Fens represent a large array of ecosystem services, including the highest biodiversity found among wetlands, hydrological services, water purification and carbon sequestration. Land-use change and drainage has severely damaged or annihilated these services in many parts of North America and Europe; restoration plans are urgently needed at the landscape level. We review the major constraints on the restoration of rich fens and fen water bodies in agricultural areas in Europe and disturbed landscapes in North America: (i) habitat quality problems: drought, eutrophication, acidification, and toxicity, and (ii) recolonization problems: species pools, ecosystem fragmentation and connectivity, genetic variability, and invasive species; and here provide possible solutions. We discuss both positive and negative consequences of restoration measures, and their causes. The restoration of wetland ecosystem functioning and services has, for a long time, been based on a trial-and-error approach. By presenting research and practice on the restoration of rich fen ecosystems within agricultural areas, we demonstrate the importance of biogeochemical and ecological knowledge at different spatial scales for the management and restoration of biodiversity, water quality, carbon sequestration and other ecosystem services, especially in a changing climate. We define target processes that enable scientists, nature managers, water managers and policy makers to choose between different measures and to predict restoration prospects for different types of deteriorated fens and their starting conditions.

1 A survey of plant and soil parameters was carried out in dry dune grasslands along the Dutch coast in the lime‐ and iron‐poor Wadden district and initially lime‐ and iron‐rich Renodunaal district, in order to detect differences in nutrient availability related to soil characteristics and potential sensitivity to atmospheric deposition of nitrogen. 2 Plant biomass and phosphorus pools in the shoot were higher in the Wadden district. The low foliar nitrogen concentrations and nitrogen/phosphorus ratios in the Wadden district suggested nitrogen‐limitation, while in the Renodunaal district there appeared to be a balanced supply of both nitrogen and phosphorus. 3 Soil pH, soil organic matter, soil nitrogen and phosphorus concentrations and total amounts were generally higher in the Renodunaal district. In both districts mineral phosphorus decreased with acidification and phosphorus oxalate (iron and aluminium bound) increased. 4 In the Wadden district iron is present primarily in iron–organic matter complexes, which leads to reversible binding of phosphorus. In the Renodunaal district large amounts of iron (hydr)oxides occur and at high pH may contribute to reversible phosphorus‐sorption, but at low pH this probably leads to immobilization of phosphorus. 5 While pools of soil phosphorus are low in the Wadden district, the phosphorus availability may be relatively high due to the comparatively loose nature of phosphorus‐sorption. As a result the area may be nitrogen‐limited and grass‐encroachment may thus have resulted from atmospheric deposition of nitrogen. 6 In the Renodunaal district, atmospheric deposition probably only accelerates grass‐encroachment, because deposition of acid and nitrogen increases the availability of both nitrogen and phosphorus and maintains the ‘co‐limitation’.

Respiratory energy costs for the maintenance of biomass, for growth and for ion uptake in roots of Carex diandra and Carex acutiformis. -Physiol. Plant. 72: 483491.The respiratory characteristics of the roots of Carex diandra Schrank and Carex acutiformis Ehrh. were investigated. The aims were, firstly to determine the respiratory energy costs for the maintenance of root biomass, for root growth and for ion uptake, and secondly to explain the higher rate of root respiration and ATP production in C. diandra. The three respiratory energy components were derived from a multiple regression analysis, using the relative growth rate and the net rate of nitrate uptake as independent variables and the rate of ATP production as a dependent variable. Although the rate of root respiration and ATP production was significantly higher in C. diandra than in C. acutiformis, the two species showed no significant difference in their rate of ATP production for the maintenance of biomass, in the respiratory energy coefficient for growth (the amount of ATP production per unit of biomass produced) and the respiratory energy coefficient for ion uptake (amount of ATP production per unit of ions absorbed). It is concluded that the higher rate of root respiration of C. diandra is caused by a higher rate of nitrate uptake. At relatively high rates of growth and nitrate uptake, the contribution of the rate of ATP production for ion uptake to the total rate of ATP production amounted to 38 and 25% for C. diandra and C. acutiformis, respectively. At this growth rate, the respiratory energy production for growth contributed 37 and 50%, respectively, to the total rate of ATP production. The relative contribution of the rate of ATP production for the maintenance of biomass increased from 25 to 70% with increasing plant age for both species. The results suggest that ion uptake is one of the major sinks for respiratory energy in roots. These experimentally derived values for the rate of ATP production for the maintenance of biomass, the respiratory energy coefficient for growth and the respiratory energy coefficient for ion uptake are discussed in relation to other experimentally and theoretically derived values. A. van der werf (corresponding author) et al.,

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Summary 1Measurements of above-ground productivity, plant nutrient levels, in situ mineralization and litter decomposition in four localities differing in soil chemical conditions were used to assess the availability of N and P in Dutch coastal dune grasslands. 2 P-availability is regulated by soil chemical conditions and seems to be a key factor regulating biomass production, whereas N-availability seems to be determined by litter input from this biomass, and thus indirectly controlled by P. 3 Contrary to expectation, N-availability is much higher in acid soils (with low rates of decomposition and high soil C : N ratios) than in calcareous soils (with high decomposition and low C : N ratios). Similar results have been reported from other ecosystems and may be due to a lower microbial N-demand at low rates of decomposition, increasing the amount of N left over for the vegetation. 4 In contrast to 'conventional wisdom', low-degradable litter may be a good plant strategy to improve the ecosystem recycling of nutrients and increase their availability. This may at least partly explain the success of Ammophila arenaria in lime-and iron-poor dunes.