ABSTRACT
Gross primary productivity (GPP), the gross uptake of carbon dioxide (CO2) by plant photosynthesis, is the primary driver of the land carbon sink, which presently removes around one quarter of the anthropogenic CO2 emissions each year. GPP, however, cannot be measured directly and the resulting uncertainty undermines our ability to project the magnitude of the future land carbon sink. Carbonyl sulfide (COS) has been proposed as an independent proxy for GPP as it diffuses into leaves in a fashion very similar to CO2, but in contrast to the latter is generally not emitted. Here we use concurrent ecosystem-scale flux measurements of CO2 and COS at four European biomes for a joint constraint on CO2 flux partitioning. The resulting GPP estimates generally agree with classical approaches relying exclusively on CO2 fluxes but indicate a systematic underestimation under low light conditions, demonstrating the importance of using multiple approaches for constraining present-day GPP.
ABSTRACT
Mine tailings represent a source of toxic pollutants, mainly heavy metals, which may spread to the surrounding areas. Phytostabilization, a long-term and cost-effective rehabilitation strategy, can be achieved by promoting the establishment of vegetation to reduce the risk of pollutant transfer. In this work, the application of pyrolyzed biomass (biochar) was studied to evaluate the amelioration of the mine tailings properties for potential use as a phytostabilization technology. Four substrates were obtained by mixing the mine tailings from a dumping site in Cave del Predil (NE, Italy) with biochar from orchard prune residues at four dosages (0%, 1%, 5% and 10% biochar in the mine tailings). The physical and chemical properties were determined and the bioavailability and leachability of the contaminants were estimated. The pH, the nutrient retention in terms of cation exchange capacity and the water-holding capacity increased as the biochar content increased in the substrates and the bioavailability of Cd, Pb, Tl and Zn of the mine tailings decreased. The changes promoted by the biochar seem to be in favor of its use on mine wastes to help the establishment of a green cover in a phytostabilization process.
