Bulbing in Long-day Onion (Allium cepa L.) Cultured In Vitro: Comparison Between Sugar Feeding and Light Induction

Bulbs were obtained on onion plants cultured in vitro. No bulbinghappened under long days with fluorescent light and 30–40g l^–1 sucrose. Bulb formation was mainly dependent eitheron sucrose concentration in the culture medium, or on lightspectral composition. Raising the sucrose concentration from40 to 120 g l^–1 increased plant basal swelling and stoppedfurther vegetative development. These plants were not dormant.When fluorescent light was enriched in incandescence duringa long day period, bulbs were obtained in two months and underwenta consecutive dormancy. Bulb, dormancy, light spectral quality, photoperiod, R: FR ratio, sugar, tissue culture     

Primary production dynamics and climate variability: ecological consequences in semiarid Chile

Increase in rainfall variability has important consequences for organisms in arid and semiarid regions around the world. In South American and Australian deserts, the El Niño/Southern Oscillation (ENSO) phenomenon greatly influences rainfall patterns, and therefore the dynamics of plant communities. However, the field data needed to assess the effect of climate change on vegetational patterns is difficult to obtain because of the large spatial scale required for such studies. Normalized Difference Vegetation Index (NDVI) characteristics allow the use of several indexes related to vegetational structure. Due to its direct relationship with primary productivity, it is possible to obtain several measures of annual productivity. These include annual plant yield, annual maximum yield, onset of 'greening-up' and senescence phases, length of the 'green' season, vegetation peak, and therefore, the periods when more or less food is available for herbivores. After verification with ground-truth measures, we used NDVI data from two semiarid localities in north-central Chile (Fray Jorge and Aucó) to determine the relationship between rainfall patterns and vegetation cover and productivity related to El Niño phenomenon. With this information we gauge the influence of climatic processes on primary productivity in western South America, an area subject to strong climate variability. We predict significant variation in Chilean semiarid regions due to climate change, affecting mainly the extent and timing of annual growth season of vegetation, and also including a shorter and delayed greening-up season. Also, we predict that important decreases in rainfall levels will not have strong effects on primary production in these semiarid ecosystems.     

A new Spanish species of Linaria Miller (Scrophulariaceae)

Linaria arabiniana sp. nov. is described from coastal sand dunes of a very reduced area in Alicante Province (south-eastern part of the Iberian Peninsula). It is a perennial herb characterized by its 3–4-verticillate leaves, glabrous stems, large violet or rarely yellow flowers, and bicoloured usually flat seeds. Morphological characteristics and taxonomic affinities of this taxon are discussed, as are data on its ecology, phytosociology, and eventual conservation features.     

Similar breakdown rates and benthic macroinvertebrate assemblages on native and Eucalyptus globulus leaf litter in Californian streams

1. Eucalyptus globulus, a tree species planted worldwide in many riparian zones, has been reported to affect benthic macroinvertebrates negatively. Although there is no consensus about the effects of Eucalyptus on aquatic macrobenthos, its removal is sometimes proposed as a means of ecological restoration. 2. We combined the sampling of macroinvertebrates with measurement of the colonisation of leaf packs in mesh bags, to examine the effects of riparian Eucalyptus and its litter on benthic macroinvertebrates in three small streams in California, U.S.A. Each stream included one reach bordered by Eucalyptus (E‐site) and a second bordered by native vegetation (N‐site). 3. The macrobenthos was sampled and two sets of litter bags were deployed at each site: one set with Eucalyptus litter (Euc‐bags) and one with mixed native tree litter (Nat‐bags) containing Quercus, Umbellularia, Acer and Alnus. Bags were exposed for 28, 56 and 90 days and this experiment was repeated in the autumn, winter and spring to account for effects of changing stream flow and insect phenology. 4. Litter input (average dry mass: 950 g m^?2 year^?1 in E‐sites versus 669 g m^?2 year^?1 in N‐sites) was similar, although in‐stream litter composition differed between E‐ and N‐sites. Litter broke down at similar rates in Euc‐bags and Nat‐bags (0.0193 day^?1 versus 0.0134 day^?1), perhaps reflecting the refractory nature of some of the leaves of the native trees (Quercus agrifolia). 5. Summary metrics for macroinvertebrates (taxon richness, Shannon diversity, pollution tolerance index) did not differ significantly between the E and N sites, or between Euc‐bags and Nat‐bags. No effect of exposure time or site was detected by ordination of the taxa sampled. However, distinct seasonal ordination clusters were observed in winter, spring and autumn, and one of the three streams formed a separate cluster. 6. The presence of Eucalyptus was less important in explaining the taxonomic composition of the macrobenthos than either ‘season’ or ‘stream’. Similarly, these same two factors (but not litter species) also helped explain the variation in leaf breakdown. We conclude that patches of riparian Eucalyptus and its litter have little effect on stream macrobenthos in this region.