Rolf Theodor Walter Siegwolf

• PhD
• Guest researcher at Swiss Federal Institute for Forest, Snow and Landscape Research, WSL

Covariation of temperature (T) and vapour pressure deficit (VPD) under natural conditions make it difficult to predict the individual impact of each effect on plant physiology and leaf gas-exchange. For separating the covarying effects, we conducted 1) a T-response experiment (5-40°C) at constant VPD (0.8 kPa), as well as a 2) a VPD-response experi...

Climate change not only leads to higher air temperatures but also increases the vapour pressure deficit (VPD) of the air. Understanding the direct effect of VPD on leaf gas exchange is crucial for precise modelling of stomatal functioning. We conducted combined leaf gas exchange and online isotope discrimination measurements on four common European...

Abstract Perennially frozen soil, also known as permafrost, is important for the functioning and productivity of most of the boreal forest, the world’s largest terrestrial biome. A better understanding of complex vegetation-permafrost interrelationships is needed to predict changes in local- to large-scale carbon, nutrient, and water cycle dynamics...

The strong covariation of temperature and vapour pressure deficit (VPD) in nature limits our understanding of the direct effects of temperature on leaf gas exchange. Stable isotopes in CO2 and H2O vapour provide mechanistic insight into physiological and biochemical processes during leaf gas exchange. We conducted combined leaf gas exchange and onl...

The vapor pressure deficit reflects the difference between how much moisture the atmosphere could and actually does hold, a factor that fundamentally affects evapotranspiration, ecosystem functioning, and vegetation carbon uptake. Its spatial variability and long-term trends under natural versus human-influenced climate are poorly known despite bei...

Background Weather conditions and fungal morphology may influence spatial and temporal dynamics of carbon transfer to ectomycorrhizal fungi from their tree hosts but field studies of these dynamics are challenging. Methods Broad-leaved trees in a Swiss forest were labeled with ¹³C-depleted CO2 from 2001–2005 and ¹³C traced into ectomycorrhizal spo...

The combined study of carbon (C) and oxygen (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 ch...

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...

Boreal regions are changing rapidly with anthropogenic global warming. In order to assess risks and impacts of this process, it is crucial to put these observed changes into a long-term perspective. Summer air temperature variability can be well reconstructed from conifer tree rings. While the application of stable isotopes can potentially provide...

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 relat...

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 photosynt...

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...

About this book: This Open Access volume highlights how tree ring stable isotopes have been used to address a range of environmental issues from paleoclimatology to forest management, and anthropogenic impacts on forest growth. It will further evaluate weaknesses and strengths of isotope applications in tree rings. In contrast to older tree ring s...

The environmental and physiological interpretation of stable isotope variation in organic matter is affected by many different and interacting factors. This is especially true when considering isotope variation in tree rings, which are influenced not only by leaf-level photosynthetic gas exchange processes but also by post-photosynthetic fractionat...

This chapter aims at summarizing strengths and caveats on the suitability of stable carbon and oxygen isotopes in tree rings as recorders for fingerprints of environmental influences. First, environmental constraints limiting tree growth and shaping tree species distribution worldwide are discussed. Second, examples are presented for environmental...

Anthropogenic activities such as industrialization, land use change and intensification of agriculture strongly contribute to changes in the concentrations of atmospheric trace gases. Carbon dioxide (CO 2 ), oxidized N compounds(NOx), sulfur dioxide (SO 2 ) and ozone(O 3 ) have particularly significant impacts on plant physiology. CO 2 , the substr...

Nutritive, but detrimental if at high levels, several nitrogen (N) forms involved in air and soil biogeochemical reactions constitute the N load trees assimilate. Although a large body of literature describes series of tree-ring N isotopes (δ ¹⁵ N) as archival systems for environmental changes, several questions relative to the isotopic integrity a...

Plain Language Summary In the middle of a hot and dry summer, we often think that a large rain event can “rescue” a forest from drought. However, it is not clear whether trees can or do consistently use the water from summer rains. A growing body of research indicates that over the course of the summer growing season, trees take up significant amou...

Temperature and precipitation changes are crucial for larch trees growing at high-elevation sites covered by permafrost in the Altai-Sayan mountain range (ASMR). To contextualize the amplitude of recent climate fluctuations, we have to look into the past by analyzing millennial paleoclimatic archives recording both temperature and precipitation. We...

Carbon (C) allocation plays a crucial role for survival and growth of the alpine treeline trees, which, however, is still poorly understood. Using in situ 13CO2 labeling, we investigated the leaf photosynthesis and the allocation of 13C labeled photoassimilates in various tissues (leaves, twigs and fine roots) in treeline trees and low-elevation tr...

Recent studies have challenged the interpretation of plant water isotopes obtained through cryogenic vacuum distillation (CVD) based on observations of large 2H-fractionations. These studies have hypothesized the existence of a H-atom exchange between water and organic tissue during CVD extraction with the magnitude of H-exchange related to relativ...

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. T...

The combined study of C and O isotopes in plant organic matter has emerged as a powerful tool for understanding plant functional response 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 draw inferences about chang...

The uptake of carbon dioxide (CO2) from the atmosphere through photosynthesis is accompanied by an inevitable loss of water vapor through the stomata of leaves. The rate of leaf-level CO2 assimilation per unit stomatal conductance, i.e. intrinsic water-use efficiency (WUEi), is thus a key characteristic of terrestrial ecosystem functioning that is...

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...

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 tre...

Picea abies and Fagus sylvatica are important tree species in Europe, but their physiological performance under climate change at temperate sites is not yet fully understood. We, investigated tree-ring width and stable isotope chronologies (δ13C/δ18O) at 10 sites in Central Europe. In these uneven-aged stands, we compared the year-to- year variabil...

Picea abies (L.) Karst. and Fagus sylvatica (L.) are important tree species in Europe, and the foreseen increase in temperature and vapour pressure deficit (VPD) could increase the vulnerability of these species. However, their physiological performance under climate change at temperate and productive sites is not yet fully understood, especially i...

A strong increase in the mean annual air temperature during the past 50 years by up to 0.54 °C was recorded in the Altai region (45°–52° N; 84°–99° E) compared to the global value of 0.07 °C over the period 1901–2008. The impact of the climatic changes on the hydrology are complex in these mountainous forest ecosystems and not fully understood. We...

Newly developed millennial δ13C larch tree-ring chronology from Siberia allows reconstruction of summer (July) vapor pressure deficit (VPD) changes in a temperature-limited environment. VPD increased recently, but does not yet exceed the maximum values reconstructed during the Medieval Warm Anomaly. The most humid conditions in the Siberian North w...

The carbon isotopic composition (δ¹³C) of foliage is often used as proxy for plant performance. However, the effect of N O 3 – vs. N H 4 + supply on δ¹³C of leaf metabolites and respired CO2 is largely unknown. We supplied tobacco plants with a gradient of N O 3 – to N H 4 + concentration ratios and determined gas exchange variables, concentrations...

The carbon and oxygen isotopic composition of water and assimilates in plants reveals valuable information on plant response to climatic conditions. Yet, the C and O uptake, incorporation, and allocation processes determining isotopic compositions are not fully understood. We carried out a dual-isotope labelling experiment at high humidity with 18O...

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 d...

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....

Recent decades have been characterized by increasing temperatures worldwide, resulting in an exponential climb in vapor pressure deficit (VPD). VPD has been identified as an increasingly important driver of plant functioning in terrestrial biomes and has been established as a major contributor in recent drought‐induced plant mortality independent o...

Wildfires are an important factor in controlling forest ecosystem dynamics across the circumpolar boreal zone. An improved understanding of their direct and indirect, short- to long-term impacts on vegetation cover and permafrost–vegetation coupling is particularly important to predict changes in carbon, nutrient and water cycles under projected cl...

Stratospheric volcanic eruptions have had significant impacts on the radiation budget, atmospheric and surface temperatures, precipitation and regional weather patterns, resulting in global climatic changes. The changes associated with such eruptions most commonly result in cooling during several years after events. This study aimed to reveal eco-p...

A multimedia approach is presented to evaluate the atmospheric impact on Alpine torests in Switzerland. The aim of this approach is the determination of anthropogenic air pollutants leading to wet and dry depositions in an area along the Sankt Gotthard transect crossing the Alps in the North-South direction and to evaluate the possible changes in t...

Stable carbon isotopes in tree rings are a promising tool in palaeoclimate research, provided attempts are made to disentangle climatic from local effects (e.g. soil properties, competition, light). The 13 C/ 12 C variations in cellulose of tree rings of beech (Fagus sylvatica) were determined at several sites in the Swiss Central Plateau covering...

The 18O‐signature of atmospheric water vapour (δ18OV) is known to be transferred via leaf water to assimilates. It remains, however, unclear how the 18O‐signal transfer differs among plant species and growth forms. We performed a 9 h greenhouse fog experiment (relative humidity ≥ 98%) with 18O‐depleted water vapour (‐106.7‰) on 140 plant species of...

Stomata control the gas exchange of terrestrial plant leaves, and are therefore essential to plant growth and survival. We investigated gas exchange responses to vapor pressure deficit (VPD) in two grey poplar (Populus × canescens) lines: wild type (WT), and abscisic acid-insensitive (abi1) with functionally impaired stomata. Transpiration rate in...

Climatic effects on Picea abies and Fagus sylvatica, two of the most important tree species in Europe, have been extensively investigated. However, their physiology at temperate sites is not yet fully understood. For each species, we sampled five sites along a climate gradient in Central Europe. Tree-ring width and stable isotope ratios (C and O) w...

mDatabases describing branch gas exchange of Picea abies L. at two montane forest sites, Lägeren, Switzerland (National Forschungsprojekt 14 of the Schwei-zerische Nationalfonds) and Oberwarmensteinach, Ger-many (Bayerische Forschungsgruppe Forsttoxikologie), were analyzed in conjunction with a physiologically based model. Parameter estimates for d...

Stratospheric volcanic eruptions have far-reaching impacts on global climate and society. Tree rings can provide valuable climatic information on these impacts across different spatial and temporal scales. To detect temperature and hydroclimatic changes after strong stratospheric Common Era (CE) volcanic eruptions for the last 1500 years (535 CE un...

Rain recharges soil water storages and either percolates downward into aquifers and streams or is returned to the atmosphere through evapotranspiration. Although it is commonly assumed that summer rainfall recharges plant-available water during the growing season, the seasonal origins of water used by plants have not been systematically explored. W...

Elevated CO2 along with rising temperature and water deficits can lead to changes in tree physiology and leaf biochemistry. These changes can increase heat- and drought-induced tree mortality. We aim to reveal the impacts of climatic drivers on individual compounds at the leaf level among European larch (Larix decidua) and mountain pine (Pinus mugo...

Measurements of methane (CH4) mole fractions and δ¹³C−CH4 that resolve the diel cycle in the agriculturally dominated Reuss Valley, Switzerland, were used to quantify the contributions of different CH4 sources to the atmospheric CH4 source mix. Both a nocturnal (NBL) and a diurnal convective boundary layer (CBL) approach were employed. A diel cours...

The tree-ring stable carbon and oxygen isotope chronologies from two forest sites located in the Forni Glacier forefield (Italy)—one along the glacier stream (GL) and the other toward the valley slope (SL)—were analyzed with the aim of disentangling the precipitation and glacier meltwater inputs in source water δ¹⁸O, as reflected by the tree-ring c...

The isotope and thus the information transfer of climatic signals from photosynthetic active leaves towards potential sinks such as tree-rings under different environmental and hydrological conditions is still not fully understood. 13CO 2-pulse-labeling experiments allow for assessing carbon allocation from sinks to sources, however, much less is k...

Studies of stable isotopes of water in the environment have been fundamental to advancing our understanding of how water moves through the soil-plant-atmosphere continuum; however, much of this research focuses on how water isotopes vary in time, rather than in space. We examined the spatial variation in the δ18O and δ2H of throughfall and bulk soi...

Rain recharges soil water storages and either percolates downward into aquifers and streams, or is returned to the atmosphere through evapotranspiration. Although it is commonly assumed that summer rainfall recharges plant-available water during the growing season, the seasonal origins of water used by plants have not been systematically explored....

Studies of stable isotopes of water in the environment have been fundamental to advancing our understanding of how water moves through the soil‐plant‐atmosphere continuum; however, much of this research focuses on how water isotopes vary in time, rather than in space. We examined the spatial variation in the δ18O and δ2H of throughfall and bulk soi...

In this commentary, we summarize and build upon discussions that emerged during the workshop “Isotope-based studies of water partitioning and plant–soil interactions in forested and agricultural environments” held in San Casciano in Val di Pesa, Italy, in September 2017. Quantifying and understanding how water cycles through the Earth's critical zo...

Stable isotopes ratios in tree rings have become an important proxy for paleoclimatology, particularly in temperate regions. Yet, temperate forests are often characterized by heterogeneous stand structures, and the effects of stand dynamics on carbon (δ¹³C) and oxygen isotope ratios (δ¹⁸O) in tree rings are not well explored. In this study we inves...

For more than two decades, research groups in hydrology, ecology, soil science, and biogeochemistry have performed cryogenic water extractions (CWEs) for the analysis of δ2H and δ18O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soi...

Stratospheric volcanic eruptions have far-reaching impacts on global climate and society. Tree rings can provide valuable climatic information on these impacts across different spatial and temporal scales. Here we explore the suitability of tree-ring width (TRW), maximum latewood density (MXD), cell wall thickness (CWT), and δ¹³C and δ¹⁸O in tree-r...

Increasing biodiversity has been linked to higher primary productivity in terrestrial ecosystems. However, the underlying ecophysiological mechanisms remain poorly understood. We investigated the effects of surrounding species richness (monoculture, two‐ and four‐species mixtures) on the ecophysiology of Lithocarpus glaber seedlings in experimental...

In this commentary, we build on discussions that emerged during the workshop "Isotope-based studies of water partitioning and plant-soil interactions in forested and agricultural environments" held in San Casciano Val di Pesa, Italy, in September 2017. Quantifying and understanding how water cycles through the Earth's critical zone is important to...

We investigated seasonal variations in δ¹³C values and concentrations of carbohydrates and organic acids in needles of declining and healthy mountain pine (Pinus mugo ssp. uncinata (DC.) Domin) trees from the Swiss National Park (SNP), using compound-specific isotopes analysis (CSIA). Our goal was to study the impact of climatic drivers on the indi...

The poster shows an overview of experiments, focusing on the importance of d18O of water vapour on the d18O of plant organic material.

For more than two decades, research groups in hydrology, ecology, soil science and biogeochemistry have performed cryogenic water extractions for the analysis of δ²H and δ¹⁸O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water...

Drought is a major environmental constraint to trees, causing severe stress and thus adversely affecting their functional integrity. European beech (Fagus sylvatica L.) is a key species in mesic forests that is commonly expected to suffer in a future climate with more intense and frequent droughts. Here, we assessed the seasonal response of leaf ph...

Our understanding of how temporal variations of atmospheric water vapour and its isotopic composition (δ ¹⁸ O V ) influence water and assimilates in plants remains limited, restricting our ability to use δ ¹⁸ O as a tracer of ecophysiological processes. We exposed oak ( Quercus robur ) saplings under wet and dry soil moisture conditions to ¹⁸ O‐dep...

Understanding climate change impacts on drought-prone forests is a critical issue. We investigated ring-width and stable isotopes (Δ¹³C and δ¹⁸O) in two Pinus sylvestris stands of the cold–dry Siberian forest–steppe growing under contrasting climatic trends over the last 75 years. Despite regional warming, there was increasing precipitation during...

Time series of tree-ring growth show significant increases since the early 1970s at the alpine tree line, with simultaneously increasing temperatures and atmospheric CO2 concentration. For a comprehensive understanding of this growth change, the physiological response patterns at both the leaf and stem level need to be separately analyzed and ident...

Rationale: Levoglucosan is formed from cellulose during biomass burning. It is therefore often used as a specific tracer to quantify the contribution of wood burning to the aerosol loading. The stable oxygen isotope composition (δ(18) O value) of biomass is determined by the water cycle and varies regionally, and hence the δ(18) O value of levoglu...

The ability of treeline conifers in the Central European Alps to cope with recent climate warming and increasing CO 2 concentration is still poorly understood. We determined basal area increment (BAI) and tree ring stable carbon isotope ratios (δ 13 C) of Pinus cembra trees from 1925 through 2013. Stable isotope ratios and BAI were compared with le...

A growing number of studies have described the direct absorption of water into leaves, a phenomenon known as foliar water uptake. The resultant increase in the amount of water in the leaf can be important for plant function. Exposing leaves to isotopically enriched or depleted water sources has become a common method for establishing whether or not...

Rationale: In this study, we tested stable hydrogen isotope ratios of wood lignin methoxyl groups (δ (2) Hmethoxyl values) as a palaeoclimate proxy in dendrochronology. This is a quite new method in the field of dendrochronology and the sample preparation is much simpler than the methods used before to measure δ(2) H values from wood. Methods: W...

Adjustment mechanisms of trees to changes in soil‐water availability over long periods are poorly understood, but crucial to improve estimates of forest development in a changing climate. We compared mature trees of Scots pine ( Pinus sylvestris ) and European larch ( Larix decidua ) growing along water‐permeable channels (irrigated) and under natu...

Measurements of the stable carbon isotope ratio (δ13C) on annual tree rings offer new opportunities to evaluate mechanisms of variations in photosynthesis and stomatal conductance under changing CO2 and climate conditions, especially in conjunction with process-based biogeochemical model simulations. The isotopic discrimination is indicative of the...

The presence of vegetation alters hydrological cycles of ecosystems. Complex plant–soil interactions govern the fate of precipitation input and water transitions through ecosystem compartments. Disentangling these interactions is a major challenge in the field of ecohydrology and a pivotal foundation for understanding the carbon cycle of semi-arid...

Almost no δ(18) O data are available for leaf carbohydrates, leaving a gap in the understanding of the δ(18) O relationship between leaf water and cellulose. We measured δ(18) O values of bulk leaf water (δ(18) OLW ) and individual leaf carbohydrates (e.g. fructose, glucose, sucrose) in grass and tree species, and δ(18) O of leaf cellulose in grass...

Carbon reserves are important for maintaining tree function during and after stress. Increasing tree mortality driven by drought globally has renewed the interest in how plants regulate allocation of recently fixed C to reserve formation. Three year-old seedlings of two species (Tilia platyphyllos, Pinus sylvestris) were exposed to two intensities...

Drought frequency is increasing in many parts of the world and may enhance tree decline and mortality. The underlying physiological mechanisms are poorly understood, however, particularly regarding chronic effects of long-term drought and the response to increasing temperature and vapor pressure deficit (VPD). We combined analyses of radial growth...