Microbial activity is known to be high under permanent grassland, but consequences for soil phosphorus (P) dynamics and availability are not well understood. Our main objective was to assess the microbial P turnover derived from the seasonal fluctuations in microbial P (measured as hexanol-labile P (P hex ) at 13 sampling times during 9 months) in a permanent grassland in Switzerland as affected by different P fertilization treatments (P inputs of 0 (NK) or 17 kg P ha −1 year −1 in the form of superphosphate (NPK) or dairy slurry (DS)). Plant P uptake, available inorganic P measured as resin-extractable P (P res ), potential organic P mineralization indicated by acid phosphomonoesterase activity and climatic conditions were also recorded. Despite significant differences in plant P uptake and P res (NPK>DS>NK), the turnover rate of P hex was similar in all treatments (approximately once per growing season). Thus, the seasonal P flux through P hex was similar to the stock of P hex , which was about 18, 25 and 37 kg P ha −1 in NK, NPK and DS, respectively, and larger than the corresponding seasonal plant P uptake of 6, 17 and 12 kg P ha −1 . The estimate of P hex turnover based on seasonal dynamics did not confirm previous tracer-based findings of a much faster P hex turnover under low availability of inorganic P, and the magnitude of P hex turnover depended on the number of sampling points taken into account. Fluctuations in P res and P hex were related to soil moisture and indicated competition between plants and microorganisms for available P.
Electrification in volcanic ash plumes often leads to syn-eruptive lightning discharges. High temperatures in and around lightning plasma channels have the potential to chemically alter, re-melt, and possibly volatilize ash fragments in the eruption cloud. In this study, we experimentally simulate temperature conditions of volcanic lightning in the laboratory, and systematically investigate the effects of rapid melting on the morphology and chemical composition of ash. Samples of different size and composition are ejected towards an artificially generated electrical arc. Post-experiment ash morphologies include fully melted spheres, partially melted particles, agglomerates, and vesiculated particles. High-speed imaging reveals various processes occurring during the short lightning-ash interactions, such as particle melting and rounding, foaming, and explosive particle fragmentation. Chemical analyses of the flash-melted particles reveal considerable bulk loss of Cl, S, P and Na through thermal vaporization. Element distribution patterns suggest convection as a key process of element transport from the interior of the melt droplet to rim where volatiles are lost. Modeling the degree of sodium loss delivers maximum melt temperatures between 3290 and 3490 K. Our results imply that natural lighting strikes may be an important agent of syn-eruptive morphological and chemical processing of volcanic ash.
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