Exploring Growth Variability and Crown Vitality of Sessile Oak (Quercus Petraea) in the Czech Republic

Unraveling climatic effects on growth of oak - Europe’s most ecologically and economically important forest species - has been the subject of many recent studies; however, more insight based on field data is necessary to better understand the relationship between climate and tree growth and to adapt forest management strategies to future climate change. In this report, we explore the influence of temperature, precipitation and drought variability on the productivity and vitality of oak stands in the Czech Highlands. We collected 180 cores from mature oaks (Quercus petraea) at four forest stands in the Czech Drahany Highlands. Standard dendromethods were used for sample preparation, ring width measurements, cross-dating, chronology development, and the assessment of growth-climate response patterns. Crown vitality was also evaluated, using the modified ICP Forests methodology. Late spring precipitation totals between May and June as well as the mean July temperature for the year of ring formation were found to be the most important factors for oak growth, whereas crown condition was significantly affected by spring and summer drought. This study is rep-resentative for similar bio-ecological habitats across Central Europe and can serve as a dendroclima-tological blueprint for earlier periods for which detailed meteorological information is missing .

Fruit production in three masting tree species does not rely on stored carbon reserves

Fruiting is typically considered to massively burden the seasonal carbon budget of trees. The cost of reproduction has therefore been suggested as a proximate factor explaining observed mast-fruiting patterns. Here, we used a large-scale, continuous 13C labeling of mature, deciduous trees in a temperate Swiss forest to investigate to what extent fruit formation in three species with masting reproduction behavior (Carpinus betulus, Fagus sylvatica, Quercus petraea) relies on the import of stored carbon reserves. Using a free-air CO2 enrichment system, we exposed trees to 13C-depleted CO2 during 8 consecutive years. By the end of this experiment, carbon reserve pools had significantly lower δ13C values compared to control trees. δ13C analysis of new biomass during the first season after termination of the CO2 enrichment allowed us to distinguish the sources of built-in carbon (old carbon reserves vs. current assimilates). Flowers and expanding leaves carried a significant 13C label from old carbon stores. In contrast, fruits and vegetative infructescence tissues were exclusively produced from current, unlabeled photoassimilates in all three species, including F. sylvatica, which had a strong masting season. Analyses of δ13C in purified starch from xylem of fruit-bearing shoots revealed a complete turn-over of starch during the season, likely due to its usage for bud break. This study is the first to directly demonstrate that fruiting is independent from old carbon reserves in masting trees, with significant implications for mechanistic models that explain mast seeding.

Multiple tree-ring proxies (earlywood width, latewood width and δ13C) from pedunculate oak (Quercus robur L.), Hungary

The aim of this study was to analyse the effects of climatic factors (i.e. monthly mean temperature and total precipitation) on radial growth (earlywood width, latewood width, and total ringwidth) and on latewood stable carbon isotope composition in a pedunculate oak (Quercus robur L) stand in northeastern Hungary. Earlywood widths showed the weakest common variance and lack of statistically significant relationship to monthly precipitation and temperature. Latewood width showed the strongest common chronological signal. Correlation analysis with the monthly climate series pointed out the strongest positive/negative correlation with June precipitation for latewood width/stable carbon isotope ratio. These parameters shared the strongest climatic response also for seasonal scale since the highest correlation coefficients, 0.49 and -0.62 for latewood width and stable carbon isotope ratio, respectively, were obtained for both with a 10-month precipitation total (from previous November to current August of the growing season). A combined parameter, derived as difference between latewood width and stable carbon isotope indices showed improved statistical relationship compared to the hydroclimatic calibration target both for local and regional spatial scales. Spatial correlation analysis indicated that the hydroclimatic signal encoded in these moisture sensitive tree-ring parameters from Bakta Forest is expected to be representative for the northeastern Carpathians and for the large part of the Great Hungarian Plain. In addition, the hydroclimatic signal of latewood width chronology was compared to three independent records. Results showed that neither the strength nor the rank of the similarity of the local hydroclimate signals were stable throughout the past two centuries. Future palaeo(hydro)climatological efforts targeting the Carpathian(-Balkan) region are recommended to track carefully the spatial domains for which a given, local, proxy-derived hydroclimate reconstruction might provide useful information.

Sulfate and Nitrate Assimilation in Leaves of Quercus ilex and Quercus pubescens Grown Near Natural CO2 Springs in Central Italy

The effect of long-term exposure to elevated pCO2 concentrations on sulfate and nitrate assimilation was studied under field conditions using leaves from Quercus ilex and Quercus pubescens trees growing with ambient or elevated CO2 concentrations in the vicinity of three natural CO2 springs, Bossoleto, Laiatico and Sulfatara, in Tuscany, Italy. The activity of the key enzymes of sulfate assimilation, adenosine 5′-phosphosulfate reductase (APR) and nitrate assimilation, nitrate reductase (NR), were measured together with the levels of acid soluble thiols, and soluble non-proteinogenic nitrogen compounds. Whereas NR activity remained unaffected in Q. ilex or increased Q. pubescence, APR activity decreased in the area of CO2 springs. The latter changes were often accompanied by increased GSH concentrations, apparently synthesized from H2S and SO2 present in the gas mixture emitted from the CO2 springs. Thus, the diminished APR activity in leaves of Q. ilex and Q. pubescence from spring areas can best be explained by the exposure to gaseous sulfur compounds. Although the concentrations of H2S and SO2 in the gas mixture emitted from the vents at the CO2 springs were low at the Bossoleto and Laiatico spring, these sulfur gases pose physiological effects, which may override consequences of elevated pCO2.

Migration and population expansion of Abies, Fagus, Picea, and Quercus since 15000 years in and across the Alps, based on pollen-percentage threshold values

Aims: The aim of this study is to explore the migration (colonization of new areas) and subsequent population expansion (within an area) since 15 ka cal BP of Abies, Fagus, Picea, and Quercus into and through the Alps solely on the basis of high-quality pollen data. Methods: Chronologies of 101 pollen sequences are improved or created. Data from the area delimited by 45.5–48.1°N and 6–14°E are summarized in three ways: (1) in a selection of pollen-percentage threshold maps (thresholds 0.5%, 1%, 2%, 4%, 8%, 16%, and 32% of land pollen); (2) in graphic summaries of 250-year time slices and geographic segments (lengthwise and transverse in relation to the main axis of the Alps) as pollen-percentage curves, pollen-percentage difference curves, and pollen-percentage threshold ages cal BP graphed against both the length and the transverse Alpine axes; and (3) in tables showing statistical relationships of either pollen-percentage threshold ages cal BP or pollen expansion durations (=time lapse between different pollen-percentage threshold ages cal BP) with latitude, longitude, and elevation; to establish these relationships we used both simple linear regression and multiple linear regression after stepwise-forward selection. Results: The statistical results indicate that (a) the use of pollen-percentage thresholds between 0.5% and 8% yield mostly similar directions of tree migration, so the method is fairly robust, (b) Abies migrated northward, Fagus southward, Picea westward, and Quercus northward; more detail does not emerge due to an extreme scarcity of high-quality data especially along the southern foothills of the Alps and in the eastern Alps. This scarcity allows the reconstruction of one immigration route only of Abies into the southern Alps. The speed of population expansion (following arrival) of Abies increased and of Picea decreased during the Holocene, of Fagus it decreased especially during the later Holocene, and of Quercus it increased especially at the start of the Holocene.

Life-long growth of Quercus ilex L. at natural CO2 springs acclimates sulphur, nitrogen and carbohydrate metabolism of the progeny to elevated pCO2

The aim of the present study was to analyse whether offspring of mature Quercus ilex trees grown under life-long elevated pCO2 show alterations in the physiological response to elevated pCO2 in comparison with those originating from mature trees grown at current ambient pCO2. To investigate changes in C- (for changes in photosynthesis, biomass and lignin see Polle, McKee & Blaschke Plant, Cell and Environment 24, 1075–1083, 2001), N-, and S-metabolism soluble sugar, soluble non-proteinogenic nitrogen compounds (TSNN), nitrate reductase (NR), thiols, adenosine 5′-phosphosulphate (APS) reductase, and anions were analysed. For this purpose Q. ilex seedlings were grown from acorns of mother tree stands at a natural spring site (elevated pCO2) and a control site (ambient pCO2) of the Laiatico spring, Central Italy. Short-term elevated pCO2 exposure of the offspring of control oaks lead to higher sugar contents in stem tissues, to a reduced TSNN content in leaves, and basipetal stem tissues, to diminished thiol contents in all tissues analysed, and to reduced APS reductase activity in both, leaves and roots. Most of the components of C-, N- and S-metabolism including APS reductase activity which were reduced due to short-term elevated pCO2 exposure were recovered by life-long growth under elevated pCO2 in the offspring of spring oaks. Still TSNN contents in phloem exudates increased, nitrate contents in lateral roots and glutathione in leaves and phloem exudates remained reduced in these plants. The present results demonstrated that metabolic adaptations of Q. ilex mother trees to elevated pCO2 can be passed to the next generation. Short- and long-term effects on source-to-sink relation and physiological and genetic acclimation to elevated pCO2 are discussed.

Inhibition of photosynthesis by high temperature in oak (Quercus pubescens L.) leaves grown under natural conditions closely correlates with a reversible heat-dependent reduction of the activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase

Inhibition of the net photosynthetic CO2 assimilation rate (Pn) by high temperature was examined in oak (Quercus pubescens L.) leaves grown under natural conditions. Combined measurements of gas exchange and chlorophyll (Chl) a fluorescence were employed to differentiate between inhibition originating from heat effects on components of the thylakoid membranes and that resulting from effects on photosynthetic carbon metabolism. Regardless of whether temperature was increased rapidly or gradually, Pn decreased with increasing leaf temperature and was more than 90% reduced at 45 °C as compared to 25 °C. Inhibition of Pn by heat stress did not result from reduced stomatal conductance (gs), as heat-induced reduction of gs was accompanied by an increase of the intercellular CO2 concentration (Ci). Chl a fluorescence measurements revealed that between 25 and 45 °C heat-dependent alterations of thylakoid-associated processes contributed only marginally, if at all, to the inhibition of Pn by heat stress, with photosystem II being remarkably well protected against thermal inactivation. The activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) decreased from about 90% at 25 °C to less than 30% at 45 °C. Heat stress did not affect Rubisco per se, since full activity could be restored by incubation with CO2 and Mg2+. Western-blot analysis of leaf extracts disclosed the presence of two Rubisco activase polypeptides, but heat stress did not alter the profile of the activase bands. Inhibition of Pn at high leaf temperature could be markedly reduced by artificially increasing Ci. A high Ci also stimulated photosynthetic electron transport and resulted in reduced non-photochemical fluorescence quenching. Recovery experiments showed that heat-dependent inhibition of Pn was largely, if not fully, reversible. The present results demonstrate that in Q. pubescens leaves the thylakoid membranes in general and photosynthetic electron transport in particular were well protected against heat-induced perturbations and that inhibition of Pn by high temperature closely correlated with a reversible heat-dependent reduction of the Rubisco activation state.

Unearthing the roots of degradation of Quercus pyrenaica coppices: A root-to-shoot imbalance caused by historical management?

Slow growth, branch dieback and scarce acorn yield are visible symptoms of decay in abandoned Quercus pyrenaica coppices. A hypothetical root-to-shoot (R:S) imbalance provoked by historical coppicing is investigated as the underlying driver of stand degradation. After stem genotyping, 12 stems belonging to two clones covering 81 and 16 m2 were harvested and excavated to measure above- and below-ground biomass and nonstructural carbohydrate (NSC) pools. To study root system functionality, root connections and root longevity were assessed by radiocarbon analysis. Seasonality of NSC was monitored on five additional clones. NSC pools, R:S biomass ratio and fine roots-to-foliage ratio were higher in the large clone, whose centennial root system, estimated to be 550 years old, maintained large amounts of sapwood (51.8%) for NSC storage. 248 root connections were observed within the large clone, whereas the small clone showed comparatively simpler root structure (26 connections). NSC concentrations were higher in spring (before bud burst) and autumn (before leaf fall), and lower in summer (after complete leaf expansion); they were always higher in roots than in stems or twigs. The persistence of massive and highly inter-connected root systems after coppicing may lead to increasing R:S biomass ratios and root NSC pools over time. We highlight the need of surveying belowground organs to understand aboveground dynamics of Q. pyrenaica, and suggest that enhanced belowground NSC storage and consumption reflect a trade-off between clonal vegetative resilience and aboveground performance.