Dr. Contreras-Quintana, Sergio

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◦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 (δ13C, δ18O, δD) 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 nalkane δD values more closely follow changes in precipitation δD, evaporative enrichment seems to have a dominant influence on cellulose δ18O values. Cellulose δD values are highly enriched compared to n-alkane δD values, likely reflecting a predominant metabolic imprint on δD. δ13C 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.

Leaf cuticular waxes are one of the most important environment-plant interaction structural systems that enable desert plants to withstand extreme climatic conditions. We present a long chain n-alkyl lipids study in fresh plant leaves and rodent palaeomiddens collected along an elevational gradient in the south-central Atacama Desert of Chile, covering six different vegetation belts: Steppe (4500-4000 m asl), Puna (4000-3300 m asl), pre-Puna (3300-2400 m asl), Absolute Desert (2400-1000 m asl) and Coastal Desert (1000-0 m asl). The 28 rodent palaeomiddens analyzed from Quebrada Incahuasi (25.6 °S, 3600 m asl) span the last 17,000 years. Modern-day distribution of long-chain n-alkanes and n-alkanoic acids varies among the dominant plant associations of the Atacama Desert. These plants show a species-specific chemotaxonomy linked to the climatic conditions. Furthermore, differences in average chain length (ACL) and carbon preference index (CPI) suggest that these plant communities are highly adapted to extreme environmental conditions. The sum of leaf wax n-alkanes was highest under wet conditions, while n-alkanoic acids (between n-C24 and n-C28) increased with hyperaridity. Similarly, analysis of n-alkane time series from palaeomiddens showed that the greatest changes in leaf wax n-alkane distributions (ACL and CPI) corresponded to the greatest increases in moisture during the Central Andean Pluvial Event (CAPE; between 18 and 9 ka cal BP) and the Late Holocene. The shift in the palaeomidden n-alkane distributions is corroborated by the relative abundance of rainfall-dependent extra-local taxa. This is the first study to report leaf wax content obtained from ancient rodent middens, and shows promising results as a robust hydroclimate proxy for the Atacama Desert region.

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-specifc 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 µg/g) up to three times higher than fatty acids (66.7±40.7 µg/g), likely as an adaptation to the hyperarid environment. Signifcant diferences 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 fne-scale adaptations to low moisture availability along the coastal transect. Moreover, our data indicate that the predominance of n-alkanes is refecting 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.