Physiological consequences of mowing and burning of Phragmites australisstands for rhizome ventilation and amino acid metabolism

Mowing and burning of Phragmitesaustralis-stands have been recommended in the recentliterature as management tools for both protection andcontrol, and both favourable and detrimental effectsof these treatments were actually observed. This studyaims to clarify this apparent contradiction using anew physiological approach. Reed stands in thebiosphere reserves of Trebon (Czech Republic) and theDanube Delta (Romania) were investigated usingparameters of convective ventilation and amino acidpatterns. Flooded mown reed and unflooded burned reedwas compared to unmanaged control stands withcomparable hydrology and trophic level. Managementtook place in winter. The elimination of old culmsthrough mowing resulted in a lower ventilationefficiency due to a high counterpressure of rhizomes.The corresponding gas flow rates were reduced to 38%of the value in control stands, indicating a stronglyimpaired oxygen supply to basal and below-ground plantparts after mowing. Concomitantly, significantlyincreased levels of alanine and gamma-aminobutyricacid in basal culm internodes of shoots were measuredas signs of a metabolic shift due to hypoxic stress.Conversely, shoot loss by burning (without flooding)did not diminish ventilation efficiency and gas flowrate, i.e. oxygen supply to buried organs wasunaffected. Correspondingly, the level ofhypoxia-indicating amino acids (alanine,gamma-aminobutyric acid) did not indicate more severeoxygen deficiency in basal and below-ground plantparts of burned reed. It is concluded that the impactof mowing and burning on P. australisstronglydepends on the water level and on whether or notflooding occurs after the treatment. The mechanismresponsible for detrimental effects is probablyimpaired convective ventilation followed by hypoxia inbasal plant parts. This aspect should be taken intoaccount when mowing or burning in winter are used asmanagement tools for wetlands.     

Modulation of cyclic CO2 release in response to endogenous changes of metabolism during pupal development of Zophobas rugipes (Coleoptera: Tenebrionidae)

Understanding the mechanisms of gas exchange regulation in insects currently is a hot topic of insect physiology. Endogenous variation of metabolism during pupal development offers a great opportunity to study the regulation of respiratory patterns in insects. Here we show that metabolic rates during pupal development of the tenebrionid beetle Zophobas rugipes reveal a typical U-shaped curve and that, with the exception of 9-day-old pupae, the time between two bursts of CO₂ (interburst phase) was the only parameter of cyclic CO₂ gas exchange patterns that was adjusted to changing metabolic rates. The volume of CO₂ released in a burst was kept constant, suggesting a regulation for accumulation and release of a fixed amount of CO₂ throughout pupal development. We detected a variety of discontinuous and cyclic gas exchange patterns, which were not correlated with any periods of pupal development, suggesting a high among individual variability. An occasional occurrence of continuous CO₂ release patterns at low metabolic rates was very likely caused by single defective non-occluding spiracles.