106 research outputs found
The influence of plant litter on soil water repellency: Insight from 13CNMR spectroscopy
No full textSoil 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 C-13-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 C-13-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 C-13-CPMAS NMR, our results provide a significant novel contribution towards a full understanding of the relationships between plant litter biochemistry and SWR
Unimodal pattern of soil hydrophobicity along an altitudinal gradient encompassing Mediterranean, temperate, and alpine ecosystems
No full textBackground 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
Erratum to: Unimodal pattern of soil hydrophobicity along an altitudinal gradient encompassing Mediterranean, temperate, and alpine ecosystems (Plant and Soil, (2016), 409, 1-2, (37-47), 10.1007/s11104-016-3020-0)
No full textLitter chemistry explains contrasting feeding preferences of bacteria, fungi, and higher plants
No full textAbstractLitter 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.</jats:p
Linking bacterial and eukaryotic microbiota to litter chemistry: Combining next generation sequencing with 13C CPMAS NMR spectroscopy
No full textMicrobial succession over decomposing litter is controlled by biotic interactions, dispersal limitation, grazing pressure, and substrate chemical changes. Recent evidence suggests that the changes in litter chemistry and microbiome during decomposition are interdependent. However, most previous studies separately addressed the microbial successional dynamics or the molecular changes of decomposing litter. Here, we combined litter chemical characterization by 13C NMR spectroscopy with next generation sequencing to compare leaf litter chemistry and microbiome dynamics using 30 litter types, either fresh or decomposed for 30 and 180 days.
We observed a decrease of cellulose and C/N ratio during decomposition, while lignin content and lignin/N ratio showed the opposite pattern. 13C NMR revealed significant chemical changes as microbial decomposition was proceeding, with a decrease in O-alkyl C and an increase in alkyl C and methoxyl C relative abundances. Overall, bacterial and eukaryotic taxonomical richness increased with litter age. Among Bacteria, Proteobacteria dominated all undecomposed litters but this group was progressively replaced by members of Actinobacteria, Bacteroidetes, and Firmicutes. Nitrogen-fixing genera such as Beijerinckia and Rhizobium occurred both in un- decomposed as well as in aged litters. Among Eukarya, fungi belonging to the Ascomycota phylum were dominant in undecomposed litter with the typical phyllospheric genus Aureobasidium. In aged litters, phyllo- spheric species were replaced by zygomycetes and other ascomycetous and basidiomycetous fungi. Our analysis of decomposing litter highlighted an unprecedented, widespread occurrence of protists belonging to the Amebozoa and Cercozoa. Correlation network analysis showed that microbial communities are non-randomly structured, showing strikingly distinct composition in relation to litter chemistry. Our data demonstrate that the importance of litter chemistry in shaping microbial community structure increased during the decomposition process, being of little importance for freshly fallen leaves
Frequent Applications of Organic Matter to Agricultural Soil Increase Fungistasis
No full textSoil–borne plant pathogens are among the most important limiting factors for the productivity of agro–ecosystems. Fungistasis is the natural capability of soils to inhibit the germination and growth of soil–borne fungi in the presence of optimal abiotic conditions. The objective of this study was to assess the effects of different soil managements, in terms of soil amendment types and frequency of application, on fungistasis. For this purpose, a microcosm experiment was performed by conditioning a soil with frequent applications of organic matter with contrasting biochemical quality (i. e., glucose, alfalfa straw and wheat straw). Thereafter, the fungistasis response was assessed on four fungi (Aspergillus niger, Botrytis cinerea, Pyrenochaeta lycopersici and Trichoderma harzianum). Conditioned soils were characterized by measuring microbial activity (soil respiration) and functional diversity using the BIOLOG EcoPlatesTM method. Results showed that irrespective of the fungal species and amendment types, frequent applications of organic matter reduced fungistasis relief and shortened the time required for fungistasis restoration. The frequent addition of easily decomposable organic compounds enhanced soil respiration and its specific catabolic capabilities. This study demonstrated that frequent applications of organic matter affected soil fungistasis likely as a result of higher microbial activity and functional diversity
Soil fertility promotes decomposition rate of nutrient poor, but not nutrient rich litter through nitrogen transfer
No full textBackground 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
Exploring Dittrichia viscosa (L.) Greuter phytochemical diversity to explain its antimicrobial, nematicidal and insecticidal activity
No full textDittrichia 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
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