One ring to rule them all: an ecosystem engineer fungus fosters plant and microbial diversity in a Mediterranean grassland.

Species coexistence in grasslands is regulated by several environmental factors and interactions with the soil microbial community. Here, the development of the Basidiomycetes fungus Agaricus arvensis, forming fairy rings, in a species-rich Mediterranean grassland, is described. Effects of the mycelial front on plants, fungi and bacteria were assessed by vegetation survey and next generation sequencing approaches. Our results showed a fungal-dependent shift in the community structure operated by a wave-like spread of fairy rings that decreased plant, fungal and bacterial diversity, indicating a detrimental effect of fairy rings on most species. The fairy rings induced successional processes in plants that enhanced the replacement of a community dominated by perennial plants with short-living and fast-growing plant species. In parallel, fungal and bacterial communities showed evident differences in species composition with several taxa associated within distinct sampling zone across the fairy rings. Notably, bacteria belonging to the Burkholderia genus and fungi of the genus Trichoderma increased in response to the advancing mycelium of A. arvensis. The profound changes in community composition and the overall increase in taxa diversity at ecosystemic scale suggest that fairy ring-forming fungi may act as ecosystem engineer species in Mediterranean grasslands.

Comparing chemistry and bioactivity of burned vs. decomposed plant litter: different pathways but same result?

Litter burning and biological decomposition are oxidative processes co-occurring in many terrestrial ecosystems, producing organic matter with different chemical properties and differently affecting plant growth and soil microbial activity. We tested the chemical convergence hypothesis, i.e., materials with different initial chemistry converge toward a common profile, with similar biological effects, as the oxidative process advances, for burning and decomposition. We compared the molecular composition, assessed by 13 C NMR, of seven plant litter types either fresh, decomposed for 30, 90, 180 d in a microcosms incubation experiment, or heated at 100°C, 200°C, 300°C, 400°C, 500°C for 30 minutes. We used litter water extracts (5% dry weight) as treatments in bioassays on plant (Lepidium sativum) and fungal (Aspergillus niger) growth, and a washed quartz sand amended with litter (0.5% dw) to assess heterotrophic respiration by flux chamber (i.e., [µg of CO2 released]·[g added litter]-1 ·d-1 ). We observed different molecular variations for materials either burning (i.e., a sharp increase of aromatic C and a decrease of other fractions above 200°C) or decomposing (i.e., early increase of alkyl, methoxyl, and N-alkyl C and decrease of O-alkyl and di-O-alkyl C fractions). Soil respiration and fungal growth decreased with litter age and heating severity, down to 20% relative to fresh litter. Plants were inhibited on fresh litter (on average 13% of the control), but recovered on aged (180 d) and heated (30 min at 500°C) materials, up to 126% and 63% of the control, respectively. Correlation between the intensity of 13 C NMR signals in litter spectra and bioassay results showed that O-alkyl, methoxyl, and aromatic C fractions are crucial to understand organic matter effects, with plant response negatively affected by labile C but positively associated to lignification and pyrogenic C. The pattern of association of soil respiration and fungal growth to these C fractions was essentially opposite to that observed for plant root growth. Our findings suggest a functional convergence of decomposed and burned organic substrates, emerging from the balance between the bioavailability of labile C sources and the presence of recalcitrant and pyrogenic compounds, oppositely affecting different trophic levels.

Topography modulates near-ground microclimate in the Mediterranean Fagus sylvatica treeline.

Understanding processes controlling forest dynamics has become particularly important in the context of ongoing climate change, which is altering the ecological fitness and resilience of species worldwide. However, whether forest communities would be threatened by projected macroclimate change or unaffected due to the controlling effect of local site conditions is still a matter for debate. After all, forest canopy buffer climate extremes and promote microclimatic conditions, which matters for functional plant response, and act as refugia for understory species in a changing climate. Yet precisely how microclimatic conditions change in response to climate warming will depend on the extent to which vegetation structure and local topography shape air and soil temperature. In this study, we posited that forest microclimatic buffering is sensitive to local topographic conditions and canopy cover, and using meteorological stations equipped with data-loggers we measured this effect during 1 year across a climate gradient (considering aspect as a surrogate of local topography) in a Mediterranean beech treeline growing in contrasting aspects in southern Italy. During the growing season, the below-canopy near-ground temperatures were, on average, 2.4 and 1.0 °C cooler than open-field temperatures for south and north-west aspects, respectively. Overall, the temperature offset became more negative (that is, lower under-canopy temperatures at the treeline) as the open-field temperature increased, and more positive (that is, higher under-canopy temperatures at the treeline) as the open-field temperature decreased. The buffering effect was particularly evident for the treeline on the south-facing slope, where cooling of near-ground temperature was as high as 8.6 °C for the maximum temperature (in August the offset peaked at 10 °C) and as high as 2.5 °C for the average temperature. In addition, compared to the south-facing slope, the northern site exhibited less decoupling from free-air environment conditions and low variability in microclimate trends that closely track the free-air biophysical environment. Although such a decoupling effect cannot wholly isolate forest climatic conditions from macroclimate regional variability in the south-facing treeline, it has the potential to partly offset the regional macroclimatic warming experienced in the forest understory due to anthropogenic climate change.

Organic Amendments Modulate Soil Microbiota and Reduce Virus Disease Incidence in the TSWV-Tomato Pathosystem.

Application of organic amendments is considered an eco-friendly practice to promote soil fertility and suppressiveness against a wide range of soil-borne pathogens. However, limited information is available about the capabilities of organic amendments to control virus disease. In this study, the suppressiveness of different organic amendments (i.e., compost manure, biochar, alfalfa straw, and glucose) was determined against the Tomato spotted wilt virus (TSWV) on tomato plants in a 1-year-long mesocosm experiment. Organic treatments were compared to the ordinary soil management based on mineral fertilizers and fumigation. Tomato seedlings were inoculated with TSWV and the infection and symptoms were assessed three weeks later. The disease incidence was higher in soil treated with mineral fertilizers and fumigation (> 80%) compared to the application of organic amendments, with alfalfa straw and biochar recording the lowest incidence (< 40%). Moreover, soil microbiota structure and diversity were assessed by high-throughput sequencing of bacterial and eukaryotic rRNA gene markers. Several members belonging to the bacterial phyla of Acidobacteria, Actinobacteria, Bacteroidetes, and Proteobacteria, as well as members of the fungal genus Acremonium, were positively associated with plant health. This study showed that conventional practices, by shifting microbiome composition, may increase TSWV incidence and severity.

Decomposition and organic amendments chemistry explain contrasting effects on plant growth promotion and suppression of Rhizoctonia solani damping off.

Organic Amendments (OAs) has been used in agroecosystems to promote plant growth and control diseases caused by soilborne pathogens. However, the role of OAs chemistry and decomposition time on plant growth promotion and disease suppression is still poorly explored. In this work, we studied the effect of 14 OAs at four decomposition ages (3, 30, 100, and 300 days) on the plant-pathogen system Lactuca sativa-Rhizoctonia solani. OAs chemistry was characterized via 13C-CPMAS NMR spectroscopy as well as for standard chemical (i.e. N content, pH, EC) and biological parameters (i.e. phytotoxicity and R. solani proliferation bioassay). OAs have shown variable effects, ranging from inhibition to stimulation of Lactuca sativa and Lepidium sativum growth. We recorded that N rich OAs with high decomposability were conducive in the short-term, while converting suppressive in the long term (300 days). On the other hand, cellulose-rich OAs with high C/N ratio impaired L. sativa growth but were more consistent in providing protection from damping-off, although this property has significantly shifted during decomposition time. These results, for the first time, highlight a consistent trade-off between plant growth promotion and disease control capability of OAs. Finally, we found that OAs effects on growth promotion and disease protection can be hardly predictable based on the chemical characteristic, although N content and some 13C CPMAS NMR regions (alkyl C, methoxyl C, and carbonyl C) showed some significant correlations. Therefore, further investigations are needed to identify the mechanism(s) behind the observed suppressive and conducive effects and to identify OAs types and application timing that optimize plant productivity and disease suppression in different agro-ecosystems.

The fate of cigarette butts in different environments: Decay rate, chemical changes and ecotoxicity revealed by a 5-years decomposition experiment.

Cigarette butts (CBs) are the most common litter item on Earth but no long-term studies evaluate their fate and ecological effects. Here, the role of nitrogen (N) availability and microbiome composition on CBs decomposition were investigated by a 5-years experiment carried out without soil, in park grassland and sand dune. During decomposition, CBs chemical changes was assessed by both 13C CPMAS NMR and LC-MS, physical structure by scanning electron microscope and ecotoxicity by Aliivibrio fischeri and Raphidocelis subcapitata. Microbiota was investigated by high-throughput sequencing of bacterial and eukaryotic rRNA gene markers. CBs followed a three-step decomposition process: at the early stage (∼30 days) CBs lost ∼15.2% of their mass. During the subsequent two years CBs decomposed very slowly, taking thereafter different trajectories depending on N availability and microbiome composition. Without soil CBs showed minor chemical and morphological changes. Over grassland soil a consistent N transfer occurs that, after de-acetylation, promote CBs transformation into an amorphous material rich in aliphatic compounds. In sand dune we found a rich fungal microbiota able to decompose CBs, even before the occurrence of de-acetylation. CBs ecotoxicity was highest immediately after smoking. However, for R. subcapitata toxicity remained high after two and five years of decomposition.

Faster N Release, but Not C Loss, From Leaf Litter of Invasives Compared to Native Species in Mediterranean Ecosystems.

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 1-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.

Biochars from olive mill waste have contrasting effects on plants, fungi and phytoparasitic nematodes.

Olive mill waste (OMW), a byproduct from the extraction of olive oil, causes serious environmental problems for its disposal, and extensive efforts have been made to find cost-effective solutions for its management. Biochars produced from OMW were applied as soil amendment and found in many cases to successfully increase plant productivity and suppress diseases. This work aims to characterize biochars obtained by pyrolysis of OMW at 300 °C to 1000 °C using 13C NMR spectroscopy, LC-ESI-Q-TOF-MS and SEM (Scanning Electron Microscopy). Chemical characterization revealed that biochar composition varied according to the increase of pyrolysis temperature (PT). Thermal treated materials showed a progressive reduction of alkyl C fractions coupled to the enrichment in aromatic C products. In addition, numerous compounds present in the organic feedstock (fatty acids, phenolic compounds, triterpene acids) reduced (PT = 300 °C) or completely disappeared (PT ≥ 500 °C) in biochars as compared to untreated OMW. PT also affected surface morphology of biochars by increasing porosity and heterogeneity of pore size. The effects of biochars extracts on the growth of different organisms (two plants, one nematode and four fungal species) were also evaluated. When tested on different living organisms, biochars and OMW showed opposite effects. The root growth of Lepidium sativum and Brassica rapa, as well as the survival of the nematode Meloidogyne incognita, were inhibited by the untreated material or biochar produced at 300 °C, but toxicity decreased at higher PTs. Conversely, growth of Aspergillus, Fusarium, Rhizoctonia and Trichoderma fungi was stimulated by organic feedstock, while being inhibited by thermally treated biochars. Our findings showed a pattern of association between specific biochar chemical traits and its biological effects that, once mechanistically explained and tested in field conditions, may lead to effective applications in agriculture.

Litter chemistry explains contrasting feeding preferences of bacteria, fungi, and higher plants.

Litter decomposition provides a continuous flow of organic carbon and nutrients that affects plant development and the structure of decomposer communities. Aim of this study was to distinguish the feeding preferences of microbes and plants in relation to litter chemistry. We characterized 36 litter types by 13C-CPMAS NMR spectroscopy and tested these materials on 6 bacteria, 6 fungi, and 14 target plants. Undecomposed litter acted as a carbon source for most of the saprophytic microbes, although with a large variability across litter types, severely inhibiting root growth. An opposite response was found for aged litter that largely inhibited microbial growth, but had neutral or stimulatory effects on root proliferation. 13C-CPMAS NMR revealed that restricted resonance intervals within the alkyl C, methoxyl C, O-alkyl C and di-O-alkyl C spectral regions are crucial for understanding litter effects. Root growth, in contrast to microbes, was negatively affected by labile C sources but positively associated with signals related to plant tissue lignification. Our study showed that plant litter has specific and contrasting effects on bacteria, fungi and higher plants, highlighting that, in order to understand the effects of plant detritus on ecosystem structure and functionality, different microbial food web components should be simultaneously investigated.

Biochar As Plant Growth Promoter: Better Off Alone or Mixed with Organic Amendments?

Biochar is nowadays largely used as a soil amendment and is commercialized worldwide. However, in temperate agro-ecosystems the beneficial effect of biochar on crop productivity is limited, with several studies reporting negative crop responses. In this work, we studied the effect of 10 biochar and 9 not pyrogenic organic amendments (NPOA), using pure and in all possible combinations on lettuce growth (Lactuca sativa). Organic materials were characterized by 13C-CPMAS NMR spectroscopy and elemental analysis (pH, EC, C, N, C/N and H/C ratios). Pure biochars and NPOAs have variable effects, ranging from inhibition to strong stimulation on lettuce growth. For NPOAs, major inhibitory effects were found with N poor materials characterized by high C/N and H/C ratio. Among pure biochars, instead, those having a low H/C ratio seem to be the best for promoting plant growth. When biochars and organic amendments were mixed, non-additive interactions, either synergistic or antagonistic, were prevalent. However, the mixture effect on plant growth was mainly dependent on the chemical quality of NPOAs, while biochar chemistry played a secondary role. Synergisms were prevalent when N rich and lignin poor materials were mixed with biochar. On the contrary, antagonistic interactions occurred when leaf litter or woody materials were mixed with biochar. Further research is needed to identify the mechanisms behind the observed non-additive effects and to develop biochar-organic amendment combinations that maximize plant productivity in different agricultural systems.

The Influence of Plant Litter on Soil Water Repellency: Insight from 13C NMR Spectroscopy.

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.

Climate, Soil Management, and Cultivar Affect Fusarium Head Blight Incidence and Deoxynivalenol Accumulation in Durum Wheat of Southern Italy.

Fusarium head blight (FHB) is a multifaceted disease caused by some species of Fusarium spp. A huge production of mycotoxins, mostly trichothecenes, often accompanied this disease. Amongst these toxic compounds, deoxynivalenol (DON) and its derivatives represent a major issue for human as well as for animal health and farming. Common and durum wheat are amongst the hosts of trichothecene-producing Fusaria. Differences in susceptibility to fungal infection and toxin accumulation occur in wheat cultivars. Recently, increasing incidence and severity of Fusarium infection and a higher DON accumulation in durum wheat were observed in Italy, especially in Northern regions. In this study, we analyzed wheat yield, technological parameters, the incidence of Fusarium infection and DON content in kernel samples of durum wheat coming from three locations of Southern Italy with different climatic conditions and grown during two seasons, with two methods of cultivation. Four different durum wheat cultivars prevalently cultivated in Southern Italian areas were chosen for this study. Our analysis showed the effects of environment and cultivar types on wheat productivity and key technological parameters for the quality level of the end-product, namely pasta. Notably, although a low rate of mycotoxin contamination in all study sites was assessed, an inverse relation emerged between fungal infection/DON production and durum wheat yield. Further, our study pinpoints the importance of environment conditions on several quality traits of durum wheat grown under Mediterranean climate. The environmental conditions at local level (microscale) and soil management practices may drive FHB outbreak and mycotoxin contamination even in growing area suitable for cropping this wheat species.

Cigarette butt decomposition and associated chemical changes assessed by 13C CPMAS NMR.

Cigarette butts (CBs) are the most common type of litter on earth, with an estimated 4.5 trillion discarded annually. Apart from being unsightly, CBs pose a serious threat to living organisms and ecosystem health when discarded in the environment because they are toxic to microbes, insects, fish and mammals. In spite of the CB toxic hazard, no studies have addressed the effects of environmental conditions on CB decomposition rate. In this study we investigate the interactive effects of substrate fertility and N transfer dynamics on CB decomposition rate and carbon quality changes. We carried out an experiment using smoked CBs and wood sticks, used as a slow decomposing standard organic substrate, incubated in both laboratory and field conditions for two years. CB carbon quality changes during decomposition was assessed by 13C CPMAS NMR. Our experiment confirmed the low degradation rate of CBs which, on average, lost only 37.8% of their initial mass after two years of decomposition. Although a net N transfer occurred from soil to CBs, contrary to our hypothesis, mass loss in the medium-term (two years) was unaffected by N availability in the surrounding substrate. The opposite held for wood sticks, in agreement with the model that N-rich substrates promote the decomposition of other N-poor natural organic materials with a high C/N ratio. As regards CB chemical quality, after two years of decomposition 13C NMR spectroscopy highlighted very small changes in C quality that are likely to reflect a limited microbial attack.