Nectar yeasts of two southern Spanish plants: the roles of immigration and physiological traits in community assembly.

Recent studies have shown that dense yeast populations often occurring in floral nectar are numerically dominated by a few species from the flower-insect interface specialized genus Metschnikowia, while generalist yeast species commonly occurring on leaf surfaces, soil, freshwater, and air were rarely isolated from nectar samples. This study was designed to understand the main factors responsible for the assembly of nectar yeast communities, by combining field experiments with laboratory tests characterizing the physiological abilities of all yeast species forming the pool of potential colonizers for two Spanish flowering plants (Digitalis obscura and Atropa baetica). Yeast frequency and species richness were assessed in external sources (bee glossae, air, plant phylloplane) as well as in pollinator rewards (pollen, nectar). Yeasts were most frequent in external sources (air, flower-visiting insects), less so in the proximate floral environment (phylloplane), and least in pollen and nectar. Nectar communities appeared to be considerably impoverished versions of those in insect glossae and phylloplane. Nectar, pollen, and insect yeast assemblages differed in physiological characteristics from those in other substrates. Nectarivorous Metschnikowia were not more resistant than other yeast species to plant secondary compounds and high sugar concentrations typical of nectar, but their higher growth rates may be decisive for their dominance in ephemeral nectar communities.

Improvement of sexual destination in Atropa acuminata Royle (Solanaceae)--a critically endangered medicinal plant of Northwestern Himalaya.

Good seed set is no guarantee of absolute sexual destination in plants. Seed viability and seed vigour are crucial phases in the life cycle of every sexually reproducing plant. The present study was an attempt to improve the sexual destination-the germination and seedling survival of Atropa acuminata Royle (Solanaceae), an endemic and extremely restricted sub-alpine medicinal plant of North West Himalayas under ex situ conditions at (1580 m) with an aim to develop a successful germination protocol and agrotechnique in order to revegetate disturbed areas. Among various treatments given to the seeds, GA3, Scarification, warm water treatment and chilling at 4 degrees C for 90 days were found to be most effective with percentage germination of 73.3 +/- 18.80, 79.95 +/- 9.40, 66.6 +/- 6.6, 45 +/- 7.07 (X +/- SE), respectively. The results reveal that the seeds do not germinate unless specific environmental signals or events occur which trigger the genetic and hormonal response of the seeds thereby facilitating their germination. The diversity and the extent of the dormancy mechanisms encountered here suggest that under harsh conditions, natural selection may favour seeds with a genetic system for dormancy and delayed germination. A relation was observed between seed size/weight, % age germination and subsequent seedling survival. Seedling survival is also effected by specific habitat requirement and stiff intra and inter-specific competition particularly the whimsical behaviour of Sambucus wigthiana (an alien species which grows in the vicinity of Atropa) is beyond the ken of Atropa, adding fuel to the already burning candle apart from habitat fragmentation and herbivory.