Sucrose synthase determines carbon allocation in developing wood and alters carbon flow at the whole tree level in aspen

Despite the ecological and industrial importance of biomass accumulation in wood, the control of carbon (C) allocation to this tissue and to other tree tissues remain poorly understood. We studied sucrose synthase (SUS) to clarify its role in biomass formation and C metabolism at the whole tree level in hybrid aspen (Populus tremula x tremuloides). To this end, we analysed source leaves, phloem, developing wood, and roots ofSUSRNAitrees using a combination of metabolite profiling,(13)CO(2)pulse labelling experiments, and long-term field experiments. The glasshouse grownSUSRNAitrees exhibited a mild stem phenotype together with a reduction in wood total C. The(13)CO(2)pulse labelling experiments showed an alteration in the C flow in all the analysed tissues, indicating that SUS affects C metabolism at the whole tree level. This was confirmed when theSUSRNAitrees were grown in the field over a 5-yr period; their stem height, diameter and biomass were substantially reduced. These results establish that SUS influences C allocation to developing wood, and that it affects C metabolism at the whole tree level

Near-distance imaging spectroscopy investigating chlorophyll fluorescence and photosynthetic activity of grassland in the daily course

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 4m for temperate montane grassland in the Czech Republic. Simultaneously, measurements of Chl-F and total chlorophyll content (Chl a+b) were made on a single leaf at ground level were collected. A specifically designed \u27shade removal\u27 experiment revealed the influence of dynamic physiological plant processes on hyperspectral reflectance of three wavelengths: 532, 686 and 740nm. Based on this information, the vegetation indexes R686/R630, R740/R800 and PRI calculated as (R532R570)/(R532+R 570) 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, ΠII). 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 (R 2) for best-fit relationships between PRI-ΠII and PRI-Chl-Fs, measured in the daily course, show a high variability of 0.230.78 and 0.200.65, respectively. Similarly, R2 for the R 686/R630-ΠII and R686/R 630-Chl-Fs relationships varied between 0.200.73 and 0.410.70, 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

Předzávodní charakteristiky a závodní výkon hyponatremických a normonatremických závodníků českých ultra-závodů.

The aim of the study was to compare pre-race characteristics, race performance and plasma sodium [Na+] levels of hyponatremic and normonatremic ultra-endurance athletes and choosen variables in all finishers (n = 138). We assessed age, gender, club membership, pre-race training history and experience, pre-race body mass and body mass index (BMI) in 138 finishers of ultra-races (stage mountain bikers, 24-hr mountain bikers, 24-hr ultra-runners and 100-km ultra-runners) and post-race plasma [Na+] in a subgroup of 113 ultra-athletes.Cílem studie bylo porovnat předzávodní charakteristiky, závodní výkon a úrovneň sodíku v plazmě, a to u hyponatremických a normonatremických ultra-vytrvalostních sportovců

Birds girdling activity on exotic tree species as a form of adaptive behavior?

Four tree species in the Kostelec n. . l. arboretum (Czech Republic) have been repeatedly damaged by Dendrocopos medius. The unique aspect of this otherwise common behavior called girdling consists in regularly visiting the same trees every spring, although there are more than 1.200 tree species within the arboretum. We monitored transpiration, leaf phenology and the chemical composition of the xylem sap of girdled and nongirdled trees. Spectral analysis revealed slightly higher amounts of sugars, especially saccharose, in Cladrastis Raf. as the most regularly girdled tree among other conditions, comparing girdled to non-girdled trees. Higher transpiration rates were not confirmed in connection with girdling-quite the opposite-Cladrastis Raf. as the most highly favored tree for girdling showed the lowest transpiration rates (in average 6 kg water per day within spring months) compared to other non-girdled trees. We presume that the birds do not choose a particular tree on the basis of any visible or chemical traits but they examine many trees within their territory. Afterwards they probably remember the position of trees whose xylem sap starts to flow early in the spring compared to other trees, as their transpiration stream is enriched with sweet organic substances that represent an advantage for the forthcoming nesting period

Assessing inter- and intraspecific variability of xylem vulnerability to embolism in oaks

The genus Quercus comprises important species in forestry not only for their productive value but also for their ability to withstand drought. Hence an evaluation of inter- and intraspecific variation in drought tolerance is important for selecting the best adapted species and provenances for future afforestation. However, the presence of long vessels makes it difficult to assess xylem vulnerability to embolism in these species. Thanks to the development of a flow centrifuge equipped with a large rotor, we quantified (i) the between species variability of embolism resistance in four native and two exotic species of oaks in Europe and (ii) the within species variability in Quercus petraea. Embolism resistance varied significantly between species, with the pressure inducing 50% loss of hydraulic conductivity (P-50) ranging between -7.0 and -4.2 MPa. Species native to the Mediterranean region were more resistant than pan-European species. In contrast, intraspecific variability in embolism resistance in Q. petraea was low within provenances and null between provenances. A positive correlation between P-50 and vessel diameter among the six oak species indicates that the more embolism resistant species had narrower xylem vessels and a higher amount of hydraulic bridges between vessels. However, this tradeoff between hydraulic efficiency and safety was not observed between Q. petraea provenances