Biochar application and summer temperatures reduce N2O and enhance CH4 emissions in a Mediterranean agroecosystem: Role of biologically-induced anoxic microsites.

Biochar applications have been proposed for mitigating some soil greenhouse gas (GHG) emissions. However, results can range from mitigation to no effects. To explain these differences, mechanisms have been proposed but their reliability depends on biochar type, soil and climatic conditions. Furthermore, it is found that the mitigation capacity is dependent on how the biochar is aging under field conditions. The effects on N2O, CH4 and CO2 emission rates of a gasification pine biochar (applied as 0, 5, and 30 t ha-1) were studied between 8 and 21 months of the application in an alkaline soil cropped to barley under Mediterranean climate. Together with GHG, soil chemical and biological properties were assessed, namely, changes in labile organic matter content and nutrient status, and pH, as well as microbial abundance, activity, and functional composition. During the 2 years of the application, significant changes were observed at the highest rate of biochar application such as higher contents of water, K+, Mg2+, SO42-, higher basal respiration, and with non-significant changes in microbial community, though with some temporal effects. Regarding GHG, N2O decreases coupled with CH4 increases in the summer sampling were measured, although only for the highest application rate scenario. Such effects were unrelated to pH, bioavailable nitrogen status, or bulk soil microbial community shifts. We hypothesized that the key is the porous structure of our wood biochar, which is able to provide more and diversified microbial microhabitats in comparison to bulk soil. At higher temperatures in summer, biologically-induced anoxic conditions in biochar pores acting as microsites may be promoted, where total denitrification to N2 occurs which leads to N2O uptake, while CH4 production is promoted.

High-contrast Brillouin and Raman micro-spectroscopy for simultaneous mechanical and chemical investigation of microbial biofilms.

Mechanical mapping with chemical specificity of biological samples is now made possible by joint micro-Brillouin and micro-Raman measurements. In this work, thanks to the unprecedented contrast of a new tandem Fabry-Perot interferometer, we demonstrate simultaneous detection of Brillouin and Raman spectra from different Candida biofilms. Our proof-of-concept study reveals the potential of this label-free joint micro-spectroscopy technique in challenging microbiological issues. In particular, heterogeneous chemo-mechanical maps of Candida biofilms are obtained, without the need for staining or touching the sample. The correlative Raman and Brillouin investigation evidences the role of both extracellular polymeric substances and of hydration water in inducing a marked local softening of the biofilm.

Raman micro-spectroscopy study of living SH-SY5Y cells adhering on different substrates.

In this paper we test the ability of Raman micro-spectroscopy and Raman mapping to investigate the status of cells grown in adhesion on different substrates. The spectra of immortalized SH-SY5Y cells, grown on silicon and on metallic substrates are compared with those obtained for the same type of cells adhering on organic polyaniline (PANI), a memristive substrate chosen to achieve a living bio-hybrid system. Raman spectra give information on the status of the single cell, its local biochemical composition, and on the modifications induced by the substrate interaction. The good agreement between Raman spectra collected from cells adhering on different substrates confirms that the PANI, besides allowing the cell growth, doesn't strongly affect the general biochemical properties of the cell. The investigation of the cellular state in a label free condition is challenging and the obtained results confirm the Raman ability to achieve this information.