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Over the past 25 years, the study of driving forces of landscape change has developed into a central theme in land change science by contributing to theory development, promoting the analysis of causation of change and gaining insights into how landscape development could be steered into a societally more desirable direction. Based on this progress, we designate important research avenues, reviewing critical challenges forming the base for advancing the study of driving forces of landscape change and addressing the question on how the study of driving forces can contribute to system transformative research. For each of the research avenues, we describe the current dominant approach and provide some specific ways of advancing both the conceptualization and the research methods. Together, advancing on these research avenues will promote a more social-ecological systems perspective to the study of driving forces of landscape change. Journal of Land Use Science, 17 (1) ISSN:1747-4248 ISSN:1747-423X

Gross primary production (GPP) by boreal forests is highly sensitive to environmental changes. However, GPP simulated by land surface models (LSMs) remains highly uncertain due to the lack of direct photosynthesis observations at large scales. Carbonyl sulfide (COS) has emerged as a promising proxy to improve the representation of GPP in LSMs. Because COS is absorbed by vegetation following the same diffusion pathway as CO2 during photosynthesis and not emitted back to the atmosphere, incorporating a mechanistic representation of vegetation COS uptake in LSMs allows using COS observations to refine GPP representation. Here, we perform ecosystem COS flux and GPP data assimilations to constrain the COS- and GPP-related parameters in the ORCHIDEE LSM for boreal evergreen needleleaf forests (BorENF). Assimilating ecosystem COS fluxes at Hyytiälä forest increases the simulated net ecosystem COS uptake by 14%. This increase largely results from changes in the internal conductance to COS, highlighting the need to improve the representation of COS internal diffusion and consumption. Moreover, joint assimilation of ecosystem COS flux and GPP at Hyytiälä improves the simulated latent heat flux, contrary to the GPP-only data assimilation, which fails to do so. Finally, we scaled this assimilation framework up to the boreal region and find that the joint assimilation of COS at Hyytiälä and GPP fluxes at 10 BorENF sites increases the modeled vegetation COS uptake up to 18%, but not GPP. Therefore, this study encourages the use of COS flux observations to inform GPP and latent heat flux representations in LSMs. Journal of Geophysical Research: Biogeosciences, 128 (7) ISSN:2169-8961 ISSN:0148-0227 ISSN:2169-8953

Pathogenic fungi impose a great threat to the global food production. They are globally distributed and display a huge amount of phenotypic diversity. They demonstrate high adaptability to diverse environments and to fluctuating conditions within their hosts. However, not much is known about the mechanisms underlying these processes of adaptation. Deciphering the genetic basis of phenotypic diversity may help us to get a deeper insight into the mechanisms that regulate complex adaptive traits. Furthermore, these findings may help in improving strategies for an effective and sustainable management of pathogens. In my PhD study, I aimed to understand the genetic basis of adaptation to variable environments using Zymoseptoria tritici. Z. tritici causes septoria leaf blotch of wheat and is considered to be the most devastating fungal wheat pathogen in Europe. In the first chapter of my thesis, I studied the role of melanin in adaptation of Z. tritici. I, demonstrated that melanin is essential for protection against harmful chemical fungicides such as bixafen. Remarkably, I observed high phenotypic variability in melanin accumulation levels in different Zymoseptoria tritici strains, most probably reflecting its role in adaptation to variable environments. Using genetic mapping, I was able to demonstrate that variability in melanization levels between two Swiss strains of Z. tritici was mediated by differential expression of the transcription factor Zmr1 (Zymoseptoria melanin regulation 1). I identified nucleotide mutations in the promoter region and an insertion of transposable elements (TEs) upstream of the promoter region as two mechanisms responsible for this observed differential expression of Zmr1. My findings clearly demonstrated the significance of gene expression regulation, mediated by the insertion of TEs and SNPs, in optimizing the growth and adaptation of the fungus under variable environments. Furthermore, these adaptive changes are responsible for the phenotypic diversity that we observe in Z. tritici strains from all over the world. In the second part of my thesis, I analyzed the expression of several secreted peptidases of Z. tritici at distinct stages during the infection process of wheat plants. Using computational genetic methods, I also analyzed nucleotide data sets of the peptidase genes for evolutionary signatures of genetic adaptation. By combining both approaches, I aimed at obtaining a more detailed picture of the relevance and the role of each enzyme during the infection process. I was able to show that the peptidases belonging to MEROPS families A1 and G1 were significantly up regulated during the asymptomatic phase of infection and displayed signatures of accelerated evolution, suggesting their key role in suppression of plant defenses and host specialization. In the third part of my thesis, I evaluated the role of a cellulase-encoding gene (JGI Prot. ID: 76589) using molecular biology techniques. This cellulase was only expressed during the final necrotrophic phase of Z. tritici infection and the nucleotide sequences of the gene showed signatures of diversifying selection. This pattern is consistent with the hypothesis of evasion from host recognition during the first phases of infection and subsequent induction of host-cell death by the secretion of an array of different cellulase isoforms by the fungus. To test this hypothesis, I constitutively expressed the cellulase-encoding gene in Z. tritici during all infection stages by inserting a constitutive promoter (originally from the Glyceraldehyde-3-phosphate dehydrogenase gene of Aspergillus nidulans) upstream of the start codon of the cellulase gene. I was able to show that the progress of infection in this mutant was delayed compared to the non-modified Z. tritici isolates. This suggests that the cellulase acts as an elicitor molecule that is detected by the plant and triggers the defense machinery that will hinder the growth of the pathogen. In summary, my PhD work demonstrated the significance of fine-tuning of gene expression regulation of various genes in plant pathogenic fungi to facilitate adaptation to different environmental conditions and host colonization. Remarkably, I was able to show that gene expression fine-tuning resulted in large amounts of phenotypic diversity in adaptive traits.

European Journal of Wood and Wood Products, 68 (3) ISSN:1436-736X ISSN:0018-3768