Leaf gas films, underwater photosynthesis and plant species distributions in a flood gradient

Traits for survival during flooding of terrestrial plants include stimulation or inhibition of shoot elongation, aerenchyma formation and efficient gas exchange. Leaf gas films form on superhydrophobic cuticles during submergence and enhance underwater gas exchange. The main hypothesis tested was that the presence of leaf gas films influences the distribution of plant species along a natural flood gradient. We conducted laboratory experiments and field observations on species distributed along a natural flood gradient. We measured presence or absence of leaf gas films and specific leaf area of 95 species. We also measured, gas film retention time during submergence and underwater net photosynthesis and dark respiration of 25 target species. The presence of a leaf gas film was inversely correlated to flood frequency and duration and reached a maximum value of 80% of the species in the rarely flooded locations. This relationship was primarily driven by grasses that all, independently of their field location along the flood gradient, possess gas films when submerged. Although the present study and earlier experiments have shown that leaf gas films enhance gas exchange of submerged plants, the ability of species to form leaf gas films did not show the hypothesized relationship with species composition along the flood gradient.

Determining the date of ice-melt for low Arctic lakes along Søndre Strømfjord, southern West Greenland

The length of ice cover has considerable influence on the functioning of lake ecosystems, particularly so in continental and high-latitude regions where lakes freeze annually. Long-term trends in the length of ice cover and the date of ice break-up can be related to regional weather patterns, such as the North Atlantic Oscillation. It is this relationship to weather patterns that has generated considerable interest in the use of long-term icerecords as climate proxies. Although it is reasonable to assume a relationship between the length of the icefree period and lake productivity, it is unclear if this relationship influences the sedimentary record. Whether these ice-climate interactions can be identified in the sediment record is important for distinguishing long-term palaeoclimatic trends from variations in the sediment record (Anderson et al. 2000).

Holocene temperature and environmental reconstruction from lake sediments in the Søndre Strømfjord region, southern West Greenland

Instrumental temperature records indicate that the mean annual surface-air temperature of the Earth has risen approximately 0.6°C since 1860 (IPCC 2001). Increased global warming can have considerable influence at high latitudes, and among the major concerns are the effects on the sensitive arctic ecosystems and the possible reduction in the diversity of regional flora and fauna. Arctic organisms are highly adapted to extreme environmental conditions and have difficulties coping with any additional stresses or disturbances.