Myrica cerifera L. (Myricaceae), the dominant woody species on many barrier islands along the southeastern coast of the United States, is expanding into grass-dominated, mesic, interdunal depressions where it forms dense thickets. Expansion may be attributed to a symbiotic nitrogen fixation with the bacterium Frankia, an evergreen leaf habit and, possibly, corticular photosynthesis (CP, i.e. refixation of respired CO2, %ref). We quantified seasonal variations in CP characteristics in first through fifth order branches of M. cerifera to determine the extent and relevance of CP to shrub expansion in coastal environments. Maximum mean %ref was 110±39 % of CO2 efflux in the dark (RD) in first order branches during winter. Minimum %ref was 18±3 % in fifth order branches during summer. Variations in %ref paralleled changes in incident photosynthetic photon flux density (PPFD). As incident PPFD attenuated with increasing branch order, %ref decreased. A less dense canopy in winter led to increased PPFD and increases in %ref. Total chlorophyll (Chl) content and Chl a/b ratios were consistent with shade acclimation as branch order increased. CP may be a mechanism to enhance M. cerifera shrub expansion because of the potential increase in whole plant carbon use efficiency and water use efficiency attributed to refixation of respired CO2. and J. K. Vick, D. R. Young.
The paper contains short description of a special device developed for study of electrical after-effect in vegetable cellular tissues after short electric pulses applied to the tissue. The device contains generator of the pulses and the microprocessor controlling circuits for time arrangement of the pulse amplification and collection of data for further evaluation. The pulses are based on AC signal with frequency 10-100 kHz with the amplified voltage up to ±240V and duration 1-10 ms. After finishing the individual pulse, the AC source signal continues, but amplitude on the tissue is 21. 5times lower. The data about AC voltage and current intensity are continuously collected with frequency 800 kHz and then fed to PC USB input that was used to calculate time chart of electric properties of the tissue, its complex permittivity and specific complex conductivity. An example of the obtained results on potato tissue is given. and Práce obsahuje krátký popis speciálního zařízení vyvinutého pro studium elektrických jevů v zeleninové buněčné tkáni po krátkých elektrických pulsech. Zařízení se skládá z generátoru nosného signálu, mikroprocesorem řízené jednotky pro amplitudovou modulaci uvedeného nosného signálu, zesilovače pro výkonové zesílení a jednotky pro sběr dat pro další vyhodnocení. Užívá se nosný signál frekvence 10-100 kHz, modulovaný do pulsů strváním 1-10 ms a amplitudě do ±240 V. Po skončení individuálního pulsu střídavý signál pokračuje, ale jeho amplituda se snižuje 21,5krát; měření na tkáni pokračuje jako nedestruktivní. Data okamžitých hodnot napětí a proudu na zkoumané tkáni jsou snímána sfrekvencí 800 kHz. Tato data jsou přivedena na USB vstup PC a zde použita k výpočtu časového průběhu elektrických vlastností tkáně, její komplexní permitivity a měrné komplexní vodivosti. Analýza je demonstrována na příkladu (pletivo bramboru).