On the structure and evolutionary relationships of the Cerro Cuadrado fossil conifer seedlings*

Seedlings from the Cerro Cuadrado (Jurassic) Petrified Forest in Argentina have been shown to be comparable to extant araucarian seedlings from the sections Eutacta, Bunya and Colombea. Anatomically they are compared to the cone axes and embryos in the fossil cones of Araucaria mirabilis and Pararaucaria patagonica. Two seedlings previously described by Wieland are shown on pith structure to belong to P. patagonica. The remaining turbinate to top-shaped structures are compared with first year extant Bunya and Columbia seedlings and the cone A. mirabilis. Corm-like structures may represent an older seedling stage. From earlier work on the embryonic anatomy and germination stages described here, P. patagonica is deduced to have been epigeal and A. mirabilis hypogeal.     

Uptake by rice seedlings and in-plant degradation of atrazine as influenced by the oxidative stress induced by added arsenic or phosphate deficiency

The uptake and degradation of atrazine (ATR) by rice seedlings (Oryza sativa L.) was investigated with and without arsenate and phosphate nutrient in the cultured solution over a period of 48 h. The hydrogen peroxide (H₂O₂) contents in plants under different treatments were measured to evaluate the oxidative stress of the plant cell and its influence on the plant uptake and degradation of ATR. Results indicated that the ATR levels and main degradation products, deethylatrazine (DEA) and deisopropylatrazine (DIA), in plants varied significantly in different treatments. Added arsenate in solution increased the level of DEA and the ratios of DEA to the total (ATR, DEA, and DIA) in roots, while it either increased or decreased the H₂O₂ content in roots. Added arsenate increased the ratios of degradation products to the total in shoots, which corresponded to the 110%–285% increase of the H₂O₂ content. In phosphate-deficient systems, the H₂O₂ contents in shoots increased significantly, especially when exposed to a low level of ATR while the ratios of DIA and DEA to the total in shoots increased. The oxidative stress in rice seedlings induced by arsenic coexisting with ATR and by phosphate deficiency affected the plant uptake and degradation of ATR.     

Chloroplast-released inhibitor of phenylalanine ammonia-lyase from barley (Hordeum vulgare) seedlings

Isolated chloroplasts of barley seedlings ( Hordeum vulgare L.) when kept in light, released a soluble, thermostable factor that inhibited phenylalanine ammonia-lyase (PAL) in vitro . Highest inhibition was found when chloroplasts were suspended in PAL-containing extract and kept in light. Efficiency of PAL activity inhibition did not depend greatly on the type of medium used for chloroplast isolation, nor on the composition of buffer in which the enzymatic activity was measured. It is proposed that in green tissues chloroplasts may participate in regulation of cytoplasmic PAL activity.     

Survival,recruitment and dynamics of Acacia drepanolobium Sjøstedt seedlings at Olpejeta Conservancy,Kenya, between 1999 and 2009

Survival and recruitment of the whistling thorn (Acacia drepanolobium Sjøstedt) seedlings was studied in Olpejeta Conservancy, Kenya, between 1999 and 2009. Seedlings were monitored for damage by drought and herbivores as well as survival and recruitment into adult trees. We determined variability in seedling damage, survival and recruitment before and after two management interventions; the elephant translocation in 2001 and the expansion of the reserve in 2007. Seedling survival over 8 years was low, with mortalities being initially high between 2000 and 2001. Reduction in elephant numbers was followed by a gradual reduction in seedling mortality. We recorded a 47% survival over 8 years; 63% of the mortality having been caused by browsers, drought or other factors. Only 8 (0.75%) of the seedlings had grown into trees. Seedlings experienced greater damage at higher densities and exhibited a storage effect underneath grass cover. Survival and recruitment of A. drepanolobium seedlings is very low and of concern. The expansion of conservation area and the opening of wildlife migration corridors have, however, resulted in a steady recovery for seedlings. We recommend enclosing sections of the conservancy to exclude grazers and browsers such as elephants and to allow seedling survival and recruitment.     

The influence of tree canopies and elephants on sub-canopy vegetation in a savannah

The apparent influence of elephants on the structure of savannahs in Africa may be enhanced by management activities, fire and other herbivores. We separated the effect elephants have on grasses, woody seedlings (<0.5 m) and saplings (0.5–2 m) from the effect of tree canopies (canopy effect), and herbivory (park effect). We defined the canopy effect as the differences between plant abundances and diversity indices under tree canopies and 20 m away from these. Our testing of the park effect relied on the differences in the sub-canopy plant indices inside and outside a protected area that supported a range of herbivores. We based our assessment of the elephant effect on sub-canopy vegetation indices associated with elephant induced reductions in tree canopies. The park and canopy effects were more pronounced than the elephant effect. The park effect suppressed the development of woody seedlings into saplings. Conditions associated with tree canopies benefited woody plants, but not the grasses, as their indices were lower under trees. Elephants reducing canopies facilitated grass species tolerant of direct solar radiation. We concluded that management should consider other agents operating in the system when deciding on reducing the impact that elephants may have on vegetation.     

Survival and recruitment favored by safe site-strategy – the case of the high alpine, non-clonal cushions of Eritrichium nanum (Boraginaceae)

In 14 permanent plots at four distant sites in the European Alps life tables, cohorts and recruitment of Eritrichium nanum were studied during a period of 5 resp. 6 years. The germination rates were tested in the Botanical Institute of the University of Basel and besides the life tables of the plots at natural habitats we followed the early stages of development in pot cultures at the University Botanical Garden in Basel. Most of the seedlings of E. nanum emerged in spring, in the pot cultures as well as under natural conditions, a behavior which confirms general findings. But the germination rates (0–30%) were markedly low. The pot cultures show that some seeds are after 4 or 5 years still viable. Premature flowering in the second summer is a rather common behavior of E. nanum seedlings, which happened in all the cohorts observed during five years, partly up to 20% of the total of living plants in the corresponding plots. It is evident that life expectancy of E. nanum plants increase rapidly with rising size, to such a degree that cushions of only 10–20 cm² surface have a survival chance of more than 70%, those of 20–30 cm² even of more than 95% during a period of 5 years. But it has to be mentioned that juvenile plants are not growing parallel to their lifetime, many of them persist during several years in the size categories I/II (0–5 cm²), while others suddenly arise from category I to III (–10 cm²) or even IV (–20 cm²), what is mostly caused by joining, a specific type of safe site strategy. Though not obligatory, juvenile plants growing close together, often add their sizes to form one larger cushion, which was found to be particularly advantageous for recruitment. This is obviously a primary strategy of E. nanum and favors, especially on bare ground, the survival of its descendants which was found higher than expected (average of 26% after 5 years’ growth at natural habitats). Focusing on the whole life cycle of E. nanum, the present studies show constraints in pollination, a small seed production and low germination rates to be well compensated by the high survivorship and successful recruitment of the seedlings.     

Ectomycorrhizal morphotypes of naturally grownAbies firma seedlings

Ectomycorrhizas of naturally grown Momi fir (Abies firma) seedlings were characterized based on morphological features of fungal partners. A total of 128 seedlings were collected over three years (1995–1997) from a 10×30 m plot where occurrences of ectomycorrhizal fungal fruitbodies were monitored for the same period. Thirty-seven morphologically distinct ectomycorrhizal types were distinguished based mainly on the color of ectomycorrhizas and the characteristics of fungal mantles. Type 37 was thought to beCenococcum geophilum because of the jet-black mycorrhizas and the characteristic structure of mantle surfaces. For half of the classified morphotypes, fungal partners were inferred to be the generaLactarius, Russula, andTuber, and unidentified Basidiomycetes, based on earlier references.