【氮矿化（氨化）中的同位素分馏】Jürgen Möbius. Isotope fractionation during nitrogen remineralization (ammonification): Implications for nitrogen isotope biogeochemistry.Geochimica et Cosmochimica Acta2013 105: 422–432
Abstract
The 15N-14N isotopic ratio of marine particulate organic matter usually increases as a consequence of preferential 14N-remineralization (ammonification) during decay in the oxic water-column and at the oxic seafloor. However a fractionation factor 15ε of sediment ammonification in natural environments has not been determined yet. Here the 15ε of sedimentary ammonification is calculated in a set of seven sapropel containing sediment cores two subrecent sediment cores and four sediment trap deployments from the Eastern Mediterranean Sea. Data clearly reveal Rayleigh type isotope fractionation and a fractionation factor 15ε between −1.43‰ and −2.3‰. Hence sediments – and probably sinking particulate organic matter as well – can be important sources of isotopically depleted reactive nitrogen. The knowledge of 15ε further enables to reconstruct paleo export fluxes from sediment cores if original and actual δ15N as well as N accumulation rates are known.
【农业集约化】Karl S. Zimmerer.The compatibility of agricultural intensification in a global hotspot of smallholder agrobiodiversity (Bolivia). PNAS
Integrating the conservation of biodiversity by smallholder farmers with agricultural intensification is increasingly recognized as a leading priority of sustainability and food security amid global environmental and socioeconomic change. An international research project investigated the smallholder agrobiodiversity of maize (corn) in a global hotspot (Bolivia) undergoing significant intensification. Peach-based intensification was pronounced (300–400%) and prolonged (2000–2010) in study areas. Intensification and maize agrobiodiversity were found to co-occur within smallholder landscapes. Interactions of these field systems did not trigger land-change tipping points leading to landrace extirpation. By