ALBERT

Description: Recently, indirect evidence was obtained for inhibition of soil net N mineralization by sterols in soil organic matter, which could have been caused by their antioxidant or antimicrobial properties. The objective of this study was to test the effect of potential inhibitors ( i.e., individual compounds with known antioxidant and/or antimicrobial properties) on soil microbial mineralization processes during incubation for 7 and 14 d. A sandy agricultural soil was amended with four substances: two phenolic acids differing in their antioxidant capacity (AOC) (acetovanillone with no AOC, ferulic acid with large AOC), Trolox, an analogue of vitamin E (large AOC), and β-sitosterol (no AOC, but potential antimicrobial properties). The two compounds with large AOC (ferulic acid and Trolox) showed no significant inhibition of C and net N mineralization; and the Trolox amendment actually caused a significant increase in C and net N mineralization after 7 d of incubation. Acetovanillone with no measurable AOC caused a significant increase in C mineralization (109% of substance C added), indicating degradation of the substance, and a very pronounced negative net N mineralization within 7 d (–356%), which was interpreted as N immobilization. Only β-sitosterol showed strong inhibition of net N mineralization after 7 and 14 d (–59% and –26%, respectively) which was not interpreted as N immobilization, since there was no concomitant increase in C mineralization. Thus, an antimicrobial effect of β-sitosterol specificly on microorganisms of the N cycle was suggested, but there was no clear inhibitory effect caused by the antioxidant compounds.

Description: Unusually low net N mineralization in soils relatively rich in total organic C and N was repeatedly reported for sandy arable soils in NW Europe. In order to adequately account for it in simulation models, it is necessary to know the involved substances and processes. Therefore, 9 arable top soils (〈 6% clay) with a wide range of total organic C (1.1%–5.2%) and C : N ratios (12–35) were studied. The soils varied strongly in the mineralizability of soil organic N which was determined via long-term laboratory incubations (〉 200 d). It was hypothesized that mineralization was controlled by antioxidants, and the Trolox equivalent antioxidant capacity (TEAC) of the soils was measured. In addition, pyrolysis–field ionization mass spectrometry (Py-FIMS) was applied to investigate the influence of the molecular-chemical composition of soil organic matter. In these soils, the compound class of sterols from Py-FIMS analysis was most closely, negatively correlated with the mineralizability of soil organic N ( r 〈?h.3〉 2 = 0.75, p = 0.003). This was probably not an antioxidative effect, because the TEAC values did not correlate sufficiently with the mineralizability and the sterol intensities. However, the negative relation with sterols could be causal, since the correlation was about as close with other components of the compound class of sterols and even closer with the main plant sterol beta-sitosterol ( r 〈?h.3〉 2 = 0.84, p = 0.001). In addition, the variability among samples was strongly governed by the proportions of sterols, and sterols also had a high discriminating power in discriminant analysis. Furthermore, the proportions of sterols were extraordinary in those arable podzol soils that developed under previous heath- or woodland (up to 10.2% of total ion intensity from Py-FIMS). In conclusion, the inhibitory effect of these compounds needs to be investigated in more detail in order to optimize parameterization of N as well as C simulation models especially for podzolized, sandy arable soils with former heath- or woodland vegetation.

Description: Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). The input of marine halogens to the stratosphere is based on observations and modeling studies using low resolution oceanic emission scenarios derived from top down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface observations within the HalOcAt database (https://halocat.geomar.de/). Global maps of marine and atmospheric surface concentrations are derived from the data which are divided into coastal, shelf and open ocean regions. Considering physical and biogeochemical characteristics of ocean and atmosphere, the open ocean water and atmosphere data are classified into 21 regions. The available data are interpolated onto a 1° × 1° grid while missing grid values are interpolated with latitudinal and longitudinal dependent regression techniques reflecting the compounds' distributions. With the generated surface concentration climatologies for the ocean and atmosphere, global concentration gradients and sea-to-air fluxes are calculated. Based on these calculations we estimate a total global flux of 1.5/2.5 Gmol Br yr−1 for CHBr3, 0.78/0.98 Gmol Br yr−1 for CH2Br2 and 1.24/1.45 Gmol I yr−1 for CH3I (Robust Fit/Ordinary Least Square regression technique). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic region. "Hot spots" for global polybromomethane emissions are located in the equatorial region, whereas methyl iodide emissions are enhanced in the subtropical gyre regions. Inter-annual and seasonal variation is contained within our calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An underrepresentation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom up emission estimate and top down approaches