NUTRIENT LIMITATIONS AND THEIR IMPLICATIONS ON THE EFFECTS OF ATMOSPHERIC DEPOSITION IN COASTAL DUNES - LIME-POOR AND LIME-RICH SITES IN THE NETHERLANDS

1 A survey of plant and soil parameters was carried out in dry dune gr asslands along the Dutch coast in the lime- and iron-poor Wadden distr ict and initially lime- and iron-rich Renodunaal district, in order to detect differences in nutrient availability related to soil character istics 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 sup ply of both nitrogen and phosphorus. 3 Soil pH, soil organic matter, s oil nitrogen and phosphorus concentrations and total amounts were gene rally higher in the Renodunaal district. In both districts mineral pho sphorus decreased with acidification and phosphorus oxalate (iron and aluminium bound) increased. 4 In the Wadden district iron is present p rimarily in iron-organic matter complexes, which leads to reversible b inding of phosphorus. In the Renodunaal district large amounts of iron (hydr)oxides occur and at high pH may contribute to reversible phosph orus-sorption, but at low pH this probably leads to immobilization of phosphorus. 5 While pools of soil phosphorus are low in the Wadden dis trict, the phosphorus availability may be relatively high due to the c omparatively 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'.