Organic matter quality defined by 13C NMR spectroscopy explains nitrogen mineralization and soil aggregation better than C/N ratio

Soil organic matter (SOM) plays a key role in sustainable agricultural production by the improvement of physical, chemical and biological properties of soils. The decline in organic matter (OM) content of many soils is becoming a major process of soil infertility and degradation, particularly in European semi-arid Mediterranean regions. Organic amendments can increase SOM content, thus influence soil characteristics by the interdependent modification of biological, chemical and physical properties. Then, a better understanding of the impact of organic amendment on soil processes is required. The underlying hypothesis of this thesis is that the organic amendment can regulate soil processes which directly linked to its initial chemical characteristics. However, identifying and defining OM quality based on molecular composition is operationally difficult. In fact, OM contain multiple types of biomolecules with different aqueous solubility, and, hence, the different susceptibility to microbial decomposition (e.g. peptides, carbohydrates, lipids, lignin, organic acids, and polyphenols). Generally, lignin/N and C/N ratios are extensively used as descriptors of OM quality, but those simple indicators are not always give reliable information about their potential of effects on soil functions. In this context, several chemical throughput methods, such as pyrolysis-gas chromatography/mass spectrometry, near infrared reflectance spectroscopy and nuclear magnetic resonance (NMR) spectroscopy have been utilized to characterize OM at the molecular level. In particular, solid-state13C-CPMAS NMR spectra were found useful to provide an overview of the total organic chemical composition of complex matrices of SOM. This thesis showed that the chemical quality of OM, defined by solid-state 13C-CPMAS NMR spectra, can be an important indicator of soil functions, which explain nitrogen mineralization and soil aggregation process better than classical C/N and lignin/N ratio indices. Finally, modeling approach based on novel implementation of OM quality by 13C-CPMAS NMR, to purposely overcome the limitations of C/N as a single OM quality indicator and to explore the relationship between OM quality and soil structural stability. This thesis provides evidence for the importance of OM, and in particular its chemical quality, which influences soil processes by inter-depended modification of soil physical, chemical and biological parameters

Different pathways but same result? Comparing chemistry and biological effects of burned and decomposed litter

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. Here, we tested the chemical convergence hypothesis (i.e. materials with different initial chemistry tend to converge towards a common profile, with similar biological effects, as the oxidative process advances) for burning and decomposition. We compared the molecular composition of 63 organic materials - 7 litter types either fresh, decomposed for 30, 90, 180 days, or heated at 100, 200, 300, 400, 500 \ub0C - as assessed by 13C NMR. We used litter water extracts (5% dw) as treatments in bioassays on plant (Lepidium sativum) and fungal (Aspergillus niger) growth, and a washed quartz sand amended with litter materials (0.5 % dw) to assess heterotrophic respiration by CO2 flux chamber. We observed different molecular variations for materials either burning (i.e. a sharp increase of aromatic C and a decrease of most other fractions above 200 \ub0C) 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 progressively decreased with litter age and temperature. Plant growth underwent an inhibitory effect by untreated litter, more and less rapidly released over decomposing and burning materials, respectively. Correlation analysis between NMR and bioassay data showed that opposite responses for soil respiration and fungi, compared to plants, are related to essentially the same C molecular types. Our findings suggest a functional convergence of decomposed and burnt 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

Windstorm disturbance triggers multiple species invasion in an urban Mediterranean forest

Plant invasion in forest ecosystems is a serious ecological and economic issue, deserving attention by researchers, managers and policy-makers worldwide. Many invasive plants have been reported as early successional species able to colonize disturbed areas following abrupt changes in microhabitat and resource availability. We investigated disturbance effects of a severe windstorm generated by a wet microburst (hail and rain at 160 mm h-1) remarkably affecting the canopy cover of an old-growth Quercus ilex urban forest in Southern Italy. This stand-replacing disturbance produced a mosaic of 103 gaps, 5.6 to 1632 m2 in size, over an area of 1.53 ha, uprooting 76% of the trees and decreasing thereby 85% of the standing above-ground dry biomass into the gaps. By intensive monitoring we compared above- and below-ground microclimate, soil moisture and mineral N availability in paired disturbed and control areas of the study forest. Within newly formed gaps we observed a seasonally consistent 70% higher content of nitrate nitrogen, 29% and 47% decreases of ammonia nitrogen in summer and autumn, respectively, and a higher moisture in topsoil, in addition to different above- and below-ground microclimatic conditions, with canopy cover mitigating extreme temperatures. One year after the windstorm, the microhabitat shift promoted the establishment in gaps of 15 native and 10 alien taxa previously absent in both disturbed and control plots. In such conditions, the rarefaction of the dominant Q. ilex canopy cover and the occurrence of empty niches prone to invasion could dramatically affect the local community structure and diversity. Our data indicate that stand-replacing windstorm can transiently transform the studied urban evergreen forest to an early allogenic successional community dominated, in the medium and large gaps, by annual and perennial non-native species. This is particularly relevant under a perspective of possible increasing frequency of windstorm events in the Mediterranean region in the near future

Physico-chemical Profile and Microbial Diversity During Bioconversion of Sugarcane Press Mud Using Bacterial Suspension

This study was aimed at investigating the physico-chemical and microbial diversity for rapid composting of sugarcane press mud (PM) leading to organic manure. Five bacterial strains (Cellulomonas sp., Klebsiella sp., Proteus sp., Enterobacter sp., Salmonella sp.) were tested under in vivo conditions for bioconversion of PM using pile method. Results revealed that combined inoculation of bacterial consortia was found to be the best decomposer of PM resulting reduction of organic carbon content (26.75%), C:N ratio (12.44%). In parallel, it increased the nitrogen (2.34%), phosphorous (1.15%) and potassium (1.37%) content along with the population of microorganisms i.e. bacteria, fungi and actinomycetes. However, the population of tested bacteria was gradually depleted after completion of PM decomposition together with pathogenic bacteria and fungi due to full conversion of carbon component into other minerals, i.e. N, P, K etc. Taken together, these findings certainly pinpoints the effective role of bacterial suspension for composting sugarcane press mud which the eventually be used as organic manure

Antitumor properties of two traditional aromatic rice genotypes (Kalijira and Chinigura)

Objective: Methanol extract of bran and unpolished grain of two traditional aromatic rice genotypes viz. Kalijira and Chinigura were assayed for their activity on the growth and initiation of crown-gall tumors on potato disks. Materials and Methods: Three Agrobacterium tumefaciens (A. tumefaciens) strain AtSl0105, AtTa0112, and AtAc0114 were used as the tumor forming agent. Collected rice was separated to bran and unpolished grain by different milling processes and made into fine powder before extracting using methanol. Antitumor assay of plant extracts was performed according to standard potato disc bioassay. Disc diffusion assay (Kirby-Bauer Method) was used to screen A. tumefaciens sensitivity test. Results: The results demonstrated a high correlation between the ability of aromatic rice to inhibit the initiation and growth of crown-gall tumors on potato disks. Maximum tumor inhibitions were observed against the strain AtSl0105 by Kalijira bran (73.91%) and Chinigura bran (69.56%). Both unpolished grains showed significant effect (Kalijira 57.43%, Chinigura 55.53%) to inhibit the tumor. Conclusion: It can be concluded that aromatic rice (Kalijira and Chinigura) might be a potential source of antitumor agent that can be used for further drug development for tumor treatment

Soil fertility promotes decomposition rate of nutrient poor, but not nutrient rich litter through nitrogen transfer

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

Modelling decomposition, intermolecular protection and physical aggregation based on organic matter quality assessed by 13C-CPMAS-NMR

Modelling organic matter decomposition is fundamental to predict biogeochemical cycling in terrestrial ecosys- tems. 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 that includes a description of biomolecular dynamics obtained by 13C-CPMAS NMR spectroscopy. Baseline decay rates for relevant molec- ular 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. Our innova- tive approach accurately predicted decomposition of a wide range of litters across different climates. Simulations correctly reproduced mass loss data and variations of selected molecular classes both in controlled conditions and in the field, across different plant molecular compositions and environmental conditions. Prediction accuracy emerged from the species-specific partitioning of molecular types and from the representation of intermolecular interactions. The ongoing model implementation and calibration are oriented at representing organic matter dy- namics in soil, including processes of interaction between mineral and organic soil fractions as a function of soil texture, physical aggregation of soil organic particles, and physical protection of soil organic matter as a function of aggregate size and abundance. Prospectively, our model shall satisfactorily reproduce C sequestration as resulting from experimental data of soil amended with a range of organic materials with different biomolecular quality, rang- ing from biochar to crop residues. Further application is also planned based on long-term decomposition datasets from different natural and agro-ecosystems

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 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

Combined application of photo-selective mulching films and beneficial microbes affects crop yield and irrigation water productivity in intensive farming systems

Cultivation of vegetables under plastic tunnels is a steadily growing farming system, nevertheless there are concerns about its environmental sustainability. This work tests a new cultivation system based on the application of photo-selective mulching films to the soil combined with beneficial microbes to improve crop yield, save irrigation water and enhance crop irrigation water productivity. A two-year project was carried out in three farms of southern Italy that practice cultivation in greenhouses with different soil characteristics. Photo-selective mulching films (PS) were used alone or in combination with microbial consortia (M) containing beneficial microbes (i.e. antagonistic fungi of the genus Trichoderma, mycorrhizal fungi of the genus Glomus and the plant growth promoting bacterium Bacillus subtilis) and compared with black plastic mulching (B). Soil temperature, soil water content, and irrigation water volumes were continuously monitored for eight cropping cycles including tomato, sweet pepper, lettuce, melon, and kohlrabi. Crop yields were assessed at the end of each cycle. PS films in combination with M significantly increased crop yields with respect to control, with the most positive effects on winter crops. Soil temperature under PS was consistently lower than that under B mulch. All mulching films allowed the saving of irrigation water compared with untreated control, but no difference was detected between PS and B. However, PS increases crop irrigation water productivity (CIWP) compared with B film in 25% of the experimental cases. In conclusion, our results indicate that combining PS films with beneficial microbes in cultivation under plastic tunnel greenhouses promotes crop yield and increases CIWP compared with control in 87.5% and 75% of the study cases, respectivel