Vegetation in grasslands is changing at an unprecedented rate. In the Nebraska Sandhills, this shift is attributed in part to encroachment of the woody species Juniperus virginiana. We investigated changes in resource availability and their feedback on seasonal trends in photosynthetic characteristics of J. virginiana trees scattered in open grasslands vs. a dense 57-year-old stand. Dense stand exhibited lower volumetric soil water content, NH4+, NO3-, and δ13C, as well as foliage δ13C, δ15N, and N content, compared to grasslands. Water potential was higher in trees in grasslands compared to dense stand. J. virginiana in dense stand exhibited similar trends to trees in grasslands for net photosynthetic rate (PN), stomatal conductance, transpiration, maximum photochemical efficiency of PSII, maximum carboxylation velocity, and maximum rate of electron transport. PN peaked early summer and declined in the fall, with trees in open grasslands lagging behind those in dense stand. Plasticity of this species may place it at a competitive advantage in the Sandhills, further altering grasslands vegetation and ecosystem processes., J. Msanne, T. Awada, N. M. Bryan, W. Schacht, R. Drijber, Y. Li, X. Zhou, J. Okalebo, D. Wedin, J. Brandle, J. Hiller., and Obsahuje bibliografii
An ecophysiological approach was used to determine if competition can be detected among plants in a recently abandoned old-field and in a native tallgrass prairie in northeastern Kansas. In situ photosynthetic parameters and water potentials (Ψ) of target plants were measured 1-2 d after neighbor (intra- and interspecific) removal as well as 1-4 weeks later, and compared with values for plants with neighbors. Only two of the six study species (four old-field and two prairie species) responded to removal of neighboring plants, and only after several weeks had elapsed. Net photosynthetic rates (PN) and stomatal conductances (gs) of Ambrosia trifida in an old-field increased after removal of both intra- and interspecific neighbors. For Apocynum cannabinum, another old-field species, PN of target plants without neighbors was significantly higher than that of target plants with neighbors. For both these species, values of Ψ were not different between target plants with and without neighbors, suggesting that increased availability of nutrients may have been responsible for the observed ecophysiological responses. Though numerous past studies indicate that competition is a major factor influencing plants in old-field and in prairie communities, the experimental approach used in this study revealed that neighbor removal had only limited effects on ecophysiology of the target plants in either community. and F. Norman, C. E. Martin.
There is a great uncertainty about the effect of land use change on grassland ecosystem in the Tibetan Plateau. Net ecosystem carbon exchange (NEE) was measured for native alpine meadow with winter grazing (NAM), abandoned cropland/pasture (APL), perennial Elymus nutans (PEN), and annual oat pasture (AO) on the Tibetan plateau, during the growing seasons in 2009 and 2010 using a transparent chamber technique (Licor-6400). AO significantly decreased annual average NEE by 21.6, 23.7, and 15.7% compared to PEN, NAM, and APL during the growing season in 2010. Compared to PEN, NAM, and APL, AO significantly decreased average ecosystem respiration (Re) by 21.1, 52.3, and 39.3%, respectively, during the growing season in 2009. Soil moisture and total aboveground and belowground biomass together explained 39.6% of NEE variation and 71% in gross primary productivity variation. Soil moisture and belowground biomass explained about 83.1% of the Re variation. Our results indicated that it is possible to convert APL to PEN in the region because it could result in a higher NEE together with higher forage production compared to AO., C.-Y. Luo, X.-X. Zhu, S.-P. Wang, S.-J. Cui, Z.-H. Zhang, X.-Y. Bao, L. Zhao, Y. Li, X.-Q. Zhao., and Obsahuje seznam literatury
A mixture of ryegrass (Lolium italicum A. Braun) and clover (Trifolium alexandrinum L.) was sown in Eboli (Salerno, Southern Italy) in September 2007. Crop growth, leaf and canopy gas exchange and ecophysiological traits were monitored throughout the growth cycle. The gross primary production (GPP) was not affected by air temperature (T air); on the contrary the ecosystem respiration (R eco) decreased as T air decreased while net ecosystem CO2 exchange (NEE) increased. When was normalized with leaf area index (LAI), GPP decreased with T air, a likely response to cold that down-regulated canopy photosynthesis in order to optimize the light use at low winter temperatures. Net photosynthetic rates (PN), the effective quantum yield of PSII (ΦPSII) and photosynthetic pigment content were higher in clover than ryegrass, in relation to the higher leaf N content. The lower ΦPSII in ryegrass was linked to lower photochemical quenching coefficient (qP) values, due to a reduced number of reaction centres, in agreement with the lowest Chl a content. This behaviour can be considered as an adaptive strategy to cold to avoid photooxidative damage at low temperature rather than an impairment of PSII complexes., L. Vitale ... [et al.]., and V klíčových slovech chybně uvedené jméno Lolium italicum A. Barum
Enzymes that hydrolyze extracellular ATP, i.e. ecto-ATPase and ecto-ATP diphosphohydrolase (ATPDase), can be differentiated by ability of the latter to hydrolyze ADP and by slightly different kinetic properties of the two enzymes. Synaptic plasma membrane fractions isolated from rat hippocampus and caudate nucleus exhibit ADP-hydrolyzing activity, as revealed by the enzyme assay, and the presence of ecto-ATPase protein, as revealed by immunological identification on Western blot. These findings indicate that both enzymes are co-expressed in the synaptic membrane compartment of hippocampal and caudate nucleus neurons. Kinetic analysis was performed to determine the relative contribution of each enzyme to the total ATP-hydrolyzing activity, while an inhibition study was carried out in order to exclude the interference of other nonspecific ATPase and phosphatase activities. Based on the kinetic properties, sensitivity to inhibitors and VATP/VADP ratio of about 2, we concluded that a substantial portion of ATP-hydrolyzing activity in both synaptic membrane preparations can be ascribed to the catalytic action of ATPDase. On the other hand, the highest catalytic efficacy when ATP is the substrate and the greater abundance of ecto-ATPase protein in caudate nucleus preparation suggest that the relative contribution of ecto-ATPase to the total ATP-hydrolyzing activity in the caudate nucleus is higher than in the hippocampus., N. Nedeljkovic, A. Banjac, A. Horvat, M. Stojiljkovic, G. Nikezic., and Obsahuje bibliografii
The article stands as the fourth part of a series about the question answering process during standardized surveys and elaborates the phase of editing the response. Major moments and processes are explained that affect the shape of final answer at this stage and the narrow relationship of these facts to the nature and quality of survey data is pointed out. Step by step those phenomenons like rounding of numerical answers, the effect of answering scales in terms of its range, frequency, polarity or response order are elaborated and facts like response styles, range-frequency effect or positivity bias are mentioned. In the end, the problem of social desirability and its influence onto final answer is addressed, as well as some opportunities of elimination. Described aspects are related mainly to the distinction between factual and attitudinal questions, nonetheless in the course of presentation there are mentioned also particularities of some other question formats., Jak bylo v předchozích částech seriálu několikrát zmíněno, dosažení rozhodnutí ještě není definitivní tečkou za procesem zodpovídání výzkumného dotazu. V poslední fázi kognitivních procesů musí respondenti takto dosaženou odpověď většinou ještě nějakým způsobem upravit. Například je třeba výsledek hledání v paměti a rozhodování přizpůsobit některé z možností, kterou nabízí dotazník, nebo se respondent rozhodne svou výpověď modifikovat k sociálně přijatelnější podobě. Také v této fázi tedy dochází k přímému vlivu kognitivních aspektů na podobu výsledné odpovědi a také zde je tedy vhodné zkoumat, které procesy a faktory mohou odpověď ovlivnit a jaké dopady to může mít na povahu a kvalitu dat získaných v rámci dotazníkového šetření., Jiří Vinopal., and Seznam literatury