Abstract
AbstractSoil organic matter (SOM) and pH are key ecosystem drivers, influencing resilience to environmental change. We tested the separate effects of pH and SOM on nutrient availability, plant strategies, and soil community composition in calcareous and acidic Grey dunes (H2130) with low, intermediate, and/or high SOM, which differ in sensitivity to high atmospheric N deposition. Soil organic matter was mainly important for biomass parameters of plants, microbes, and soil animals, and for microarthropod diversity and network complexity. However, differences in pH led to fundamental differences in P availability and plant strategies, which overruled the normal soil community patterns, and influenced resilience to N deposition. In calcareous dunes with low grass‐encroachment, P availability was low despite high amounts of inorganic P, due to low solubility of calcium phosphates and strong P sorption to Fe oxides at high pH. Calcareous dunes were dominated by low‐competitive arbuscular mycorrhizal (AM) plants, which profit from mycorrhiza especially at low P. In acidic dunes with high grass‐encroachment, P availability increased as calcium phosphates dissolved and P sorption weakened with the shift from Fe oxides to Fe‐OM complexes. Weakly sorbed and colloidal P increased, and at least part of the sorbed P was organic. Acidic dunes were dominated by nonmycorrhizal (NM) plants, which increase P uptake through exudation of carboxylates and phosphatase enzymes, which release weakly sorbed P, and disintegrate labile organic P. The shifts in P availability and plant strategies also changed the soil community. Contrary to expectations, the bacterial pathway was more important in acidic than in calcareous dunes, possibly due to exudation of carboxylates and phosphatases by NM plants, which serve as bacterial food resource. Also, the fungal AM pathway was enhanced in calcareous dunes, and fungal feeders more abundant, due to the presence of AM fungi. The changes in soil communities in turn reduced expected differences in N cycling between calcareous and acidic dunes. Our results show that SOM and pH are important, but separate ecosystem drivers in Grey dunes. Differences in resilience to N deposition are mainly due to pH effects on P availability and plant strategies, which in turn overruled soil community patterns.
Highlights
Soil organic matter (SOM) and pH are major ecosystem drivers that influence soil communities, plant-available nutrients, and vegetation in many ways (Ellenberg et al 1974, Swift et al 1979)
The results were surprising and showed that SOM mainly influenced biomass parameters, but that pH led to fundamental differences in P nutrition and plant mycorrhizal strategies, which in turn overruled the normal patterns in soil community composition and N cycling
The results demonstrate that differences in pH in sandy coastal dunes of the temperate zone lead to fundamental changes in plant strategies, from arbuscular mycorrhizal (AM) plants in calcareous to NM plants in acidic dunes
Summary
Soil organic matter (SOM) and pH are major ecosystem drivers that influence soil communities, plant-available nutrients, and vegetation in many ways (Ellenberg et al 1974, Swift et al 1979). Older dunes with acidic topsoils alternate with younger calcareous dunes, both consisting of mosaics of low and high SOM, due to differences in eolian activity (Aggenbach et al 2017). PH and SOM are important to Grey dunes because different dune zones respond in a different way to high atmospheric N deposition (Bobbink et al 2010, Kooijman et al 2017). Grass-encroachment, that is, the dominance of tall graminoid species and associated loss of plant diversity, is generally higher in acidic than in calcareous Grey dunes, and more pronounced on soils with high than with low SOM (Fig. 1; Remke et al 2009a, b, Kooijman et al 2017)
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