Effect of hydrothermally carbonized char application on trace gas emissions from two sandy soil horizons.

The application of biochar to soil is a potential tool for the long-term sequestration of C and a possible mitigation of greenhouse gas (GHG) emissions. Among the various processes available to produce biochar, hydrothermal carbonization is one technique that is suitable for moist feedstock like digestates from biogas production. The aim of this study was to investigate the stability of C and emissions of NO after the addition of (i) digested wheat ( L.) straw (digestate) and (ii) hydrothermally carbonized (HTC) char of wheat straw as well as (iii) HTC char of digested wheat straw to two soil horizons that differed in C content. The HTC chars were obtained from wheat straw and digested wheat straw that were hydrothermally carbonized at 230°C for 6 h. The digestate and HTC chars were mixed with soil and incubated in 125-mL vessels. The GHG emissions of CO and NO were measured at regular intervals. Additionally, after 108 d, N was applied in the form of NHNO equivalent to 100 kg N ha. After 500 d of incubation, the digestate had lost 34% of C, while the soil mixture with the corresponding HTC char lost 12% of C in the form of CO from the topsoil. The estimated bi-exponential half-life of the recalcitrant C was more than 50% longer for the carbonized material than for the untreated digestate. The NO emissions from both HTC chars were significantly reduced compared with untreated digestate. The reductions were up to 64% for the topsoil and 60% for the subsoil samples. These laboratory results show that HTC holds the potential to increase the C stability of fermented and carbonized biomasses and to reduce NO emissions.

Raman study of chromophore states in photochromic fluorescent proteins.

The photophysical mechanism underlying the photochromic behavior of green fluorescent protein (GFP) mutants is investigated by means of preresonant Raman spectroscopy and model calculations. The studied molecules are reversibly switchable fluorophores that can be repeatedly converted between fluorescent and nonfluorescent states by irradiation and are attracting a broad interest for a number of new applications. Experimental results on chemically synthesized isolated chromophores are analyzed within a density functional theory approach that allows us to link the detected vibrational modes to specific ground-state configurations before and after photoconversion. These data are compared to results obtained for the case of complete folded proteins including the same chromophores. Our results highlight the impact of chromophore cis-trans isomerization and protonation state in the photophysics of these proteins and provide useful guidelines for novel mutant design.

Degradability of raw and post-processed chars in a two-year field experiment.

The object of the present work was to analyse the degradation dynamics of four chars and a digestate applied to a sandy soil as well as possible initial priming effects on the mineralisation of soil organic carbon in a two-year field experiment. For that purpose, soil carbon content, soil respiration and the corresponding carbon isotopic abundances were repeatedly measured throughout two consecutive vegetation periods. In order to quantify and separate the amount and the degradation of the substrate-derived carbon and to assess soil priming effects, isotopic mixing models were applied to soil-derived and substrate-derived carbon, and to the respired CO2. Pyrolysis char was degraded with decreasing intensity over time with an estimated half-life of about 80years. HTC (HydroThermal Carbonisation) char showed a high degradation during the first year but, during the second year, the remaining recalcitrant pool was degraded much slower with a half-life between 49 and 61years. Digestate was degraded at a constant intensity with a half-life of about 14years. When the chars were fermented before being applied to the soil, the initial degradation of HTC char was reduced, but on the two-year scale, the degradation of both chars was higher than for untreated chars, yielding a half-life between 11 and 15years, comparable to digestate. The results showed considerable stability of the untreated pyrolysis and HTC chars under field conditions, and moreover, no net influence of chars as well as of digestate on the degradation of soil organic carbon after two years.