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Stable isotope ratio analysis of tree rings has been widely and successfully applied in recent decades for climatic and environmental reconstructions. These studies were mostly conducted at an annual resolution, considering one measurement per tree ring, often focusing on latewood. However, much more information could be retrieved with high-resolution intra-annual isotope studies, based on the fact that the wood cells and the corresponding organic matter are continuously laid down during the growing season. Such studies are still relatively rare, but have a unique potential for reconstructing seasonal climate variations or short-term changes in physiological plant properties, like water-use efficiency. The reason for this research gap is mostly technical, as on the one hand sub-annual, manual splitting of rings is very tedious, while on the other hand automated laser ablation for high-resolution analyses is not yet well established and available. Here, we give an update on the current status of laser ablation research for analysis of the carbon isotope ratio (δ13C) of wood, describe an easy-to-use laser ablation system, its operation and discuss practical issues related to tree core preparation, including cellulose extraction. The results show that routine analysis with up to 100 laser shot-derived δ13C-values daily and good precision and accuracy (ca. 0.1‰) comparable to conventional combustion in an elemental analyzer are possible. Measurements on resin-extracted wood is recommended as most efficient, but laser ablation is also possible on cellulose extracted wood pieces. Considering the straightforward sample preparation, the technique is therefore ripe for wide-spread application. With this work, we hope to stimulate future progress in the promising field of high-resolution environmental reconstruction using laser ablation.

Comparison of assimilate delta C-13 values estimated from different leaf carbon pools, Picarro measurements, and modelled data demonstrates the potential for misinterpretation arising from bulk organic matter delta C-13 analysis.Sucrose has a unique role in recording environmental and physiological signals during photosynthesis in its carbon isotope composition (delta C-13) and transport of the signal to tree rings. Yet, instead of sucrose, total organic matter (TOM) or water-soluble carbohydrates (WSC) are typically analysed in studies that follow delta C-13 signals within trees. To study how the choice of organic material may bias the interpretation of delta C-13 records, we used mature field-grown Scots pine (Pinus sylvestris) to compare for the first time delta C-13 of different leaf carbon pools with delta C-13 of assimilates estimated by a chamber-Picarro system (delta C-13(A_Picarro)), and a photosynthetic discrimination model (delta C-13(A_model)). Compared with sucrose, the other tested carbon pools, such as TOM and WSC, poorly recorded the seasonal trends or absolute values of delta C-13(A_Picarro) and delta C-13(A_model). Consequently, in comparison with the other carbon pools, sucrose delta C-13 was superior for reconstructing changes in intrinsic water use efficiency (iWUE), agreeing in both absolute values and intra-seasonal variations with iWUE estimated from gas exchange. Thus, deriving iWUE and environmental signals from delta C-13 of bulk organic matter can lead to misinterpretation. Our findings underscore the advantage of using sucrose delta C-13 to understand plant physiological responses in depth.

Recent methodological advancements in determining the nonexchangeable hydrogen isotopic composition (δ2Hne) of plant carbohydrates make it possible to disentangle the drivers of hydrogen isotope (2H) fractionation processes in plants. Here, we investigated the influence of phylogeny on the δ2Hne of twig xylem cellulose and xylem water, as well as leaf sugars and leaf water, across 73 Northern Hemisphere tree and shrub species growing in a common garden. 2H fractionation in plant carbohydrates followed distinct phylogenetic patterns, with phylogeny reflected more in the δ2Hne of leaf sugars than in that of twig xylem cellulose. Phylogeny had no detectable influence on the δ2Hne of twig or leaf water, showing that biochemistry, not isotopic differences in plant water, caused the observed phylogenetic pattern in carbohydrates. Angiosperms were more 2H-enriched than gymnosperms, but substantial δ2Hne variations also occurred at the order, family, and species levels within both clades. Differences in the strength of the phylogenetic signals in δ2Hne of leaf sugars and twig xylem cellulose suggest that the original phylogenetic signal of autotrophic processes was altered by subsequent species-specific metabolism. Our results will help improve 2H fractionation models for plant carbohydrates and have important consequences for dendrochronological and ecophysiological studies., New Phytologist, 239 (2), ISSN:0028-646X, ISSN:1469-8137

Incomplete knowledge of carbon (C) allocation dynamics in trees hinders accurate modeling and future predictions of tree growth. We studied C allocation dynamics in a mature Pinus sylvestris L. dominated forest with a novel analytical approach, allowing the first comparison of: (i) magnitude and delta C-13 of shoot, stem and soil CO2 fluxes (A(shoot), R-stem and R-soil), (ii) concentration and delta C-13 of compound-specific and/or bulk non-structural carbohydrates (NSCs) in phloem and roots and (iii) growth of stem and fine roots. Results showed a significant effect of phloem NSC concentrations on tracheid growth, and both variables significantly impacted R-stem. Also, concentrations of root NSCs, especially starch, had a significant effect on fine root growth, although no effect of root NSC concentrations or root growth was detected on R-soil. Time series analysis between delta C-13 of A(shoot) and delta C-13 of R-stem or delta C-13 of R-soil revealed strengthened C allocation to stem or roots under high C demands. Furthermore, we detected a significant correlation between delta C-13 of R-stem and delta C-13 of phloem sucrose and glucose, but not for starch or water-soluble carbohydrates. Our results indicate the need to include C allocation dynamics into tree growth models. We recommend using compound-specific concentration and delta C-13 analysis to reveal C allocation processes that may not be detected by the conventional approach that utilizes bulk organic matter.

It is essential to comprehensively understand past climate and tree response to climate change because trees are directly exposed to rapid, intensifying, and widespread climate change. Both tree rings and leaf n-alkanes are long-term biomarkers which can help to better understand past climate and/or tree response to climate change. For example, interpreting carbon and oxygen stable isotopes in tree rings contribute to understanding past climate and tree response to climate change. However, greater insight could be achieved if hydrogen stable isotopes can also be clearly interpreted. To clearly interpret hydrogen isotopes in tree rings it is necessary to discover which aspects of climatic variability and tree physiology are most clearly expressed by hydrogen isotopes in tree rings. Additionally, the climatic signal of hydrogen stable isotopes in leaf n-alkanes can be deposited to soil and sediments from plants, and their climatic soil record can date back to thousands to millions of years ago. However, there are still aspects of plant physiology that have not been accounted for in leaf n-alkane hydrogen isotope interpretation, which limits the reliability of their interpretation. While data from tree rings and leaf n-alkanes are rarely combined, both tree rings and leaf n-alkanes contain a hydrogen isotope signal that originates from a hydrogen isotope signal in source water that is changed by physiological processes and interacting climatic factors during their biosynthesis. This project aims to improve our understanding of the physiological and climatic signals contained in the hydrogen isotope signal in both tree rings and leaf n-alkanes. It helps increase the useability of the hydrogen isotope signal in tree rings and helps improve the reliability of interpreting climatic signals from leaf n-alkanes. It uses a unique dataset from a field survey with samples collected multiple times during a growing season, with high temporal resolution, at one to two boreal forests in southern Finland (e.g., Leppä et al. 2022; Tang et al., 2022). This dataset is rich with information from multiple sources, such as multiple element isotope concentrations in various plant tissues and water isotope pools, as well as leaf gas exchange data, meteorological data, and eddy covariance data. The hydrogen isotope signal is traced from the climatic signal in source water, to the physiological and climatic signal in leaf water, sugars and starches and leaf n-alkanes, then from the same leaf water, sugars, and starches to bark and stem phloem sugars and starches, to high-resolution intra-annual tree ring α-cellulose. This presentation gives the project outline and some main findings.Leppä et al. (2022) doi:10.1111/nph.18227Tang et al. (2022) doi: 10.1093/treephys/tpac079

Recent methodological achievements in determining the non-exchangeable hydrogen isotopic composition (δ2Hne) of non-structural carbohydrates such as sugars allow to disentangle of so far hidden hydrogen isotope (2H) fractionation processes influencing δ2Hne of plant carbohydrates. We conducted two climate chamber experiments to have a closer look at the basic biochemical drivers of the photosynthetic 2H fractionation between water and sugar and the post-photosynthetic 2H fractionation between sugars and cellulose in leaves: First, we studied the impact of the different biochemical reactions in 10 species with C3, 7 species with C4, and 8 species with CAM carbon fixation pathways, and their response to changes in temperature and vapor pressure deficit (VPD). Second, we investigated the impact of a temperature increase from 10 to 40°C in 5°C steps under a constant VPD on leaf level photosynthesis and metabolic functioning of 7 plant species. The first experiment revealed distinct differences in the photosynthetic 2H fractionation between C3, C4, and CAM plants. In addition, the observed intensity and direction of the shifts in δ2Hne in response to changes in temperature and VPD in C3 plants was species specific, absent in C4 plants, and again species-specific in CAM plants. However, post-photosynthetic 2H fractionation was very similar among the three types of carbon fixation. We demonstrate that, in contrary to widespread believes, the 2H enrichment during post-photosynthetic 2H fractionation is driven by the carbohydrate metabolism, and not by an isotopic exchange with surrounding water. The results of the second experiment identified a plants’ metabolic activity, and its response to changes in temperature, as a major driver of the post-photosynthetic 2H fractionation of leaf sugars in C3 species. Our results clearly demonstrate that δ2Hne of plant carbohydrates are driven by plants metabolism and its response to the environment, which are species-specific. This will help to improve our current ability to interpret δ2Hne chronologies in tree rings and other plant archives, and to use 2H fractionation in carbohydrates as a novel proxy to study a plants’ metabolic properties.

Classical tree-ring parameters like tree-ring width, maximum latewood density and cell wall thickness record summer air temperature at high latitudes well and allow for the reconstruction of summer temperature over centuries and millennia. However, information about other climatic factors (e.g. moisture and sunshine duration) is limited in these proxies, especially for temperature-limited environments in subarctic forests growing on permafrost soils. The application of stable hydrogen and oxygen isotopes can provide complementary information about moisture changes and solar irradiation.Solar irradiation and its seasonal distribution play an important role for trees in terms of photosynthesis and carbohydrate production, which can influence deuterium variations in organic matter in addition to hydrological processes. We found that hydrogen and oxygen isotopes in larch tree-ring cellulose from Siberia show a strong link with summer sunshine duration during the growth season. Negative correlations with sunshine duration during autumn of the previous year and winter of the current year can be related to the lack of light during polar nights at subarctic sites (> 60º N) and lack of needles in larch trees to produce photosynthates in a cold environment. Indirect effects might also arise as a high amount of winter sunshine means persistent high-pressure systems with low precipitation, therefore negatively affecting snow accumulation, which is an important water source after snow melt.Uptake of winter precipitation is possible in the warming spring and summer months after snowmelt and thawing of the active soil layer, resulting in significant correlations between tree-ring oxygen values and winter-spring air temperatures. Oxygen isotopes in organic matter are influenced by variations in the isotopic composition of source water, which is closely related to that of precipitation and soil water (though modified by evaporation at the soil surface).Furthermore, we observed that summer vapor pressure deficit is positively and significantly recorded in stable oxygen isotopes from northeastern Siberia, while continuously represented through spring-summer months in western Canada. Hydrogen tree-ring isotopes from the Canadian subarctic recorded a negative significant correlation with summer relative humidity, opposite to northeastern Siberia.The application of dual hydrogen and oxygen stable isotopes in tree rings can expand our knowledge beyond traditional summer air temperature reconstructions and will help to improve climate reconstructions over the past millennia.Acknowledgements: This work was supported by the project RSF 21-17-00006.

Soil organic matter (SOM) originates from various sources such as foliar litter, roots and microbial (e.g. fungal) components. The relative sources contribution represents one of the key unknowns in SOM dynamics. Our study aimed to explore whether stable isotope ratios of non-exchangeable hydrogen (Hn) bound to organic matter can be used to differentiate SOM sources, since natural 2Hn abundance can strongly differ between root and foliar tissues. We also investigated if long-term irrigation with 2H-depleted water in a pine forest can be used to track Hn incorporation into organic matter inputs and eventually in the soil pools.In a 17-year-long irrigation experiment in a dry pine forest, we assessed variations in natural abundance of 2Hn, 13C, and 15N in SOM sources (foliar litter, fine roots, fungal mycelia), decomposing litter, soil (organic layers and uppermost 5 cm-mineral soil) and particle-size fractions. We then applied a Bayesian mixing model (including δ2Hn,δ13C, and δ15N) to estimate the relative sources contribution to SOM.Natural 2Hn abundance was significantly higher in roots vs. foliar litter (up to +39‰), and in fungal mycelia vs. roots (up to +41‰). Results from Bayesian mixing model suggest that foliar litter contributed to approximately 68 ± 10% of SOM in organic layers and in coarse particulate organic matter (POM). Foliar litter and roots contributed similarly to upper 2 cm of mineral soil (46 ± 11%), while 2-5 cm of mineral soil were largely derived from roots (61 ± 13%). Fungal mycelia contributed to 18 ± 8% of mineral-associated organic matter (MOM), while only to 1-2% of coarse and fine POM. Bayesian mixing models provided only a general indication of the sources contribution to SOM, also considering that isotopic signatures shifted during decomposition. Measurements of isotope signatures in microbial necromass might allow a more accurate assessment of the different SOM sources contribution.The δ2Hn depletion of soil water under irrigation was paralleled by a comparable decrease in δ2Hn of roots (~12‰). In comparison, the natural 2Hn abundance in fresh needles and foliar litter decreased less strongly (~ 7‰ and 4‰, respectively), likely due to photosynthetic adjustments that may have counterbalanced the irrigation water 2H-depletion. Similar to soil water 2H-depletion, δ2Hn values in coarse POM were 11‰ lower in irrigated vs. dry plots, suggesting that nearly all organic Hn turned over or exchanged with soil water in less than two decades. In contrast, δ2Hn values in fine POM and MOM decreased only by 3‰ under irrigation, which indicate that these fractions comprise slower cycling Hn pools.Our study showed that the natural 2Hn abundance represents a promising tool to differentiate among SOM sources. While 13C and 15N did not clearly separate between roots and foliar litter, Hn isotopic signatures allowed a good discrimination between SOM sources. In addition, long-term irrigation can provide a potential in situ 2H-labelling of SOM, which may help to examine organic Hn turnover rates across SOM pools.

The analysis of a Europe-wide network of tree-ring stable isotopes has shown that the climatic signal of δ2H in tree-ring cellulose (C6H10O5), is far weaker compared to those recorded in carbon (δ13C) and oxygen (δ18O)isotopes. Furthermore, the δ2H and δ18O relationships were shown to be site dependent and significantly deviated from the Global Meteoric Water Line. These results suggest that non-climatic effects are modifying the hydrological signature of δ2H. Recent experiments have underlined the potential of δ2H in tree-ring cellulose as a physiological indicator of shifts in autotrophic versus heterotrophic processes. However, the impact of these processes has not yet been quantified under natural conditions.Defoliating insect outbreaks can disrupt photosynthetic production and carbon allocation, stimulating the remobilization of stored carbohydrates. Such disturbance events, therefore, provide unique opportunities to evaluate the impact of changes in the use of fresh versus stored non-structural carbohydrates, i.e., of non-climatic signals stored in δ2H. By exploring a 700-year tree-ring record from Switzerland, we assess the impact of 79 larch budmoth (LBM, Zeiraphera griseana) outbreaks on the growth of its Larix decidua host trees.LBM outbreaks significantly altered the tree-ring isotopic signature, creating a 2H-enrichment and a depletion in 18O 13C. Changes in tree physiology during outbreak years are shown by the decoupling of δ2H and δ18O (O–H relationship), in contrast to the positive correlation in non-outbreak years. The O–H relationship in outbreak years was not significantly affected by temperature, indicating that non-climatic physiological processes dominate over climate in determining δ2H variations. We conclude that the combination of these isotopic parameters may serve as a metric for assessing changes in physiological mechanisms over time and that hydrogen isotopes can be considered as a proxy for non-climatic disturbance signals in dendrochronological research.

Background To assess the extent of belowground carbon transfer to ectomycorrhizal fungi in natural forests, we used δ13C and loge C/N measurements to calculate spatial dynamics of carbon movement into ectomycorrhizal sporocarps. Methods Fourteen broad-leaved trees were labeled with 13C-depleted CO2 from 2001–2005 in Switzerland and 13C traced into ectomycorrhizal sporocarps collected at different distances. We then used stepwise regressions on patterns of δ13C and loge C/N in ectomycorrhizal sporocarps as a function of distance (zone), solar radiation, fungal genus, and association type. Results CO2-labeled trees contributed 76 ± 5%, 36 ± 6%, and 19 ± 7% of sporocarp carbon at 0–6 m, 6–12 m, and 12–18 m from labeled trees, respectively. Literature estimates of hyphal development in different taxa did not correlate with carbon acquisition patterns. After drought in 2003, sporocarp loge C/N was low in 2004 and 13C-depleted carbon from elevated CO2 trees contributed less than in other years to sporocarps. In contrast, sporocarp loge C/N peaked in 2005 and contributions from elevated CO2 trees to the 6–12 m zone increased. Therefore, carbohydrate transport belowground decreased in 2004, reflecting plant allocation priorities, and increased in 2005. Sporocarp loge C/N varied less among years under elevated CO2 than elsewhere. Conclusions These patterns indicated that 1) belowground transport was influenced by climate and plant allocation, 2) root transport rather than ectomycorrhizal transport drove carbon spatial dynamics of ectomycorrhizal fungi, and 3) elevated CO2 decreased the sensitivity of belowground allocation to climatic fluctuations, suggesting improved drought resistance in a high-CO2 world.

Intrinsic water-use efficiency (iWUE), a key index for carbon and water balance, has been widely estimated from tree-ring delta C-13 at annual resolution, but rarely at high-resolution intraseasonal scale. We estimated high-resolution iWUE from laser-ablation delta C-13 analysis of tree-rings (iWUE(iso)) and compared it with iWUE derived from gas exchange (iWUE(gas)) and eddy covariance (iWUE(EC)) data for two Pinus sylvestris forests from 2002 to 2019. By carefully timing iWUE(iso) via modeled tree-ring growth, iWUE(iso) aligned well with iWUE(gas) and iWUE(EC) at intraseasonal scale. However, year-to-year patterns of iWUE(gas), iWUE(iso), and iWUE(EC) were different, possibly due to distinct environmental drivers on iWUE across leaf, tree, and ecosystem scales. We quantified the modification of iWUE(iso) by postphotosynthetic delta C-13 enrichment from leaf sucrose to tree rings and by nonexplicit inclusion of mesophyll and photorespiration terms in photosynthetic discrimination model, which resulted in overestimation of iWUE(iso) by up to 11% and 14%, respectively. We thus extended the application of tree-ring delta C-13 for iWUE estimates to high-resolution intraseasonal scale. The comparison of iWUE(gas), iWUE(iso), and iWUE(EC) provides important insights into physiological acclimation of trees across leaf, tree, and ecosystem scales under climate change and improves the upscaling of ecological models.

Intrinsic water-use efficiency (iWUE) is a key index for evaluating carbon and water balance of terrestrial ecosystems. A common approach to estimate iWUE is via measuring tree-ring stable carbon isotope composition (δ13C), which has been widely applied at annual resolution, but rarely at high-resolution intra-seasonal scale. In this study, we examined the reliability and accuracy of tree-ring δ13C in estimating intra-seasonal iWUE (iWUEiso), with the aid of laser ablation IRMS analysis of tree-rings, by comparing iWUEiso with iWUE derived from leaf gas exchange (iWUEgas) and eddy covariance (iWUEEC) data for two Pinus sylvestris L. dominated boreal forests from 2002 to 2019. By carefully timing iWUEiso via modelled yearly tree-ring growth, intra-seasonal variability of iWUEiso aligned well with that of iWUEgas and iWUEEC. However, absolute values of iWUEiso were apparently higher than that of iWUEgas and iWUEEC, which could be ascribed to post-photosynthetic 13C-enrichment from leaf assimilates to tree-rings and to nonexplicit inclusion of mesophyll and photorespiration terms in iWUEiso estimation. These two factors overestimated iWUEiso by up to 11% and 14%, respectively. Our study demonstrates that tree-ring δ13C data can be used to trace intra-seasonal variability of iWUE, and thus provides a valuable tool for detecting short-term dynamics in carbon and water trade for areas and periods with no instrumental data. We encourage more comparisons between iWUEgas, iWUEiso and iWUEEC, which can deepen our understanding of how trees physiologically adapt to climate change across leaf, tree and ecosystem levels.

The intensity and frequency of droughts events are projected to increase in future with expected adverse effects for forests. Thus, information on the dynamics of tree water uptake from different soil layers during and after drought is crucial. We applied an in situ water isotopologue monitoring system to determine the oxygen isotope composition in soil and xylem water of European beech with a 2-h resolution together with measurements of soil water content, transpiration and tree water deficit. Using a Bayesian isotope mixing model, we inferred the relative and absolute contribution of water from four different soil layers to tree water use. Beech took up more than 50% of its water from the uppermost 5 cm soil layer at the beginning of the 2018 drought, but then reduced absolute water uptake from the drying topsoil by 84%. The trees were not able to quantitatively compensate for restricted topsoil water availability by additional uptake from deeper soil layers, which is related to the fine root depth distribution. Absolute water uptake from the topsoil was restored to pre-drought levels within 3 wk after rewetting. These uptake patterns help to explain both the drought sensitivity of beech and its high recovery potential after drought release.

Rapid changes in the hydrological and temperature regimes over the past decades at the northern latitudes enhance significantly permafrost degradation accelerating carbon release, increase the frequency of drought events and extensive wildfires. However, the mechanisms and dynamics driving drought events and their influence on Siberian forests are currently the subject of numerous research activities. Newly developed and annually resolved stable carbon and oxygen isotope chronologies of larch tree-ring cellulose (δ13Ccell and δ18Ocell) for the period 516–2009 CE allowed the reconstruction of July precipitation and Arctic Oscillation (AO) in May, respectively. Unprecedented drought events occurred towards twentieth–twenty-first centuries as indicated by the July precipitation reconstruction. Positive AO phases in May were most pronounced during the second part of the first millennium, but also increased in frequency in the modern period of the twentieth–twenty-first centuries. Negative AO phases are associated with cold anomalies and show a remarkable decrease in the nineteenth century caused by a series of major volcanic eruptions. Our findings help explaining the increased frequency of Siberian forest fires over the past decades in Central Siberia consistent with a reduction of summer precipitation, triggered by a positive phase of the Arctic Oscillation in May.

Recent climatic changes significantly affected forest ecosystems in northern Eurasia. Trees growing in Siberia are very sensitive to climate change due to strong temperature limitation of their growth. Our study covers high-latitude (northeastern Yakutia, eastern Taimyr, central Evenkia) and high-altitude (Russian Altai) zones in Eurasia, where tree-ring parameters (tree-ring width, cell-wall thickness, and maximum latewood density) mainly record summer air temperature variations. To reveal the impact of moisture changes (e.g., amount of precipitation, vapor pressure deficit, relative humidity and potential evapotranspiration) on tree growth in Siberian forest ecosystems, we evaluated δ13C in tree-ring cellulose over the past century. We found that at all the study sites mainly June-July precipitation and June-July evapotranspiration affect larch radial growth, while the strongest influence of vapor pressure deficit on the δ13C was observed in northeastern Yakutia. Further increase of vapor pressure deficit and rise of air temperature in the coming decades in Siberian regions will probably lead to drought and related forest mortality even under additional source of water due to permafrost thaw.

Recent studies have challenged the interpretation of plant water isotopes obtained through cryogenic vacuum distillation (CVD) based on observations of a large 2H fractionation. These studies have hypothesized the existence of an H-atom exchange between water and organic tissue during CVD extraction with the magnitude of H exchange related to relative water content of the sample; however, clear evidence is lacking. Here, we systematically tested the uncertainties in the isotopic composition of CVD-extracted water by conducting a series of incubation and rehydration experiments using isotopically depleted water, water at natural isotope abundance, woody materials with exchangeable H, and organic materials without exchangeable H (cellulose triacetate and caffeine). We show that the offsets between hydrogen and oxygen isotope ratios and expected reference values (Δ2H and Δ18O) have inversely proportional relationships with the absolute amount of water being extracted, i.e. the lower the water amount, the higher the Δ2H and Δ18O. However, neither Δ2H nor Δ18O values, were related to sample relative water content. The Δ2H pattern was more pronounced for materials with exchangeable H atoms than with non-exchangeable H atoms. This is caused by the combined effect of H exchange during the incubation of materials in water and isotopic enrichments during evaporation and sublimation that depend on absolute water amount. The H exchange during CVD extraction itself was negligible. Despite these technical issues, we observed that the water amount-dependent patterns were much less pronounced for samples at natural isotope abundance and particularly low when sufficiently high amounts of water were extracted (>600 µL). Our study provides new insights into the mechanisms causing isotope fractionation during CVD extraction of water. The methodological uncertainties can be controlled if large samples of natural isotope abundance are used in ecohydrological studies.

The combined study of C and O isotopes in plant organic matter has emerged as a powerful tool for understanding plant functional responses to environmental change. The approach relies on established relationships between leaf gas exchange and isotopic fractionation to derive a series of model scenarios that can be used to infer changes in photosynthetic assimilation and stomatal conductance driven by changes in environmental parameters (CO2, water availability, air humid-ity, temperature, nutrients). We review the mechanistic basis for a conceptual model, in light of recently published research, and discuss where isotopic observations don’t match our current understanding of plant physiological response to environment. We demonstrate that 1) the mod-el was applied successfully in many, but not all studies, 2), while originally conceived for leaf isotopes, the model has been applied extensively to tree ring isotopes in the context of tree physiology and dendrochronology. Where isotopic observations deviate from physiologically plau-sible conclusions, this mismatch between gas-exchange and isotope response provides valuable insights on underlying physiological processes. Overall, we found that isotope responses can be grouped into situations of increasing resource limitation versus higher resource availability. The dual isotope model helps to interpret plant responses to a multitude of environmental factors.

Background. The spatial extent and timing of carbon fluxes from mature trees to ectomycorrhizal fungi associated with different hosts is challenging to assess in natural forests but could provide insights into carbon dynamics of fungi differing in exploration capabilities. Methods. We analyzed carbon movement into ectomycorrhizal sporocarps at the Swiss Forest Free-Air CO2 Enrichment (FACE) site in 2010 and 2011 during continuous labeling of five mature Picea abies (L.) H. Karst. with 13C-depleted CO2. Sporocarps were collected 0-6 m, 6-12 m, 12-18 m, and > 18 m from 13C-labeled trees. We then used stepwise regressions on patterns of 13C:12C ratios (δ13C) in ectomycorrhizal sporocarps as a function of distance (zone), solar radiation, fungal genus, and association type. Results. 18%, 10%, 40%, and 32% of ectomycorrhizal sporocarps were associated with conifers, broad-leaved trees, both, or of unknown association, respectively. Conifer-associated sporocarps derived 58 ± 7%, 41 ± 10%, and 20 ± 7% of their carbon from labeled trees in the 0-6 m, 6-12 m and 12-18 m zones, respectively, whereas other sporocarps in the 0-6 m zone only derived 34 ± 4% of their carbon from labeled trees. Sporocarp δ13C correlated positively with solar radiation for the 16-19 days prior to sporocarp harvest. Conclusions. These patterns indicated that (1) carbon spread further through conifer-associated mycorrhizal networks than through other fungal networks, and (2) carbon accumulation, storage, and transfer dynamics for sporocarp formation can take several weeks. Mature conifers supplied carbon to mycorrhizal fungi up to ~15 m from host trees.

Stable isotope ratio analysis of tree rings has been widely and successfully applied in recent decades for climatic and environmental reconstructions. These studies were mostly conducted at an annual resolution, considering one measurement per tree ring, often focusing on latewood. However, much more information could be retrieved with high-resolution intra-annual isotope studies, based on the fact that the wood cells and the corresponding organic matter are continuously laid down during the growing season. Such studies are still relatively rare, but have a unique potential for reconstructing seasonal climate variations or short-term changes in physiological plant properties, like water-use efficiency. The reason for this research gap is mostly technical, as on the one hand sub-annual, manual splitting of rings is very tedious, while on the other hand automated laser ablation for high-resolution analyses is not yet well established and available. Here, we give an update on the current status of laser ablation research for analysis of the carbon isotope ratio (δ13C) of wood, describe an easy-to-use laser ablation system, its operation and discuss practical issues related to tree core preparation, including cellulose extraction. The results show that routine analysis with up to 100 laser shot-derived δ13C-values daily and good precision and accuracy (ca. 0.1‰) comparable to conventional combustion in an elemental analyzer are possible. Measurements on resin-extracted wood is recommended as most efficient, but laser ablation is also possible on cellulose extracted wood pieces. Considering the straightforward sample preparation, the technique is therefore ripe for wide-spread application. With this work, we hope to stimulate future progress in the promising field of high-resolution environmental reconstruction using laser ablation.

Europe’s recent summer droughts have had devastating ecological and economic consequences, but the severity and cause of these extremes remain unclear. Here we present 27,080 annually resolved and absolutely dated measurements of tree-ring stable carbon and oxygen (δ13C and δ18O) isotopes from 21 living and 126 relict oaks (Quercus spp.) used to reconstruct central European summer hydroclimate from 75 bce to 2018 ce. We find that the combined inverse δ13C and δ18O values correlate with the June–August Palmer Drought Severity Index from 1901–2018 at 0.73 (P

Intrinsic water-use efficiency (iWUE), a key index for carbon and water balance, has been widely estimated from tree-ring δ

Significant air temperature and precipitation changes have occurred since the 2000s in vulnerable Siberian subarctic regions and urged updates of available chronologies towards the third millennium. It is important to better understand recent climatic changes compared to the past decades, centuries and even millennia. In this study, we present the first annually resolved triple tree-ring isotope dataset (δ13C, δ18O and δ2H) for the eastern part of the Taimyr Peninsula (TAY) and northeastern Yakutia (YAK) from 1900 to 2021. We found that the novel and largely unexplored δ2H of larch tree-ring cellulose was linked significantly with δ18O for the YAK site, which was affected by averaged April–June air temperatures and evaporation. Simulated by the Land Surface Processes and Exchanges (LPX-Bern 1.0) model, the water fraction per year for soil depths at 0–20 and 20–30 cm was significantly linked with the new eco-hydrological tree-ring δ2H data. Our results suggest increasing evapotranspiration and response of trees’ water relation to rising thaw water uptake from lower (20–30 cm) soil depth. A positive effect of July air temperature on tree-ring δ18O and a negative impact of July precipitation were found, indicating dry conditions. The δ13C in larch tree-ring cellulose for both sites showed negative correlations with July precipitation and relative humidity, confirming dry environmental conditions towards the third millennium.

The role of carbon (C) and nutrient uptake, allocation, storage and especially their interactions in survival and recovery of trees under increased frequencies and intensities of drought events is not well understood. A full factorial experiment with four soil water content regimes ranging from extreme drought to well-watered conditions and two fertilization levels was carried out. We aimed to investigate whether nutrient addition mitigates drought effects on downy oak (Quercus pubescens Willd.) and whether storage pools of non-structural carbohydrates (NSC) are modified to enhance survival after 2.5 years of drought and recovery after drought relief. Physiological traits, such as photosynthesis, predawn leaf water potential as well as tissue biomass together with pools and dynamics of NSC and nutrients at the whole-tree level were investigated. Our results showed that fertilization played a minor role in saplings’ physiological processes to cope with drought and drought relief, but reduced sapling mortality during extreme drought. Irrespective of nutrient supply, Q. pubescens showed increased soluble sugar concentration in all tissues with increasing drought intensity, mostly because of starch degradation. After 28 days of drought relief, tissue sugar concentrations decreased, reaching comparable values to those of well-watered plants. Only during the recovery process from extreme drought, root NSC concentration strongly declined, leading to an almost complete NSC depletion after 28 days of rewetting, simultaneously with new leaves flushing. These findings suggest that extreme drought can lead to root C exhaustion. After drought relief, the repair and regrowth of organs can even exacerbate the root C depletion. We concluded that under future climate conditions with repeated drought events, the insufficient and lagged C replenishment in roots might eventually lead to C starvation and further mortality.

Rising air temperature, changes in the hydrological cycle and atmospheric circulation patterns are leading to increasing extreme events affecting human and forests worldwide. Altai relict forests are under the risk of degradation under the recent warming. Investigations of climatic impacts on the southern Siberian forest, where temperature is not the main limiting growth factor are still rare and urgently needed. Therefore, we aim to reveal and evaluate the impact of recent extreme climatic events (1919–2019) on relict larch trees (Larix sibirica Ldb.) from two contrasting sites in the Russian Altai (Ersin—HO and Chadan—CH). Application of the state-of-the-art methods of stable isotope and tree-ring analyses is very promising in this region due to high sensitivity of trees to temperature and precipitation changes. We found site-specific differences (ca. 4‰) recorded in newly developed centennial stable carbon (δ13C) and oxygen (δ18O) isotope chronologies, showing their climate sensitivity and reflecting the contrasting conditions at the dry (HO) and wet (CH) sites. The most extreme drought anomalies (σ ≥ + 3σ) over the past 100 years (1919–2019) were revealed for the HO-site in 1935 and 2018. In contrast, a wet extreme anomaly (σ = − 2.7σ) was detected for the CH site only in 1994. Moreover, trees from the CH-site are receiving a greater amount of precipitation during the summer months, especially for the years with extremes σ ≥ − 2σ (1939, 1948, 1958, 1994, 2000, and 2019). Divergent δ13C and intrinsic water-use efficiency trends after the 1980s indicate increasing drought stress at the HO- compared to the CH-site, which is confirmed by changes in the running correlation between the isotopes and comparison with declining tree-ring width data. Drought or flooding extremes are recorded heterogeneously at the two study sites in southern Altai, indicating dependence from local habitats, type of soils and freezing active soil depths. Recent climate change affected both forest and humans as public and agricultural sectors are suffering from recent droughts or flooding events. To provide measures and apply mitigation plans for the unique relict forest and public sector, our reconstruction of past anomaly events in this region is important and helpful to predict future climate changes.

Drought alters carbon (C) allocation within trees, thereby impairing tree growth. Recovery of root and leaf functioning and prioritized C supply to sink tissues after drought may compensate for drought -induced reduction of assimilation and growth. It remains unclear if C allocation to sink tissues during and following drought is controlled by altered sink metabolic activities or by the availability of new assimilates. Understanding such mechanisms is required to predict forests' resilience to a changing climate. We investigated the impact of drought and drought release on C allocation in a 100-y-old Scots pine forest. We applied (CO2)-C-13 pulse labeling to naturally dry control and long-term irrigated trees and tracked the fate of the label in aboveand belowground C pools and fluxes. Allocation of new assimilates belowground was ca. 53% lower under nonirrigated conditions. A short rainfall event, which led to a temporary increase in the soil water content (SWC) in the topsoil, strongly increased the amounts of C transported belowground in the nonirrigated plots to values comparable to those in the irrigated plots. This switch in allocation patterns was congruent with a tipping point at around 15% SWC in the response of the respiratory activity of soil microbes. These results indicate that the metabolic sink activity in the rhizosphere and its modulation by soil moisture can drive C allocation within adult trees and ecosystems. Even a subtle increase in soil moisture can lead to a rapid recovery of belowground functions that in turn affects the direction of C transport in trees.

Insect defoliation impacts forest productivity worldwide, highlighting the relevance of plant–insect interactions. The larch budmoth (Zeiraphera griseana Hübner) is one of the most extensively studied defoliators, where numerous tree ring-based analyses on its host (Larix decidua Mill.) have aided in identifying outbreak dynamics over the past millennia. Yet, outbreaks have been widely absent after the early 1980s, and little is known about the in situ tree physiological responses and the allocation of carbon resources during and after defoliation. In summer 2018, we tracked an ongoing larch budmoth outbreak in a well-studied larch forest in the Swiss Alps. We performed biweekly monitoring on an affected and unaffected site using a unique combination of xylogenesis observations, measurements of non-structural carbohydrates, isotopic analysis of needle assimilates and ground-based and remote-sensed leaf trait observations. The budmoth induced a defoliation that lasted 40 days and could be detected by satellite observations. Soluble sugars significantly decreased in needles and stem phloem of the defoliated trees, while starch levels remained stable in the stem and root xylem compared to the control. Carbon and oxygen isotope ratios in needle assimilates indicated that neither photosynthetic assimilation rates nor stomatal conductance was different between sites before, during and after the outbreak. Defoliated trees ceased cell wall thickening 17 days earlier than unaffected trees, showing the earliest halt of ring formation recorded from 2007 untill 2013 and causing significant thinner cell walls, particularly in the latewood. No significant differences were found for cell enlargement rates and ring width. Our study revealed that an outbreak causes a downregulation of cell wall thickening first, while no starch is mobilized or leaf physiology is adjusted to compensate for the reduced carbon source due to defoliation. Our observations suggest that affected larch trees prioritize leaf recovery and carbon storage over wood biomass development.

Xylella fastidiosa (Xf) Wells, Raju et al., 1986 is a bacterium that causes plant diseases in the Americas. In Europe, it was first detected on the Salento Peninsula (Italy), where it was found to be associated with the olive quick decline syndrome. Here, we present the results of the first tree-ring study of infected and uninfected olive trees (Olea europaea L.) of two different cultivars, one resistant and one susceptible, to establish the effects induced by the spread of the pathogen inside the tree. Changes in wood anatomical characteristics, such as an increase in the number of vessels and in ring width, were observed in the infected plants of both the cultivars Cellina di Nardò (susceptible to Xf infection) and Leccino (resistant to Xf infection). Thus, whether infection affects the mortality of the tree or not, the tree shows a reaction to it. The presence of occlusions was detected in the wood of both 4-year-old branches and the tree stem core. As expected, the percentage of occluded vessels in the Xf-susceptible cultivar Cellina di Nardò was significantly higher than in the Xf-resistant cultivar Leccino. The δ 18O of the 4-year-old branches was significantly higher in infected trees of both cultivars than in noninfected trees, while no variations in δ 13C were observed. This suggests a reduction in leaf transpiration rates during infection and seems to be related to the occlusions observed in rings of the 4-year-old branches. Such occlusions can determine effects at leaf level that could influence stomatal activity. On the other hand, the significant increase in the number of vessels in infected trees could be related to the tree’s attempt to enhance water conductivity in response to the pathogen-induced vessel occlusions.

In many regions, drought is suspected to be a cause of Scots pine decline and mortality, but the underlying physiological mechanisms remain unclear. Because of their relationship to ecohydrological processes, δ18O values in tree rings are potentially useful for deciphering long-term physiological responses and tree adaptation to increasing drought. We therefore analyzed both needle- and stem-level isotope fractionations in mature trees exposed to varying water supply. In a first experiment, we investigated seasonal δ18O variations in soil and needle water of Scots pine in a dry inner Alpine valley in Switzerland, comparing drought-stressed trees with trees that were irrigated for more than 10 years. In a second experiment, we analyzed twentieth-century δ18O variations in tree rings of the same forest, including a group of trees that had recently died. We observed less 18O enrichment in needle water of drought-stressed compared with irrigated trees. We applied different isotope fractionation models to explain these results, including the Péclet and the two-pool correction, which considers the ratio of unenriched xylem water in the needles to total needle water. Based on anatomical measurements, we found this ratio to be unchanged in drought-stressed needles, although they were shorter. The observed lower 18O enrichment in needles of stressed trees was therefore likely caused by increased effective path length for water movement within the leaf lamina. In the tree-ring study, we observed lower δ18O values in tree rings of dead trees compared with survivors during several decades prior to their death. These lower values in declining trees are consistent with the lower needle water 18O enrichment observed for drought-stressed compared with irrigated trees, suggesting that this needle-level signal is reflected in the tree rings, although changes in rooting depth could also play a role. Our study demonstrates that long-term effects of drought are reflected in the tree-ring δ18O values, which helps to provide a better understanding of past tree physiological changes of Scots pine.

To identify source water for trees growing on permafrost in Siberia, we applied mechanistic models that quantify physical and biochemical fractionation processes, leading to oxygen isotope variation (δ18O) in plant organic matter. These models allowed us to investigate the influence of a variety of climatic factors on tree-ring cellulose from two dominant species: Larix cajanderi Mayr. from northeastern Yakutia (69° 22′ N, 148° 25′ E, ~ 250 m a.s.l.) and Pinus sylvestris L. from Central Yakutia (62°14′ N, 129°37′ E, ~ 220 m a.s.l.). The climate of the region is highly continental with short growing seasons, low amount of precipitation and these forest ecosystems are growing on permafrost, which in turn impact the water cycle and climate variation in the δ18O of source water. We compared outputs of the Land surface Processes and eXchanges (LPX-Bern v. 1.3), and Roden-Lin-Ehleringer (RLE) models for the common period from 1945 to 2004. Based on our findings, trees from northeastern and central Yakutia may have access to additional thawed permafrost water during dry summer periods. Owing to differences in the soil structure, active thaw soil depth and root systems of trees at two Siberian sites, Larix cajanderi Mayr. trees can access water not more than from 50 cm depth, in contrast to Pinus sylvestris L. in Central Yakutia which can acquire water from up to 80 cm soil depth. The results enhance our understanding of the growth and survival of the trees in this extreme environment.

Resprouting woody species adapted to perturbations store large amounts of carbon reserves to sustain plant metabolism during and resprout following perturbations. However, it is not known how carbon sources and sinks re-adjust in response to perturbations. Here, we studied when and where different reserve pools were mobilized after an aboveground perturbation, and how were new assimilates used after resprouting. Leaf gas exchange, plant organ carbon isotopic composition (δ13C) and nonstructural carbohydrate concentrations [NSC] were measured over one year in Pinus canariensis saplings subjected to complete defoliation (D) or complete defoliation plus stem damage (DD). Growth stopped completely in D and DD trees by the second month after the treatment application and during subsequent crown development. Growth resumed in most trees (60%) by the end of the growing season. Relative to control (C) trees, stem xylem [starch] decreased in D and DD during resprouting of new buds. Stem and root [starch] were also lower during growth resumption in these trees. One year after aboveground damages, leaf and root δ13C were significantly lower in D and DD, whereas [starch] recovered to values of C trees, except in roots of DD trees. Mobilization of carbon reserves from woody organs allows for resprouting and contributes to crown regeneration, stem growth resumption and wound healing in DD trees. New 13C-depleted photoassimilates contribute to these processes, and to refilling carbohydrates reserves. High [starch], plasticity in growth during and recovery of [starch] after severe aboveground disturbance, highlights high resilience of P. canariensis to perturbation.

Wildfires are one of the most important environmental factors controlling forest ecosystem physiology and the carbon balance in the permafrost zone of North Siberia. We investigated tree-ring width (TRW) and stable isotope chronologies in tree-ring cellulose (δ13CCell, δ18OCell) of Larix Gmelinii (Rupr.) Rupr. from a wet (WS) and a dry (DS) site. These sites are characterized by different fire histories (fire in 1852 at the wet and 1896 at the dry sites, respectively). TRW and δ18OCell are identified to be the most sensitive parameters in the changing tree growth conditions after fire. The differences in the soil seasonal thermal regime of sites after fires are shown in the relationship between the studied parameters. The δ13CCell values in tree rings from the two sites are positively correlated independently of the fire impact. This fact indicates that δ13CCell chronologies might be more adequate for climatic reconstruction in the region due to the climate signal consistency. Relationships of δ18OCell values between the two sites are still significantly positive 60 years after the fire impact. Dendroclimatic analysis indicates significant changes in tree-ring growth and isotopic ratio responses to climate due to the increased demand of water for trees during the post-fire period (deeper seasonal subsidence of permafrost).

∙ To assess how belowground mycorrhizal networks may share resources, we used δ13C, δ15N, and C/N measurements to calculate spatial and temporal dynamics of carbohydrate and amino acid movement through ectomycorrhizal networks of mature trees.∙ Canopies of 14 deciduous trees were continuously labeled with 13C-depleted CO2 from 2001-2005 (Swiss Forest FACE) and the 13C label traced into ectomycorrhizal sporocarps.∙ Sporocarps derived 69±5%, 30±6%, and 16±7% of their carbon from labeled trees in the elevated (beneath labeled trees), 0-6 m, and 6-12 m distances, respectively. Sporocarp δ13C correlated positively with C/N under elevated CO2 and negatively elsewhere, reflecting that high-δ13C carbohydrates from surrounding trees contributed to sporocarps under elevated CO2 and low-δ13C carbohydrates from elevated CO2 trees contributed to sporocarps elsewhere. Sporocarp δ15N increased in Cortinarius with decreasing δ13C, suggesting that greater hyphal growth with elevated CO2 sequestered 15N-depleted N from sporocarp formation. Sporocarp loge C/N decreased during the 2004 growing season and the contribution of 13C-depleted carbon from elevated CO2 plants decreased at the 0-6 m and 6-12 m distances, suggesting decreased carbohydrate availability and network transport that year. In contrast, sporocarp loge C/N increased during the 2005 growing season and the contribution of 13C-depleted carbon from elevated CO2 plants increased at the 0-6 m distance, suggesting increased carbohydrate availability and network transport that year. Relative to other taxa, elevated CO2 reduced C/N by 15% and ambient CO2 increased C/N by 5% in taxa exclusively associated with deciduous trees, suggesting increased carbohydrate sharing by the deciduous-associated taxa.∙ These patterns indicated that 1) carbohydrates (high C/N), not amino acids (low C/N), were preferentially transferred between regions differing in source δ13C, 2) sporocarp C/N reflected yearly plant productivity, 3) network transport was influenced by climate, and 4) taxonomy influenced transport dynamics belowground.

Oxygen isotopes (δ18O) in tree rings carry a strong potential to retrospectively evaluate tree water uptake and physiological response to climate. Their interpretation can, however, be challenging due to the complexity of the isotopic fractionations along the soil-tree-atmosphere continuum. Indeed, several processes play a role in defining the final tree-ring isotopic signal: source water variations, evaporative processes at the soil surface and leaf level, and mixing of xylem water that might exchange with new assimilates associated with phloem transport and synthesis of wood constituents. Disentangling these influences along the growing season and how climate conditions modify them are remaining challenges to exploit the full potential of δ18O tree-ring records as a climate proxy.In this study, we aim at identifying the contribution of leaf water enrichment and source water on the tree-ring δ18O signature by assessing intra-annual variations of δ18O along the soil-leaf-tree ring pathway of larch (Larix decidua Mill.). We focus on two sites with contrasting water availability in the Lötschental valley (Swiss Alps) and three consecutive growing seasons (2011-2013). Our approach takes into consideration specific timing of the involved processes with a high spatio-temporal resolution: environmental conditions, diurnal sapflow-derived transpiration rates, δ18O analysis of xylem and leaf water, and intra-annual tree-ring δ18O measurements coupled with wood formation kinetics. Structural equation models (SEM) were applied to statistically assess the relations among δ18O values of the different pathway components. Furthermore, we calibrated mechanistic models of leaf-water and tree-ring cellulose δ18O to explore site-specific contributions of the fractionation processes (e.g., Péclet effect and the proportion of xylem-cellulose synthesis exchange [Pex]) and investigated their climatic drivers.Our results showed that intra-annual xylem water δ18O and transpiration rates differed between sites and years whereas needle water δ18O did not differ significantly between sites (but between years). However, tree-ring cellulose δ18O values were higher at the dry site resembling those differences observed in xylem water δ18O. SEMs reinforced these results since xylem water δ18O contributed more to cellulose δ18O in comparison to needle water δ18O, and this effect was more prominent at the dry site. Vapor pressure deficit (VPD) had strong control on the overall leaf water-related 18O-fractionations. However, mechanistic leaf-water δ18O models did not indicate a relevant role of the Péclet effect in our study. Most importantly, mechanistic models of cellulose δ18O revealed that Pex was variable along the growing season and its variability was significantly associated with variations in VPD.Our study suggests that the imprint of the source water signal on the δ18O signature in tree rings is highly dominant, particularly during episodes of high VPD, potentially overwriting signals coming from leaf fractionation processes.

Rapid temperature and vapor pressure deficit (VPD) increase along with precipitation decrease over the past decades lead to massive wildfires and permafrost degradation in boreal forests. Conifer trees growing in subarctic regions are highly sensitive to these climatic changes due to their location at the high latitudes, where air temperature is the limiting factor, but also water relations have a strong impact on tree growth.In this study, we aimed (i) to assess the usability of local vs. gridded climate data; (ii) to reveal how conifer trees capture temperature and moisture signals based on the local weather station data vs. gridded data from the two Siberian sites in northeastern Yakutia and eastern Taimyr, and one site from northwestern Canada in Mackenzie Delta; (iii) to perform trend analysis of climatic data and δ18O in tree-ring cellulose; and (iv) to carry out spatial correlation analysis of oxygen isotope patterns and determine the distribution of climatic signal over broad geographical scales in the Siberian and Canadian subarctic.Comparative analysis of the local and gridded climatic data (air temperature, precipitation and VPD) for the three study sites showed that mainly temperatures are highly correlated between each other. Subarctic trees grow in a temperature-limited environment; therefore, the large spatial coherence of temperature signals is not surprising. Conversely, insignificant correlations between local and gridded for precipitation and rather low correlations for VPD is attributed to the more heterogeneous nature of moisture variables at larger spatial scales. Therefore, analyzing moisture changes in the subarctic using local weather station data is advantageous compared to gridded data.Trend analysis of the climate data showed that drastic changes in climate variability occurred from the 1980s in the investigated subarctic regions and were even more pronounced from 2000 to 2021. Recent warming and development of drought conditions were stronger in the Canadian subarctic than the Siberian subarctic sites. Drastic precipitation changes, temperature and VPD increase mainly occurred during winter, spring and autumn in the studied subarctic regions. New updated stable isotope chronologies from remote subarctic regions allowed us to accurately reconstruct moisture changes using precipitation and VPD data from the local weather stations while reconstructing air temperature using gridded data.This research was funded by the Russian Science Foundation (RSF) grant number 21-17-00006.