Structural Features and Water Interactions of Etherified Xylan Thin Films

In this paper, the model film approach was used to investigate the structural features and humidity induced changes of the etherified xylan derivatives by using surface sensitive methods. Two routes to modify the birch xylan to generate either cross-linking xylan or more hydrophobic xylan were mastered via allylation and butylation, respectively. Thin nanometer scale model films were prepared by spin-coating and the films were further treated by UV-radical treatment and heat. The structural changes and wetting behaviour of the films before and after the post-treatment procedures were studied using atomic force microscopy and water contact angle measurements. In addition, the water vapour uptake of the xylan derivative films was monitored using quartz crystal microbalance with dissipation (QCM-D) equipped with the humidity module. With the QCM-D, the mass uptake due to the water vapour binding was defined. Simultaneously the changes in the viscoelastic properties of the films when subjected to different relative humidity conditions were determined. We show that the water sensitivity and wetting behaviour of the water soluble xylan derivatives can be altered by cross-linking the film structure and through the molecular rearrangements. Cross-linking and the conformational rearrangements of the allylated xylan reduced the water vapour uptake ability approximately 80?%. Butylated xylan as being a more hydrophobic derivative showed lower ability to uptake water vapour when compared to more hydrophilic xylan derivative. This ability was even further reduced after the post-treatments mainly due to the reassembly of the hydrophobic groups.     

Divergent composition but similar function of soil food webs of individual plants: plant species and community effects

Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.