No abstract

No abstract

Poa annua is the only flowering plant species that has established a breeding population in the maritime Antarctic, through repeated anthropogenic introduction. The first appearance of this species in the Antarctic was observed in 1953. Annual bluegrass inhabits mainly anthropogenic sites, but recently has entered tundra communities. The functioning of P. annua in the Antarctic could not have been possible without adaptations that enable the plants to persist in the specific climatic conditions typical for this zone. Poa annua is highly adaptable to environmental stress and unstable habitats: huge phenotypic and genotypic variability, small size, plastic life cycle (life-history types ranging from annual to perennial forms). The spreading of P. annua in the Antarctic Peninsula region is a classic example of the expansion process following anthropogenic introduction of an invasive species, and illustrates the dangers to Antarctic terrestrial ecosystems that are associated with increasing human traffic.

The initial stages of Umbilicaria aprina Nyl. hydration (starting from the hydration level Dm/m 0 ¼ 0.048 AE 0.004) were observed using hydration kinetics, sorption isotherm and proton NMR. The thalli were hydrated from gaseous phase. The total saturation hydration level obtained at the relative humidity p/p 0 ¼ 100% was Dm/m 0 ¼ 0.848 AE 0.009. The hydration courses revealed i) a fraction of very tightly bound water (Dm/m 0 ¼ 0.054 AE 0.011, short hydration time constant, t hyd ), ii) a fraction of tightly bound water [Dm/m 0 ¼ 0.051 AE 0.038, t hyd ¼ (4.7 AE 2.6) h], and iii) a loosely bound water pool [ t hyd ¼ (31.0 AE 1.9) h] for higher values of target humidity. The sorption isotherm of U. aprina was fitted well using Dent model. The relative mass of water saturating primary binding sites was DM/m 0 ¼ 0.054, which is close to the water fractions. Proton FIDs detected (i þ ii) the immobilized tightly bound water fraction, L 1 , and iii) the mobile, loosely bound water pool L 2 . The hydration dependence of the proton liquid signal suggests the presence of a significant contribution from a water soluble solid fraction in the thallus. Sorption isotherm fitted to NMR data showed the absence of 'sealed' water fraction trapped in pores of the thallus.