Vegetation and proximity to the river control amorphous silica storage in a riparian wetland (Biebrza National Park, Poland)

Wetlands can modify and control nutrient fluxes between terrestrial and aquatic ecosystems, yet little is known of their potential as biological buffers and sinks in the biogeochemical silica cycle. We investigated the storage of amorphous silica (ASi) in a central-European riparian wetland. The variation in storage of ASi in the soil of an undisturbed wetland was significantly controlled by two factors: dominance of sedges and grasses and distance to the river (combined R-2=78%). Highest ASi storage was found near the river and in sites with a dominance of grasses and sedges, plants which are well known to accumulate ASi. The management practice of mowing reduced the amount of variation attributed to both factors (R-2=51%). Although ASi concentrations in soils were low (between 0.1 and 1% of soil dry weight), ASi controlled the availability of dissolved silica (DSi) in the porewater, and thus potentially the exchange of DSi with the nearby river system through both diffusive and advective fluxes. A depth gradient in ASi concentrations, with lower ASi in the deeper layers, indicates dissolution. Our results show that storage and recycling of ASi in wetland ecosystems can differ significantly on small spatial scales. Human management interferes with the natural control mechanisms. Our study demonstrates that wetlands have the potential to modify the fluxes of both DSi and ASi along the land-ocean continuum and supports the hypothesis that wetlands are important ecosystems in the biogeochemical cycling of silica

Effects of mowing cessation and hydrology on plant trait distribution in natural fen meadows

Traditional grasslands are often of high conservation value, but depend on non-intensive management like mowing for their preservation. During the 20th century, traditional agricultural usage was either heavily intensified or abandoned due to socio-economic reasons. In Eastern Europe, land abandonment mainly took place in regions with qualitatively bad soils. This large scale land use change lead to secondary succession. In fens and fen meadows, this may lead to a decrease in species richness and a replacement of specialist species by more generalist ones. The main objective of the present study is to examine if and how mowing cessation interacts with hydrology in determining species and trait distribution in a fen meadow. In the Upper Course of the Biebrza National Park, Poland, we selected 15 sites along four transects, with plots in mown and abandoned parcels. In these plots we measured plant abundance, aboveground biomass and relative light intensity, while plant traits were selected from different trait databases. The relationship between these plot characteristics and the different traits was assessed using concordance analysis. Mowing cessation resulted in reduced moss cover and light availability, while vegetation height increased and higher litter deposition and tussock development were observed. This altered environment not only resulted in decreased species richness and evenness in abandoned plots but also caused shifts in plant trait distribution. Most of the significantly linked traits responded more strongly to mowing cessation than to the hydrologic gradient. Traits related to light competition, such as light requirements, plant height and shoot growth form, especially responded to mowing cessation. This stresses the importance of light competition as a major factor determining species and trait distribution in fen systems.

Effects of mowing cessation and hydrology on plant trait distribution in natural fen meadows

Traditional grasslands are often of high conservation value, but depend on non-intensive management like mowing for their preservation. During the 20th century, traditional agricultural usage was either heavily intensified or abandoned due to socio-economic reasons. In Eastern Europe, land abandonment mainly took place in regions with qualitatively bad soils. This large scale land use change lead to secondary succession. In fens and fen meadows, this may lead to a decrease in species richness and a replacement of specialist species by more generalist ones. The main objective of the present study is to examine if and how mowing cessation interacts with hydrology in determining species and trait distribution in a fen meadow. In the Upper Course of the Biebrza National Park, Poland, we selected 15 sites along four transects, with plots in mown and abandoned parcels. In these plots we measured plant abundance, aboveground biomass and relative light intensity, while plant traits were selected from different trait databases. The relationship between these plot characteristics and the different traits was assessed using concordance analysis. Mowing cessation resulted in reduced moss cover and light availability, while vegetation height increased and higher litter deposition and tussock development were observed. This altered environment not only resulted in decreased species richness and evenness in abandoned plots but also caused shifts in plant trait distribution. Most of the significantly linked traits responded more strongly to mowing cessation than to the hydrologic gradient. Traits related to light competition, such as light requirements, plant height and shoot growth form, especially responded to mowing cessation. This stresses the importance of light competition as a major factor determining species and trait distribution in fen systems