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In the cellulose of stems and leaves, δ

The growth of potted birch cuttings (one clone of Betula pendula) was studied under low O3 concentrations (0, 0.050, 0.075, 0.100 μl l-1) throughout an entire growing season. With increasing O3 dose, 20–50% of all leaves formed were prematurely shed, while 40–70% of the remaining foliage displayed advanced discoloration by the end of the season. Ozonation affected the S, P and N concentration of leaves and increased δ13C in leaves and stem, while the CO2 assimilation rate declined with increasing CO2 concentration in mesophyll intercellulars. While whole-plant production correlated negatively with the O3 dose, ozone increased the specific leaf weight (i.e. leaf weight/leaf area, SLW) but decreased the ratios of stem weight/stem length and root/shoot biomass. Neither the latter ratio nor SLW changed in experimentally defoliated control plants, whereas in ozonated plants starch accumulated along leaf veins and phloem tissue was deformed in the leaf petioles and the stem. Only in early summer was the relative growth rate higher in the ozonated than in the control plants. The ratio of whole-plant biomass production versus total foliage area formed was lowered under O3 stress. However, when relating biomass to the actual foliage area present due to leaf loss, this ratio did not differ between treatments. Similarly the ratio of actual foliage area versus basal stem area in cross-section did not differ. Overall, whole-plant production was strongly determined by O3-caused changes in crown structure and began to be limited at O3 doses (approximately 180 μl l-1 h) similar to those of rural sites in Central Europe.

[1] The oxygen isotope ratio of ice cores and sea-sediments is an extremely useful source of information on long-term climatic changes. A similar approach has been applied to the oxygen isotope ratio of tree rings to enable a pattern-based reconstruction of the isotope variations on the continents. We present an oxygen isotope map for northern Eurasia spanning from Norway to Siberia, that reflects the isotope distribution in the late 19th century, and compare it with an equivalent map for the present-day situation. The average isotope values of 130 trees show a large east-to-west gradient and are highly correlated with the isotope distribution of precipitation. Surprisingly, the 18O/16O ratio of the wood has been decreasing in the interior of the continent since the late 19th century, in contrast to the strong temperature increase recorded by meteorological data. From this isotope trend over time a change in the seasonality of precipitation can be inferred.

The measurement of δ 18 O in cellulose of tree rings is a potential means to reconstruct δ 18 O variations of precipitation and climate. We present δ 18 O data from cellulose of 3 beech trees ( Fagus silvatica ) growing on a relatively dry site in Switzerland where the roots do not have access to ground water, as well as data of 2 other groups of 4 beech trees each, one from a dry site and the other from a semi-dry site, respectively. The measurements cover the time period from 1934 to 1987 in 3-year-groups for the 1st site and 1965 to 1992 with a 1-year resolution for the other 2 sites. We find a high degree of common variance (61%) between the δ 18 O variations of the 3 trees from the 1st location suggesting a common external cause. The comparison with climate data indicates that spring temperature (April/May/June) is the main influence for the long-term isotope variations, with a temperature coefficient of 0.33‰ per °C, whereas the short-term variations are mainly influenced by the relative humidity, with a coefficient of – 0.13‰ per %. This latter value is about ⅓ of the expected model value which points to leaf water pools with different δ 18 O values influencing the isotopic composition of synthesised carbohydrates or to oxygen exchange with stem water. Tree ring δ 18 O is correlated with δ 18 O in precipitation, and the slope of the linear regression for different months most probably yield information about the growth rate function of the particular tree group. Our results confirm the potential of δ 18 O measurements in tree ring cellulose for climate reconstruction, in particular information about δ 18 O in precipitation can be gained. DOI: 10.1034/j.1600-0889.49.issue1.6.x

summary Ozone (O3) in ambient air was investigated as a possible cause of visible damage to leaves of white clover (Trifolium repens L.) in agricultural areas of Switzerland. Differences in the sensitivity of five commonly mown cultivars were studied, namely Ladino Sacramento, Ladino California, Alban, Sonja and Milkanova. Plants were grown in pots and exposed to O3 using three different experimental systems: (i) exposure to ambient air, (ii) exposure in open-top chambers to filtered air, unfiltered air, or unfiltered air to which O3 was added from 09.00 until 17.00 h during a four-day period, (iii) exposure under controlled environmental condition to filtered air with or without O3 added daily. Occurrence of injury symptoms on field-grown plants was recorded during the summers of 1987 and 1988. Ozone exposure produced visible injury expressed as small necrotic flecks on the tipper leaf surface. Irrespective of the experimental system used, the following order in O3 sensitivity was observed: L. Sacramento ≤ L. California ≪ Alban ≤ Sonja ≤ Milkanova. Injury symptoms were seen when plants were exposed to ambient O3 or to unfiltered air in open-top chambers, but not in charcoal-filtered air. In ambient air, symptoms in the most sensitive cultivars appeared after episodes with 1-h maximum concentrations of above 120-140μg m−3 occurring on several consecutive days. The symptoms of injury could be reproduced in controlled-environment fumigation experiments using concentrations comparable to those observed in ambient air. Plants of the different cultivars grown under controlled environmental conditions did not differ in superoxide dismutase or peroxidase activity, or in the content of fructose, sucrose or glucose. Differences in O3−sensitivity between cultivars were related to differences in stomatal density and to some degree to the length of the stomatal pore. Stomatal densities were related to leaf conductance, transpiration, and rate of water loss by excised leaves. Leaves of Milkanova (resistant) had higher 313values than L. California (sensitive). Compared with filtered air, exposure to unfiltered ambient air or O3–amended air in open-top chambers caused a change in δ13 value in leaves of L. California (sensitive), but not in leaves of Milkanova (resistant). It is concluded that ambient levels of O3 in Switzerland can be sufficient to produce visible leaf injury in sensitive white clover cultivars characterized by a high gas-phase conductance of the leaves, that the isotopic composition of leaf tissue could be used as an indicator of O3 sensitivity in different cultivars, and that ambient levels of O3 can change the isotopic composition of the leaf tissue in sensitive species.

We determined vertical oxygen isotope gradients of leaf organic matter for a grassland in Switzerland and a mountain beech forest (Fagus sylvatica) in Northern Italy. A distinctly positive (18)O/(16)O gradient with height above ground was found for the grassland (7.9/1000 m(-1), p < 0.001), whereas the gradient was negative for the forest (-0.077/1000 m(-1), p < 0.001). The results are consistent with microclimatic measurements, although large isotope variations between the species have to be taken into account for the grassland. A conceptual scheme is shown which relates the isotope enrichment to the canopy density, considering the effects of transpiration and canopy structure. We conclude that the analysis of the within canopy variation in delta(18)O of organic matter can be used to provide long-term estimates of leaf water isotope composition, thus improving existing isotope methods to determine the gas-exchange between vegetation and atmosphere.

Global climate change is expected to induce a dramatic increase in the frequency and intensity of drought events in the Mediterranean region. Their effects might be particularly severe in short rotation forestry systems, such as poplar plantations, with high water demands. The aim of this study was to examine the clone-specific reaction of plant-water relations and growth to a dry-down cycle in two parental clones of Populus nigra L.: Poli, which is adapted to the dry/hot climatic conditions of southern Italy, and 58–861, which prefers the cooler and moister conditions typical in northern Italy. Plants were grown in controlled conditions in an airconditioned greenhouse, under three different irrigation regimes for 44 days. Drought stress resulted in a general decrease in plant size and predawn water potential in both clones. Although the control trees grew somewhat taller and retained leaves longer than those in other treatments, the two clones responded differently to water stress. Under severe stress conditions, Poli showed proline accumulation in old leaves to preserve plants from drought damage, without reduced stomatal activity, as shown by low values of δ13C. In 58–861, the accumulation of ABA in roots during drought probably stimulated stomatal control, increasing drought avoidance in this drought-sensitive clone. Although in 58–861 the expression of aquaporin genes PIP1–2 and TIP1–3 was enhanced, in Poli gene expression was downregulated. We analysed only part of the aquaporins genes, but we assume that these clones exhibited contrasting water transport strategies during drought. Clone 58–861 seems to increase the permeability of the vascular tissue by overexpressing aquaporin genes, probably in order to facilitate water transport, and Poli appears to increase water conservation in the root cells by downregulating aquaporins.

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 com-plementary climatic information over different seasons.In this study, we developed new triple stable isotope chronologies in tree-ring cellulose (813Ctrc, 818Otrc, 82Htrc) from a study site in Canada. Additionally, we performed regional aggregated analysis of available stable isotope chronologies from 6 conifers' tree species across high-latitudinal (HL) and -altitudinal (HA) as well as Siberian (SIB) transects of the Northern Hemispheric boreal zone.Our results show that summer air temperature still plays an important role in determining tree-ring isotope variability at 11 out of 24 sites for 813Ctrc, 6 out of 18 sites for 818Otrc and 1 out of 6 sites for 82Htrc. Precipitation, relative humidity and vapor pressure deficit are significantly and consistently recorded in both 813Ctrc and 818Otrc along HL. Summer sunshine duration is captured by all isotopes, mainly for HL and HA transects, indicating an indirect link with an increase in air and leaf temperature. A mixed temperature-precipitation signal is preserved in 813Ctrc and 818Otrc along SIB transect. The 82Htrcdata obtained for HL-transect provide information not only about growing seasonal moisture and temperature, but also capture autumn, winter and spring sunshine duration signals. We conclude that a combination of triple stable isotopes in tree-ring studies can provide a comprehensive description of climate variabil-ity across the boreal forest zone and improve ecohydrological reconstructions.

Climate change exposes ecosystems to strong and rapid changes in their environmental boundary conditions mainly due to the altered temperature and precipitation patterns. It is still poorly understood how fast interlinked ecosystem processes respond to altered environmental conditions, if these responses occur gradually or suddenly when thresholds are exceeded, and if the patterns of the responses will reach a stable state. We conducted an irrigation experiment in the Pfynwald, Switzerland from 2003–2018. A naturally dry Scots pine (Pinus sylvestris L.) forest was irrigated with amounts that doubled natural precipitation, thus releasing the forest stand from water limitation. The aim of this study was to provide a quantitative understanding on how different traits and functions of individual trees and the whole ecosystem responded to increased water availability, and how the patterns and magnitudes of these responses developed over time. We found that the response magnitude, the temporal trajectory of responses, and the length of initial lag period prior to significant response largely varied across traits. We detected rapid and stronger responses from above-ground tree traits (e.g., tree-ring width, needle length, and crown transparency) compared to below-ground tree traits (e.g., fine root biomass). The altered above-ground traits during the initial years of irrigation increased the water demand and trees adjusted by increasing root biomass during the later years of irrigation, resulting in an increased survival rate of Scots pine trees in irrigated plots. The irrigation also stimulated ecosystem-level foliar decomposition rate, fungal fruit body biomass, and regeneration abundances of broadleaved tree species. However, irrigation did not promote the regeneration of Scots pine trees which are reported to be vulnerable to extreme droughts. Our results provide extensive evidence that tree- and ecosystem-level responses were pervasive across a number of traits on long-term temporal scales. However, after reaching a peak, the magnitude of these responses either decreased or reached a new stable state, providing important insights into how resource alterations could change the system functioning and its boundary conditions., Ecological Monographs, 92 (2), ISSN:0012-9615, ISSN:1557-7015, ISSN:1741-7015

For the first time we present a multi proxy data set for the Russian Altai consisting of Siberian larch tree ring width (TRW) latewood density (MXD) d13C and d18O in cellulose chronologies obtained for the period 1779 2007 and cell wall thickness (CWT) for 1900 2008. All of these parameters agree well between each other in the high frequency variability while the low frequency climate information shows systematic differences. The correlation analysis with temperature and precipitation data from the closest weather station and gridded data revealed that annual TRW MXD CWT and d13C data contain a strong summer temperature signal while d18O in cellulose represents a mixed summer and winter temperature and precipitation signal. The temperature and precipitation reconstructions from the Belukha ice core and Teletskoe lake sediments were used to investigate the correspondence of different independent proxies. Low frequency patterns in TRW and d13C chronologies are consistent with temperature reconstructions from nearby Belukha ice core and Teletskoe lake sediments showing a pronounced warming trend in the last century. Their combination could be used for the regional temperature reconstruction. The long term d18O trend agrees with the precipitation reconstruction from the Teletskoe lake sediment indicating more humid conditions during the 20th century. Therefore these two proxies could be combined for the precipitation reconstruction.

In warming climates, soil water content (SWC) may act as an important factor in determining belowground carbon dynamics in boreal forests. Here, we estimated the respiration and nonstructural carbohydrate (NSC) concentrations of tree roots in a mature Scots pine (Pinus sylvestris L.) stand in southern Finland during two growing seasons with contrasting weather conditions. Root respiration was estimated with four different methods: 1) incubating excised roots, 2) partitioning forest floor respirations with root exclusion, or 3) based on temperature response functions and 4) modelling with the whole-tree carbon model 'CASSIA'. In addition, we conducted a drought experiment in a greenhouse to determine the effect of reduced soil-water availability on respiration by incubating soil and roots of Scots pine saplings. We observed that the respiration of incubated roots of Scots pine saplings and soil decreased with drying after excluding the effect of temperature on respiration (RRES), soil being more sensitive to drought than roots. Similarly, RRES of incubated roots in the field was significantly decreased by lowered SWC, whereas respiration of the entire root system estimated with other methods was clearly higher in dryer and warmer than moister and cooler year. Nevertheless, incubated roots excavated from the topsoil are most affected by drying soil, which might not reflect the response of the entire root system. RRES of incubated roots was negatively associated with root fructose and glucose concentrations. At the same time, root fructose, glucose and sucrose concentrations were negatively associated with SWC due to their role in osmoregulation. Thereby it seems that RRES does not directly follow the changes in NSCs despite the apparent correlation. Our study highlights the responsive nature of root carbon dynamics in varying weather events that should be taken into account in estimating and modelling the impacts of warming climate.