Strategic roadmap to assess forest vulnerability under air pollution and climate change.

Although it is an integral part of global change, most of the research addressing the effects of climate change on forests have overlooked the role of environmental pollution. Similarly, most studies investigating the effects of air pollutants on forests have generally neglected the impacts of climate change. We review the current knowledge on combined air pollution and climate change effects on global forest ecosystems and identify several key research priorities as a roadmap for the future. Specifically, we recommend (1) the establishment of much denser array of monitoring sites, particularly in the South Hemisphere; (2) further integration of ground and satellite monitoring; (3) generation of flux-based standards and critical levels taking into account the sensitivity of dominant forest tree species; (4) long-term monitoring of N, S, P cycles and base cations deposition together at global scale; (5) intensification of experimental studies, addressing the combined effects of different abiotic factors on forests by assuring a better representation of taxonomic and functional diversity across the ~73,000 tree species on Earth; (6) more experimental focus on phenomics and genomics; (7) improved knowledge on key processes regulating the dynamics of radionuclides in forest systems; and (8) development of models integrating air pollution and climate change data from long-term monitoring programs.

Long-term effects of biochar application on greenhouse gas production and microbial community in temperate forest soils under increasing temperature.

Biochar management has been proposed as a promising strategy to mitigate climate change. However, the long-term effects of biochar amendment on soil greenhouse gas (GHG) production and microbial community in forest ecosystems under projected warming remain highly uncertain. In this study, we conducted a 49-day incubation experiment to investigate the impact of biochar application on soil physico-chemical properties, GHG production rates, and microbial community at three temperature levels using a temperate forest soil amended with spruce biochar four years ago. Our results showed that temperature exerted a positive effect on soil CO2, CH4 and N2O production, leading to an increase in total global warming potential by 169% and 87% as temperature rose from 5 to 15 °C and from 15 to 25 °C, respectively, and thus a positive feedback to warming. Moreover, warming was found to reduce soil microbial biomass significantly, but at the same time promote the selection of an activated microbial community towards some phyla, e.g. Acidobacteria and Actinobacteria. We observed that biochar amendment reduced soil CH4 consumption and N2O production in the absence of litter by 106% and 94%, respectively, but did not affect soil CO2 production. While biochar had no significant influence of total global warming potential of forest soil, it could promote climate change mitigation by increasing the total soil carbon content by 26% in the presence of litter. In addition, biochar application was shown to enhance soil available phosphorus and dissolved organic carbon concentrations, as well as soil microbial biomass under a warmer environment. Our findings highlighted the potential of spruce biochar as a soil amendment in improving soil fertility and carbon sequestration in temperate forest over the long term, without creating any adverse climatic impacts associated with soil GHG production.

Improved soil carbonate determination by FT-IR and X-ray analysis.

In forest soils on calcareous parent material, carbonate is a key component that influences both chemical and physical soil properties and thus fertility and productivity. At low organic carbon contents, it is difficult to distinguish between organic and inorganic carbon, e.g. carbonates, in soils. The common gas-volumetric method to determine carbonate has a number of disadvantages. We hypothesize that a combination of two spectroscopic methods, which account for different forms of carbonate, can be used to model soil carbonate in our region. Fourier transform mid-infrared spectroscopy was combined with X-ray diffraction to develop a model based on partial least squares regression. Results of the gas-volumetric Scheibler method were corrected for the calcite/dolomite ratio. The best model performance was achieved when we combined the two analytical methods using four principal components. The root mean squared error of prediction decreased from 13.07 to 11.57, while full cross-validation explained 94.5 % of the variance of the carbonate content. This is the first time that a combination of the proposed methods has been used to predict carbonate in forest soils, offering a simple method to precisely estimate soil carbonate contents while increasing accuracy in comparison with spectroscopic approaches proposed earlier. This approach has the potential to complement or substitute gas-volumetric methods, specifically in study areas with low soil heterogeneity and similar parent material or in long-term monitoring by consecutive sampling.