No abstract

Mountain-range topography is determined by the complex interplay between tectonics and climate. However, often it is not clear to what extent climate forces topographic evolution and how past climatic episodes are reflected in relief. The Andes are a tectonically active mountain belt encompassing various climatic zones with pronounced differences in rainfall and glacier extent under similar plate-boundary conditions. In the Central to South-Western Andes climatic zones range from hyperarid desert with mean annual rainfall of 5 mm/a (22.5°S) to year-round humidity with 2500 mm/a (40°S). The Andes thus provide a unique setting for investigating the relationship between climate and topography. We present the analysis of 120 catchments along the western Andean watersheds between 15.5° and 41.5°S, which is based on SRTMV3-90m data and the new medium-resolution rainfall (TRMM) dataset. For each basin, we extracted geometry, relief, and climate parameters to test whether Andean topography shows a climatic imprint and to analyze how climate influences relief. Our data document that elevation and relief decrease with increasing rainfall and descending snowline elevation. Furthermore, we show that local relief reaches high values of 750 m in a zone between 28° to 35°S. During Pleistocene glacial stages this region was affected by the northward shifting southern hemisphere Westerlies, which provided moisture for valley-glacier formation and extended glacial coverage as well as glacial erosion. In contrast, the southern regions between 35° to 40°S receive higher rainfall and have a lower local relief of 200 m, probably related to an increased drainage density. We distinguish two different, climatically-controlled mechanisms shaping topography: (1) fluvial erosion by prolonged channel-hillslope coupling, which smoothes relief, and (2) erosion by valley glaciers that generates relief. Finally, our results suggests that the catchment-scale relief of the Andes between 28° to 35°S is characterized by a pronounced transient component reflecting past climatic conditions.

Landscapes in tectonically active regions develop in response to a complex interplay between rapid tectonic deformation and surface processes. In order to understand the evolution of these environments and distinguish between the different factors, it is fundamental to identify and quantify geomorphic processes and rates on different time scales. The forearc of south-central Chile provides an ideal setting to elucidate the response of surface processes to climatic and tectonic forcing. However, in contrast to northern Chile, this region has attracted little attention due to diffi culties in quantifying the age of geomorphic surfaces.We use luminescence and stable cosmogenic nuclides ( 3 He, 21 Ne) on conglomeratic units in the Central Depression and fl uvial valley fi lls in the Coastal Cordillera to constrain exposure and burial ages of these units that form major landscape elements in the southern Chilean forearc. Our data indicate that disturbances in the drainage network are controlled by local uplift, which may be caused by deformation above an active blind thrust. In the Coastal Cordillera, local short-term uplift rates reach a minimum of 0.27 mm a -1 and are on the same order as late Quaternary minimum incision rates of 0.15 mm a -1 to 0.43 mm a -1 . The valley fi lls in the Coastal Cordillera have depositional ages of 80 ka and 255 ka, respectively. Exposure ages of the extensive alluvial surfaces in the Central Depression cluster between 135 ka and 175 ka and between 240 ka and 280 ka. Hence, the deposition of these surfaces broadly coincides with marine isotope stages (MIS) 6 and 8 and appears to be climatically driven.

The plant pathogen Fusarium graminearum is a proficient producer of mycotoxins and other in part still unknown secondary metabolites, some of which might act as virulence factors on wheat. The PKS15 gene is expressed only in planta, so far hampering the identification of an associated metabolite. Here we combined the activation of silent gene clusters by chromatin manipulation (kmt6) with blocking the metabolic flow into the competing biosynthesis of the two major mycotoxins deoxynivalenol and zearalenone. Using an untargeted metabolomics approach, two closely related metabolites were found in triple mutants (kmt6 tri5 pks4,13) deficient in production of the major mycotoxins deoxynivalenol and zearalenone, but not in strains with an additional deletion in PKS15 (kmt6 tri5 pks4,13 pks15). Characterization of the metabolites, by LC-HRMS/MS in combination with a stable isotope-assisted tracer approach, revealed that they are likely hybrid polyketides comprising a polyketide part consisting of malonate-derived acetate units and a structurally deviating part. We propose the names gramiketide A and B for the two metabolites. In a biological experiment, both gramiketides were formed during infection of wheat ears with wild-type but not with pks15 mutants. The formation of the two gramiketides during infection correlated with that of the well-known virulence factor deoxynivalenol, suggesting that they might play a role in virulence.