Abstract
AimTo further unravel P availability in mineral-rich fens, and test whether high Fe in the soil would lead to low P availability to the vegetation.MethodsMesotrophic fens were selected over gradients in Ca and Fe in central Sweden and the Netherlands, to study characteristics of vegetation, pore water and peat soil, including inorganic and organic forms of P, Fe and Al.ResultsSoil Fe was more important than region or soil Ca, and P availability to the vegetation increased from Fe-poor to Fe-rich fens. Contrary to expectations, precipitation of iron phosphates played a minor role in Fe-rich fens. Fe-rich fens were P-rich for three reasons: (1) high P sorption capacity, (2) relatively weak sorption to Fe-OM complexes and (3) high amounts of sorbed organic P, which probably consists of labile P. Also, nonmycorrhizal wetland plants probably especially take up weakly sorbed (organic) P. However, high P did not lead to high biomass or low plant diversity. Fe-rich fens were limited by other nutrients, and high P may help protect the vegetation against Fe-toxicity.ConclusionsFe-poor fens are P-poor, irrespective of Ca, and Fe-rich fens P-rich even under mesotrophic conditions. However, high P itself does not endanger Fe-rich fens.
Highlights
Mineral-rich fens are important habitats for biodiversity
Mineral-rich fens belong to protected EU-habitat types such as Transition mires (H7140), Alkaline fens (H7230) and Molinia meadows on calcareous, peaty or clayey-silt laden soil (H6410), but they have undergone a serious decline in Europe
Selection of the sites was based on the presence of bryophytes such as Calliergon giganteum (Schimp.) Kindb., Scorpidium scorpioides (Hedw.) Limpr., S. cossonii (Schimp.) Hedenäs and Hamatocaulis vernicosus (Mitt.) Hedenäs, which are characteristic for mesotrophic fens, and occur over a range of Ca-rich to Fe-rich habitats (Mettrop et al 2018)
Summary
Mineral-rich fens are important habitats for biodiversity. They are rich in spectacular and strictly restricted plant species (European Union 2013), and home to the EUhabitat directive species such as Hamatocaulis vernicosus and Liparis loeselii. Apart from habitat destruction and drainage, mineral-rich fens are threatened by eutrophication and acidification (Lamers et al 2015). They are often fed by groundwater, and can be Ca-rich and/or Fe-rich, depending on geological substrate, hydrology and water chemistry. Nutrient availability in mineral-rich fens has been studied rather extensively in the past (e.g., Boyer and Wheeler 1989; Verhoeven et al 1990; Snowden and Wheeler 1993, 1995; Wassen et al 2005; Kooijman and Paulissen 2006). Recent studies have provided controversial insights, especially related to availability of P in Fe-rich fens (Zak et al 2008; Aggenbach et al 2013; Pawlikowski et al 2013; Cusell et al 2014; van der Grift et al 2016; Emsens et al 2017)
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