Loess Deposits Research Articles

Spatial trace and rare earth elemental compositions of surficial sediments on the high Mountains, Central Asia, and implications for desert sand and Asian dust

As one of the major mountain systems in Central Asia, the Tianshan Mountains provide vast amounts of sediment to adjacent areas. The elemental compositions of surficial sediments on the piedmont of the Tianshan Mountains were investigated to track surface processes. However, spatial comparisons of the elemental compositions of the sediments in the Tianshan Mountains and adjacent areas remain limited. To address this issue, this study investigated the trace element compositions (including rare earth elements (REEs)) of surficial sediments in a vast region ranging from the Pamirs, Tarim Basin, and Tianshan Mountains to the Junggar Basin. According to statistical analyses of the selected source tracers of trace element and REE ratios, this large region can be geochemically divided into two regions. One region comprises the Pamirs, Tarim Basin, and South and Central Tianshan Mountains (PTSC), where the sediments are characterized by contrary source tracer ratios compared with the other region comprising the Yili Basin, North Tianshan, and Junggar Basin (YNTJ). We suggest that the source bedrock is the primary factor controlling the trace element and REE compositions in these two regions. The trace element and REE compositions in the PTSC and YNTJ regions represent signatures of the two endmembers of Asian dust. The trace compositions of loess deposits on the Chinese Loess Plateau (CLP) and Asian dust archived in the North Pacific Ocean (NPO) mostly resemble those of sediments in the PTSC region, suggesting that Asian dust is mainly derived from sediments eroded from the North Tibetan Plateau. Our study enriches our understanding of the source materials of Asian dust archived in the CLP and NPO.

Southward shift of the Westerlies during Heinrich Event 2: Evidence from loess deposits in Central Asia

Knowledge of past changes in the Westerlies is important for understanding the climatic and environmental evolution of Central Asia. Here, we use high-resolution grain size records from several loess deposits in Central Asia to study the spatial pattern of the Westerlies during an interval of high global ice volume during the Last Glacial Maximum. During Heinrich event 2 (H2), the Westerlies strengthened in southern Central Asia, as indicated by the high accumulation rate of dust transported by the Westerlies, while it decreased in northern Central Asia. Our grain size record, combined with climate modeling results, suggest that the main axis of the Westerlies strengthened and moved southward to southern Central Asia during Heinrich events, especially H2. Comparison with other climate records from East Asia indicates that a southward shift of the Westerlies may influence the extension of the downstream East Asian Summer monsoon rain belt into north and northwest China. Thus, the position and strength of the mid-latitude Westerlies need to be considered in future studies of the Asian monsoon.

Testing the potential of pulsed post-IR IRSL dating on Chinese loess deposits

Testing the potential of pulsed post-IR IRSL dating on Chinese loess deposits

Loess microstructure indication indexes for the study of palaeoclimatic conditions in northwest China

AbstractThe Loess Plateau of China, located to the west of the Liupan Mountains and north of the Qinling Mountains stretching across the Yellow River, is the main loess deposit area in Northwest China. The loess in the northwest of China has deposits with large thickness and extensive distribution. Scanning electron microscopy (SEM) and energy spectrum analysis of loess have been performed to study the relationship between the loess microstructures and the forming climates Era. The relevant indexes were evaluated including the sand‐dropping speed (Vn), certain sedimentary depths (hn sand particle volume (Vd) and element ratios of Ca/Fe, K/Al, Si/Al and Ca/Mg. The microstructure indexes of loess accumulation and evolution reflect paleoclimate conditions and time scales to a certain extent. The important discovery is the microscopic sand‐dropping speed (Vn) and the sedimentary depth hn) calculation method of different sedimentary ages. These indices are compared with the record of major aeolian‐forming climates from the Guliya ice core, and provide a reliable benchmark for studying climate change It also can be used as important indicators of monsoonal change and environmental evolution reconstruction. The index of sand sedimentation speed (Vn) got from loess microstructure could reflect sand‐dropping speed and loess deposition course. According the article can serve as new indicators of climatic changes of different forming loess layers. It can also be concluded that the climatic indexes obtained from loess microstructure can reflect climate conditions of loess forming. The loess forming climatic parameters are synchronous correspond to Tengger Desert and Guliya ice core for studying climate change, then microscopic parameters can also be used for preliminary analysis of loess climate formation and has be found corresponding evidence, and the loess climatic parameters correspond to the other two indexes. The analysis of loess microstructure indexes is very useful in researching climate change. Loess microstructure indexes can find new indicators and information about the monsoon climate evolution and paleoclimate changes.

Large-scale surface water-groundwater origins and connectivity in the Ordos Basin, China: Insight from hydrogen and oxygen isotopes

The sustainability of water resources is a major challenge for the Ordos Basin and Loess Plateau of China. The basis of effective water management is an understanding of the water cycle process. This study investigated the surface water-groundwater origins and connectivity using stable isotopes (δD and δ18O) of surface water and groundwater in 11 river basins in the Ordos Basin. It was found that the surface water-groundwater origins and hydraulic connection were characterized by regional differences, mainly induced by climatic characteristics, hydrogeological conditions and human activities. Specifically, the impact of thick loess deposits caused surface water and groundwater to take long time to produce a hydraulic connection. In contrast, areas with thin loess deposits and frequent human activities showed a good connectivity between surface water and groundwater. As for water origins, summer precipitation was a common source of surface water and groundwater in the study area, and groundwater discharge was another source of surface water. However, surface water and groundwater were subjected to different degrees of evaporation during receiving precipitation recharge. Notably, thick loess deposits had an impact on groundwater evaporation because both the recharge of precipitation to groundwater and the discharge of groundwater to surface water took a long time. In addition, it was found that frequent human activities (mining, irrigation and urban construction) could weaken the impact of evaporation. This large-scale analysis provided new insights into the origins and connectivity of surface water and groundwater in areas with thick unsaturated zones for water resources management.

Buried Podzols as a pedostratigraphic marker for the Medieval Climatic Optimum: Grębociny soil in the dune deposits of the European Sand Belt

The paleopedological record documented in aeolian dunes of the eastern European Sand Belt comprises predominantly Arenosols and only occasionally well-developed Podzols. There are several Late Pleistocene pedostratigraphic marker horizons of varied soil types designated in the European dune and loess deposits, but none falls within the range of the Holocene. Buried Podzol occurrences found recently in 10 inland dune sites dispersed throughout Central and Eastern Poland share similar pedological properties, geomorphological setting, and age in the 5th–15th century AD range of the historical Middle Ages. Therefore, they meet the criteria for distinction as a pedostratigraphic marker under the name Grębociny soil, after a locality with the most advanced podzolization of the paleosol dated to the High Middle Ages (1000–1300 AD). Preservation of the soils was enabled by burial during anthropogenically induced dune remobilization. At least some of the investigated dunes were used as pasture during soil development, as evidenced by tetrapod hoofprints recorded in and above the buried Podzols. Prevalent podzolization during the Middle Ages, in contrast to preceding and later times, could be facilitated by not only an impact of agriculture and forestry, but also relative warmth and humidity of the Medieval Climatic Optimum (ca. 900–1400 AD).

High-resolution luminescence chronology of loess-paleosols reveals East Asian summer monsoon and winter monsoon variation in Hexi Corridor during the past 25 kyr

The variability and interaction of the East Asian summer monsoon (EASM), East Asian winter monsoon (EAWM) and Westerlies dominate mid-latitude Asian hydroclimate and influence over a billion lives in Asia. However, how variation in the EASM, EAWM and Westerlies influences climate change in their transition zones in NW China remain unclear. Specifically, how these atmospheric systems interact during strong-weak phases variation over different timescales is still hotly debated. This study investigates four loess-paleosol sequences in the transition zone between EASM and Westerlies-influenced areas along the central Hexi Corridor of NW China, and presents 63 quartz optically stimulated luminescence (OSL) ages to generate the most detailed chronology for any loess record within the Hexi Corridor. In combination with sedimentology, proxy indexes of magnetic parameters (χlf, χfd, χARM/SIRM) and grain size of these loess-paleosol sequences, and TraCE-21 ka climatic modelling, the loess deposition and climatic changes at central Hexi Corridor regions over the past 25 ka are reconstructed. Our results indicate that: (1) loess deposition initiated by at least 25 ka at Hexi Corridor. Loess depositional rates decrease from late last glacial into the Holocene, with maximum accumulation rates (140–180 g/cm3/ka) occurring during the Last Glacial Maximum. Depositional hiatuses up to 8 ka are recognized in late Quaternary Hexi Corridor loess, which suggests that high-resolution chronologies are necessary for robust paleoclimatic reconstructions from loess records in the region. (2) Over glacial-interglacial cycles, climate in the Hexi Corridor demonstrates a cold-dry glacial and a warm-moist interglacial, consistent with moisture changes observed in the monsoonal Chinese Central Loess Plateau and Westerlies-dominated Central Asia. However, moisture in central Hexi Corridor increased from the early Holocene to mid-Holocene, with a wettest period at 8–7 ka, and followed by a relatively wet late Holocene. These changes are most consistent with the EASM-dominated Chinese Central Loess Plateau and suggests that Westerlies influence in the central Hexi Corridor is minor over at least the past 25 kyr. (3) EAWM intensities demonstrate an anti-phase relationship to EASM intensities over the past 25 kyr in the Hexi Corridor, with decreasing EAWM intensity into the early-mid Holocene and an increase into the late Holocene. (4). EASM precipitation variability in the Hexi Corridor appears to not to be a direct nor singular response to changes in 30°N summer insolation. EASM lags insolation by 3 kyr during the Holocene, supporting the idea that high-latitude forcing through changes in ice volume, greenhouse gases, and/or meltwater input to North Atlantic and Southern oceans can effectively modulate EASM intensity and critically influence Hexi Corridor paleoclimatic conditions.

Unraveling source-to-sink dust transport in Central and East Asia by identifying provenances of aeolian sediments

Loess deposits as a unique terrestrial archive of paleo-dust contribute to understanding the wide-scale and long-term dust transport from source to sink. This study provided diagnostic constraints on the sources of clay-sized particles in the Chinese Loess Plateau (CLP) loess by expanding the potential dust source areas with the Kyzylkum Desert and the Central Asian loess. Based on the grain sizes and the particle-size-specific trace elements, we characterized the major provenance and the sedimentary process of the Kyzylkum Desert sands. The results indicate the main derivation of Kyzylkum Desert sands from the Tian Shan-derived sediments, with limited large-scale mixing. The desert was thought to be a sink region, instead of an important dust source, which was supported by its weak genetic links to the Central Asian loess. With integration of the published data set about trace element and SrNd isotopic composition and our results, combined with the simulation results, we revealed that the Badain Jaran and Tengger deserts in northwestern CLP, rather than the Taklimakan and Kyzylkum deserts further west, played an important role in supply of the clay-sized particles for the CLP loess. The findings implied that the fine particles were primarily related to the East Asian winter monsoon, instead of the high-level westerly airstreams. In this context, we attributed the asynchronous timing of enhanced dust accumulation during the last glacial maximum (LGM) over Greenland and North Pacific (early LGM) and on the CLP (late LGM) to the differences in the major dust sources and in the atmospheric circulation systems.

Controlling mechanism and water quality assessment of arsenic in China's Yellow River Basin

Arsenic (As) is a well-known toxic and carcinogen element, and As contamination has gained public concerns worldwide. Mechanisms, sources, and potential health risks of high As in the China's Yellow River Basin (CYRB), a water-deficient area and the largest loess deposition area in the world, remain largely unknown. Hydrogen and oxygen isotopes, major ions, and As were analyzed in 409 river water and 164 groundwater samples in dry season to decipher these problems. Samples were alkaline (pH = 8.0 ± 0.4), and As concentrations (5.29 ± 10.5 μg/L) in the CYRB were above the world average, especially in upstream and midstream. About 9.1% and 13.0% of samples in river water and groundwater had As concentrations above the permissible limit of WHO, respectively. Based on self-organizing map (SOM) analysis, about 50.6% of samples with high As were SO4–Cl–Na type while about 46.4% of samples with low As were HCO3–Ca–Mg type. The δD (−62.5 ± 11.3‰) and δ18O (−8.5 ± 2.1‰) values of river water were higher than the groundwater (δD = −69.7 ± 10.2‰, δ18O = −9.9 ± 1.4‰), and most samples with As >10 μg/L were below the local and global meteoric water lines, indicating the evaporation effect on As enrichment, especially for river water. Evaporites dissolution of loess and ion exchange increased water salinity, accelerated desorption of As and enriched As in CYRB. Meanwhile, oil and coal exploitation contributed to the high As in the northwestern Loess Plateau. Health risk assessment indicated that 41.6% and 59.8% of groundwater samples posed high carcinogenic risk for adults and children, respectively. Therefore, corresponding measures must be implemented in these areas. In the future, As geochemistry in wet seasons in the CYRB and the characteristics among different seasons will be explored. These results highlight the impact of dry climate and anthropogenic activity on As enrichment in arid/semi-arid regions.

Magnetic Proxy of Eurasian Loess Revealing Enhanced Physical Erosion Since the Mid‐Pleistocene Transition

AbstractEolian loess deposits contain valuable information about past climate changes and erosion history in dust source regions. In contrast to the extensive investigations of paleoclimatic implications of Eurasian loess, continental erosion information in the loess deposits has received less attention, particularly on the global or hemispheric scales. The present study combines citrate‐bicarbonate‐dithionite (CBD) magnetic mineral extraction procedures and linear regression of magnetic parameters to analyze Eurasian loess. We find that lithogenic susceptibility of Quaternary loess deposits in Central Asia, Europe and the Chinese Loess Plateau shows synchronous long‐term increases since ∼0.6–0.5 Ma, suggesting intensive glacial erosion and/or river incision to have occurred in the surrounding mountains of dust source regions after the mid‐Pleistocene climate Transition. The dramatic increase in lithogenic susceptibility of Eurasian loess provides new insights into the close relationships between global climate changes and dust source erosion since the late Cenozoic.

Comprehensive magnetic analysis of the tephras in Middle-Late Pleistocene loess records of Serbia, and implications for tephra identification, correlation and loess chronology

Tephras are highly valuable for achieving precise chronologies and secure correlations for sedimentary sequences. Rock magnetic investigations provide a simple, rapid tool for tephra identification especially for weathered tephra, cryptotephra (hidden tephra), thin and dispersed distal tephra. But so far, the most diagnostic magnetic properties for tephra identification and for differentiation of specific tephras are still uncertain. Three laterally continuous and representative tephras/cryptotephras embedded in Serbian loess deposits provide a rare opportunity to explore application of magnetic approaches in tephrostratigraphy. Systematic rock magnetic and petrographic comparison of tephra and its host loess reveal that the characteristic magnetic mineral of the studied tephras is moderate-Ti titanomagnetite of magmatic origin, with a dominant magnetic grain size of non-interacting single domain (SD) and pseudo-single domain (PSD) state. We identify the most diagnostic magnetic properties for tephra identification in loess and many other sediments. The Curie temperature of titanomagnetite is the most diagnostic property of tephras. A low-temperature alternating current (AC) magnetic susceptibility peak at ∼20–100 K is a sensitive indicator of coarse-grained titanomagnetite. SIRM-χfd and χARM-χfd plots can easily differentiate tephras from loess-paleosol sequences and possibly other pedogenesis-influenced sediments. Furthermore, our results suggest Curie temperatures can be a promising tool of regional tephra correlation. Our magnetic evidence and mineral composition analysis support the same origin of Tephra-L5 as Tephra-L4 from Alban Hills Volcanic District, possibly from the ∼457 ka eruption, which would promote a robust chronostratigraphic model of Danube loess.

Mechanism of groundwater recharge in the thick loess deposits by multiple environmental tracers

The loess−covered region accounts for ∼10 % of global land surface. Because of dry climate and thick vadose zones, the subsurface water flux is low but the water storage is relatively large . As a result, the groundwater recharge mechanism is complicated and currently controversial (e.g., piston flow or dual mode with piston and preferential flow). Taking typical tablelands in China's Loess Plateau as example study area, this study aims to qualitatively and quantitively evaluate the forms/rates and controls of groundwater recharge considering space and time. We collected 498 precipitation, soil water and groundwater samples in 2014–2021 for hydrochemical and isotopic analysis (Cl−, NO3−, δ18O, δ2H, 3H and 14C). A graphical method was employed to determine appropriate model to correct 14C age. Dual model exhibited in the recharge: regional−scale piston flow and local−scale preferential flow. Piston flow dominated groundwater recharge with a proportion of 77 %–89 %. Preferential flow gradually declined with increasing water table depths, and the upper depth limit may be <40 m. The dynamics of tracers proved that mixing and dispersion effects of aquifers limited the ability of tracers to capture preferential flow at short−time scales. Long−term average potential recharge (79 ± 49 mm/year) was close to actual recharge (85 ± 41 mm/year) at the regional scale, indicating the hydraulic equilibrium between unsaturated and saturated zones. The thickness of vadose zone controlled recharge forms, and precipitation dominated the potential and actual recharge rates. Land−use change can also affect the potential recharge rates at point and field scales but maintain the dominance of piston flow. The revealed spatially−varied recharge mechanism is useful for groundwater modeling and the method can be referred for studying recharge mechanism in thick aquifers.

Link between Lesser Himalayan Neoproterozoic Krol succession and the Adelaide rift complex of Australia ‒ evidence from the mudstone deposits of Krol succession, Himachal Pradesh, India

The mudstone deposits, a major constituent of the Lesser Himalayan Krol succession, represents the terminal phase of Marinoan snowball melting, an important part of the most significant events of the Proterozoic time, the Cryogenian Snowball Earth. The Facies analysis suggests that the sediments were supplied to the shelf by meltwater flows, and were later dispersed to the deeper part of the shelf by current/wave-enhanced bottom currents. The upper part of the deposit bears the signature of gradual shallowing of the basin caused due to glacioisostatic rebound. Petrographic study of the samples, randomly collected from different parts of the deposit, reveals that the mud deposit is composed of silt-sized particles of quartz and dolomite, and argillaceous material. Besides the variation in proportion of these constituent components, no other material was found within this deposit. This compositional homogeneity of this huge deposit primarily suggest derivation from some preexisting sediments. Mineralogical similarity and perfect match in trace and Rare Earth elements composition suggest that this mud was derived from the periglacial loess deposits of the Nuccaleena Formation of South Australia. This is in agreement with the provenance of the underlying Krol Sandstone. The mudstones, along with the underlying Krol Sandstone, thus suggest that the Lesser Himalayan Krol succession represent an extended part of the Adelaide rift system of South Australia. The relative position of India and Australia during Neoproterozoic, as per the reconstructed configuration of the Rodinia supercontinent, corroborates this inference.

Aeolian process and climatic changes in loess records from the eastern Tibetan Plateau: Implications for paleoenvironmental dynamics since MIS 3

The Tibetan Plateau (TP) is extremely sensitive to climate change. However, climate variability during the last glaciation in the TP is not well-understood. The widely distributed loess deposits on the eastern TP serve as a significant archive for retrieving past climate changes and aeolian dust dynamics. Through detailed quartz optically stimulated luminescence and radiocarbon dating and the analysis of environmental proxies, we have established a reliable chronology of the Maerkang loess sequence in the eastern TP and reconstructed well-constrained histories of dust activities and environmental variation. Our results demonstrate that the accumulation of aeolian loess in this region occurred at least 60 thousand years ago. The dust mass accumulation rate (MAR) varied highly in the last glacial period, with high MARs in the Last Glacial Maximum and relatively low MARs in marine isotope stage (MIS) 3. Humid conditions occurred in MIS 3 (approximately 50–32 ka) due to the intensified Indian summer monsoon. The rapid climate variations of the Maerkang loess might be correlated to the Dansgaard–Oeschger cycles and the Heinrich events, which implies the significant impact of the North Atlantic climatic system on the TP. Our findings provide new evidence for a better understanding of the history of environmental variations since MIS 3 in the eastern TP.

Assessing Weathering, Pedogenesis, and Silt Generation in Granitoid‐Hosted Soils From Contrasting Hydroclimates

AbstractThe origin and production of silt are key factors in the formation of loess deposits. Although many processes can potentially lead to silt generation, few are known to produce silt in the volumes and particle‐size modes required to form geologically significant loess deposits. Here, we investigate the hypothesis that soil‐associated weathering in tropical and Mediterranean climates can generate abundant in situ silt, and therefore contribute significantly to loess formation throughout geologic time. We utilize granulometric and geochemical data from two granitoid‐hosted soils formed in Puerto Rico (hot‐humid climate) and Southern California (hot‐arid climate) to discern whether the silt + clay fraction (&lt;62.5 μm) is generated from bedrock weathering (autochthonous) or sourced from eolian contributions (allochthonous). Our study demonstrates that the PR soil contains abundant (up to 72%) silt‐ and clay‐sized particles compared to the Southern California soil (&lt;6%). However, the silt fraction of the PR soil is at least partially derived from eolian inputs, and the silt fraction of the Southern California soil is geochemically indistinguishable from allochthonous dust sources. Furthermore, while intense chemical weathering in PR can produce abundant fines, the majority are significantly finer (average mode ∼15 μm) than the modes of most “typical” loess deposits (modes more than 20–30 μm). In contrast, weathering in the Southern California soil produces volumetrically sparse silt. Hence, weathering processes within these two profiles, representing hot‐humid and hot‐dry climates, appear to be ineffectual for producing the volume and size distributions of silt needed to generate significant loess deposits.

Understanding the characteristics of loess strata and quaternary climate changes in Luochuan, Shaanxi Province, China, through core analysis

Abstract Profile sampling, which causes missing or overlapping horizons, has been generally used while studying loess stratigraphy and paleoclimate. Conversely, drill sampling of thick loess can provide a relatively complete and actual record of the Quaternary climate and environmental changes. Here, paleomagnetic chronological analysis and particle size and magnetic susceptibility analyses were performed to accurately reveal the loess stratigraphy characteristics of Luochuan loess tableland in Fu County, Shaanxi Province, China. The FX core revealed that the Quaternary loess layer was 167.03 m thick and consisted of 33 layers of developed loess/paleosol sequences and 37 loess/paleosol assemblages. The paleosol horizons indicated relatively warm and humid climatic period, while loess/sand reflected cold and arid climate. Since 2.6 Ma, the climate of the region has undergone 37 warm and cold cycles trending toward an increasingly dry and cold climate. During this time, 10 paleoclimate cycles occurred during 2.6–1.6 Ma, 15 climate cycles occurred during 1.6–0.8 Ma, and 12 loess–paleosol cycles have occurred from 0.8 Ma to the present day. Our study provides a basis for accurately and comprehensively interpreting the paleoclimate and paleoenvironment during loess deposition formation.

Paleo-pedological record in loess deposits in the south of the East European plain, based on Beglitsa-2017 section study

Loess-paleosol sequences (LPSs) are one of the main components of the natural environment, which traces how the climate has changed in the past. The article discusses changes in the landscape and climatic conditions from the Middle Pleistocene to the present, identified by the results of the LPS of the Beglitsa-2017 section study. We obtained new data on soil cover change in the Late and Middle Pleistocene in the North-Eastern Azov region based on multi-proxy analysis with high-resolution sampling along the section. The first data on the polygenetic origin of the Salyn interglacial paleosol (MIS 5e) profile which developed according to the Gypsic Calcic Chernozems type in the interglacial optimum, was obtained. Still, in the last stage of soil formation, its type changed to the more arid Gypsic Chernozems (Arenic). During MIS 5c and MIS 5a, the paleosols developed in a more arid climate; their modern analogues may be Gypsic Kastanozems and Calcic Gypsisols, respectively. The period of MIS 3 in the study area is marked by severe cryo-arid conditions, which influenced the formation of incipient Calcic Gypsisols. The profiles of the Middle Pleistocene paleosols in the lower part of the LPS of the Beglitsa-2017 section were subject to gleying processes, which formed specific Gleysols or Stagnosols paleosols. The preliminary age of these paleosols corresponds to MIS 13/15 and 8/9. The MIS 7 paleosols are structurally similar to modern Calcic Kastanozems, currently distributed in the dry steppe zone. Reconstruction of the formation of the LPS paleosol cover in the Beglitsa-2017 section made it possible to trace the trend of changes in climatic conditions in the past. Climate aridity decreases in the interval between MIS 5e and MIS 1, and the maximum drought peaks were recorded in MIS 3 paleosols. Earlier, climate aridization intensified from MIS 13/15 and continued until MIS 7/6. The results will complement our understanding of the soil cover changing over time and will expand the reconstruction of climate change throughout the East European Plain.

Links of apple tree water uptake strategies with precipitation and soil water dynamics in the deep loess deposits

Understanding how trees absorb water is important for the sustainable management of water resources and vegetation restoration. However, the water uptake strategy of apple trees and its link with precipitation and soil water dynamics (i.e., contents, recharge proportion and residence time) remains poorly understood. In this study, we determined the source water of apple trees, the recharge proportion and mean residence time (MRT) of soil water through collecting precipitation, soil water and xylem water samples with a high frequency. Results indicated that apple trees mainly absorbed water from shallow soil layers of 0–2 m (>64%) in the early growing season (May to July), but deep soil water below 2 m (∼60%) in the late growing season (August to October). As such, apple trees had seasonal variations in water uptake strategies by shifting water sources from shallow to deep soils. In addition, the proportions of water uptake from the same soil layer varied with tree ages. The proportions of water uptake from different soil layers were not significantly correlated to the corresponding soil water contents (p > 0.05), which may be attributed to the long residence time of soil water (14–99 days). Therefore, the water uptake strategies of apple trees were likely to be influenced by precipitation and MRT of soil water, as well as stand ages. The indicated relationship between water uptake strategies and precipitation and soil water dynamics can improve insights into the interaction between soil and vegetation.

Squamates, rodents, and birds from Holocene deposits of the Illa Grossa Island (Columbretes Islands, Castellón, Spain): an unexpected diverse assemblage

The Columbretes Islands (eastern Spain) comprise a volcanic archipelago 50 km off the eastern Spanish coast. Illa Grossa is the main island of the archipelago. After the settlement of humans during the mid-19th century, strong modifications in biodiversity took place, including the reduction of the non-flying vertebrate fauna to a single taxon, Podarcis liolepis atratus (Boscá, 1916). The study of the fossils yielded at the COLT site (dated by AMC between 2780-2724 cal BP and 2600-2492 cal BP) from a loess deposit located at the south of Illa Grossa Island shows that this fauna was more diverse in the past. The assemblage was dominated by squamate reptiles, belonging to two lizards (Chalcides bedriagai (Boscá, 1880) and cf. Podarcis Wagler, 1830) and one snake (Vipera cf. latastei Boscá, 1878). The record in the late Holocene of Columbretes of Vipera cf. latastei settles the existing controversy about the identity of snakes in the archipelago. Regarding Chalcides bedriagai, this is the first record of its presence in the Columbretes Islands. Other faunal elements recovered from the site include at least six species of undetermined birds (passeriforms and procellariforms) and the anthropophilic Mus cf. musculus Linnaeus, 1758. The origin of the squamates taxa from Columbretes palaeontological site (COLT) is still unclear, but was probably related to the Late Pleistocene-Greenlandian (11 700 to 8300 BP, Early Holocene) sea transgression, natural passive colonization, and/or human introduction. We hypothesize implications for the conservation and management of the Natural Reserve.

Divergent response of soil microbes to environmental stress change under different plant communities in the Loess Plateau

Soil microorganisms play a crucial role in the proper functioning and stability of grassland ecosystems, and are influenced by the nutrient acquisition strategies of their host plants. The Loess Plateau in China, is known for its severe soil erosion and distinctive loess deposits, with soil nutrient levels declining from southeast to northwest. However, little is known about the relative effects of different host plants on soil microbial communities under different environmental stress in the Loess Plateau. We investigated the microbial community within soil profiles (0–100 cm) under two types of grasses community (Agropyron cristatum and Stipa spp.) with different drought tolerances, which are widely distributed in three different climate regions of the Loess Plateau. The diversity, composition, community assembly, and predicted functions of the bacterial and fungal community were evaluated. We discovered that the climate-plant-soil microbe interactions were the most significant factor affecting the community composition of bacteria and fungi on the regional scale. In addition, the effects of edaphic factors (e.g., soil organic carbon [SOC], total nitrogen [TN], and total phosphorus [TP]) on the soil bacterial and fungal communities increased from the warm-temperate to the desert steppe environment. Furthermore, the microbial community and assembly processes were driven by TP content of Agropyron grass, which is more resistant to environmental stress, while the soil of Stipa grass was driven by SOC. This may have occurred because the soil microbes in the Agropyron grassland had a stronger ability to utilize refractory organic matter thus reducing dependence on SOC, compared to soil microbes in the Stipa grassland. Collectively, our results show that the soil microbes recruited by the different plant communities responded differently in microbial composition, assembly, and functions to adapt the environmental stress change.