Browsing by Author "Rethemeyer, Janet"

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    Evaluating the isotopic composition of leaf organic compounds in fog-dependent Tillandsia landbeckii across the coastal Atacama Desert: Implications for hydroclimate reconstructions at the dry limit
    (2024) Jaeschke, Andrea; Boehm, Christoph; Schween, Jan H.; Schefuss, Enno; Koch, Marcus A.; Latorre, Claudio; Contreras, Sergio; Rethemeyer, Janet; Wissel, Holger; Luecke, Andreas
    Fog is an important component of the coastal climate of northern Chile and southern Peru. Moisture and nutrients from fog maintain highly endemic vegetation (lomas) as well as unique Tillandsia landbeckii ecosystems that thrive at elevations of ca. 900-1200 m asl. Although this epiphytic CAM bromeliad is well adapted to the extreme climate, declining Tillandsia stocks observed over the past decades question the long-term survival with ongoing climate change. Here, we aim at better understanding the hydroclimatic signal encoded in the leaf organic compounds of Tillandsia landbeckii across the Atacama Desert's coastal mountain range (ca. 18-21 degrees S). First, we investigate spatiotemporal patterns of fog occurrence and related moisture sources available for the plants applying a new satellite -based fog -detection approach. We then use stable carbon, oxygen and hydrogen ( delta 13 C, delta 18 O, delta D) isotope analysis of leaf wax n -alkanes and cellulose to identify photosynthetic pathway as well as environmental and physiological processes that shape the isotopic composition in Tillandsia landbeckii . We find that leaf wax n -alkanes and cellulose reflect the balance of climatic and physiological drivers differently. While n - alkane delta D values more closely follow changes in precipitation delta D, evaporative enrichment seems to have a dominant influence on cellulose delta 18 O values. Cellulose delta D values are highly enriched compared to n -alkane delta D values, likely reflecting a predominant metabolic imprint on delta D. delta 13 C signatures in the organic compounds are valid proxies for CAM activity. Our results prove the general applicability of the isotopic biomarkers for reconstructing environmental change in the coastal Atacama Desert. This approach can be extended globally to west -coast deserts that share fog as a major source of moisture.
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    Leaf wax composition and distribution of Tillandsia landbeckii reflects moisture gradient across the hyperarid Atacama Desert
    (2022) Contreras, Sergio; Landahur, Manlio; Garcia, Karla; Latorre, Claudio; Reyers, Mark; Rethemeyer, Janet; Jaeschke, Andrea
    In the hyperarid Atacama Desert, water availability plays a crucial role in allowing plant survival. Along with scant rainfall, marine advective fog frequently occurs along the coastal escarpment fueling isolated mono-specific patches of Tillandsia vegetation. In this study, we investigate the lipid biomarker composition of the bromeliad Tillandsia landbeckii (CAM plant) to assess structural adaptations at the molecular level as a response to extremely arid conditions. We analyzed long-chain n-alkanes and fatty acids in living specimens (n = 59) collected from the main Tillandsia dune ecosystems across a 350 km coastal transect. We found that the leaf wax composition was dominated by n-alkanes with concentrations (total average 160.8 +/- 91.4 mu g/g) up to three times higher than fatty acids (66.7 +/- 40.7 mu g/g), likely as an adaptation to the hyperarid environment. Significant differences were found in leaf wax distribution (Average Chain Length [ACL] and Carbon Preference Index [CPI]) in the northern zone relative to the central and southern zones. We found strong negative correlations between fatty acid CPI and n-alkane ACL with precipitation and surface evaporation pointing at fine-scale adaptations to low moisture availability along the coastal transect. Moreover, our data indicate that the predominance of n-alkanes is reflecting the function of the wax in preventing water loss from the leaves. The hyperarid conditions and good preservation potential of both n-alkanes and fatty acids make them ideal tracers to study late Holocene climate change in the Atacama Desert.
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    Microbial hotspots in a relict fog-dependent Tillandsia landbeckii dune from the coastal Atacama Desert
    (2024) Jaeschke, Andrea; May, S. Matthias; Hakobyan, Anna; Morchen, Ramona; Bubenzer, Olaf; Bernasconi, Stefano M.; Schefu, Enno; Hoffmeister, Dirk; Latorre, Claudio; Gwozdz, Martina; Rethemeyer, Janet; Knief, Claudia
    The hyperarid Atacama Desert in northern Chile is considered to be one of the most hostile habitats for microbial life. Despite the extreme environmental conditions, isolated patches of vegetation exist in an otherwise barren landscape. Unique dune ecosystems dominated by rootless Tillandsia landbeckii vegetation occur at elevations of about 900-1200 m asl within the coastal mountain range and receive water and nutrients mostly from the Pacific Ocean via fog deposition. The largest dunes can form over thousands of years, and may host diverse and abundant populations of microorganisms, sustained by fog moisture and nutrients via plant litter deposition. Relict dune ecosystems, with no living plants, are also common on this landscape. We investigated the microbial community structure in such a relict and stratified Tillandsia dune, located north of the Rio Loa canyon, to explore links between plant occurrence and past hydroclimatic variations using a multi-proxy approach. Our results indicated multiple phases of dune growth with alternating plant colonization, dieback, and sand accumulation during the past similar to 1300 years. Hydrogen isotope analysis of fossil leaf wax n-alkanes showed a distinct pattern of more humid conditions during the Medieval Climate Anomaly and increasing aridity during the Little Ice Age. We found that microbial abundance and diversity were generally higher in and just beneath core sections with elevated amounts of plant material. Recurrent rewetting events during specific climatic periods in the past may have supported active microbial communities in the sand dune, sustained by plant resources. This is further supported by significant changes in foliar and sedimentary delta N-15 values. Most negative delta N-15 values concurred with higher n-alkane abundances and distinct shifts in microbial community structure, pointing to increased biological nitrogen cycling in the central part of the dune, where niche occupation occurred by nitrifying Thaumarchaeota. In contrast, the upper part of the dune core was characterized by low microbial diversity and abundance. The community was dominated by members of the Bacilli, which may have dispersed via dust during a generally more arid climate. The sand dune thus retains a unique and well-preserved environmental record that reflects concomitant changes in past hydrological (i.e., fog) conditions, plant growth and microbial abundance and diversity during late Holocene climate extremes.