SummaryPlant-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.

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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 13 C 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.

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? Location: Species-rich, mowed calcareous grassland, central Italy (43° 17′26″ N, 12° 51′29″ E). Methods: Fairy rings were monitored for total plant biomass, species richness and composition in four zones: external grassland (OUT), fungal front (FF), area with flourishing vegetation (BELT) and internal grassland (IN). In each zone, 17 soil parameter were analysed: physical and chemical properties (water-holding capacity, pH, electrical conductivity, organic C, Olsen P, total N, NH 4 +, NO 3 -, hydrophobicity and cyanide concentration), total enzyme activity (FDA) and microbiological features (community-level physiological profile using BIOLOG EcoPlates ™, microbial biomass, fungal mycelium, culturable actinomycetes, bacteria and fungi). A bioassay was performed to evaluate responses of three co-existing species (Bromus erectus, Cynosurus echinatus and Centaurea ambigua) growing on soil collected from different fairy ring zones. Results: Plant species composition dramatically changed in response to fairy ring development, with disappearance of most grassland species in the ring-affected area. Plant biomass and species richness were higher in OUT and IN areas, and lowest in FF. Profound changes in soil properties occurred after fungal passage, with consistent reductions of C and N content and increases of FDA and microbial physiological profiles. Soil from the FF zone had remarkable increases of mineral N forms, electrical conductivity and hydrophobicity, with no trace of cyanide. The bioassay showed species-specific responses to different soil types. Conclusions: This study provides evidence that the spread of fairy ring fungi, coupled with a reduction of perennial plant cover, creates empty niches for many short-lived species

The vast majority of grass species retain their leaves as they become senescent, inducing an accumulation of dead biomass that may limit plant productivity. In this research, we tested the hypothesis that dead leaf retention by grasses act as a defense against large herbivores. In a natural grassland of the Flooding Pampa, we carried out a factorial experiment with dead‐leaf removal and grazing as main factors. Dead leaves were removed from the palatable grass Paspalum dilatatum, and growth was measured either in the absence or in the presence of large grazers. In the absence of grazers, dead‐leaf removal promoted plant growth. In the presence of grazers, dead‐leaf removal increased consumption by cattle, particularly among the largest plants. As a result, in the presence of grazers, plants with dead leaves removed grew less than intact plants. The results indicate that retaining dead leaves is costly for grass species in the absence of grazers, but, as proposed by our hypothesis, that cost is compensated by a corresponding reduction of grazing consumption.

This study aims to explore the effect of environmental factors (temperature, light, storage time) on germination response and dormancy patterns in eight Mediterranean native wildplants, belonging to the Euphorbia L. genus. In detail, we considered E. amygdaloides subsp. arbuscula, E. bivonae subsp. bivonae, E. ceratocarpa, E. characias, E. dendroides, E. melapetala, E. myrsinites, and E. rigida. We collected seeds from natural plant populations and performed germination assays in climatic chambers at seven constant temperatures (from 5 to 35°C, with 5°C increments), and four fluctuating temperature regimes (8/15, 8/20, 8/25, and 8/30°C, with a 12/12 hr thermoperiod). Germination assays were set up both in dark (D) and in light/dark conditions (L/D, 12/12 hr photoperiod), after short and long seed storage (SS around 30 days and LS around 150 days). For all these species, except E. amygdaloides subsp. arbuscula, results show that the final germinated proportions were improved by a long storage period (>150 days), which supports the existence of nondeep physiological dormancy. Optimal temperature levels ranged from 14.3 to 21.3°C and base temperatures ranged from 5.6 to 12.1°C, while ceiling temperatures from 25.6 to 34.7°C. For none of these species, germinations were favored by an alternating daily temperature regime, while in several instances, germinations were quicker and more complete in darkness, than in an alternating light/dark regime. In some instances, extreme temperature levels (5 and 30°C) induced dormancy and germinations did not resume when seeds were exposed at optimal temperature levels. Results are discussed in terms of the dynamics of emergences and how this might be affected by climate changes.

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We compared the capacity to accumulate airborne heavy metals of two lichens (Flavoparmelia caperata and Parmotrema chinense) and one higher plant (Nerium oleander) at a very densely populated urban site near Naples. After 15, 45, 75, and 120 days of exposure at four sites with different levels of air pollution, equal portions of thalli and 20 leaves were collected, and four environmentally significant elements, Fe, Cu, Zn, and Pb, were measured by inductively coupled plasma analysis. To compare the accumulation rates of lichens and the vascular plant, we determined an index of relative accumulation rate of pollutants during time and the ratio between the concentrations of each element in exposed samples to that of control samples (exposed-to-control ratio). Our data indicate F. caperata as being the most suitable bioaccumulator, followed by P. chinense. N. oleander was also found to be a useful heavy metal biomonitor though not suitable as a bioaccumulator.