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The biogenic silica extracted from samples of 28 alpine plant species belonging to 23 genera and nine families collected in the Swiss Alps (Valais) accounted for between 0. 01 and 5. 9 % of the dry biomass of leaves and wood. Silica content, and plant contribution to the soil biogenic silica pool, varied widely among taxa. Plant net productivity and biogenic silica production from this study and from the literature have been used to predict the input made by dierent subalpine and alpine plant communities to soil-borne phytolith assemblages, and their contribution to the silicon biocycle.

The uppermost limits of past treelines in the Alps are established using soil type and soil charcoal mass. In all the studied sites, a sharp decrease of soil charcoal mass is correlated with the upper altitudinal limit of podzols. On the basis of this evidence, the uppermost tree limit reached 2500i: 100m a.s.l. in the Valaisan Alps during the Holocene, i.e., it was 250 100m higher than today's potential treeline. Consequently, the timberline would have reached 2400 100m a.s.l.. From the strong decline of charcoals concentration in soils above 2500m a.s.l., we infer that conifer species were rare or very rare above this A altitude during the Holocene. Joint interpretation of charcoal, pollen, soil and macrofossil data suggest HOLOCENE that alpine meadows with at most scattered conifers were present throughout the Holocene in the today's RESEARCH middle and upper alpine belt. PAPER

This paper reports general patterns of relative growth rate and related traits in response to elevated atmospheric CO # in eight woody species ranging widely in life form, leaf habit, taxonomy and ecology. Young plants of these species, all of comparable ontogenetic phases, were grown simultaneously in large containers with favourable nutrient and water availability in transparent outdoor chambers at 350 and 700 µl l −" CO # for one growing season. We found the following consistent responses. (1) All species grew faster at elevated CO # , whereas the following leaf and allocation traits were consistently lower in CO # -enriched environments : specific leaf area (quotient of leaf area and leaf weight), leaf area ratio (quotient of total leaf area and plant weight), weight-based foliar N concentration and, to a smaller extent, leaf weight fraction (quotient of leaf weight and plant weight). (2) There was important interspecific variation in the magnitude of the response of relative growth rate to CO # . Specific leaf area at ambient CO # explained 88% of the variation in relative growth rate response to CO # among the eight species. At ambient CO # , relative growth rate itself, was significantly correlated with the relative growth rate response to CO # only if the leafless species Ulex gallii was excluded from analysis. (3) The four deciduous species had a significantly stronger relative growth rate response to CO # than the four evergreens. This corresponded with their generally higher specific leaf area. (4) Specific leaf area and leaf habit might be useful for scaling up exercises, as easy-to-measure substitutes for growth responses of (woody) vegetation to elevated CO # . However, the usefulness of such traits in this context needs to be tested in realistic, longer-term manipulative experiments in real ecosystems.

Summary0 Stands of the annual Brassica kaber were grown at a range of six densities in both ambient and elevated CO 1 environments\ and measurements of shoot growth were made from seedling emergence through to reproduction[ 1 Early in stand development "10 days following emergence#\ CO 1 enhancement "b# for above!ground biomass was highly density!dependent\ ranging from 0

X-ray microanalysis was employed to screen biogenic plant silica extracted from the aboveground tissues of 20 species (Gramineae, Cyperaceae, Ericaceae, and Coniferae) occurring in subalpine and alpine grasslands, heaths, and woodlands on siliceous bedrock in the Valaisan Swiss Alps. Among the taxa investigated, only woody species produced a high proportion of phytoliths containing aluminum in the form of aluminosilicates. This difference between the chemical composition of wood and that of herbaceous phytoliths has important implications for the sourcing of phytoliths. As applications for palaeoenvironmental studies can be expected to be far-reaching, the potential of this microanalytical technique is discussed.

Abstract:The strength and temporal rigidity of climate signals are important characteristics of proxy data used to reconstruct climate variability over pre-instrumental periods. Here, we assess the performance of different tree-ring proxies, including ring width, maximum latewood density, δ 13 C, and δ 18 O, during exceptional cold (1800-1850) and warm periods . The analysis was conducted at a spruce (Picea abies) timberline site in the Swiss Alps in proximity to long homogenized instrumental records to support calibration tests against early temperature and precipitation data. In this cold environment, tree-ring width, maximum latewood density, and δ 18O are mainly controlled by temperature variations. δ 13 C is influenced by various factors including temperature, precipitation, sunshine, and relative humidity. When comparing the response patterns during cold and warm periods, ring width and maximum latewood density revealed temporally stable temperature signals. In contrast, the association between the stable isotopes and climate changed considerably between the early 19th and late 20th centuries. The temperature signal in δ 18O was stronger during the recent warm period, whereas the opposite is true for δ 13 C. In δ 13 C, the temperature signal weakened from the early 19th to the late 20th centuries, but an (inverse) precipitation signal evolved indicating that soil moisture conditions additionally limited recent carbon isotope ratios. An attempt to combine the tree-ring proxies in a multiple regression model did not substantially improve the strength of the dominating temperature signal retained in the latewood density data as this proxy already explained a significant fraction of summer temperature variability. Our findings underscore the importance of split calibration/verification approaches including cold and warm periods, and challenge transfer models based on only late 20th century observational data.

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