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.

The n-alkyl leaf waxes of the temperate forest of South America are poorly studied, despite being a bio-geographically isolated forest spanning wide environmental conditions. To evaluate whether local species adaptation and environmental changes influence the n-alkyl leaf wax composition, we measured the molecular abundance and distribution of n-alkyl leaf waxes (n-alkanoic acids, n-alkanes and n-alka-nols) of three dominant native species from southern temperate forest in South America. We surveyed Araucaria araucana (n = 9), Nothofagus dombeyi (n = 17) and Chusquea sp. (n = 21) at different elevations. The relationship of n-alkyl leaf wax abundance and distribution with elevation is not significant in any species, except for n-alkane ACL (average chain length) in Chusquea sp. Significant correlations are found for n-alkanoic acid abundance with precipitation and aridity in Chusquea sp. and n-alkane abundance and ACL with temperature in A. araucana. These data suggest a species-specific response to environmental variables. The main similarity in the three species is a higher abundance of n-alkanoic acids (>60%) relative to other n-alkyl leaf waxes. Only n-alkanols are not correlated to any environmental variable, and neither ACL nor C max overlap among species. These results suggest n-alkanols as a potential chemotaxo-nomic indicator at a lower taxonomic level in the region.

The study of fatty acid biomarkers in trophic structures at sub-polar latitudes is fundamental in describing energy fluxes across ecosystems characterized by complex inter-specific interactions. Due to the presence of certain essential fatty acids obtained exclusively from predator–prey interactions, fatty acid biomarkers are widely used to identify trophic interactions. This study analyzed fatty acid compositions in three species inhabiting a relatively pristine Patagonian fjord. This fjord is geographically difficult to access, so there are very little sampling opportunities, biological and oceanographic information. In the three species collected (Ctenodiscus australis (Loven in Lütken 1871) (Echinodermata, Asteroidea, Ctenodiscidae); Munida gregaria (Fabricius 1793) (Arthropoda, Malacostraca, Munididae); Eleginops maclovinus (Cuvier 1830) (Chordata, Actinopterygii, Eleginopsidae)) along this remote area were evaluated their fatty acid trophic markers as a tool to differentiate dietary components and dietary habits. The study reported significant differences in the amount of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA), with the highest concentrations of all fatty acids in M. gregaria. The last suggests that M. gregaria is considered as a good quality food source or biological component that might support the fjord trophic web in the Southern Hemisphere. The results describe diet compositions in sampled species, and differences among species for fatty acid compositions and proportions. This provides an initial basis for future modeling or projecting how benthic ecosystems of fjords and Patagonian channels respond to food intake, particularly in environments associated with glacial systems characterized by a low phytoplankton biomass and greater sensitivity to climate variability.

Plant leaf waxes are used as vegetation biomarkers in several archives (i.e. soils, lake and marine sediments), study of these compounds in modern plants is needed to makes their application and interpretation more robust. However, in the South American Temperate Forest (STF), few species have been studied. The main goal of this research was to characterize twelve dominant modern species of the STF using three classes of leaf wax compounds, n-alkanoic acids, n-alkanes and n-alkanols. In addition, we evaluate the potential of leaf waxes as a vegetation and chemotaxonomic biomarker in the region, considering species that were found in different sampling sites and therefore environmental conditions. Clear differences among leaf wax abundance (μg/g) and ACL (average chain length) within and among the twelve species were found. Only the ACL of n-alkanoic acids and n-alkanols allows differentiation between leaf habit species (i.e. evergreen vs. deciduous), with high values associated with evergreen and low values with deciduous plants. This study differentiates the five species found in more than one site (i.e. different environmental condition) using different combinations of leaf waxes and in addition using only n-alkanes. It was not possible to differentiate among all sites with any combination of leaf waxes. The differences in the distribution of leaf waxes among species is an expected pattern in the study area, and it seems reliable to use the ACL as a vegetation biomarker differentiating between evergreen and deciduous species. The clear chemotaxonomic differences among the five species exposed to different and natural environmental conditions and the high preservation potential of the study area allow us to suggest that leaf waxes are likely a reliable tool to be incorporated in quantitative models to track vegetation and may be useful as a chemotaxonomic biomarker at the species level.

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.

Southern South America is the only large landmass that extends through the core of the Southern Westerly Winds (SWW), controlling hydrological and ecosystem variability in the region. In fact, the vegetation along the west coast changes from Temperate and Valdivian Rain Forest to the North Patagonian Evergreen Forest (ca. 42°S) due to the latitudinal influence of the SWW. Climate is an important driver of organic matter accumulation in lakes, hence changes in vegetation would be recorded in lacustrine sedimentary archives. This study evaluated leaf waxes contained in lake surface sediments as indicators of climate change along the west coast of southern South America, providing a biogeochemical dataset for ongoing and future (paleo)climate and environmental research. The fatty acid and n-alkane sediment leaf wax datasets are compared with latitudinal, orographic, and climatic (Mean Annual air Temperature [MAT] & Precipitation [MAP]) trends extracted from a monthly gridded reanalysis product of the Climate Forecast System Reanalysis. Fatty acids are more abundant than n-alkanes, with high abundances characterizing the transition between seasonal and year-round precipitation along the coast (ca. 42°S). The abundance of both leaf wax groups increases with MAP, suggesting precipitation as the main control on sedimentary leaf wax delivery to the lake sediments in the study area. The Carbon Preference Index (CPI) of the two groups show opposite trends, but both highlight the climate transition at ca. 42°S, and have a linear relationship with MAP. The opposite significant trends between n-alkane CPI and fatty acid CPI with MAP are interpreted as higher n-alkane production at much higher precipitation because leaf wax fatty acids are the precursors of n-alkanes. Hence, past periods during which these leaf waxes show opposite trends in CPI might be interpreted as a precipitation change, especially if additional information such as pollen, diatoms, chironomids and stable isotopes is available.

A. araucana is an endemic species of the temperate forests from Chile and Argentina; protected in both countries and categorized as in danger of extinction. Individuals of this species have begun to show foliar damage (i.e., discoloration) in branches and upper parts. The discoloration begins from the base to the top and from the trunk to the branches with necrotic rings appearing; in some cases causing death; and is currently attributed to an as yet unknown disease. This study focuses on the first protective layer of plants against environmental stress and pathogens; known as leaf waxes. The abundance and distribution of three classes of leaf waxes (long chain fatty acids; alkanes and alcohols) were measured in healthy individuals of A. araucana from different sites and individuals that present foliar damage (sick individuals). In the case of sick individuals; their leaf waxes were measured considering the level of leaf damage; that is; leaves without; medium and full foliar damage. The most abundant class of leaf wax in both sick and healthy individuals was fatty acids; followed by alkanes and then alcohols; with common dominant chains; C28 fatty acid; C29 alkane and C24 alcohol. Sick individuals have higher abundances of alkanes and alcohols than healthy individuals. The leaves of sick individuals have lower values of distribution indices (the carbon preference index of fatty acids and average chain length of alkanes) as foliar damage increases that are interpreted as a reduction of in vivo biosynthesis of waxes. This is the first evidence of A. araucana response to a still unknown disease that is killing individuals of this endemic species.

Quantitative reconstructions of past continental climates are vital for understanding contemporary and past climate change. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are unique bacterial lipids that have been proposed as universal paleothermometers due to their correlation with temperature in modern settings. Thus, brGDGTs may serve as a crucial paleotemperature proxy for understanding past climate variations and improving regional climate projections, especially in critical but under constrained regions. That said, complications can arise in their application due to varying source contributions (e.g., soils vs. peats vs. lacustrine). As such, this study investigates brGDGT distributions in Chilean lake surface sediments and corresponding watershed soils to determine the source of brGDGTs to lake sediments. Global datasets of brGDGTs in lake sediments and soils were additionally compiled for comparison. Distinct brGDGT distributions in Chilean lakes and soils indicate minimal bias from soil inputs to the lacustrine sediments as well as in situ lacustrine production of brGDGTs, which supports the use of brGDGTs in lake sediments as reliable paleotemperature proxies in the region. The ΣIIIa/ΣIIa ratio, initially promising as a brGDGT source indicator in marine settings, shows global complexities in lacustrine settings, challenging the establishment of universal thresholds for source apportionment. That said, we show that the ratio can be successfully applied in Chilean lake surface sediments. Direct comparisons with watershed soils and further research are crucial for discerning brGDGT sources in lake sediments and improving paleotemperature reconstructions on regional and global scales moving forward. Overall, this study contributes valuable insights into brGDGT variability, essential for accurate paleoreconstructions.

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.

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a family of bacterial lipids which have emerged over time as robust temperature and pH paleoproxies in continental settings. Nevertheless, it was previously shown that other parameters than temperature and pH, such as soil moisture, thermal regime or vegetation can also influence the relative distribution of brGDGTs in soils and peats. This can explain a large part of the residual scatter in the global brGDGT calibrations with mean annual air temperature (MAAT) and pH in these settings. Despite improvements in brGDGT analytical methods and development of refined models, the root-mean-square error (RMSE) associated with global calibrations between brGDGT distribution and MAAT in soils and peats remains high ( 5 °C). The aim of the present study was to develop a new global terrestrial brGDGT temperature calibration from a worldwide extended dataset (i.e. 775 soil and peat samples, i.e. 112 samples added to the previously available global calibration) using a machine learning algorithm. Statistical analyses highlighted five clusters with different effects of potential confounding factors in addition to MAAT on the relative abundances of brGDGTs. The results also revealed the limitations of using a single index and a simple linear regression model to capture the response of brGDGTs to temperature changes. A new improved calibration based on a random forest algorithm was thus proposed, the so called random Forest Regression for PaleOMAAT using brGDGTs (FROG). This multi-factorial and non-parametric model allows to overcome the use of a single index, and to be more representative of the environmental complexity by taking into account the non-linear relationships between MAAT and the relative abundances of the individual brGDGTs. The FROG model represents a refined brGDGT temperature calibration (R2 = 0.8; RMSE = 4.01 °C) for soils and peats, more robust and accurate than previous global soil calibrations while being proposed on an extended dataset. This novel improved calibra- tion was further applied and validated on two paleo archives covering the last 110 kyr and the Pliocene, respectively.