Showing papers by "Kerstin Huss-Danell published in 2014"

Ecological consequences of the expansion of N2-fixing plants in cold biomes

Abstract: Research in warm-climate biomes has shown that invasion by symbiotic dinitrogen (N2)-fixing plants can transform ecosystems in ways analogous to the transformations observed as a consequence of anthropogenic, atmospheric nitrogen (N) deposition: declines in biodiversity, soil acidification, and alterations to carbon and nutrient cycling, including increased N losses through nitrate leaching and emissions of the powerful greenhouse gas nitrous oxide (N2O). Here, we used literature review and case study approaches to assess the evidence for similar transformations in cold-climate ecosystems of the boreal, subarctic and upper montane-temperate life zones. Our assessment focuses on the plant genera Lupinus and Alnus, which have become invasive largely as a consequence of deliberate introductions and/or reduced land management. These cold biomes are commonly located in remote areas with low anthropogenic N inputs, and the environmental impacts of N2-fixer invasion appear to be as severe as those from anthropogenic N deposition in highly N polluted areas. Hence, inputs of N from N2 fixation can affect ecosystems as dramatically or even more strongly than N inputs from atmospheric deposition, and biomes in cold climates represent no exception with regard to the risk of being invaded by N2-fixing species. In particular, the cold biomes studied here show both a strong potential to be transformed by N2-fixing plants and a rapid subsequent saturation in the ecosystem’s capacity to retain N. Therefore, analogous to increases in N deposition, N2-fixing plant invasions must be deemed significant threats to biodiversity and to environmental quality.

Does nitrogen transfer between plants confound 15N-based quantifications of N2 fixation?

Abstract: Transfer of fixed N from legumes to non-legume reference plants may alter the 15N signature of the reference plant as compared to the soil N available to the legume. This study investigates how N transfer influences the result of 15N-based N2 fixation measurements. We labelled either legumes or non-legumes with 15N and performed detailed analyses of 15N enrichment in mixed plant communities in the field. The results were used in a conceptual model comparing how different N transfer scenarios influenced the 15N signatures of legumes and reference plants, and how the resulting N2 fixation estimate was influenced by using reference plants in pure stand or in mixture with the legume. Based on isotopic signatures, N transfer was detected in all directions: from legume to legume, from legume to non-legume, from non-legume to legume, from non-legume to non-legume. In the scenario of multidirectional N transfer, N2 fixation was overestimated by using a reference plant in pure stand. Fixed N transferred to neighbouring reference plants modifies the 15N signature of the soil N available both to the reference plant and the N2-fixing legume. This provides strong support for using reference plants growing in mixture with the legumes for reliable quantifications of N2 fixation.