Lukács et al. (2015) Tuexenia

Lukács, B. A., Török, P., Kelemen, A., Várbíró, G., Radócz, Sz., Takács, S., Miglécz, T., Tóthmérész B., Valkó O. (2015): Rainfall fluctuations and vegetation patterns in alkali grasslands – Self-organizing maps in vegetation analysis. Tuexenia, 35: 381-397


Abstract
Knowledge about the drivers of vegetation dynamics in grasslands is fundamental to select appropriate management for conservation purposes. In this study, we provide a detailed analysis of vegetation dynamics in alkali grasslands, a priority habitat of the Natura 2000 network. We studied vegetation dynamics in five stands of four alkali grassland types in the Hortobágy National Park (eastern Hungary), between 2009 and 2011. We analysed the effect of fluctuations in precipitation on both the overall vegetation composition and on the cover of each species using Self Organizing Map neural networks (SOM). We found that SOM is a promising tool to reveal plant community dynamics. As we analysed species cover and overall vegetation composition separately, we were able to identify the species responsible for particular vegetation changes. Fluctuations in precipitation (a dry season, followed by a wet and an average season) caused quick shifts in plant species composition because of an increasing cover of halophyte forbs, probably because of salinisation. We observed a similar effect of stress from waterlogging in all studied grassland types. The species composition of Puccinellia grasslands was the most stable over the three years with varying precipitation. This was important as this grassland type contained many threatened halophyte species. Self-organising maps revealed small-scale vegetation changes and provided a detailed visualisation of short-term vegetation dynamics, thus we suggest that the application of this method is also promising to reveal community dynamics in more species-rich habitat types or landscapes.

Keywords

halophytes, neural network, precipitation changes, salt stress, SOM, water stress

Loreto et al. (2013) Global Ecology and Biogeography

Loreto, F., Bagnoli, F., Calfapietra, C., Cafasso, D., De Lillis, M., Filibeck, G., Fineschi, S., Guidolotti, G., Sramkó, G., Tökölyi, J. and Ricotta, C. (2013): Isoprenoid emission in hygrophyte and xerophyte European woody flora: ecological and evolutionary implications. Global Ecology and Biogeography doi: 10.1111/geb.12124

Abstract
Aim
The relationship between isoprenoid emission and hygrophily was investigated in woody plants of the Italian flora, which is representative of European diversity.
Methods
Volatile isoprenoids (isoprene and monoterpenes) were measured, or data collected from the literature, for 154 species native or endemic to the Mediterranean. The Ellenberg indicator value for moisture (EIVM) was used to describe plant hygrophily. Phylogenetic analysis was carried out at a broader taxonomic scale on 128 species, and then refined on strong isoprene emitters (Salix and Populus species) based on isoprene synthase gene sequences (IspS).
Results
Isoprene emitters were significantly more common and isoprene emission was higher in hygrophilous EIVM classes, whereas monoterpene emitters were more widespread and monoterpene emission was higher in xeric classes. However, when controlling for phylogeny, isoprene emission was not associated with EIVM, possibly due to the large presence of Salicaceae among hygrophilous isoprene emitters. Moreover, the distribution of isoprene emitters among EIVM classes was not related to IspS-based phylogenesis in Populus and Salix, suggesting that the gene has not undergone evolution linked to ecological pressure. In contrast, the monoterpene emission pattern is independent of phylogeny, suggesting that the evolution of monoterpenes is associated with transitions to more xeric habitats.
Main conclusions
Our results reveal an interesting ecological pattern linking isoprenoids and water availability. We suggest that isoprene is a trait that: (1) evolved in plants adapted to high water availability; (2) is replaced by more effective protection mechanisms, e.g. more stable isoprenoids, in plants adapting to more xeric environments; and (3) being strongly constrained by phylogeny, persists in Salicaceae adapted to more xeric environments.

 

Keywords
Adaptation, chemo-taxonomy, hygrophytes, isoprene, monoterpenes, phylogenies, salicaceae, xerophytes, water stress