Leaf wax composition and distribution of Tillandsia landbeckii reflects moisture gradient across the hyperarid Atacama Desert

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 µg/g) up to three times higher than fatty acids (66.7 ± 40.7 µg/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.

Phenotypic Plasticity and Local Adaptation of Leaf Cuticular Waxes Favor Perennial Alpine Herbs under Climate Change

Six perennial herbs (Plantago asiatica, Polygonum viviparum, Anaphalis lactea, Kobresia humilis, Leontopodium nanum and Potentilla chinensis) widely distributed in alpine meadows were reciprocally transplanted at two sites in eastern edge of Qinghai-Tibetan Plateau, Hongyuan (3434 m, 2.97 °C, 911 mm) and Qilian (3701 m, 2.52 °C, 472 mm), aiming to evaluate the responses of alpine plants to changing environments. When plants were transplanted from Hongyuan to Qilian, most plant species showed a decrease of total wax coverage in first year and reverse trend was observed for some plant species in second year. However, when plants were transplanted from Qilian to Hongyuan, the response of total wax coverage differed greatly between plant species. When compared with those in first year, plasticity index of average chain length of alkane decreased whereas carbon preference index of alkane increased at both Hongyuan and Qilian in second year. The total wax coverage differed between local and transplanted plants, suggesting both environmental and genetic factors controlled the wax depositions. Structural equation modeling indicated that co-variations existed between leaf cuticular waxes and leaf functional traits. These results suggest that alpine herbs adjust both wax depositions and chain length distributions to adapt to changing environment, showing climate adaptations.

Mid-Miocene Lake Level Fluctuations in the Lunpola Basin, Central Tibetan Plateau

Knowledge of paleolake evolution is highly important for understanding the past hydroclimate regime on the Tibetan Plateau and associated forcing mechanisms. However, the hydrological history of paleolakes on the central plateau, the core region of the plateau, remains largely inconclusive. Here we present new biomarker records from lacustrine deposits of the Lunpori section in the Lunpola Basin to reconstruct detailed lake-level fluctuations during the mid-Miocene. A set of n-alkane indexes, including the proportion of aquatic macrophytes (Paq), average chain length and carbon preference index as well as the content of n-alkanes, vary substantially and consistently throughout the studied interval. Our results altogether show relatively low lake level at ∼16.3–15.5 Ma and high lake level before and after the interval, which is in line with the lithological observations in the section. Further comparison with existing regional and global temperature records suggests that lake level fluctuations can be largely linked to global climatic conditions during the mid-Miocene, with lake expansion during relatively warm periods and vice versa. Therefore, we infer that global climatic changes might have controlled the lake-level fluctuations in this region during the mid-Miocene, whereas the tectonic uplift likely played a subordinate role on this timescale.

Organic matter characteristics of a rapidly eroding permafrost cliff in NE Siberia (Lena Delta, Laptev Sea region)

Organic carbon (OC) stored in Arctic permafrost represents one of Earth’s largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits are still poorly quantified. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ~52 ka. We show that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt%).We found that the OM quality, which we define as the intrinsic potential to further transformation, decomposition, and mineralization, is also high as inferred by the lipid biomarker inventory. The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal kyr BP) and is overlaid by Last Glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n-alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso and anteiso-branched FAs relative to long chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits, suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high C / N ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease of HPFA values downwards along the profile probably indicates a relatively stronger OM decomposition in the oldest (MIS 3) deposits of the cliff. The characterisation of OM from eroding permafrost leads to a better assessment of the greenhouse gas potential of the OC released into river and nearshore waters in future, which is important to understand the consequences of a warming climate in Arctic environments on the global carbon cycle.

Cenozoic Antarctic climate evolution based on molecular and isotopic biomarker reconstructions from geological archives in the Ross Sea region

<p>During the Cenozoic Era (the last 65 Ma), Antarctica’s climate has evolved from ice free conditions of the ‘Greenhouse world’, which at its peak (~ 55 Ma) supported near-tropical forests, to the ‘Icehouse’ climate of today with permanent ice sheets, and a very sparse macroflora. This long-term cooling trend is punctuated by a number of major, abrupt, and in some cases, irreversible climate transitions. Reconstructing past changes in vegetation, sea surface temperature, hydroclimate and the carbon cycle require robust geological proxies that in turn can provide insights into climatic thresholds and feedbacks that drove major transitions in the evolution of Antarctica’s ice sheets. Biomarkers allow climate and environmental proxy reconstructions for this region, where other more traditional paleoclimate methods are less suitable. This study has two aims. Firstly to assess the suitability and applicability of biomarkers in Antarctic sediments across a range of depositional settings and ages, and secondly to apply biomarker-based climate proxies to reconstruct environmental and climate conditions during key periods in the development of the Antarctic Ice Sheets. The distribution and abundances of n-alkanes are assessed in Oligocene and Miocene sediments from a terrestrial outcrop locality in the Transantarctic Mountains, and two glaciomarine sediment cores and an ice-distal deep marine core from the western Ross Sea. Comparisons are made with n-alkane distributions in Eocene glacial erratics and sedimentary rocks of the Mesozoic Beacon Supergroup, both likely sources of reworked material. A shift in dominant chain length from n-C₂₉ to n-C₂₇ occurs between the Late Eocene and Early Oligocene, considered a response to a significant climate cooling. Samples from glaciofluvial environments onshore, and subglacial and ice-proximal environments offshore display a reworked n-alkane distribution, characterised by low carbon preference index (CPI), high average chain length (ACL) and high n-C₂₉/n-C₂₇ values. Whereas, samples from lower-energy, more benign lacustrine and ice-distal marine environments predominantly contained contemporary material. Palynomorphs and biomarker proxies based on n-alkanes and glycerol dialkyl glycerol tetraethers (GDGTs) are applied to a Late Oligocene and Early Miocene glaciomarine succession spanning the large transient excursion of the Mi-1 glaciation (~23 Ma) in DSDP Site 270 drill core from the central Ross Sea. While the Late Oligocene is marked by relatively warm conditions, regional cooling initiated a transition into Mi-1. This was likely driven by a combination of decreasing atmospheric CO₂ and an orbital geometry favouring low seasonality and cool summers, leading to an intensification of proto-Antarctic bottom water production as the Ross Sea deepened and cooled. Mi-1 manifests as a regionally cool period, with minimum subsurface temperatures of ~4°C and onshore mean summer temperatures of ~8°C. A negative n-alkane δ¹³C excursion of up to 4.8‰ is interpreted as a vegetation response to cold, restricted growing seasons, with plants driven to lower altitudes and more stunted growth forms. However, ocean temperatures remained too warm for marine-based ice sheets to advance onto the outer continental shelf and over-ride the drill site. The large increase in ice volume associated with this event, implied by global δ¹⁸O records, was probably held on a higher, terrestrial West Antarctica of greater extent than present day. The relative lack of ice rafted debris during Mi-1, suggests the presence of a marginal marine-terminating ice sheet with fringing ice shelves to the south of DSDP site 270, calving icebergs lacking a basal debris layer, similar to those calving from the Ross Ice Shelf today. This extensive ice cover may explain a large decrease in marine n-alkanes at this time restricting marine productivity on the continental shelf. The biomarker data for the Early Miocene in DSDP 270 indicates a relative warming in both terrestrial and marine temperatures following the transient Mi-1 glacial expansion, but an overall baseline cooling of climate between Late Oligocene and the Early Miocene in the Ross Sea embayment. Isoprenoid GDGTs are used to reconstruct a Cenozoic subsurface ocean temperature compilation for the Ross Sea, a key source region of ocean deep water. The ocean temperature TEXL86 calibration and BAYSPAR in standard subsurface mode were considered, through comparison with independent microfossil and sedimentological data, the most appropriate for use in this region. Ocean temperatures cool prior to the Eocene/Oligocene transition and remain cool for the rest of the Cenozoic, with the exception of short periods of relative warmth in the Late Oligocene and Mid-Miocene Climate Optimum, and long-term trends broadly mirror that of the foraminiferal δ¹⁸O record from the deep Pacific. The Δ Ring Index is used to assess non-thermal influences on GDGT distributions, and displays a long term shift from more positive to more negative deviations. This correlates with %GDGT-0, and also relates to a declining trend in the Methane Index, which reflect the contribution of methanogenic and methanotrophic archaea. These changes suggest that these archaea contributed more to the archaeal community in the early to mid Cenozoic, potentially indicating a more anoxic depositional environment in the Ross Sea. The Branched to Isoprenoid Tetraether index (BIT) steadily declines over the Cenozoic, reflecting increasingly hyper-arid conditions onshore, with less active glaciofluvial systems, limited soil development and less ice-free land.</p>

Cenozoic Antarctic climate evolution based on molecular and isotopic biomarker reconstructions from geological archives in the Ross Sea region

<p>During the Cenozoic Era (the last 65 Ma), Antarctica’s climate has evolved from ice free conditions of the ‘Greenhouse world’, which at its peak (~ 55 Ma) supported near-tropical forests, to the ‘Icehouse’ climate of today with permanent ice sheets, and a very sparse macroflora. This long-term cooling trend is punctuated by a number of major, abrupt, and in some cases, irreversible climate transitions. Reconstructing past changes in vegetation, sea surface temperature, hydroclimate and the carbon cycle require robust geological proxies that in turn can provide insights into climatic thresholds and feedbacks that drove major transitions in the evolution of Antarctica’s ice sheets. Biomarkers allow climate and environmental proxy reconstructions for this region, where other more traditional paleoclimate methods are less suitable. This study has two aims. Firstly to assess the suitability and applicability of biomarkers in Antarctic sediments across a range of depositional settings and ages, and secondly to apply biomarker-based climate proxies to reconstruct environmental and climate conditions during key periods in the development of the Antarctic Ice Sheets. The distribution and abundances of n-alkanes are assessed in Oligocene and Miocene sediments from a terrestrial outcrop locality in the Transantarctic Mountains, and two glaciomarine sediment cores and an ice-distal deep marine core from the western Ross Sea. Comparisons are made with n-alkane distributions in Eocene glacial erratics and sedimentary rocks of the Mesozoic Beacon Supergroup, both likely sources of reworked material. A shift in dominant chain length from n-C₂₉ to n-C₂₇ occurs between the Late Eocene and Early Oligocene, considered a response to a significant climate cooling. Samples from glaciofluvial environments onshore, and subglacial and ice-proximal environments offshore display a reworked n-alkane distribution, characterised by low carbon preference index (CPI), high average chain length (ACL) and high n-C₂₉/n-C₂₇ values. Whereas, samples from lower-energy, more benign lacustrine and ice-distal marine environments predominantly contained contemporary material. Palynomorphs and biomarker proxies based on n-alkanes and glycerol dialkyl glycerol tetraethers (GDGTs) are applied to a Late Oligocene and Early Miocene glaciomarine succession spanning the large transient excursion of the Mi-1 glaciation (~23 Ma) in DSDP Site 270 drill core from the central Ross Sea. While the Late Oligocene is marked by relatively warm conditions, regional cooling initiated a transition into Mi-1. This was likely driven by a combination of decreasing atmospheric CO₂ and an orbital geometry favouring low seasonality and cool summers, leading to an intensification of proto-Antarctic bottom water production as the Ross Sea deepened and cooled. Mi-1 manifests as a regionally cool period, with minimum subsurface temperatures of ~4°C and onshore mean summer temperatures of ~8°C. A negative n-alkane δ¹³C excursion of up to 4.8‰ is interpreted as a vegetation response to cold, restricted growing seasons, with plants driven to lower altitudes and more stunted growth forms. However, ocean temperatures remained too warm for marine-based ice sheets to advance onto the outer continental shelf and over-ride the drill site. The large increase in ice volume associated with this event, implied by global δ¹⁸O records, was probably held on a higher, terrestrial West Antarctica of greater extent than present day. The relative lack of ice rafted debris during Mi-1, suggests the presence of a marginal marine-terminating ice sheet with fringing ice shelves to the south of DSDP site 270, calving icebergs lacking a basal debris layer, similar to those calving from the Ross Ice Shelf today. This extensive ice cover may explain a large decrease in marine n-alkanes at this time restricting marine productivity on the continental shelf. The biomarker data for the Early Miocene in DSDP 270 indicates a relative warming in both terrestrial and marine temperatures following the transient Mi-1 glacial expansion, but an overall baseline cooling of climate between Late Oligocene and the Early Miocene in the Ross Sea embayment. Isoprenoid GDGTs are used to reconstruct a Cenozoic subsurface ocean temperature compilation for the Ross Sea, a key source region of ocean deep water. The ocean temperature TEXL86 calibration and BAYSPAR in standard subsurface mode were considered, through comparison with independent microfossil and sedimentological data, the most appropriate for use in this region. Ocean temperatures cool prior to the Eocene/Oligocene transition and remain cool for the rest of the Cenozoic, with the exception of short periods of relative warmth in the Late Oligocene and Mid-Miocene Climate Optimum, and long-term trends broadly mirror that of the foraminiferal δ¹⁸O record from the deep Pacific. The Δ Ring Index is used to assess non-thermal influences on GDGT distributions, and displays a long term shift from more positive to more negative deviations. This correlates with %GDGT-0, and also relates to a declining trend in the Methane Index, which reflect the contribution of methanogenic and methanotrophic archaea. These changes suggest that these archaea contributed more to the archaeal community in the early to mid Cenozoic, potentially indicating a more anoxic depositional environment in the Ross Sea. The Branched to Isoprenoid Tetraether index (BIT) steadily declines over the Cenozoic, reflecting increasingly hyper-arid conditions onshore, with less active glaciofluvial systems, limited soil development and less ice-free land.</p>

Yield, Grain Quality and Starch Physicochemical Properties of 2 Elite Thai Rice Cultivars Grown under Varying Production Systems and Soil Characteristics

Rice production systems and soil characteristics play a crucial role in determining its yield and grain quality. Two elite Thai rice cultivars, namely, KDML105 and RD6, were cultivated in two production systems with distinct soil characteristics, including net-house pot production and open-field production. Under open-field system, KDML105 and RD6 had greater panicle number, total grain weight, 100-grain weight, grain size, and dimension than those grown in the net-house. The amounts of reducing sugar and long amylopectin branch chains (DP 25–36) of the RD6 grains along with the amounts of long branch chains (DP 25–36 and DP ≥ 37), A-type starch granules, and average chain length of the KDML105 were substantially enhanced by the open-field cultivation. Contrastingly, the relative crystallinity of RD6 starch and the amounts of short branch chains (DP 6–12 and DP 13–24), B- and C-type granules, and median granule size of KDML105 starch were significantly suppressed. Consequently, the open-field-grown RD6 starch displayed significant changes in its gelatinization and retrogradation properties, whereas, certain retrogradation parameters and peak viscosity (PV) of KDML105 starches were differentially affected by the distinct cultivating conditions. This study demonstrated the influences of production systems and soil characteristics on the physicochemical properties of rice starches.

Vegetation History in a Peat Succession Over the Past 8,000 years in the ISM-Controlled Kedarnath Region, Garhwal Himalaya: Reconstruction Using Molecular Fossils

The Holocene epoch has witnessed several natural climate variations and these are well encoded in various geological archives. The present biomarker investigation in conjunction with previously published multi-proxy records was applied to reconstruct organic matter (OM) sources forming the peat succession spanning the last 8000 cal yr BP and shift in hydrological conditions from the Kedarnath region, Garhwal Himalaya. Intensified monsoon prevailed from ∼7515 until ∼2300 cal yr BP but with reversal to transient arid period particularly between ∼5200 and ∼3600 cal yr BP as revealed by the variability in n-C23/n-C31, ACL (average chain length of n-alkanes) and Paq (P-aqueous) values. A prolonged arid phase is recognizable during the interval between ∼2200 and ∼370 cal yr BP suggested by the n-alkane proxies. Regional scale heterogeneity in the monsoonal pattern is known in the studied temporal range of mid to late Holocene across the Indian subcontinent that is probably a result of complex climate dynamics, sensitivity of proxies and impact of teleconnections. The biomarker signatures deduced from gas chromatography mass spectrometry (GCMS) analysis are suggestive of a mixed biotic input that includes prokaryotes, Sphagnum spp. and gymnosperm flora. The mid chain alkanes viz. n-C23 and n-C25 denote the presence of typical peat forming Sphagnum moss that preferentially grows in humid and waterlogged conditions. Diterpane marker such as ent-kaurane indicates contribution of gymnosperms, whereas the hopanes are signatures of microbial input. The preservation of organic matter is attributed to little microbial degradation in a largely suboxic depositional environment. Our study strengthens the applicability of organic geochemical proxies for the reconstruction of past climate history and indicates their suitability for use on longer timescales given the high preservation potential of the molecular remains.

Analyses of depositional environments of the Marcellus formation in New York using biomarker and trace metal proxies

The purpose of this study was to observe how the composition of organic matter (OM) and the extent of anoxia during deposition within the Marcellus Formation in New York varied by distance from the sediment source in eastern New York. Lipid biomarkers (n-alkanes and fatty acids) in the extractable organic component (bitumen) of the shale samples were analyzed, and proxies such as the average chain length (ACL), aquatic to terrestrial ratio (ATR) and carbon preference index (CPI) of n-alkanes were calculated. Fatty acids were relatively non-abundant due to the age of the shale bed, but n-alkane distributions revealed that the primary component of the OM was terrigenous plants. The presence of shorter n-alkane chain lengths in the samples indicated that there was also a minor component of phytoplankton and algal (marine) sourced OM. Whole rock analyses were also conducted, and cerium anomalies were calculated as a proxy for anoxia. All samples had a negative anomaly value, indicating anoxic conditions during deposition. Two samples, however, contained values close to zero and thus were determined to have suboxic conditions. Anoxia and total organic matter (TOM) did not show any spatial trends across the basin, which may be caused by varying depths within the basin during deposition. A correlation between nickel concentrations and TOM was observed and indicates that algae was the primary source of the marine OM, which supports the lipid biomarker analysis. It was determined that the kerogen type of the Marcellus Formation in New York State is type III, consistent with a methane-forming shale bed.

Going Beyond the Carothers, Flory and Stockmayer Equation by Including Cyclization Reactions and Mobility Constraints

A challenge in the field of polymer network synthesis by a step-growth mechanism is the quantification of the relative importance of inter- vs. intramolecular reactions. Here we use a matrix-based kinetic Monte Carlo (kMC) framework to demonstrate that the variation of the chain length distribution and its averages (e.g., number average chain length xn), are largely affected by intramolecular reactions, as mostly ignored in theoretical studies. We showcase that a conventional approach based on equations derived by Carothers, Flory and Stockmayer, assuming constant reactivities and ignoring intramolecular reactions, is very approximate, and the use of asymptotic limits is biased. Intramolecular reactions stretch the functional group (FG) conversion range and reduce the average chain lengths. In the likely case of restricted mobilities due to diffusional limitations because of a viscosity increase during polymerization, a complex xn profile with possible plateau formation may arise. The joint consideration of stoichiometric and non-stoichiometric conditions allows the validation of hypotheses for both the intrinsic and apparent reactivities of inter- and intramolecular reactions. The kMC framework is also utilized for reverse engineering purposes, aiming at the identification of advanced (pseudo-)analytical equations, dimensionless numbers and mechanistic insights. We highlight that assuming average molecules by equally distributing A and B FGs is unsuited, and the number of AB intramolecular combinations is affected by the number of monomer units in the molecules, specifically at high FG conversions. In the absence of mobility constraints, dimensionless numbers can be considered to map the time variation of the fraction of intramolecular reactions, but still, a complex solution results, making a kMC approach overall most elegant.