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Plant-soil negative feedback (NF) is recognized as an important factor affecting plant communities. The objectives of this work were to assess the effects of litter phytotoxicity and autotoxicity on root proliferation, and to test the hypothesis that DNA is a driver of litter autotoxicity and plant-soil NF. The inhibitory effect of decomposed litter was studied in different bioassays. Litter biochemical changes were evaluated with nuclear magnetic resonance (NMR) spectroscopy. DNA accumulation in litter and soil was measured and DNA toxicity was assessed in laboratory experiments. Undecomposed litter caused nonspecific inhibition of root growth, while autotoxicity was produced by aged litter. The addition of activated carbon (AC) removed phytotoxicity, but was ineffective against autotoxicity. Phytotoxicity was related to known labile allelopathic compounds. Restricted (13) C NMR signals related to nucleic acids were the only ones negatively correlated with root growth on conspecific substrates. DNA accumulation was observed in both litter decomposition and soil history experiments. Extracted total DNA showed evident species-specific toxicity. Results indicate a general occurrence of litter autotoxicity related to the exposure to fragmented self-DNA. The evidence also suggests the involvement of accumulated extracellular DNA in plant-soil NF. Further studies are needed to further investigate this unexpected function of extracellular DNA at the ecosystem level and related cellular and molecular mechanisms.

Self-inhibition of growth has been observed in different organisms, but an underlying common mechanism has not been proposed so far. Recently, extracellular DNA (exDNA) has been reported as species-specific growth inhibitor in plants and proposed as an explanation of negative plant-soil feedback. In this work the effect of exDNA was tested on different species to assess the occurrence of such inhibition in organisms other than plants. Bioassays were performed on six species of different taxonomic groups, including bacteria, fungi, algae, plants, protozoa and insects. Treatments consisted in the addition to the growth substrate of conspecific and heterologous DNA at different concentration levels. Results showed that treatments with conspecific DNA always produced a concentration dependent growth inhibition, which instead was not observed in the case of heterologous DNA. Reported evidence suggests the generality of the observed phenomenon which opens new perspectives in the context of self-inhibition processes. Moreover, the existence of a general species-specific biological effect of exDNA raises interesting questions on its possible involvement in self-recognition mechanisms. Further investigation at molecular level will be required to unravel the specific functioning of the observed inhibitory effects.

Bioactive natural compounds from garlic and onions have been the focus of researches for decades, firstly due to their pharmacological effects, and secondly due to their defence properties against plant diseases. In fact, garlic and onion, belonging to Allium genus, are among the oldest food plants known since ancient times and used as ingredient of many recipes and for therapeutic properties. These plants are well known to produce bioactive apolar sulphur compounds but less is known about their polar natural compounds, such as phenols, sapogenins and saponins, that are more stable to cooking, So, we continued our work on the discovery of polar bioactive metabolites from Allium with the isolation of a number of sapogenins and saponins from the wild onion species Allium elburzense, Allium hirtifolium, Allium atroviolaceum, and Allium minutiflorum, and, more recently, from the cultivated white onion, Allium cepa, and garlic, Allium sativum. In particular, the sapogenins and saponins isolated from A. elburzense and A. hirtifolium, named elburzensosides and hirtifoliosides respectively, exhibited significant antispasmodic properties. In addition, the saponins named minutosides isolated from A. minutiflorum showed promising antimicrobial activity. More recently the phytochemical analysis of A. cepa and A. sativum has been undertaken and afforded the characterization of saponins, phenols and N-cynnamic amides which showed significant antifungal activity

Modelling the inter-relationships between litter accumulation and plant–soil feedback is a major challenge to predict natural and agricultural ecosystem dynamics. At increasing levels of undecomposed plant litter, seedling growth tends to show a multi-faceted response trend, characterised by a peak of positive stimulation at lower dosage followed by inhibition at higher dosage. In this study, a new logistic model was developed to describe such trend and disentangle substrate-specific positive and negative effects of plant litter. The model was tested on 35 litter types applied to the common phytometer Lepidium sativum; all litter types were collected in Mediterranean shrublands of Campania region (southern Italy). Model fitting resulted to be generally higher relative to the widely used linear log response model, although in only half of the cases it also gave more parsimonious results in terms of minimising information loss. Positive and negative effects of plant litter resulted to be uncorrelated, showing that the overall trend is probably the result of the combined action of separate factors rather than the effect of a single factor behaving differently at the different doses. The results of this work provide new tools to finely tune the optimal doses in experiments on hormesis and litter phytotoxicity, through the identification of the most suited doses to centre the range of nearly linear response to litter concentration. A wide screening is also presented on the phytotoxicity profiles of a number of spontaneous plant species widely distributed in the Mediterranean area.

The exploration of new bioactive compounds from natural resources as alternatives to synthetic chemicals has recently attracted the attention of scientists and researchers. To our knowledge, the essential oil (EO) of Kickxia aegyptiaca has not yet been explored. Thus, the present study was designed to explore the EO chemical profile of K. aegyptiaca for the first time, as well as evaluate its antioxidant and antibacterial activities, particularly the extracts of this plant that have been reported to possess various biological activities. The EO was extracted from the aerial parts via hydrodistillation and then characterized by gas chromatography-mass spectrometry (GC-MS). The extracted EO was tested for its antioxidant activity via the reduction in the free radicals, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). In addition, the EO was tested as an antibacterial mediator against eight Gram-negative and Gram-positive bacterial isolates. Forty-three compounds were identified in the EO of K. aegyptiaca, with a predominance of terpenoids (75.46%). Oxygenated compounds were the main class, with oxygenated sesquiterpenes attaining 40.42% of the EO total mass, while the oxygenated monoterpenes comprised 29.82%. The major compounds were cuminic aldehyde (21.99%), caryophyllene oxide (17.34%), hexahydrofarnesyl acetone (11.74%), ar-turmerone (8.51%), aromadendrene oxide (3.74%), and humulene epoxide (2.70%). According to the IC50 data, the K. aegyptiaca EO revealed considerable antioxidant activity, with IC50 values of 30.48 mg L−1 and 35.01 mg L−1 for DPPH and ABTS, respectively. In addition, the EO of K. aegyptiaca showed more substantial antibacterial activity against Gram-positive bacterial isolates compared to Gram-negative. Based on the minimum inhibitory concentration (MIC), the EO showed the highest activity against Escherichia coli and Bacillus cereus, with an MIC value of 0.031 mg mL−1. The present study showed, for the first time, that the EO of K. aegyptiaca has more oxygenated compounds with substantial antioxidant and antibacterial activities. This activity could be attributed to the effect of the main compounds, either singular or synergistic. Thus, further studies are recommended to characterize the major compounds, either alone or in combination as antioxidants or antimicrobial agents, and evaluate their biosafety.

Environmental and land-use changes put severe pressure on wild plant habitats. The present study aims to assess the biodiversity of wild plant habitats and the associated spatiotemporal environmental changes in the coastal region of Dakahlia Governorate following an integrated approach of remote sensing, GIS, and samples analysis. Thirty-seven stands were spatially identified and studied to represent the different habitats of wild plants in the Deltaic Mediterranean coastline region. Physical and chemical characteristics of soil samples were examined, while TWINSPAN classification was used to identify plant communities. Two free Landsat images (TM and OLI) acquired in 1999 and 2019 were processed to assess changes via the production of land use and cover maps (LULC). Moreover, NDSI, NDMI, and NDSI indices were used to identify wild plant habitats. The floristic composition indicated the existence of 57 species, belonging to 51 genera of 20 families. The largest families were Asteraceae, Poaceae, and Chenopodiaceae. The classification of vegetation led to the identification of four groups. Canonical Correspondence Analysis (CCA) revealed that electrical conductivity, cations, organic carbon, porosity, chlorides, and bicarbonates are the most effective soil variables influencing vegetation. The results of the spectral analysis indicated an annual coverage of bare lands (3.56 km2), which is strongly related to the annual increase in vegetation (1.91 km2), water bodies (1.22 km2), and urban areas (0.43 km2). The expansion of urban and agricultural regions subsequently increased water bodies and caused occupancy of bare land, resulting in the development of wild plant habitats, which are mostly represented by the sparse vegetation class as evaluated by NDVI. The increase in mean moisture values (NDMI) from 0.03 in 1999 to 0.15 in 2019 might be explained by the increase in total areas of wild plant habitats throughout the study period (1999–2019). This may improve the adequacy of environments for wild habitats, causing natural plant proliferation.

Past anthropogenic disturbances lowered the altitudinal distribution of the Mediterranean Fagus sylvatica forests below 2,000 m a.s.l. Accordingly, our current understanding of the southern distribution range of F. sylvatica forests is restricted to managed stands below this elevation, neglecting relic forests growing above. This study has shed light on the structure and species assemblage of an unmanaged relict subalpine F. sylvatica stand growing within the core of its southernmost glacial refugia and at its highest species range elevation limit (2,140 m a.s.l.) in southern Apennines (Italy). Here, tree biometric attributes and understory species abundances were assessed in eight permanent plots systematically positioned from 1,650 to 2,130 m a.s.l. In the subalpine belt, F. sylvatica had formed a dense clonal stem population that was layered downward on the steepest slopes. The density and spatial aggregation of the stems were increased, while their stature and crown size were decreased. Above 2,000 m, changes in tree growth patterns, from upright single-stemmed to procumbent multi-stemmed, and canopy layer architecture, with crowns packed and closer to the floor, were allowed for the persistence of understory herbaceous species of biogeographic interest. Clonal layering represents an adaptive regeneration strategy for the subalpine belt environmental constraints not previously recognized in managed Mediterranean F. sylvatica forests. The clonal structure and unique species assemblage of this relic forest highlight the value of its inclusion in the priority areas networks, representing a long-term management strategy of emblematic glacial and microclimatic refugia.

Soilborne pathogens and pests in agroecosystems are serious problems that limit crop yields. In line with the development of more ecologically sustainable agriculture, the possibility of using biochar to control pests has been increasingly investigated in recent years. This work provides a general overview of disease and pest suppression using biochar. We present an updated view of the literature from 2015 to 2022 based on 61 articles, including 117 experimental case studies. We evaluated how different biochar production feedstocks, pyrolysis temperatures, application rates, and the pathosystems studied affected disease and pest incidence. Fungal pathogens accounted for 55% of the case studies, followed by bacteria (15%), insects and nematodes (8%), oomycetes and viruses (6%), and only 2% parasitic plants. The most commonly studied belowground pathogen species were Fusarium oxysporum f. sp. radicis lycopersici in fungi, Ralstonia solanacearum in bacteria, and Phytophthora capisci in oomycetes, while the most commonly studied pest species were Meloidogyne incognita in nematodes, Epitrix fuscula in insects, and both Phelipanche aegyptiaca and Orobanche crenata in parasitic plants. Biochar showed suppression efficiencies of 86% for fungi, 100% for oomycetes, 100% for viruses, 96% for bacteria, and 50% for nematodes. Biochar was able to potentially control 20 fungal, 8 bacterial, and 2 viral plant pathogens covered by our review. Most studies used an application rate between 1% and 3%, a pyrolysis temperature between 500 °C and 600 °C, and a feedstock based on sawdust and wood waste. Several mechanisms have been proposed to explain disease suppression by biochar, including induction of systemic resistance, enhancement of rhizosphere competence of the microbial community, and sorption of phytotoxic compounds of plant and/or microbial origin. Overall, it is important to standardize biochar feedstock and the rate of application to improve the beneficial effects on plants in terms of disease control.

Introduction: Arbutus unedo L. (strawberry tree), Ceratonia siliqua L. (carob), Eucalyptus camaldulensis Dehnh. (eucalyptus), Laurus nobilis L. (laurel), Mentha aquatica L. (water mint), Myrtus communis L. (common myrtle), and Rosmarinus officinalis L. (rosemary) are aromatic plants from the Mediterranean region whose parts and preparations are used for their nutritional properties and health benefits. Objectives: To evaluate and compare the metabolites profile, total phenol content (TPC), and antioxidant activity of plant leaves for their future use. Gas chromatography-mass spectrometry (GC-MS) was used for metabolomics. Data comparison was performed by chemometrics. Methodology: Polar and apolar extracts were analysed using untargeted GC-MS metabolomics followed by chemometrics (principal component analysis, heatmap correlation and dendrogram) to identify, quantify and compare the major organic compounds in the plants. Additionally, nuclear magnetic resonance (NMR) spectroscopy was used for the laurel polar extract to identify d-gluco-l-glycero-3-octulose whose presence was unclear from the GC-MS data. TPC and antioxidant assays were performed using classical methods (Folin-Ciocalteu, 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH)) and correlated to the phytochemical profiles. Results: Forty-three metabolites were identified including amino acids, organic acids, carbohydrates, phenols, polyols, fatty acids, and alkanes. Eight metabolites (d-fructose, d-glucose, d-mannose, gallic acid, quinic acid, myo-inositol, palmitic and stearic acids) were in common between all species. d-Gluco-l-glycero-3-octulose (37.29 ± 1.19%), d-pinitol (31.33 ± 5.12%), and arbutin (1.30 ± 0.44%,) were characteristic compounds of laurel, carob, and strawberry tree, respectively. Carob showed the highest values of TPC and antioxidant activity. Conclusion: GC-MS metabolomics and chemometrics analyses are fast and useful methods to determine and compare the metabolomics profiling of aromatic plants of food and industrial interest.

Litter decomposition releases nutrients beneficial to plants but also induces phytotoxicity. Phytotoxicity can result from either labile allelopathic compounds or species specific and caused by conspecific DNA. Aquatic plants in flowing water generally do not suffer phytotoxicity because litter is regularly removed. In stagnant water or in litter packs an impact on root functionality can occur. So far, studies on water plant roots have been carried out in laboratory and never in field conditions. The effect of conspecific vs heterospecific litter and purified DNA were assessed on aquatic roots of the riparian woody species Alnus glutinosa L. using a novel method, using closed and open plastic tubes fixed to single roots in the field with closed tubes analogous to stagnant water. Four fresh and four decomposed litter types were used and analysed on extractable C, cellulose, lignin, N content and using 13 C-CPMAS NMR spectroscopy. Inhibitory effects were observed with fresh litter in closed systems, with a positive correlation with extractable C and negative with lignin and lignin : N ratio. Alnus self-DNA, but not heterologous one, caused acute toxic effects in the closed system. Our results demonstrate the first field-based evidence for self-DNA inhibition as causal factor of negative feedback between plants and substrate.

Soil aggregation, a key aspect of soil physical health, is a crucial component of agroecosystem sustainability as it affects numerous soil processes and agroecosystem productivity. Application of organic amendment (OA) plays a vital role in improving soil aggregation. In this review, we provide a comprehensive synthesis and a critical assessment of the current state of knowledge in soil aggregation in relation to OA. We first highlight factors (such as soil texture and clay mineralogy, source and type of OA, OA application rate and frequency, and OA application mode) determining the effect of OA on soil aggregation. Secondly, we review how OA regulates soil aggregation and point out that OA improves soil aggregation mainly via: (i) increasing soil organic carbon (SOC) content where OA acts as an external source of SOC, (ii) promoting soil biotic activity where OA acts as a substrate for microbes, and (iii) increasing soil hydrophobicity, thus reducing aggregate turnover. Finally, we draw reader’s attention to the complex linkages between OA quality and soil aggregation. The OA quality defined by 13C-NMR spectroscopy in terms of organic C type can explain variable effects of OA on soil aggregation better than C/N and lignin/N ratio indices. Considering organic C types, OA rich in carbohydrate C fractions tends to induce rapid but short- and medium-term effects on soil aggregation, while OA riched in aromatic C fractions barely affects soil aggregation. We conclude that soil structure can be significantly modified through better agronomic practices of OA application which will enhance soil aggregation, reduce soil erosion, and subsequently increase overall productivity.

The exploration of new green, ecofriendly bioactive compounds has attracted the attention of researchers and scientists worldwide to avoid the harmful effects of chemically synthesized compounds. Persicaria lapathifolia has been reported to have various bioactive compounds, while its essential oil (EO) has not been determined yet. The current work dealt with the first description of the chemical composition of the EO from the aerial parts of P. lapathifolia, along with studying its free radical scavenging activity and herbicidal effect on the weed Echinochloa colona. Twenty-one volatile compounds were identified via GC–MS analysis. Nonterpenoids were the main components, with a relative concentration of 58.69%, in addition to terpenoids (37.86%) and carotenoid-derived compounds (1.75%). n-dodecanal (22.61%), α-humulene (11.29%), 2,4-dimethylicosane (8.97%), 2E-hexenoic acid (8.04%), γ-nonalactone (3.51%), and limonene (3.09%) were characterized as main compounds. The extracted EO exhibited substantial allelopathic activity against the germination, seedling root, and shoot growth of the weed E. colona in a dose-dependent manner, showing IC50 values of 77.27, 60.84, and 33.80 mg L−1, respectively. In addition, the P. lapathifolia EO showed substantial antioxidant activity compared to ascorbic acid as a standard antioxidant. The EO attained IC50 values of 159.69 and 230.43 mg L−1, for DPPH and ABTS, respectively, while ascorbic acid exhibited IC50 values 47.49 and 56.68 mg L−1, respectively. The present results showed that the emergent leafy stems of aquatic plants such as P. lapathifolia have considerably low content of the EO, which exhibited substantial activities such as antioxidant and allelopathic activities. Further study is recommended to evaluate the effects of various environmental and climatic conditions on the production and composition of the EOs of P. lapathifolia.

The organic matter cycle is one of the most fundamental processes in ecosystems affecting the soil and controlling its functions. The soil complex microbiome is made up of thousands of bacterial and hundreds of fungal strains that coexist on the many different available organic carbon sources. In natural plant communities, freshly fallen leaf-litter and dead roots are subject to decomposition by a complex food-web composed of both microbial saprotrophs and invertebrate detritivores. The litter chemical composition varies dramatically among species in relation to plant life forms (conifer, broadleaf, nitrogen-fixing, graminoid) and, within species, with plant organs (leaf, root, woody tissues). This paper reviews the usefulness of advanced chemical technologies to study the composition of both plant litter and organic amendments, supporting the description of their mechanism of action and attention to their potential applications. First, a critical review is presented on the limitations of C/N and lignin/N ratios, still widely used as basic indicators of litter chemistry. Second, the potential of the solid state 13C-CPMAS NMR is reported as a powerful tool to assess the chemical composition of both litter and organic amendments. Finally, six different study cases are reported to provide evidence of the usefulness of such metabolomic approach for the description of organic matter chemistry aimed to an effective prediction of its impact on soil ecosystem functions.

The Asteraceae (Compositae) family is one of the largest angiosperm families that has a large number of aromatic species. Pulicaria undulata is a well-known medicinal plant that is used in the treatment of various diseases due to its essential oil (EO). The EO of both Saudi and Egyptian ecospecies were extracted via hydrodistillation, and the chemical compounds were identified by GC–MS analysis. The composition of the EOs of Saudi and Egyptian ecospecies, as well as other reported ecospecies, were chemometrically analyzed. Additionally, the phytotoxic activity of the extracted EOs was tested against the weeds Dactyloctenium aegyptium and Bidens pilosa. In total, 80 compounds were identified from both ecospecies, of which 61 were Saudi ecospecies, with a preponderance of β-pinene, isoshyobunone, 6-epi-shyobunol, α-pinene, and α-terpinolene. However, the Egyptian ecospecies attained a lower number (34 compounds), with spathulenol, hexahydrofarnesyl acetone, α-bisabolol, and τ--cadinol as the main compounds. The chemometric analysis revealed that the studied ecospecies and other reported species were different in their composition. This variation could be attributed to the difference in the environmental and climatic conditions. The EO of the Egyptian ecospecies showed more phytotoxic activity against D. aegyptium and B. pilosa than the Saudi ecospecies. This variation might be ascribed to the difference in their major constituents. Therefore, further study is recommended for the characterization of authentic materials of these compounds as allelochemicals against various weeds, either singular or in combination.

Dittrichia viscosa is a perennial small shrub belonging to the Compositae family (Asteraceae) widespread in the Mediterranean basin. This plant has been extensively used in traditional medicine since the Roman times as reported by the Roman Naturalist Gaius Plinius Secundus. Nowadays, many studies about chemical composition and biological activity of D. viscosa are available. Chemical analyses of plant extracts revealed the presence of several metabolites belonging to different classes of natural products such as sesquiterpenes, flavonoids and caffeic acids. In addition, the essential oil of D. viscosa is rich in volatile short chain metabolites with aldehydes, alcohols and esters functional groups, as well as long chain fatty acids esters and alkyls. Some of these compounds are known for their biological activities against a wide range of micro- and macroorganisms. Scientific evidence reported that derivates of caffeic acids and flavonoids were the compounds mainly related to inhibition of bacterial and fungal growth, whereas sesquiterpene lactones and eudesmane sesquiterpenes were most active against nematodes, mites, insects and parasitic plants. In this paper, information about the phytochemical composition and the biological activity of D. viscosa against bacteria, fungi, nematodes, mites, insect and parasitic plants have been summarized.

Biodeterioration, the alteration caused by living organisms, on historical buildings and stone monuments is a well-known problem affecting two-thirds of the world’s cultural heritage. The study of the flora growing on wall surface is of particular importance for the assessment of the risk of biodeterioration of stone artifacts by vascular plants, and for maintenance planning. In this study, we investigate how rock type, exposure and inclination of the wall affect the biodeteriogenic flora at 13 sites of the Archaeological Park of the Phlegraean Fields located in the province of Naples, in southern Italy. For each site, we analysed randomly selected square areas with 2 × 2 m size, representing the different vegetation types in terms of vascular plant species cover. The total number of plant species recorded was 129, belonging to 43 families.Erigeron sumatrensis, Sonchus tenerrimus, andParietaria judaicaare the most commonly reported species, whileCapparis orientalisis the species with the highest average coverage. Substrate type, exposure and surface inclination affect the floristic composition, with the average plant cover significantly higher on vertical surfaces and at western and southern exposure. All the main biodeteriogenic vascular plant species grow on more or less porous lythotype like yellow tufa, conglomerate and bricks. Finally, woody plants eradications methods are proposed by the tree cutting and local application of herbicides, to avoid stump and root sprouting and to minimize the dispersion of chemicals in the surrounding environment.

Background and Aims: Soil water repellency (SWR, i.e. the reduced affinity for water due to the presence of hydrophobic coatings on soil particles) has relevant hydrological implications on the rate of water infiltration, surface runoff, and overland flow. Here, we test how SWR varies along a 2490 m altitudinal gradient encompassing six ecosystems including Mediterranean, Temperate, and Alpine vegetation types. Methods: Water repellency, measured by the Molarity of an Ethanol Droplet (MED) test, was quantified in 80 soil samples collected for 16 different elevations. Soil quality was assessed by measuring soil texture, pH, organic carbon, salinity, and nutrient availability. Results: SWR showed a unimodal pattern along the 2490 m transect, peaking at intermediate elevations. Unexpectedly, SWR was the highest under broad-leaf deciduous forests, and the lowest under evergreen, sclerophyllous Mediterranean vegetation types. The soil organic carbon content, and the pH were the main determinants of water repellency, showing respectively a positive, and a negative correlation with the SWR. In contrast, soil texture and salinity resulted unrelated to the SWR. Conclusions: With this study we demonstrated a linkage between SWR, vegetation type and soil pH and organic carbon content along the elevation gradient. Further studies are needed to explicitly evaluate the impact SRW on erosion risk at catchment scale in the context of climatic change.

Italy is among the European countries with the greatest plant diversity due to both a great environmental heterogeneity and a long history of man–environment interactions. Trait-based approaches to ecological studies have developed greatly over recent decades worldwide, although several issues concerning the relationships between plant functional traits and the environment still lack sufficient empirical evaluation. To draw insights on the association between plant functional traits and direct and indirect human and natural pressures on the environmental drivers, this article summarizes the existing knowledge on this topic by reviewing the results of studies performed in Italy adopting a functional trait approach on vascular plants, bryophytes and lichens. Although we recorded trait measurements for 1418 taxa, our review highlighted some major gaps in plant traits knowledge: Mediterranean ecosystems are poorly represented; traits related to belowground organs are still overlooked; traits measurements for bryophytes and lichens are lacking. Finally, intraspecific variation has been little studied at community level so far. We conclude by highlighting the need for approaches evaluating trait–environment relationship at large spatial and temporal scales and the need of a more effective contribution to online databases to tie more firmly Italian researchers to international scientific networks on plant traits.

Aims Facilitation has been reported in a wide range of plant communities, with evidence of positive interactions between beneficiary and nurse plants shifting during their ontogenetic development. This study explored the hypothesis that shrubs of Juniperus communis subsp. nana (thereafter Juniperus) play a crucial role in the successional sequence of plant communities acting as nurse for different species, but only after reaching a certain size. In addition, we examined whether plant–plant interaction changes during ontogenesis of these shrubs in the presence of contrasting disturbance regimes in terms of substrate stability. Location Sibillini National Park, central Italy. The vegetation is semi-natural dry grasslands (92/43/EEC Habitats Directive: Habitat 6210 - Festuco-Brometalia). Methods Field measurements were carried out to assess the effects of Juniperus on (1) the distribution of co-existing vascular species, (2) the above- and below-ground microclimate, and (3) changes in soil fertility and hydrology. Results The capacity of Juniperus shrubs to facilitate heterospecific plants considerably increases during its ontogenetic development, i.e. small shrubs mainly compete for resources with local vegetation, whereas large shrubs act as nurse plants for herbaceous and especially for woody species. The facilitation effect was slight, albeit significantly higher in the disturbed area than in the more stable one. Juniperus was able to promote the formation of an island of fertility under its canopy by accumulating a considerable amount of organic matter, N, P, Ca2+, Mg2+ and K+ in a few decades. Juniperus shrubs improve soil hydrological properties and mitigate the daily range of soil temperature, reducing the exposure of co-existing plants to high temperatures and water loss through soil evaporation, particularly during the growing periods in spring and summer. Conclusions This study demonstrates that biogenic amelioration of soil quality, coupled with the mitigation of below-canopy microclimatic conditions, control the establishment and growth of co-existing plants during Juniperus shrub development.

Organic amendments (OAs) and soilborne biocontrol agents or beneficial microbes (BMs) have been extensively studied and applied worldwide in most agriculturally important plant species. However, poor integration of research and technical approaches has limited the development of effective disease management practices based on the combination of these two bio-based strategies. Insights into the importance of the plant-associated microbiome for crop productivity, which can be modified or modulated by introducing OAs and/or BMs, are providing novel opportunities to achieve the goal of long-term disease control. This review discusses novel ways of functionally characterizing OAs and how they may be used to promote the effect of added biocontrol agents and/or beneficial soil microbiota to support natural suppressiveness of plant pathogens.

Intensive farming in agriculture raises questions in relation to environmental sustainability and the widespread use of agrochemicals. In the present work, we compare the impact of organic and intensive farming, in connection to the soil suppressiveness against the soilborne pathogen Rhizoctonia solani. Three farms were considered in the study: two practicing organic cultivation (for 10 and 20 years, respectively), and one applying conventional cultivation. Soil suppressiveness was assessed in a greenhouse bioassay with lettuce (Lactuca sativa). Soil microbiome was characterized by combining BIOLOG EcoPlates™ with high‐throughput sequencing of bacterial and eukaryotic rRNA gene markers. Suppressiveness towards R. solani was higher in organic than in conventional farming soil, but this property was lost after soil sterilization. Functional biodiversity was significantly higher in the two organic soils, and this parameter was predictive of the suppressiveness towards R. solani. According to our analyses, the overall microbial taxonomic diversity was unlinked to suppressiveness. A correlation analysis, carried out at the genus level for the most abundant bacterial and eukaryotic microbial taxa, showed that 58.7% of the genera had a statistically significant correlation with suppressiveness. In particular, the genera Flavisolibacter, Massilia, Pseudomonas, Ramlibacter, Rhizophus and the oligochaete worms belonging to the Enchytraeidae family positively correlated with the disease suppression.

Plant invasions can have relevant impacts on biogeochemical cycles, whose extent, in Mediterranean ecosystems, have not yet been systematically assessed comparing litter carbon (C) and nitrogen (N) dynamics between invasive plants and native communities. We carried out a one-year litterbag experiment in 4 different plant communities (grassland, sand dune, riparian and mixed forests) on 8 invasives and 24 autochthonous plant species, used as control. Plant litter was characterized for mass loss, N release, proximate lignin and litter chemistry by 13C CPMAS NMR. Native and invasive species showed significant differences in litter chemical traits, with invaders generally showing higher N concentration and lower lignin/N ratio. Mass loss data revealed no consistent differences between native and invasive species, although some woody and vine invaders showed exceptionally high decomposition rate. In contrast, N release rate from litter was faster for invasive plants compared to native species. N concentration, lignin content and relative abundance of methoxyl and N-alkyl C region from 13C CPMAS NMR spectra were the parameters that better explained mass loss and N mineralization rates. Our findings demonstrate that during litter decomposition invasive species litter has no different decomposition rates but greater N release rate compared to natives. Accordingly, invasives are expected to affect N cycle in Mediterranean plant communities, possibly promoting a shift of plant assemblages.

A bioassay guided phytochemical analysis of the bulbs of Allium sativum L. var. Voghiera, typical of Voghiera, Ferrara (Italy), allowed the isolation of six new sulfur compounds with dithiosulfinates and sulfoxides functionalities. Structure elucidation of the isolated compounds was carried out by spectroscopic analyses, including NMR spectroscopy and MS spectrometry. Compounds showed significant antimicrobial activity towards two fungal species, the air-borne pathogen Botrytis cinerea and the beneficial fungus Trichoderma harzianum.

Decomposition of plant debris is a critical process during the filling phase of water reservoir. Here we investigated the impact of decomposition of the plant species (Cytisus scoparius, Pteridium aquilinum and Juncus effusus) in the Alaco reservoir (southern Italy). To simulate lake ecological conditions, a microcosm experiment was carried-out for 100 days with litters incubated in water lake in aerobic conditions in the light at two temperatures (+12 °C and +24 °C). Litter types were characterized by classic proximate chemical analyses (total C and N, labile C, cellulose and lignin content, C/N and lignin/N ratios) and, at molecular level, by solid-state 13C CPMAS NMR. Water quality was monitored through pH, electrolytic conductivity, DOC, BOD5 and dissolved oxygen. Decomposition was more rapid for C. scoparius, intermediate for J. effusus and slower for P. aquilinum. After 100 days of decomposition for all litter type the O-alkyl-C region, associated with sugars and polysaccharides, decreased and the aliphatic alkyl-C region increased for C. scoparius and P. aquilinum. Immediately after litter submergence, DOC and BOD5 dramatically increased, reaching high values for P. aquilinum and C. scoparius. However, after 100 days of incubation, DOC concentration sharply decreased reaching values usually below 50 mg l−1, and after 10 days of incubation BOD5 values dropped to values close to zero. Although carried out in laboratory, the experiment showed that submerged plant litter during decomposition produces a short-term changes of water quality that rapidly returns to background level.

The antimicrobial activity of garlic (Allium sativum L.) has been known since ancient times. The first citation dates back to the Egyptian period of 15th century B.C. when garlic was reported to be used in folk medicine as a remedy for microbial infections. Scientific investigations on garlic started in 1858 with the work of Pasteur who first noted antibacterial properties of garlic extracts. From that date to the discovery of antibiotics, garlic has been used against amoebic dysentery and epidemic diseases such as typhus, cholera, diphtheria, and tuberculosis. But what makes garlic and Allium species effective against pathogenic microbes? The volatile sulphur compound allicin and other thiosulfinates, giving pungency to Allium plants, are well-studied and are the main element responsible for garlic activity against microbes. The thiosulfinates or alkane(ene) thial-S-oxide are formed by the action of the enzyme alliinase (EC 4.4.1.4) from their respective S-alk(en)yl cysteine sulfoxides when the bulbs are cut. However, depending on the Allium species, and under differing conditions, thiosulfinates can decompose to form additional sulfur constituents, including diallyl, methyl allyl, and dipropyl mono-, di-, tri- e tetra-sulfides, and (E)- and (Z)-ajoene without losing antimicrobial activity. Besides these apolar compounds, onion and garlic are characterized by more polar compounds of steroidal and phenolic origin, often glycosilated, showing also interesting antimicrobial activity. These latter compounds, compared to the more studied thiosulfinates, have the advantages of not being pungent an are more stable during cooking. Recently, there has been increasing scientific attention given to such compounds. Compounds possessing nitrogen atoms, like alkaloids and polypeptides, have also been isolated from these plants and have shown antimicrobial activity. In this paper, the literature about the major volatile and non-volatile organic compounds of garlic and other Allium plants has been reviewed. Particular attention is given to the compounds possessing antimicrobial activity and to the correlation between the observed activity and the chemical structure of the tested compounds

Background and Aims Modelling organic matter decomposition is fundamental to understand biogeochemical cycling in terrestrial ecosystems. Current models use C/N or Lignin/N ratios to describe susceptibility to decomposition, or implement separate C pools decaying with different rates, disregarding biomolecular transformations and interactions and their effect on decomposition dynamics. We present a new process-based model of decomposition including a description of biomolecular dynamics obtained by 13C-CPMAS NMR spectroscopy. Methods Baseline decay rates for relevant molecular classes and intermolecular protection were calibrated by best fitting of experimental data from leaves of 20 plant species decomposing for 180 days in controlled optimal conditions. The model was validated against field data from leaves of 32 plant species decomposing for 1-year at four sites in Mediterranean ecosystems. Results Simulations correctly reproduced mass loss data and variations of selected molecular classes both in controlled conditions and in the field, for a wide range of plant molecular composition and environmental conditions. Conclusions Our innovative approach accurately predicted decomposition of a wide range of litters across different climates. Prediction accuracy emerged from the species-specific partitioning of molecular types and from the representation of intermolecular interactions. Further application should be planned in other ecosystems based on long-term decomposition datasets.

Post-fire reproductive niche of Aleppo pine (Pinus halepensis) is deeply interlaced with fire products. Indeed, the high pH and low osmotic potentials of ash beds under burnt crowns constitute the main constraints to seed germination. In this study, we aim to investigate whether fire recurrence, through the physico-chemical constraints imposed by the ash beds, affects the reproduction ability of P. halepensis at the germination stage. To this aim, Aleppo pine seeds were collected in neighboring even-aged stands subjected to 0, 1, or 2 fires (namely fire cohorts), and seed morphology and germination performance, in terms of cumulative germination and germination kinetics, were studied under increasing osmotic potentials (from 0.0 to −1.2 MPa) and pH (from 6 to 11). Besides fire history, the role of ontogenetic age of mother plants on seed morphology and germination was also investigated. Differences in seed morphology among the three cohorts have been highlighted in a multivariate context, with anisotropic enlargement of the seeds produced by pine stands experiencing repeated fires. The patterns of seed germination varied primarily in relation to the fire cohort, with seeds from the pine stand experiencing repeated fires exhibiting enhanced tolerance to pH stress. Conversely, germination performances under osmotic constraints mainly depends on tree ontogenetic stage, with an involvement of fire history especially in the timing of seed germination. Our results suggest that, at least in the short term, fire recurrence does not constrain the reproduction ability of Aleppo pine. These results highlight the need for further research to elucidate the mechanisms behind these responses to recurrent fires.

Background and aims Litter decomposition is a critical process in terrestrial ecosystems and understanding the effects of soil fertility on the litter decay rate is of great ecological relevance. Here we test the hypothesis that N transfer from soil to litter will promote the decay rate of N poor but not N rich litter types. Methods Ten organic substrates, encompassing a wide range of biochemical quality in terms of C/N and lignin/N ratios, were decomposed in microcosms over three soil types with different N content, but inoculated with the same microbiome. Organic substrates were characterized for mass loss, C and N content to assess N transfer from soil to litter. Results The decay rate response to soil fertility was related to their initial N content: positive for substrates with little initial N content and not significant for N rich plant residues. A significant N transfer, generally larger from N rich soil to N poor substrates, was found. Litter C/N and lignin/N ratios showed variable relationships with the litter decay according with the soil fertility gradient, with positive and negative correlations in N rich and N poor soils, respectively. Conclusions Our study demonstrated that the decomposition of N rich litter proceeded irrespective of soil fertility while the decay rate of N poor substrates, either lignin poor or rich, was controlled by soil fertility likely as a result of N transfer. Litter C/N and lignin/N ratios were reliable indicators of litter quality to predict their decay rate in N poor soil, but not in N rich soils.

A bioassay-guided phytochemical analysis of the polar extract from the bulbs of garlic, Allium sativum L., var. Voghiera, typical of Voghiera, Ferrara (Italy), allowed the isolation of ten furostanol saponins; voghieroside A1/A2 and voghieroside B1/B2, based on the rare agapanthagenin aglycone; voghieroside C1/C2, based on agigenin aglycone; and voghieroside D1/D2 and E1/E2, based on gitogenin aglycone. In addition, we found two known spirostanol saponins, agigenin 3-O-trisaccharide and gitogenin 3-O-tetrasaccharide. The chemical structures of the isolated compounds were established through a combination of extensive nuclear magnetic resonance, mass spectrometry and chemical analyses. High concentrations of two eugenol diglycosides were also found for the first time in Allium spp. The isolated compounds were evaluated for their antimicrobial activity towards two fungal species, the air-borne pathogen Botrytis cinerea and the antagonistic fungus Trichoderma harzianum.

Three saponins, named ceposide A, ceposide B, and ceposide C were isolated from the bulbs of white onion, Allium cepa L. Elucidation of their structure was carried out by comprehensive spectroscopic analyses, including 2D NMR spectroscopy and mass spectrometry, and chemical evidences. The structures of the compounds were identified as (25R)-furost-5(6)-en-1b,3b,22a,26-tetraol 1-O-b-D-xylopyranosyl 26-O-a-D-rhamnoyranosyl-(1 ?2)-O-b-D-galactopyranoside (ceposide A), (25R)-furost-5(6)-en-1b,3b,22a,26-tetraol 1-O-b-D-xylopyranosyl 26-O-a-D-rhamnoyranosyl-(1 ?2)-O-b-D-glucopyranoside (ceposide B), and (25R)-furost-5(6)-en-1b,3b,22a,26-tetraol 1-O-b-D-galactopyranosyl 26-O-a-D-rhamnoyranosyl-( 1?2)-O-b-D-galactopyranoside (ceposide C). The isolated compounds, alone and in combinations, were evaluated for their antimicrobial activity on ten fungal species. Antifungal activity of all three saponins increased with their concentration and varied with the following rank: ceposide B > ceposide A–ceposide C. We found a significant synergism in the antifungal activity of the three ceposides against Botrytis cinerea and Trichoderma atroviride, because growth of these fungi was strongly inhibited when the three saponins were applied in combination. In contrast, Fusarium oxysporum f. sp. lycopersici, Sclerotium cepivorum and Rhizoctonia solani were very little affected by saponins.

Summary •Litter decomposition provides nutrients that sustain ecosystem productivity, but litter may also hamper root proliferation. The objectives of this work were to assess the inhibitory effect of litter decomposition on seedling growth and root proliferation; to study the role of nutrient immobilization and phytotoxicity; and to characterize decomposing litter by 13C NMR spectroscopy. •A litter-bag experiment was carried out for 180 d with 16 litter types. Litter inhibitory effects were assessed by two bioassays: seed germination and root proliferation bioassays. Activated carbon (C) and nutrient solutions were used to evaluate the effects of phytotoxic factors and nutrient immobilization. •An inhibitory effect was found for all species in the early phase of decomposition, followed by a decrease over time. The addition of activated C to litter removed this inhibition. No evidence of nutrient immobilization was found in the analysis of nitrogen dynamics. NMR revealed consistent chemical changes during decomposition, with a decrease in O-alkyl and an increase in alkyl and methoxyl C. •Significant correlations were found among inhibitory effects, the litter decay rate and indices derived from NMR. The results show that it is possible to predict litter inhibitory effects across a range of litter types on the basis of their chemical composition.

Soil water repellency (SWR, i.e. reduced affinity for water owing to the presence of organic hydrophobic coatings on soil particles) has relevant hydrological implications because low rates of infiltration enhance water runoff, and untargeted diffusion of fertilizers and pesticides. Previous studies investigated the occurrence of SWR in ecosystems with different vegetation cover but did not clarify its relationships with litter biochemical quality. Here, we investigated the capability of different plant litter types to induce SWR by using fresh and decomposed leaf materials from 12 species, to amend a model sandy soil over a year-long microcosm experiment. Water repellency, measured by the Molarity of an Ethanol Droplet (MED) test, was tested for the effects of litter species and age, and compared with litter quality assessed by 13C-CPMAS NMR in solid state and elemental chemical parameters. All litter types were highly water repellent, with MED values of 18% or higher. In contrast, when litter was incorporated into the soil, only undecomposed materials induced SWR, but with a large variability of onset and peak dynamics among litter types. Surprisingly, SWR induced by litter addition was unrelated to the aliphatic fraction of litter. In contrast, lignin-poor but labile C-rich litter, as defined by O-alkyl C and N-alkyl and methoxyl C of 13C-CPMAS NMR spectral regions, respectively, induced a stronger SWR. This study suggests that biochemical quality of plant litter is a major controlling factor of SWR and, by defining litter quality with 13C-CPMAS NMR, our results provide a significant novel contribution towards a full understanding of the relationships between plant litter biochemistry and SWR.

Litter decomposition is a critical process in terrestrial ecosystems and, since in natural conditions plant litter occurs in mixtures, understanding the interactive effects of mixed litter is of great ecological relevance. In this context, we test the hypothesis that N transfer between high quality litter to N-poor substrates are at the base of synergistic interactions, positively affecting litter decay rate, temperature sensitivity, and changes of organic C quality. We carried out a manipulative experiment using four organic substrates, encompassing a wide range of biochemical quality (Hedera helix and Quercus ilex leaf litter, cellulose strips and woody sticks), each decomposing either separately or in matched pair mixtures for 360 days. Organic substrates were characterized for mass loss, C and N content and by 13C CPMAS NMR to assess biochemical quality changes. Litter response to mixing was related to the biochemical quality of the components in the mixture: additive when substrates with similarly high (H. helix and Q. ilex) or low (cellulose and wood) N content were paired, but synergistic when substrates with contrasting N content were associated (either of the two leaf litters with either cellulose or wood). Overall, no antagonist effects were observed in this experiment. Interestingly, decomposition of cellulose and wood showed an higher temperature sensitivity, compared to monospecific substrates, when paired with N rich materials. Significant N transfer was found from N rich litter to N poor substrates and 13C CPMAS NMR showed rapid changes of C quality of cellulose and wood sticks only when paired with N rich litter. Our findings support the hypothesis that mixing litters of different quality, with quality expressed in terms of C/N ratio and N content, increases decomposition rate and temperature sensitivity of the lower quality substrates.

Garlic (Allium sativum L.) is a bulb-shaped plant belonging to the Allium genus which also includes onions (Allium cepa L.), leek (Allium ampeloprasum L. var. porrum Gay), shallot (Allium ascalonicum L), scallion (A. fistulosum L.) and chives (Allium schoenoprasum L.). The biological activity of garlic has been known since ancient times. Babylonians, Egyptians, Phoenicians, Greeks and Romans used garlic as a remedy for intestinal disorders, respiratory infections, skin diseases, bacterial infections, worms, wounds and tumors. In particular, before the discovery of antibiotics, garlic has been used against amoebic dysentery and epidemic diseases such as typhus, cholera, diphtheria, and tuberculosis. To date, more than 3,000 publications scientifically supported the use of garlic in the ethno-medicine. But what makes garlic and Allium species effective against cancer? The effect of garlic may arise from its antibacterial properties or from its ability to block formation on cancer-causing substances, half the activation of cancer causing substances, enhance DNA repair, reduce cell proliferation or induce cell death. Epidemiological studies have found that an increase of consumptions of Allium spp. reduce the risk of prostate and gastric cancers and this has been mainly related to two main classes of compounds: the apolar sulphur compounds and the polar saponins. These latter compounds, compared to the more studied thiosulphinates, have the advantages of not being pungent and more stable during cooking. Recently, there has been increasing scientific attention given to such compounds. In this paper, the literature about the major volatile and non-volatile organic compounds of garlic and other Allium plants has been reviewed. Particular attention is given to the compounds possessing antibacterial and cytotoxic activity in garlic and in the other Allium species and their mechanism of action.

DNA is usually known as the molecule that carries the instructions necessary for cell functioning and genetic inheritance. A recent discovery reported a new functional role for extracellular DNA. After fragmentation, either by natural or artificial decomposition, small DNA molecules (between ∼50 and ∼2000 bp) exert a species specific inhibitory effect on individuals of the same species. Evidence shows that such effect occurs for a wide range of organisms, suggesting a general biological process. In this paper we explore the possible molecular mechanisms behind those findings and discuss the ecological implications, specifically those related to plant species coexistence.

Questions: Does the fairy ring fungus Agaricus campestris affects spatial distribution of co-existing plant species? Is ring development related to changes of soil physical, chemical, enzymatic and microbiological properties? What are the causes of weakening and subsequent luxuriance of vegetation during fairy ring dynamics in the soil?

Plants alter environmental conditions enhancing the recruitment of other species. In spite of prior reviews of facilitation, the variability of its occurrence, mechanisms, and specificity across terrestrial ecosystems has not yet been assessed. In this article, we analyze facilitative mechanisms and the distribution of specific traits, such as nitrogen fixation and the presence of fleshy fruits, across ecosystems. A comprehensive database including 2,080 cases of facilitation among higher plants from 539 articles was analyzed with descriptive statistics for occurrences of positive interactions and underlying mechanisms in different terrestrial ecosystems. Positive interactions by plant-induced environmental changes are widespread in a range of ecosystems and not limited to conditions of chronic abiotic stress such as semiarid, alpine, and wetland ecosystems. The capability to act as nurse largely varied among different growth forms, and was observed more frequently for woody than for herbaceous plants. Nitrogen fixers occur much more frequently as nurse plants than as beneficiary plants in facilitation cases due to increasing soil fertility. As known for Mediterranean ecosystems, fleshy-fruited species appear more dependent on facilitative interactions than other plants, being more frequent among beneficiaries than among nurses. The pattern can be extended worldwide being consistent in wetland, temperate, and alpine ecosystems as well. Our description of the relationship between distribution, mechanisms, and specificity of facilitation in terrestrial ecosystems has implications for the understanding of plant community organization considering that plant nursing capacity is affected by their size, architecture, and life span.

Semi‐natural calcareous grasslands are of great interest in conservation because of their high species richness, but presently they are threatened by both land abandonment and nitrogen eutrophication. The paper reports on a three‐year field experiment conducted in a species‐rich Mediterranean grassland to study the effects of nitrogen application coupled with removal of plant litter and artificial cutting on plant species diversity. Vegetation treatments were applied both to abandoned and adjacent long‐term mowed grassland, to evaluate their restoration value and impact of management abandonment. Cutting significantly increased species diversity in the abandoned area by positively affecting the cover of almost all annual and biennial species and several perennial forbs. Cutting strongly reduced the dominance of perennial grasses. Litter removal had similar effects to cutting, although it was far less effective in increasing species diversity. In the mowed area, cutting abandonment did not reduce ...

Positive plant-soil feedback by “ecosystem engineers” is an important driver for the structuring and organization of resource-limited ecosystems. Although ample evidence demonstrates that plant-soil feedbacks can range from positive to strongly negative, their co-occurrence in plant communities have not yet been investigated. We test the hypothesis that the plant-soil feedback generated by the nitrogen-fixer shrub Medicago marina during primary succession in a sand dune community has a positive effect on the coexisting grass Lophochloa pubescens and a negative effect on the shrub species itself. We conducted field measurements and laboratory bioassays to evaluate (1) the effects of islands of fertility on the recruitment and growth of its ecosystem engineer and on the performance of a coexisting species and (2) the mechanisms involved that can explain the opposite effects of islands of fertility on coexisting species. Islands of fertility were present under Medicago crowns evidenced by higher available nitrogen, extractable phosphorus and potassium, organic matter, microbial activity, water holding capacity, soil humidity, and lower salt concentrations. The effects of these islands of fertility were clearly species-specific, with a facilitative impact on Lophochloa and a negative effect on Medicago recruitment. Lophochloa was denser and produced more biomass when rooted inside as compared to outside the crown area of the shrub. Contrarily, the number of seedlings of Medicago was lower inside, despite the higher seed abundance, and higher outside the crown area of adult shrubs as compared to predictions based on random distribution, thus showing a Janzen-Connell distribution. Laboratory experiments demonstrate the occurrence of Medicago negative plant-soil feedback, and that the auto-toxicity of the aboveground senescent plant material is a potentially important underlying mechanism explaining this negative feedback and the resulting Janzen-Connell distribution in the field.

Summary • Allelopathic effects of plant litter have been extensively studied, but less attention has been given to the dynamics of phytotoxicity during the decomposition processes. • Decomposition experiments were carried out on above- and below-ground plant materials of 25 species of different functional groups (nitrogen fixer, forbs, woody and grasses–sedges) in aerobic and anaerobic conditions. The phytotoxicity of aqueous extracts of decomposing material was assessed by bioassay in 30 d of laboratory and 90 d of litterbag decomposition experiments. • Phytotoxicity was widespread with c. 90% of the tested species showing significant phytotoxic releases. Phytotoxicity largely varied between different plant functional groups (nitrogen fixer > forbs = woody >> grasses–sedges) and was higher for leaf compared with root materials. In all species tested during decomposition, phytotoxicity rapidly decreased in aerobic conditions but sharply increased and became stable in anaerobic conditions. • The results demonstrate an unexpectedly widespread occurrence of phytotoxicity with clear dynamic patterns during the decomposition processes of plant materials. The ecological consequences of this might have been underestimated.

Increasing evidence shows that facilitative interaction and negative plant–soil feedback are driving factors of plant population dynamics and community processes. We studied the intensity and the relative impact of negative feedback on clonal growth and seed germination of Scirpus holoschoenus, a ‘ring’ forming sedge dominant in grazed grassland, and the consequences for species coexistence. The structure of aboveground tussocks was described. A Lithium tracer assessed belowground distribution of functional roots. Seed rain and seedling emergence were compared for different positions in relation to Scirpus tussocks. Soil bioassays were used to compare growth on soil taken from inside and outside Scirpus tussocks of four coexisting species (Mentha acquatica, Pulicaria dysenterica, Scirpus holoschoenus and Dittrichia viscosa). We also compared plant performance of dominant plant species inside and outside Scirpus tussocks in the field. The ‘ring’ shaped tussocks of S. holoschoenus were generated by centrifugal rhizome development. Roots were functional and abundant under the tillers and extending outside the tussocks. The large roots mats that were present in the inner tussock zone were almost all dead. Seedling emergence and growth both showed a strong negative feedback of Scirpus in the inner tussock zone. Scirpus clonal development strongly reduced grass biomass. In the degenerated tussock zone, Pulicaria and Mentha mortality was lower, and biomass of individual plants and seed production were higher. This positive indirect interaction could be related to species-specific affinity to soil conditions generated by Scirpus, and interspecific competitive release in the degenerated tussock zone. We conclude that Scirpus negative feedback affects its seedling emergence and growth contributing to the development of the degenerated inner tussock zone. Moreover, this enhances species coexistence through facilitative interaction because the colonization of the inner tussock zone is highly species-specific.

Intensive agriculture is a farming system characterised by a large use of inputs, causing a large pressure on the environment. As peculiar and efficient example of intensive agriculture cultivation under plastic tunnels provides several advantages for farmers due to improvement of microclimatic conditions coupled with a relatively low investment costs. In the Mediterranean Basin such cultivation systems reach about 200,000 ha mainly in Spain, Turkey, Italy, and Morocco. As downside, intensive agriculture negatively affects soil fertility principally because of a loss in soil organic matter. Sustainable practices providing organic amendments could be a useful tool to maintain or increase organic matter content in agricultural soils, preserving and improving soil fertility. An improved knowledge of management factors affecting soil quality is crucial to plan farming systems that effectively maintain soil fertility. Therefore, this review focuses on the potential value of organic amendments in the recovery of soil fertility, in particular in sites under plastic cover intensive farming system. Following a brief overview of the effects of intensive agriculture on soil, the review describes various organic amendments used in agriculture and their benefits on soil fertility, to conclude with the need, in the future researches, to identify organic amendments able to maximize a recovery of soil fertility.