Drought is a normal, recurrent feature of climate. In order to understand the potential effect of increasing atmospheric CO2 concentration (Ca) on ecosystems, it is essential to determine the combined effects of drought and elevated Ca (EC) under field conditions. A severe drought occurred in Central Florida in 1998 when precipitation was 88 % less than the average between 1984 and 2002. We determined daytime net ecosystem CO2 exchange (NEE) before, during, and after the drought in the Florida scrub-oak ecosystem exposed to doubled Ca in open-top chamber since May 1996. We measured diurnal leaf net photosynthetic rate (PN) of Quercus myrtifolia Willd, the dominant species, during and after the drought. Drought caused a midday depression in NEE and PN at ambient CO2 concentration (AC) and EC. EC mitigated the midday depression in NEE by about 60 % compared to AC and the effect of EC on leaf PN was similar to its effect on NEE. Growth in EC lowered the sensitivity of NEE to air vapor pressure deficit under drought. Thus EC would help the scrub-oak ecosystem to survive the consequences of the effects of rising atmospheric CO2 on climate change, including increased frequency of drought, while simultaneously sequestering more anthropogenic carbon. and J. H. Li ... [et al.].
Fracture behavior of foam core composite sandwich Split Cantilever Beam (SCB) loaded in torsion was analyzed theoretically using the apparatus of linear-elastic fracture mechanics. A loading method is proposed to create two transverse forces of identical magnitude which load the beam in torsion. In this way, mixed-mode II/III crack loading conditions were induced. A three-dimensional finite element model was developed for simulating the mechanical response of the sandwich SCB. The strain energy release rate was used as a fracture characterizing parameter. The analysis by virtual crack closure technique revealed that the strain energy release rate mode components were distributed non-uniformly along the crack front through the width of the sandwich SCB. The relation between the fracture behavior and the sandwich core material was studied. For this purpose, three foam core composite sandwich SCB configurations (with three different rigid celullar foams used as core material) were simulated. It was found that the fracture behaviour of the sandwich beam can be improved by using foams with higher density as a core material. and Obsahuje seznam literatury
Since 2002, Silver buffaloberry (Shepherdia argentea) has been introduced from North America in order to improve the fragile ecological environment in western China. To elucidate the
salt-resistance mechanism of S. argentea, we conducted a test with two-year-old seedlings subjected to 0, 200, 400, and 600 mM NaCl solutions for 30 d. The results showed that significant salt-induced suppression of plant fresh mass (FM) and stem height of S. argentea seedlings occurred only at the highest salinity level (600 mM). Leaf number, plant dry mass (DM), and chlorophyll (Chl) content declined markedly at both 400 and 600 mM. Leaf area (LA) and leaf water potential (Ψw) continuously declined with the increase of salinity. There was also a progressive and evident decrease in net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) with the increase of salinity and time. The correlation analysis indicated that PN was positively correlated with gs at all salinity levels while correlated with intercellular CO2 concentration (Ci) only at moderate salinity levels (<600 mM). Based on the initial slope of the PN/Ci curves, the estimated carboxylation efficiency (CE) was strongly inhibited at 600 mM. We confirm that S. argentea is highly tolerant to salinity. Moreover, our results show that at moderate salinity levels, salt-induced inhibition of photosynthesis is mainly attributed to the stomatal efficient closure predetermined by a low water potential in leaves; while at the high salinity levels, the inhibition is mainly due to the suppression of chloroplast capacity to fix CO2 caused by the serious decline in both CE and Chl contents. and J. Qin ... [et al.].
A new species of Proteocephalus, P. joanae sp. n„ is described from the intestine of the colubrid snake, Xenodon neuwiedi (Günther, 1863) (Serpentes: Xenodontinae), from Brazil. The new species differs from all other members of Proteocephalus by possessing a swollen elongated posterior part of the scolex herein considered as a metascolex. Furthermore, it is the only member of New World Proteocephalus possessing a voluminous glandular apical organ larger than suckers. P. joanae is also characterized by very elongated gravid proglottides. This is the first member of the Proteocephalidea occurring in Xenodon. Even though the species differs significantly from other species of the genus Proteocephalus, which currently contains many species that are morphologically very distinctive, it seems prudent to refrain from reworking the classification of the group until accurate redescriptions of Neotropical species can be conducted, preferably based on examination of type and freshly collected material. The definition of the metascolex is discussed herein.
R.L Mössbauer died a few weeks before the 50th anniversary of his Nobel prize award, which he shared with R. Hofstadter. This description of the work which led to the discovery of recoilless resonance absorption of γ rays, later named Mössbauer effect, is based on his personal reminiscences. Applications of Mössbauer spectroscopy are discussed with emphasis on the successful Mars mission that included facilities for this method of spectroscopy., Karel Závěta,Jaroslav Kohout, Adriana Lančok., and Obsahuje seznam literatury
In respect of its morphology, biology and epidemiology, Hyalomma (Euhyalomma) impressum Koch, 1844 is one of the more poorly studied ticks of the genus Hyalomma Koch, 1844. No comprehensive morphological study has been done to date, and the nymph has not been described. Here the adults and larva are redescribed, and the nymph is described for the first time. Data on hosts, geographical distribution and disease relationships are provided.