A re-evaluation of plants referred to as Pteridiutn herediae (Colmeiro) Love & Kjellqvist

SHEFFIELD, E., WOLF, P. G., HAUFLER, C. H., RANKER, T. A. & JERMY, A. C, 1989. Are-evaluation of plants referred to as Pteridiutn herediae (Colmeiro) Love & Kjellqvist. Based on perceived differences in morphology, chromosome number and habitat, specimens of Pteridiutn from southern Spain have been segregated by previous authors as a species distinct from Pteridium aquilinum , and called Pteridium herediae. However, type specimens of this taxon cannot be found. New collections of Pteridium from similar habitats in the area were examined and analysed in the present study and the results compared with those from British plants (P. aquilinum). The Spanish plants were not found to differ significantly from P. aquilinum morphologically, and all yielded chromosome counts (sporophytes, 104; gametophytes, 52) considered typical for the genus. Genotype frequency data obtained from isozyme electrophoresis of Spanish and British Pteridium yielded a genetic identity of 0.86; well within intraspecific distances found in other ferns.
These data indicate that there are currently no grounds for accepting that a form of Pteridium , distinguishable from P. aquilinum on the basis of differences in morphology, chromosome number, habitat or biochemistry, exists on the limestone soils of the Sierra de Cazorla region of southern Spain.     

The Effect of Nitrogen Fertilization and Irrigation Frequency on Photosynthesis of Potatoes (Solanum tuberosum)

Gas exchange parameters for the potato (Solanum tuberosum L.,cv. ‘Desiree’) crop were measured under field conditions.Nitrogen nutrition was found to have a positive effect on photosynthesisthroughout the growing season. The gas exchange data and thechlorophyll content in the leaves indicated that this effectwas essentially in the mesophyll. Stomatal resistance increasedas photosynthetic rate decreased, but substomatal CO₂ concentration(Ci) was not affected by nitrogen treatments. Long term effects of water deficit on photosynthetic capacitywere also mostly mesophyllic in origin. A reduction in photosyntheticrate was observed after a period of moisture stress and alsoafter relief of drought by irrigation, indicating a limitedcapacity for recovery. A short term afternoon increase in stomatalresistance, associated with lower Ci values, occurred afterlong periods without irrigation. Leaf water potential was affectedby irrigation frequency, but less strongly than the gas exchangeparameters. Mesophyll activity and stomatal behaviour were bothaffected by water stress and by nitrogen deficiency, whereasCi values were not affected in most cases. Solanum tuberosum L, photosynthesis, mesophyll, stomata, irrigation frequency, nitrogen deficiency, chlorophyll, leaf water potential     

Potassium Fluxes in Excised Barley Roots

The method of the modified compartmental analysis for excisedroots has been adopted for measuring K⁺-fluxes and compartmentationin barley (Hordeum distichon) roots. Efflux of ⁴²K and ⁸⁶Rbindicated that more than two intracellular compartments wereinvolved in the tracer exchange; the ⁴²K data clearly showedthe components. On the basis of the efflux behaviour of theapical and more basal tissues of the roots, the three componentsof efflux were attributed to the cytoplasm of differentiated(fast) and meristematic tissues (intermediate) and to the vacuoles(slow exchange) of the roots. A model is proposed on the basisof which, the fluxes corresponding to the meristematic and differentiatedtissues of the root can be estimated. Additionally, fluxes ofthe differentiated root tissues were determined by using effluxdata obtained with root segments without apical tissues. Thedata obtained in both ways compare reasonably well and agreeto independent chemical measurements. Comparison of the ⁴²K and ⁸⁶Rb efflux data show strong discriminationof K^– in favour of Rb⁺ and indicate that ⁸⁶Rb is not suitableas a tracer for K⁺ in efflux measurements, at least with barleyroots.