Using a Macroalgal Functional Form Approach to Assess the Level of Disturbance of Seagrass Meadows in Bahía of Nuevitas,Cuba(2000-2002)

A study on the spatial and seasonal variations of the associate macroalgae and epiphytes of Thalassia testudinum was carried out in Bahía de Nuevitas. Sixty-two species were identified: 3 Cyanophyta, 25 Chlorophyta, 8 Phaeophyceae, 23 Rhodophyta and 3 Magnoliophyta, with two new records for Cuba and 43 for the area. The differences in the specific composition of the macroalgae communities are determined by a space component related to the type of affectation in each area. The morpho-functional groups of macroalgae in the station with more nutrient influence were mainly foliaceous and filamentous. In the stations far from the city, the predominant morpho-types were the leathery and articulate calcareous indicators of lower nitrification levels. The abundance and diversity of macroalgae in the site affected by fisheries were lower due to the damage by bottom trawls. Seasonal variations were found in the relative abundance of the species, not in the diversity, which makes evident seasonal changes in the structure of the seaweeds, where some species replace others in the community.

Trans-generational effects in the clonal invader Alternanthera philoxeroides

Aims Recent studies have revealed heritable phenotypic plasticity through vegetative generations.In this sense,changes in gene regulation induced by the environment,such as DNA methylation(i.e.epigenetic changes),can result in reversible plastic responses being transferred to the offspring generations.This trans-generational plasticity is expected to be especially relevant in clonal plants,since reduction of sexual reproduction can decrease the potential for adaptation through genetic variation.Many of the most aggressive plant invaders are clonal,and clonality has been suggested as key to explain plant invasiveness.Here we aim to determine whether trans-generational effects occur in the clonal invader Alternanthera philoxeroides,and whether such effects differ between populations from native and non-native ranges.Methods In a common garden experiment,parent plants of A.philoxeroides from populations collected in Brazil(native range)and Iberian Peninsula(non-native range)were grown in high and low soil nutrient conditions,and offspring plants were transplanted to control conditions with high nutrients.To test the potential role of DNA methylation on trans-generational plasticity,half of the parent plants were treated with the demethylating agent,5-azacytidine.Important Findings Trans-generational effects were observed both in populations from the native and the non-native ranges.Interestingly,trans-generational effects occurred on growth variables(number of ramets,stem mass,root mass and total mass)in the population from the native range,but on biomass partitioning in the population from the non-native range.Trans-generational effects of the population from the native range may be explained by a‘silver-spoon’effect,whereas those of the population from the non-native range could be explained by epigenetic transmission due to DNA methylation.Our study highlights the importance of trans-generational effects on the growth of a clonal plant,which could help to understand the mechanisms underlying expansion success of many clonal plants.

Fraying around the edges:negative effects of the invasive Tradescantia zebrina Hort.ex Bosse(Commelinaceae)on tree regeneration in the Atlantic Forest under different competitive and environmental conditions

Aims Invasive plants modify the structure and functioning of natural en-vironments and threat native plant communities.Invasive species are often favored by human interference such as the creation of arti-ficial forest edges.Field removal experiments may clarify if invasive plants are detrimental to native plant regeneration and how this is related to other local factors.We assessed the joint effect of envir-onment and competition with the invasive Tradescantia zebrina on tree species recruitment in an Atlantic Forest fragment.Methods We carried out the experimental study in the Iguaçu National Park,located in southern Brazil,using 30 plots distributed across five invaded sites during 6 months.We counted T.zebrina leaves and recorded the abundance and height of tree recruits over time under contrasting environmental(forest edge vs.forest interior)and removal(all aboveground biomass,only T.zebrina removal,and control)treatments.We analyzed the effects of environment and re-moval treatment using generalized linear mixed models.Important Findings The invasive species performed better at the forest edge than in the interior.The higher competitive pressure of T.zebrina led to higher mortality and lower height of tree recruits.Invader removal favored tree recruitment,especially in the forest interior.Our study shows that T.zebrina hampers woody species regeneration in tropical Atlantic Forests,especially at the forest edge.