Freshwater biodiversity has been threatened by eutrophication due to excessive nutrients in the environment. Releasing the freshwater species from such pressures requires efforts from industry and... Show moreFreshwater biodiversity has been threatened by eutrophication due to excessive nutrients in the environment. Releasing the freshwater species from such pressures requires efforts from industry and manufacturers to avoid emissions to vulnerable and high-risk regions. The first step is to know which nutrient influences where and the effects thereof on species loss. These impacts can be assessed by methods of life cycle impact assessment (LCIA). This thesis contributes to such knowledge by improving the LCIA method, for instance, by developing more regionalized and comprehensive indicators as well as adding the consideration of both phosphorus (P) and nitrogen (N) and which of these two nutrients is limiting. Show less
Aim The influence of soil properties on photosynthetic traits in higher plants is poorly quantified in comparison with that of climate.We address this situation by quantifying the unique and joint... Show moreAim The influence of soil properties on photosynthetic traits in higher plants is poorly quantified in comparison with that of climate.We address this situation by quantifying the unique and joint contributions to global leaf-trait variation from soils and climate. Location Terrestrial ecosystems world-wide. Methods Using a trait dataset comprising 1509 species from 288 sites, with climate and soil data derived from global datasets, we quantified the effects of 20 soil and 26 climate variables on light-saturated photosynthetic rate (Aarea), stomatal conductance (gs), leaf nitrogen and phosphorus (Narea and Parea) and specific leaf area (SLA) using mixed regression models and multivariate analyses. Results Soil variables were stronger predictors of leaf traits than climatic variables, except for SLA. On average, Narea, Parea and Aarea increased and SLA decreased with increasing soil pH and with increasing site aridity. gs declined and Parea increased with soil available P (Pavail). Narea was unrelated to total soil N. Joint effects of soil and climate dominated over their unique effects on Narea and Parea, while unique effects of soils dominated for Aarea and gs. Path analysis indicated that variation in Aarea reflected the combined independent influences of Narea and gs, the former promoted by high pH and aridity and the latter by low Pavail. Main conclusions Three environmental variables were key for explaining variation in leaf traits: soil pH and Pavail, and the climatic moisture index (the ratio ofprecipitation to potential evapotranspiration). Although the reliability of global soil datasets lags behind that of climate datasets, our results nonetheless provide compelling evidence that both can be jointly used in broad-scale analyses, and that effects uniquely attributable to soil properties are important determinants of leaf photosynthetic traits and rates. A significant future challenge is to better disentangle the covarying physiological, ecological Show less
The focus of this thesis is on the dynamics and functions of saprotrophic soil fungi during conversion from an arable land into a natural ecosystem (heathland) and to asses their effects on soil... Show moreThe focus of this thesis is on the dynamics and functions of saprotrophic soil fungi during conversion from an arable land into a natural ecosystem (heathland) and to asses their effects on soil ecosystem processes. Chapter 2 describes that fungal biomass in abandoned arable land is not increasing for at least 3 decades to the level of a natural ecosystem. Opportunistic fungi showed to be responsible for the decomposition processes, and these fungi are stimulated by large sizes of nitrogen-rich substrate buried in soil (Chapter 4& 5). Chapter 3 presents that no large amounts of phosphorus seem to leach into deeper soil layers after land abandonment. In Chapter 6 it is shown that the establishment of Calluna vulgaris in a recently abandoned arable land can be due to a fast colonization of Calluna immediately after abandonment and the reduction of microbial nitrogen mineralization, in combination with the colonization of Calluna roots by ericoid mycorrhizal fungi. In Chapter 7 it is concluded that an increase in fungal biomass in ex-arable soils can be of interest for soil ecosystem restoration and this may be triggered by the introduction of large particles of recalcitrant organic matter together with sufficient fungal biomass. Show less
