0.595); (2) Mesoamerican and Andean gene pools were clearly distinguished in Calabrian germplasm, with the Andean gene pool predominating (83 %); (3) Calabrian landraces were largely hybridized within and between the gene pools. A model-based approach, using the STRUCTURE software, was adopted. Six groups, including 4 of Andean origin and one of Mesoamerican origin were identified. Even more interesting, a small group (8 %) showed a distinct genetic structure, in which interspecific hybridizations with runner bean (Phaseolus coccineus L.) could have occurred. Nevertheless, a relatively high proportion of Calabrian bean landraces (12.6 %) was derived from intra and interspecific hybridizations.

The high pH and electrical conductivity values of mature compost from solid wastes of citrus processing plants can severely restrict its use as a constituent of growing media in soilless cultivation. In the present work, addition of phosphoric acid was used as a chemically feasible strategy to lower the pH of mature orange waste compost. The growing media for testing were prepared by mixing commercial perlite (Agrilit®3) with increasing dosages (0, 7.5, 15 and 30%, by vol) of orange waste compost after a pH adjustement to 6.5-6.7 with the addition of phosphoric acid. In all potting mixtures the electrical conductivity never exceeded 0.7 dS m−1. Plant growth responses (i.e. fresh and dry biomass, together with root morphological parameters such as root length, surface area, fineness and tissue density) were assessed on tomato and zucchini seedlings grown in potting mixtures under greenhouse conditions for 40 and 20 days, respectively. The results indicated that orange waste compost induced species-specific...

The spatial variability of the nitrate (NO3-) uptake along the maize primary root axis was investigated at physiological and molecular levels. Net NO3- uptake rate (NNUR) and its kinetic parameters, together with the gene expression of a high-affinity NO3- transporter (NRT2.1), were evaluated. The activity and the expression of plasma membrane H+-ATPase (PM H+-ATPase), key enzyme in plant nutrition, were also analysed. The NNUR showed a heterogeneous spatial pattern along the root, where the regions closer to the root tip early exhibited higher capacity to absorb NO3- than the basal regions, because of a higher maximum NNUR and faster induction of the inducible high-affinity transport system (iHATS), the presence of the high-affinity transport system (HATS) also at external NO3- concentrations >100 µm and an improved NO3- transport because of lower Km values. ZmNRT2.1 transcript abundances were not spatially correlated with NNUR, suggesting that post-translational effects or NAR2 protein co-expression could be involved. By contrast, PM H+-ATPase displayed a similar spatial–temporal pattern as that of nitrate uptake, resulting in higher activity in the root tip than in the basal regions. Increased activities of the enzyme after nitrate supply resulted in enhanced expression of MAH3 and MAH4, PM H+-ATPase subfamily II genes, while MAH1 was not expressed.

Composting represents a valuable strategy for recycling orange processing waste for use as soil conditioner, provided compost maturity is duly evaluated. Following a 5-month aerobic bioconversion, orange waste reached an acceptable degree of maturity in terms of humification parameters, absence of phytotoxicity (determined on test plants according to ISO methods) and low content of simple phenolic compounds. A greenhouse experiment with two nursery crops (tomato and zucchini) showed that, depending on the characteristics of the growing substrate (vermiculite or perlite), orange compost addition selectively induced pH and electrical conductivity (EC) increases, which in turn would affect plant growth responses. In field crops shoot mass weight was increased after compost addition. Results suggest that at field scale, orange compost may be used for organic fertilization; while in nursery crops it can be mixed with commercial potting substrates selected in relation to plant sensitivity. In horticultural crop...

Seven-day-old maize seedlings grown in a nitrogen-free hydroponic culture were exposed for 48 h to 0, 100 and 300 μM trans-cinnamic, p-coumaric, ferulic, caffeic acids, umbelliferone and 200 μM KNO3. Net nitrate uptake was affected by trans-cinnamic, ferulic and p-coumaric acids in a concentration-dependent manner, and trans-cinnamic acid appeared to be the strongest inhibitor. Conversely, at low concentrations, caffeic acid stimulated net nitrate uptake while umbelliferone did not influence it. After 24 h of treatment, plasma membrane H+-ATPase activity significantly decreased in a concentration-dependent manner in response to trans-cinnamic, ferulic and p-coumaric acids, while umbelliferone and caffeic acid had no effect on H+-ATPase activity.

Spatial–temporal variation of the regulation and the kinetics of net nitrate (NO3−) uptake rate (NNUR) along the tap root of Citrus aurantium L. were analysed. Suberin incrustation in the peripheral cell layers and plasma membrane (PM) H+-ATPase localisation, anatomical and physiological factors involved in NO3− uptake were also investigated. The results clearly indicated a spatially uniform distribution of the regulation process, accompanied by a temporal heterogeneous pattern of the kinetics of NO3− uptake along citrus tap root. In particular, kinetic analysis had a biphasic pattern, saturating (high affinity transport system) and linear (low affinity transport system), in response to increasing external NO3− concentrations in each root region, where 200 μM NO3− represented the threshold separating these two systems. Kinetic parameters, Km and Vmax, clearly indicated that apical segments reached the maximum value of induction before basal segments. Hence, the apical root zones, early exhibiting the maximum of potential capacity to absorb the NO3−, could be considered more efficient than basal root segments for acquiring NO3− from external solution. Suberin incrustations in the hypodermal cell layer, characterised by uniform fluorescence intensity among the root segments, could be responsible for the unchanged NNUR, while the PM H+-ATPase could explain the temporal pattern of NNUR.

Batch experiments were performed to evaluate the combined effects of ionic activity, pH, and contact time on the cadmium sorption in three different minerals, vermiculite, zeolite, and pumice, commonly employed as substrata in nurseries and recently considered for their potential use in remediation methods. The extent of cadmium sorption was vermiculite > zeolite > pumice, as shown by the Langmuir and Freundlich parameters, and it was highly dependent on mineral characteristics. The percentage of cadmium sorption in zeolite and vermiculite did not depend on cadmium concentration, while in pumice this percentage was positively correlated to the initial cadmium concentration. At low cadmium concentrations (30–120 μM), the metal sorbed on zeolite was mainly present in the nonexchangeable form (70%) at levels much higher than those found for vermiculite and pumice. The primary variable responsible for determination of cadmium mobility in these minerals was confirmed to be pH. The ionic concentrations of Hoagland nutrient solution were significantly modified by both pH and mineral composition, while the presence of cadmium caused no changes. With vermiculite and zeolite, the time-course of cadmium sorption was related to mineral composition to a greater extent than to cadmium concentration. While with pumice, the percentage of cadmium sorbed after 6 weeks was lower than with the other two minerals, and it was inversely correlated to the initial cadmium concentration.

Under nutrient heterogeneous soil conditions, the ability of plants to compete for resource acquisition was closely related to the plasticity of root architecture, intended as a change of topology and geometry. Root architecture variations in response to different nitrate supplies of co-generic citrus rootstocks, ‘Rough Lemon’ (Citrus jambhiri Lush), ‘Sweet Orange’ (Citrus sinensis (L) Osbeck), ‘Cleopatra Mandarin’ (Citrus reshni Hort ex Tan.), and ‘Sour Orange’ (Citrus aurantium L.) are reported here. Root architecture was gauged by an image-specific analysis system (WinRHIZO). Based on the topological index, root topology of citrus rootstocks varied in response to nitrate treatments. In terms of root geometry, external-external and, to a lesser degree, internal-internal links of all rootstocks changed in response to nitrate supply. Among the rootstocks, ‘Cleopatra Mandarin’, both in terms of root topology (high TI) and root geometry (high length of exterior and interior link), could be consider...

Nitrogen use efficiency (NUE) definitions, commonly used in literature, are evaluated in response to nitrate availability in four citrus rootstocks, Rough Lemon (Citrus jambhiri Lush) (RL), Sweet Orange (Citrus sinensis (L.) Osbeck) (SwO), Cleopatra Mandarin (Citrus reshni Hort ex Tan.) (CM) and Sour Orange (Citrus aurantium L.) (SO). The application of diverse definitions determine different characterizations in N-efficiency among rootstocks. Nitrogen utilization efficiency (NUtE) and nitrogen efficiency ratio (NER) determine equal level of nitrogen efficiency among all rootstocks. Total nitrogen accumulation (TNA), nitrogen uptake efficiency (NUpE), shoot dry weight (SDW) and total leaf area (TLA) response curves produce the same NUE characterization: SO and SwO were nitrate use efficient and inefficient rootstocks, respectively, while the RL and CM exhibit superior and inferior genetic potential, respectively.

The event chain leading to germination blockage in durum wheat (Triticum turgidum ssp. durum Desf.) seeds exposed to the allelochemical coumarin (2H-chromen-2-one) was studied. The physiological and biochemical aspects thought to be critical for a successful seed germination were measured. At concentrations above 200 microM: , coumarin inhibited seed germination in a concentration-dependent manner. Inhibition occurred early during seed imbibition (phase I), was rapid, and irreversible. During phase I, coumarin inhibited water uptake, electrolyte retention capacity, and O(2) consumption. Later on, coumarin delayed the reactivation of peroxidases, enhanced the activity of superoxide dismutase, decreased the activities of selected marker enzymes for metabolic resumption, and repressed the transcription of molecular chaperones involved in secretory pathways. Insufficient and/or late seed rehydration caused by coumarin could have delayed membrane stabilization or decreased respiratory O(2) consumption, both of which are conducive to an overproduction of reactive O(2) species. Being unbalanced by an adequate upsurge of antioxidant defense systems, the resulting oxidative stress might have ultimately interfered with the germination program.

Root morpho-topology and net nitrate uptake of two citrus seedlings, Volkamer Lemon and Carrizo Citrange, grown at two nitrogen supplies (NO3-N 5 μM and 1000 μM, respectively) were studied. Root morphological and topological parameters were gauged by an image-specific analysis system (WinRHIZO). Net nitrate uptake was estimated using the nitrate depletion method. The main findings showed that Carrizo seedlings had a dichotomous branching root system characterized by high root tip numbers and long 2 nd order lateral roots. Conversely, Volkamer root systems had a herringbone structure with a long tap root and 1 st order lateral root. Nitrate treatment did not seem to affect the pattern of the two genotypes, except for the 2 nd order lateral roots (Carrizo more than Volkamer) and root/shoot ratio and root mass ratio (Volkamer more than Carrizo) that were significantly different at low nitrate supply. Nitrate treatments induced a diverse net nitrate uptake regulation between citrus rootstocks. Indeed, at low nitrate supply, Carrizo showed a more efficient nitrate acquisition process in terms of: 1) higher net nitrate uptake maximum of the inducible high affinity transport system or ‘full induction’ (A), (2) higher cumulative nitrate uptake (A t ) and (3) lower t1 parameter defined as the half time of the net nitrate uptake rate of the inducible transport system during the induction phase, compared to Volkamer. Conversely, at the high nitrate level, only the genotypical difference of the t1 parameter was maintained. The results suggested that, at the low nitrate level, the morphological root traits such as higher 2 nd order lateral roots and greater root tip numbers of the Carrizo compared with Volkamer seedlings, enhance the capacity to absorb nitrate from nutrient solution.

The effects of coumarin on the length, diameter, and branching density of different root types in maize seedlings (Zea mays L. cv. Cecilia) were investigated. The maize root system represents a useful model for morphological studies, as it consists of radicle, seminal, and nodal roots whose origin and development are quite different. Maize seedlings were grown in a hydroponic culture for 6 days, and then coumarin (at concentrations of 0, 25, 100, and 400 microM) was added to the nutrient solution. Coumarin inhibited root length, but effects differed depending on the root type. C 1/2 values, representing the coumarin concentration causing a 50% inhibition of the root length, were calculated by nonlinear regression. Six, 1, and 0.25 mM coumarin were sufficient to reduce the radicle, seminal, and nodal root lengths by 50%, respectively. At the highest coumarin concentration, the subapical root zone showed swelling. The degree recorded by average diameter was higher in nodal roots than in seminal and radicle roots. Furthermore, coumarin decreased the number of lateral roots and branching density more in the seminal than in the radicle roots. These results suggest the following order of sensitivity to coumarin: nodal > seminal > radicle roots. The observed spatial effects of coumarin could be ecologically significant, since taprooted species could benefit at the disadvantage of fibrous-rooted species and could modify community composition.

Summary We used a carrot (Daucus carota L. cv. Saint Valery) cell suspension culture as a simplified model system to study the effects of the allelochemical compound coumarin (1,2 benzopyrone) on cell growth and utilisation of exogenous nitrate, ammonium and carbohydrates. Exposure to micromolar levels of coumarin caused severe inhibition of cell growth starting from the second day of culture onwards. At the same time, the presence of 50 μmol/L coumarin caused accumulation of free amino acids and of ammonium in the cultured cells, and stimulated their glutamine synthetase, glutamate dehydrogenase, glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxylase activities. Malate dehydrogenase, on the other hand, was inhibited under the same conditions. These effects were interpreted in terms of the stimulation of protein catabolism and/or interference with protein biosynthesis induced by coumarin. This could have led to a series of compensatory changes in the activities of enzymes linking nitrogen and carbon metabolism. Because coumarin seemed to abolish the exponential phase and to accelerate the onset of the stationary phase of cell growth, we hypothesise that such allelochemical compounds may act in nature as an inhibitor of the cell cycle and/or as a senescence-promoting substance.

Foliar antioxidants were measured in adult individuals of holm oak (Quercus ilex L.) and white oak (Q. pubescens Willd.) growing in the field either within the vicinity of natural CO2 springs or at a nearby control site under ambient CO2, which had been previously exposed to either daily irrigation or no irrigation. In oak trees permanently exposed to elevated CO2 the activities of antioxidant enzymes tended to be lower and the ascorbate pool was larger and more in reduced form, suggesting an attenuation of the oxidative risk in the CO2-enriched trees. In the enriched individuals of both species. the imposition of water shortage significantly increased the size of the glutathione pool and the total superoxide dismutase activity in a species-specific manner. Moreover, water-stressed trees exposed to elevated CO2 tended to have higher catalase and ascorbate peroxidase activities than water-stressed control trees. Such changes may reflect the need for an enhanced compensatory effort when trees acclimated to elevated CO2 are exposed to oxidative stress-promoting environmental factors, such as water shortage.

Summary • The effects are reported here of coumarin, an allelopathic compound, on root anatomy and growth, nitrate uptake and translocation to the shoot, as well as respiration in Triticum durum (cv. Simeto) seedlings. • Wheat seedlings were grown in nitrogen-free hydroponic culture; after 6 d, coumarin (at concentrations of 0, 25 µM, 0.1, 1, 2.5 and 5 mM) and/or nitrate (50 µM) were added to the nutrient solution. • Coumarin, in the range 25 µM–1 mM, decreased the relative growth rate of roots and increased the area of the root vessels. Within this concentration range, coumarin alone did not significantly affect net nitrate uptake. In seedlings exposed simultaneously to 100 µM coumarin and to 50 µM nitrate, the net nitrate uptake was significantly stimulated. In the presence of nitrate, even the lowest coumarin concentration tested significantly stimulated nitrate translocation from the root to the shoot. • The effects of low coumarin concentrations on root vessel size could explain this observation, though specific interactions between coumarin and systems regulating nitrate uptake and transport within the root cell cannot be excluded.