This paper introduces a modular processing chain to derive global high-resolution maps of leaf traits. In particular, we present global maps at 500 m resolution of specific leaf area, leaf dry... Show moreThis paper introduces a modular processing chain to derive global high-resolution maps of leaf traits. In particular, we present global maps at 500 m resolution of specific leaf area, leaf dry matter content, leaf nitrogen and phosphorus content per dry mass, and leaf nitrogen/phosphorus ratio. The processing chain exploits machine learning techniques along with optical remote sensing data (MODIS/Landsat) and climate data for gap filling and up-scaling of in-situ measured leaf traits. The chain first uses random forests regression with surrogates to fill gaps in the database (> 45% of missing entries) and maximizes the global representativeness of the trait dataset. Plant species are then aggregated to Plant Functional Types (PFTs). Next, the spatial abundance of PFTs at MODIS resolution (500 m) is calculated using Landsat data (30 m). Based on these PFT abundances, representative trait values are calculated for MODIS pixels with nearby trait data. Finally, different regression algorithms are applied to globally predict trait estimates from these MODIS pixels using remote sensing and climate data. The methods were compared in terms of precision, robustness and efficiency. The best model (random forests regression) shows good precision (normalized RMSE≤ 20%) and goodness of fit (averaged Pearson's correlation R = 0.78) in any considered trait. Along with the estimated global maps of leaf traits, we provide associated uncertainty estimates derived from the regression models. The process chain is modular, and can easily accommodate new traits, data streams (traits databases and remote sensing data), and methods. The machine learning techniques applied allow attribution of information gain to data input and thus provide the opportunity to understand trait-environment relationships at the plant and ecosystem scales. The new data products – the gap-filled trait matrix, a global map of PFT abundance per MODIS gridcells and the high-resolution global leaf trait maps – are complementary to existing large-scale observations of the land surface and we therefore anticipate substantial contributions to advances in quantifying, understanding and prediction of the Earth system. Show less
Research described in this thesis focused on biological, ecological and evolutionary aspects of Arbuscular Mycorrhizal Fungi (AMF), and in particular of the family Gigasporaceae (Gigaspora and... Show moreResearch described in this thesis focused on biological, ecological and evolutionary aspects of Arbuscular Mycorrhizal Fungi (AMF), and in particular of the family Gigasporaceae (Gigaspora and Scutellospora, genera). This study had two major objectives. The first objective was to obtain better knowledge about the life history strategies (LHS) of Gigasporaceae, and the second objective was to study the intragenomic polymorphism of the ribosomal rDNA copies in order to understand its origin and to test the use of such polymorphism to discriminate between closely related species. The LHS patterns observed for the Gigasporaceae species studied suggests that they behave like K-strategists, i.e. organisms adapted to live at stable and predictable environments, as compared to Glomeraceae species that form single spores in the soil. Based on LHS patterns of Gigasporaceae an hypotheses that those species will be negatively selected in disturbed ecosystems have been formulated. Although intraspecific rDNA polymorphism in Gigasporaceae has been previously reported, this study, for the first time, systematically describes this heterogeneity and analyses this phenomenon with respect to Gigasporaceae phylogeny and evolution. It has been demonstrated that the intragenomic polymorphism of the rDNA copies can be used to differentiate species and in the case of Gigaspora even isolates. The phylogenetic analysis of inter and intragenomic rDNA polymorphism of closely related Gigaspora species strongly suggested that reticulated evolution, characterized by occasional hybridization or horizontal gene transfer between two species, played a significant role in evolution of this asexual group of fungi, via parasexual recombination. In addition, a molecular method was developed to assess Gigasporaceae diversity in environmental samples. Show less
