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A long-term context is important for understanding past climatic variability. Although tree-ring widths (TRWs) are widely used as a proxy for reconstructing past climate, the use of annually-resolved values of δ13C and δ18O tree-ring stable isotopes (TRSIs) is increasing and may provide further valuable information. Here, we present a 487-year-long TRW chronology and 240-year-long TRSI chronology for Bosnian pine (Pinus heldreichii H. Christ) and compare them to each other. We demonstrate that both δ13C and δ18O values are better proxies for temperature, precipitation, and drought than TRW. The correlations between these climate parameters and TRSIs are strongest for the combined summer (JJA) period. The results of temporal and spatial field correlation indicate that TRSI chronologies are stable, reliable proxies for JJA precipitation reconstruction over the whole Balkan Peninsula and surrounding eastern Mediterranean region. However, the stability of the temperature signal of the both δ13C and δ18O chronologies declines after the 1950s. Our work supports the emerging evidence that TRSI data track climate variability more accurately than a conventional TRW approach and can be subsequently used for the reconstruction of past climate.

Tree-ring stable oxygen and carbon isotope ratios (δ18O and δ13C) are an important archive for climate reconstructions. However, it remains unclear whether the polyvinyl acetate emulsion, often used for the preservation and fixation of wood samples, influences δ18O and δ13C signals. Further uncertainties are associated with the possible effects of geographical origin and cambial age of historical samples. Here, we present annually-resolved and absolutely-dated δ18O and δ13C measurements of 21 living oaks (Quercus robur and Q. petraea) from the Czech Republic. We find that the δ18O and δ13C signals in the extracted alpha-cellulose are not affected by polyvinyl acetate treatment. Covering the entire 20th century and reaching until 2018 CE, our dataset reveals spatial and temporal coherency within and between the individual δ18O and δ13C chronologies of different oak species, sample locations, and tree ages. Highly significant (p

Hyperspectral reflectance is becoming more frequently used for measuring the functions and productivity of ecosystems. The purpose of this study was to re-evaluate the potential of the photochemical reflectance index (PRI) for evaluating physiological status of plants. This is needed because the reasons for variation in PRI and its relationships to physiological traits remain poorly understood. We examined the relationships between PRI and photosynthetic parameters in evergreen Norway spruce and deciduous European beech grown in controlled conditions during several consecutive periods of 10–12 days between which the irradiance and air temperature were changed stepwise. These regime changes induced significant changes in foliar biochemistry and physiology. The responses of PRI corresponded particularly to alterations in the actual quantum yield of photosystem II photochemistry (ΦPSII). Acclimation responses of both species led to loss of PRI sensitivity to light use efficiency (LUE). The procedure of measuring PRI at multiple irradiance-temperature conditions has been designed also for testing accuracy of ΔPRI in estimating LUE. A correction mechanism of subtracting daily measured PRI from early morning PRI has been performed to account for differences in photosynthetic pigments between irradiance-temperature regimes. Introducing ΔPRI, which provided a better estimate of non-photochemical quenching (NPQ) compared to PRI, also improved the accuracy of LUE estimation. Furthermore, ΔPRI was able to detect the effect of drought, which is poorly observable from PRI.

A dedicated field experiment was conducted to investigate the response of a green reflectance continuum removal-based optical index, called area under the curve normalized to maximal band depth between 511 nm and 557 nm (ANMB511-557), to light-induced transformations in xanthophyll cycle pigments of Norway spruce [Picea abies (L.) Karst] needles. The performance of ANMB511-557 was compared with the photochemical reflectance index (PRI) computed from the same leaf reflectance measurements. Needles of four crown whorls (fifth, eighth, 10th, and 15th counted from the top) were sampled from a 27-year-old spruce tree throughout a cloudy and a sunny day. Needle optical properties were measured together with the composition of the photosynthetic pigments to investigate their influence on both optical indices. Analyses of pigments showed that the needles of the examined whorls varied significantly in chlorophyll content and also in related pigment characteristics, such as the chlorophyll/carotenoid ratio. The investigation of the ANMB511-557 diurnal behaviour revealed that the index is able to follow the dynamic changes in the xanthophyll cycle independently of the actual content of foliar pigments. Nevertheless, ANMB511-557 lost the ability to predict the xanthophyll cycle behaviour during noon on the sunny day, when the needles were exposed to irradiance exceeding 1000 µmol m(-2) s(-1). Despite this, ANMB511-557 rendered a better performance for tracking xanthophyll cycle reactions than PRI. Although declining PRI values generally responded to excessive solar irradiance, they were not able to predict the actual de-epoxidation state in the needles examined.

Bud phenology and development of needle nitrogen content were monitored on Norway spruce (Picea abies [L.] Karst) and European beech (Fagus sylvatica [L.]) trees grown inside glass-domes for five years under ambient (385 µmol(CO2) mol−1) and elevated (700 µmol(CO2) mol−1) atmospheric CO2 concentrations ([CO2]). The spruce to beech ratio was 35:65 in both treatments. At the beginning of the experiment mean age of investigated trees was 5 years.Elevated [CO2] was responsible for premature growth of both spruce and beech buds in the E treatment (not significantly, by 3–7 days). Nevertheless the flushing of neither beech nor spruce was not significantly hastened in E treatment during the flushing within the 5 years. During the second half of flushing faster development of terminal beech buds comparing to spruce was found (Chi-square = 65, p 2] acts as growth stimulator but the nitrogen insufficiency eliminates a positive effect of [CO2]. As the global climate change express itself in many ways and relationship’s consequences among plants and/or animals are hard to forecast.

KOVAC, D., AC, A., SIGUT, L., KLEM, K., URBAN, O.: Optical indicators of plant physiological activity. Acta univ. agric. et silvic. Mendel. Brun., 2012, LX, No. 3, pp. 101–110 Retrieving information on the plant physiological status from spectral refl ectance is a challenging task in many ways. The easiest way to get the information is through normalized vegetation indices, that are based on a normalization of refl ectance in specifi c wavebands. Beside the most common spectral indices such as Photochemical Refl ectance Index PRI or Normalized Diff erence Vegetation Index NDVI, several new indices has been proposed during the past decade as potential physiological indicators. In this paper, the performance of several of them for determining the physiological status of the foliage is evaluated on an experimental Norway spruce needles (Picea abies (L.) Karst) plot. Four needle classess of 27 years old spruce have been sampled throughout cloudy and sunny day. Needle classes were represented by the needles of the branchlets of the 4 th , 7 th , 9 th and 12 th whorls. Study was conducted on one-year old needles and sampling ran over several times a day to separate infl uence of dynamic processess on parameters. Results show that the ratio of refl ectance in the green and red region (presented as ratio of refl ectance at 560 nm and 694 nm) outperforms the others examinated vegetation indices, and suggest that it would be best suited for the characterization of the leaf status. Being always the highest in the uppermost part of the crown and the lowest in shaded part of the crown, parameter is strictly stratifi cated throughout the crown. Furthermore, parameter values correspond with intensity of physiological processess ongoing in needles during midday. The values of the other indicators seem to be aff ected by leaf pigment content and morphology too much. Neither PRI nor NDVI were able to distinguish diff erences in needle properties suffi ciently. Picea abies, refl ectance, vegetation indices, photosynthesis, ecophysiology

Temperature responses of carbon assimilation processes were studied in four dominant species from mountain grassland ecosystem, i.e. Holcus mollis (L.), Hypericum maculatum (Cr.), Festuca rubra (L.), and Nardus stricta (L.), using the gas exchange technique. Leaf temperature (T L) of all species was adjusted within the range 13–30 °C using the Peltier thermoelectric cooler. The temperature responses of metabolic processes were subsequently modelled using the Arrhenius exponential function involving the temperature coefficient Q 10. The expected increase of global temperature led to a significant increase of dark respiration rate (R D; Q 10 = 2.0±0.5), maximum carboxylation rate (V Cmax; Q 10 = 2.2±0.6), and maximum electron transport rate (J max; Q 10 = 1.6±0.4) in dominant species of mountain grassland ecosystems. Contrariwise, the ratio between J max and V Cmax linearly decreased with T L [y = −0.884 T L + 5.24; r 2 = 0.78]. Hence temperature did not control the ratio between intercellular and ambient CO2 concentration, apparent quantum efficiency, and photon-saturated CO2 assimilation rate (P max). P max primarily correlated with maximum stomatal conductance irrespective of T L. Water use efficiency tended to decrease with T L [y = −0.21 T L + 8.1; r 2 = 0.87].

The differential pigment composition and photosynthetic activity of sun and shade leaves of deciduous (Acer pseudoplatanus, Fagus sylvatica, Tilia cordata) and coniferous (Abies alba) trees was comparatively determined by studying the photosynthetic rates via CO(2) measurements and also by imaging the Chl fluorescence decrease ratio (R(Fd)), which is an in vivo indicator of the net CO(2) assimilation rates. The thicker sun leaves and needles in all tree species were characterized by a lower specific leaf area, lower water content, higher total chlorophyll (Chl) a+b and total carotenoid (Cars) content per leaf area unit, as well as higher values for the ratio Chl a/b compared to the much thinner shade leaves and needles that possess a higher Chl a+b and Cars content on a dry matter basis and higher values for the weight ratio Chls/Cars. Sun leaves and needles exhibited higher rates of maximum net photosynthetic CO(2) assimilation (P(Nmax)) measured at saturating irradiance associated with higher maximum stomatal conductance for water vapor efflux. The differences in photosynthetic activity between sun and shade leaves and needles could also be sensed via imaging the Chl fluorescence decrease ratio R(Fd), since it linearly correlated to the P(Nmax) rates at saturating irradiance. Chl fluorescence imaging not only provided the possibility to screen the differences in P(N) rates between sun and shade leaves, but in addition permitted detection and quantification of the large gradients in photosynthetic rates across the leaf area existing in sun and shade leaves.

Detection of grassland canopy chlorophyll fluorescence (Chl-F) conducted with an imaging spectroradiometer provided evidence of potential remote sensing estimation of steady-state Chl-F (Chl-Fs). Daily near-nadir views of extremely high spatial resolution hyperspectral images were acquired from a distance of 4 m for temperate montane grassland in the Czech Republic. Simultaneously, measurements of Chl-F and total chlorophyll content (Chla + b) were made on a single leaf at ground level were collected. A specifically designed ‘shade removal’ experiment revealed the influence of dynamic physiological plant processes on hyperspectral reflectance of three wavelengths: 532, 686 and 740 nm. Based on this information, the vegetation indexes R686/R630, R740/R800 and PRI calculated as (R532–R570)/(R532+R570) were tested for statistical significance with directly measured Chl-F parameters (maximum fluorescence yield, Fv/Fm; steady-state chlorophyll fluorescence, Chl-Fs and actual quantum yield, ФII). The grassland species under investigation were: Festuca rubra agg. (L.), Hieracium sp., Plantago sp., Nardus stricta (L.) and Jacea pseudophrygia (C.A. Meyer). The coefficients of determination (R2) for best-fit relationships between PRI-ФII and PRI-Chl-Fs, measured in the daily course, show a high variability of 0.23–0.78 and 0.20–0.65, respectively. Similarly, R2 for the R686/R630-ФII and R686/R630-Chl-Fs relationships varied between 0.20–0.73 and 0.41–0.70, respectively. The highest average R2 values were found between PRI and Chla + b (0.63) and R686/R630 and Chla + b (0.72). The ratio R740/R800 did not yield a statistically significant relation with Chl-F parameters.