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The carbon isotope composition (δ13C) in tree rings were used to derive the intrinsic water-use efficiency (iWUE) of Araucaria araucana trees of northern Patagonia along a strong precipitation gradient. It is well known that climatic and ontogenetic factors affect growth performance of this species but little is known about their influence in the physiological responses, as iWUE. Thus, the main objective of this study was to assess the physiological reactions of young and adult trees from two open xeric and two moderately dense mesic A. araucana forests to the increases in atmospheric CO2 (C a) and air temperature during the 20th century, and to relate these responses with radial tree growth. The results indicated that the iWUE and the intercellular CO2 concentration (C i) increased 33% and 32% in average during the last century, respectively, but carbon isotope discrimination (∆13C) was more variable between sites and age classes. Trees from xeric sites presented greater iWUE and lower ∆13C and C i values than those from mesic sites. In general, iWUE was strongly related with C a and was significantly affected by mean summer maximum temperature. ∆13C from mesic sites seemed to be mainly affected by summer maximum temperature, while trees from xeric conditions did not show any influence. Tree age also presented a significant effect on iWUE. Adult trees showed higher iWUE values than young trees, indicating an incidence of the tree age and/or height, mainly in closed mesic forests. Moreover, some trees presented positive relationships between iWUE and radial tree growth, while others presented negative or no relationships, indicating that other factors may negatively influence tree growth. Broadly, the results demonstrate the incidence of climatic, environmental and ontogenetic variability in the tree responses; however, more studies are needed to better understand which forests will be more affected by actual and future climate changes. [ABSTRACT FROM AUTHOR]

Various studies report substantial increases in intrinsic water-use efficiency (Wi), estimated using carbon isotopes in tree rings, suggesting trees are gaining increasingly more carbon per unit water lost due to increases in atmospheric CO2. Usually, reconstructions do not, however, correct for the effect of intrinsic developmental changes in Wi as trees grow larger. Here we show, by comparing Wi across varying tree sizes at one CO2 level, that ignoring such developmental effects can severely affect inferences of trees' Wi. Wi doubled or even tripled over a trees' lifespan in three broadleaf species due to changes in tree height and light availability alone, and there are also weak trends for Pine trees. Developmental trends in broadleaf species are as large as the trends previously assigned to CO2 and climate. Credible future tree ring isotope studies require explicit accounting for species-specific developmental effects before CO2 and climate effects are inferred. [ABSTRACT FROM AUTHOR]

Although solar radiation at the surface plays a determinant role in carbon discrimination in tree rings, stable carbon isotope chronologies (δC) have often been interpreted as a temperature proxy due to the co-variability of temperature and surface solar radiation. Furthermore, even when surface solar radiation is assumed to be the main driver of C discrimination in tree rings, δC records have been calibrated against sunshine duration or cloud cover series for which longer observational records exists. In this study, we use different instrumental and satellite data over northeast Spain (southern Europe) to identify the main driver of tree-ring C discrimination in this region. Special attention is paid to periods in which the co-variability of those climate variables may have been weaker, such as years after large volcanic eruptions. The analysis identified surface solar radiation as the main driver of tree-ring δC changes in this region, although the influence of other climatic factors may not be negligible. Accordingly, we suggest that a reconstruction of SSR over the last 600 years is possible. The relation between multidecadal variations of an independent temperature reconstruction and surface solar radiation in this region shows no clear sign, and warmer (colder) periods may be accompanied by both higher and lower surface solar radiation. However, our reconstructed records of surface solar radiation reveals a sunnier Little Ice Age in agreement with other δC tree-ring series used to reconstruct sunshine duration in central and northern Europe. [ABSTRACT FROM AUTHOR]

In the present study, the high-resolution stable carbon (13C/12C) and oxygen (18O/16O) isotope ratio profiles in the wood of the mangroveRhizophora mucronataLam., a tropical tree species lacking distinct growth rings, were investigated. Variations of both isotope ratios revealed a remarkable annual cyclicity with lowest values occurring at the latewood/earlywood boundary (April–May) and highest values during the transition from earlywood to latewood (October–November). Based on the current knowledge of the physiology of this mangrove species, as well as on the current literature available on high-resolution profiles of stable isotope ratios in tree rings, possible driving forces responsible for this seasonal pattern are discussed. The annual cyclicity, together with a conspicuous isotope pattern appearing in the El-Niño year 1997, promises great potential for tropical dendrochronology. [ABSTRACT FROM AUTHOR]

Evidence is presented for a very specific, seasonally recurring tri-phase carbon isotope pattern in tree rings of broad-leaf deciduous tree species. It is derived from highly resolved intra-annual measurements of 13C/12C ratios of wood and cellulose from tree rings of Fagus sylvatica, Populus nigra, Quercus petraea and Morus alba. Investigations on δ13C from buds and leaves of Fagus sylvatica revealed a similar tri-phase δ13C pattern. At the very beginning of a growing season, the δ13C trend of tree rings and foliage shows a marked increase of up to 5‰. The maximum δ13C-value of each vegetation period always occurs in young heterotrophic leaves shortly after bud burst and persistently in the early wood of each tree ring, when growth depends on carbon reserves. Thereafter, δ13C profiles represent the autotrophic stage of the leaves, which show different patterns of variation, by and large characterized by a decline. The minimum δ13C-value always shows up in the late wood of each tree ring. At the very end of each tree ring δ13C-values start rising again. This increase in δ13C marks the gradual switch-over to storage-dependent growth and can also be observed in senescent leaves. Seasonal changes of more than 4‰ were measured, whereas contiguous δ13C values rarely differed from each other by more than 0.3‰. This tri-phase pattern cannot be explained by the common model of carbon isotope fractionation during photosynthesis. It appears to be primarily an indication of seasonal changes in down-stream processes of the carbohydrate metabolism. Environmental influences on the carbon isotope fractionation during photosynthesis are presumably of secondary importance and expressed by certain peculiarities showing up during the autotrophic phase, i.e. the mid-section of the seasonal δ13C pattern. [ABSTRACT FROM AUTHOR]

The stable isotopes of carbon were analysed in total wood and cellulose from the tree-rings of the tropical wood species Cariniana micrantha (Ducke). The aim was to examine the isotopic relationship between total wood and its cellulose over the last two and a half centuries. Although the correlation for the whole time period is very high (r = 0.96) it is remarkable that different sub-periods deviate strongly from this close relationship. Consequently, a good correlation from the subset of a longer isotopic record cannot necessarily prove its validity for the whole record. The study indicates that changes of the carbon isotopes of cellulose and of total wood show sometimes during short sub-periods different isotope patterns presumably caused by different environmental effects. Thorough calculations indicate that strong variations within the isotopic record especially changes of the isotopic level along a chronology lead to high correlations between δ 13 C wood and δ 13 C cel . Contrary thereto subsections with low isotopic variability lead to low correlations. The results imply that long term trends provide similar patterns. Therefore, if long term trends are of interest such as e.g. in climate reconstruction then total wood can be analysed in favour of cellulose, thus saving a tremendous amount of work. However, if short term aspects from a longer record are of interest, cellulose and total wood may sometimes provide different information. In addition it is hypothesized that during intervals of low isotopic variability the proportions of the various wood components may change relative to each other, leading for certain time intervals to different isotope patterns. [ABSTRACT FROM AUTHOR]