Summary I. INTRODUCTION – A HYPOTHESIS 374 II. EFFECTS OF CALCIUM ON PHYSIOLOGICAL PROCESSES 376 1. The chemical uniqueness of calcium 376 (a) Cytotoxicity 376 (b) Binding properties 376 (c) Stimulation/displacement potential 376 2. Calcium signaling and plant responses to environmental stress 377 (a) Control principles 377 (b) Carbohydrate metabolism 378 (c) Synthesis and function of membranes and cell walls 379 (d) Disease resistance and wound repair 380 (e) Cold tolerance 381 (f) Stomatal regulation 382 III. CALCIUM UPTAKE AND DISTRIBUTION AT THE WHOLE‐PLANT LEVEL 382 1. Uptake at the root‐soil interface 382 2. Transport and exchange in stems 384 3. Exchange of calcium by foliage 385 IV. ECOSYSTEM PROCESSES AND CALCIUM SUPPLY 387 1. Plant succession and soil acidification 387 2. Plant adaptations to nutrient deficiency 389 (a) Morphological adaptations 389 (b) Physiological adaptations 390 V. PLANT AND ECOSYSTEM RESPONSES TO HUMAN ALTERATIONS IN CALCIUM SUPPLY 391 1. Increased atmospheric inputs of acidity 391 (a) Reductions in soil cation pools 392 (b) Inhibition of calcium uptake and effects on root function 393 (c) Increased leaching of calcium from foliage 395 (d) Physiological indicators of altered forest function 397 (e) Wood chemistry, structure and function 402 2. Forest management 404 (a) Harvesting effects on nutrient supply 404 (b) Managing forest nutrient supply 405 VI. CONCLUSION 407 1. Whole‐tree perspectives 407 2. Ecosystem perspectives 408 VII. EVALUATION OF THE HYPOTHESIS 410 Acknowledgements 411 References 411 Summary Calcium occupies a unique position among plant nutrients both chemically and functionally. Its chemical properties allow it to exist in a wide range of binding states and to serve in both structural and messenger roles. Despite its importance in many plant processes, Ca mobility is low, making Ca uptake and distribution rate a limiting process for many key plant functions. Ca plays an essential role in regulating many physiological processes that influence both growth and responses to environmental stresses. Included among these are: water and solute movement, influenced through effects on membrane structure and stomatal function; cell division and cell wall synthesis; direct or signaling roles in systems involved in plant defense and repair of damage from biotic and abiotic stress; rates of respiratory metabolism and translocation; and structural chemistry and function of woody support tissues. Forest trees, because of their size and age capacity, have been examined for evidence of limitations imposed by the timing and level of Ca supply. Examination of Ca physiology and biogeochemical cycling for forested systems reveals many indications that Ca supply places important limitations on forest structure and function. These limitations are likely to be most significant with older trees, later successional stages, high levels of soil acidity and/or high canopy Ca leaching losses, or under conditions where plant competition is high or transpiration is limited by high humidity or lo...

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Larch heartwood is appreciated for its good mechanical properties, its colour and its texture, and it is often used outdoors because of its natural durability (decay resistance). In this study the colour of larch heartwood was studied in relation to extractives and decay resistance, with the aim to estimate durability of larch heartwood from its colour. On a total of 293 trees colour in the CIE L*a*b* space (L* lightness, a* red/green axis, b* yellow/blue axis), extractives content (acetone and hot-water extractives, amount of phenolics) and the brown-rot decay resistance were determined. For calculating the relative decay resistance (x), mass loss after inoculation for 16 weeks with two fungi [Coniophora puteana (Schum.ex.Fr.) Karst., Poria placenta (Fr.) Cke, European standard EN 113] of larch heartwood samples was compared to Scots pine (Pinus sylvestris L) sapwood reference samples (EN 350-1). Different species [Japanese larch (Larix kaempferi Lamb.), Hybrid larch (Larix deciduax L. kaempferi) and European larch (L. decidua Mill.)], provenances and age classes (38-year, >150-year) were included. Japanese larch heartwood turned out to be significantly more reddish (higher a*-values) compared to the European larch provenances. Reddishness of the hybrids was intermediate. The red hue (+a*) was strongly correlated with the amount of phenols (r=0.84) and decay resistance (r=0.63) and therefore suitable for prediction of both parameters. The results suggest that colour measurements of larch heartwood could be of benefit in tree breeding programs and for an optimised utilization of larch timber.

The latewood lignin content, maximum density and total ring width of ten consecutive annual increments were determined in treeline Norway spruce (Picea abies [L.] Karst.) using ultraviolet (UV) microscopy and radiodensitometry, respectively. A positive correlation between the total ring width and the mean temperature of mid-July to August was identified, as was one between the maximum density and the temperature of AugustSeptember. Lignin content in the secondary cell wall layer of the terminal latewood tracheids was positively correlated with the temperature for the period running from the beginning of September until the third week of October. It can, therefore, be concluded that lignification of the cell wall is susceptible to the influence of climatic variability, as is the case with ring width and maximum density.

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Summary• The aim of this study was to assess the hydraulic vulnerability of Norway spruce ( Picea abies ) trunkwood by extraction of selected features of acoustic emissions (AEs) detected during dehydration of standard size samples.• The hydraulic method was used as the reference method to assess the hydraulic vulnerability of trunkwood of different cambial ages. Vulnerability curves were constructed by plotting the percentage loss of conductivity vs an overpressure of compressed air.• Differences in hydraulic vulnerability were very pronounced between juvenile and mature wood samples; therefore, useful AE features, such as peak amplitude, duration and relative energy, could be filtered out. The AE rates of signals clustered by amplitude and duration ranges and the AE energies differed greatly between juvenile and mature wood at identical relative water losses.• Vulnerability curves could be constructed by relating the cumulated amount of relative AE energy to the relative loss of water and to xylem tension. AE testing in combination with feature extraction offers a readily automated and easy to use alternative to the hydraulic method.

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The feasibility of Fourier transform near infrared (FT-NIR) spectroscopy to rapidly determine extractive and phenolic content in heartwood of larch trees (Larix decidua MILL., L. leptolepis (LAMB.) CARR. and the hybrid L. x eurolepis) was investigated. FT-NIR spectra were collected from wood powder and solid wood using a fibre-optic probe. Partial Least Squares (PLS) regression analyses were carried out describing relationships between the data sets of wet laboratory chemical data and the FT-NIR spectra. Besides cross and test set validation the established models were subjected to a further evaluation step by means of additional wood samples with unknown extractive content. Extractive and phenol contents of these additional samples were predicted and outliers detected through Mahalanobis distance calculations. Models based on the whole spectral range and without data pre-processing performed well in cross-validation and test set validation, but failed in the evaluation test, which is based on spectral outlier detection. But selection of data pre-processing methods and manual as well as automatic restriction of wavenumber ranges considerably improved the model predictability. High coefficients of determination (R 2 ) and low root mean square errors of cross-validation (RMSECV) were obtained for hot water extractives (R 2 = 0.96, RMSECV = 0.86%, range = 4.9-20.4%), acetone extractives (R 2 = 0.86, RMSECV = 0.32%, range = 0.8-3.6%) and phenolic substances (R 2 = 0.98, RMSECV = 0.21%, range = 0.7-4.9%) from wood powder. The models derived from wood powder spectra were more precise than those obtained from solid wood strips. Overall, NIR spectroscopy has proven to be an easy to facilitate, reliable, accurate and fast method for non-destructive wood extractive determination.