TY - JOUR

T1 - Caught between draught and flooding on Oland's Great Alvar

AU - Sand-Jensen, Kaj

AU - Baastrup-Spohr, Lars

AU - Andersen, Mikkel Rene

AU - Christensen, Jesper Philip A.

AU - Alnoee, Anette Baisner

AU - Jespersen, Thomas Sand

AU - Riis, Tenna

AU - Bruun, Hans Henrik

PY - 2015

Y1 - 2015

N2 - The Great Alvar plain on the Swedish island of Öland is characterized by thin soils covering the hard limestone pavements. This results in widely fluctuating water levels between winter flooding and summer draught and strong hydrological gradients along small changes in elevation. The semi-natural grassland, the intermittent streams and the ponds are all strongly influenced by the fluctuating water levels and the extremely low phosphorus availability. These factors have selected for phototrophs with low metabolic rates and growth, and communities with low levels of photosynthesis and respiration. We here present some of the results of our recent studies. Plant species were distinctively distributed according to their characteristic plant traits along water gradients from ponds to dry alvar. High root porosity to ensure efficient oxygen transport was strongly selected for among species in wet soils, while small, thick leaves were strongly selected for on thin, dry soils. Overall, six plant traits could predict 66% of the variation in abundance of plant species in the communities along the gradient. The alvar streams had only modest biomasses during maximum development of benthic algae in May, and community photosynthesis was 5-10 times lower than corresponding levels in nutrient-rich streams in cultivated lowlands of Scandinavia. During June-September streams dried out and the re-establishment of flow in winter and spring led to an export of nutrients. Shallow ponds also dried out during summer and had low metabolic rates just like streams, while permanent ponds developed dense stands of charophytes, despite undetectable levels of N and P. Photosynthesis and community respiration were in approximate balance in permanent ponds. The maximum rates were comparable to those in eutrophic, phytoplankton-rich lakes.

AB - The Great Alvar plain on the Swedish island of Öland is characterized by thin soils covering the hard limestone pavements. This results in widely fluctuating water levels between winter flooding and summer draught and strong hydrological gradients along small changes in elevation. The semi-natural grassland, the intermittent streams and the ponds are all strongly influenced by the fluctuating water levels and the extremely low phosphorus availability. These factors have selected for phototrophs with low metabolic rates and growth, and communities with low levels of photosynthesis and respiration. We here present some of the results of our recent studies. Plant species were distinctively distributed according to their characteristic plant traits along water gradients from ponds to dry alvar. High root porosity to ensure efficient oxygen transport was strongly selected for among species in wet soils, while small, thick leaves were strongly selected for on thin, dry soils. Overall, six plant traits could predict 66% of the variation in abundance of plant species in the communities along the gradient. The alvar streams had only modest biomasses during maximum development of benthic algae in May, and community photosynthesis was 5-10 times lower than corresponding levels in nutrient-rich streams in cultivated lowlands of Scandinavia. During June-September streams dried out and the re-establishment of flow in winter and spring led to an export of nutrients. Shallow ponds also dried out during summer and had low metabolic rates just like streams, while permanent ponds developed dense stands of charophytes, despite undetectable levels of N and P. Photosynthesis and community respiration were in approximate balance in permanent ponds. The maximum rates were comparable to those in eutrophic, phytoplankton-rich lakes.

M3 - Journal article

VL - 109

JO - Svensk Botanisk Tidskrift

JF - Svensk Botanisk Tidskrift

SN - 0039-646X

IS - 1

ER -