Interactions between SOM accumukation, nutrient availability, and plant diversity in lime-rich and lime-poor dune grassland succession

Effective management and conservation of grasslands of Grey dune ecosystems are of great importance for drinking water companies, since they are designated as target ecosystems by national (Programmatische Aanpak Stikstof) and European (Nature 2000) laws. Biodiversity of Grey dunes has severely declined in the last decades due to increased grass and shrub encroachment, which was accelerated by high atmospheric N deposition and concommitant accumulation of soil organic matter (SOM). However, it is still poorly understood how SOM accumulation influences plant production and biodiversity under different conditions of climate, atmospheric N deposition, and soil (e.g. lime-rich and lime-poor soils).
To improve our understandings on the mechanisms of biodiversity decline in Grey dune ecosystems, this study examined in lime-rich and lime-poor dry dune grassland ecosystems: 1) which factors influence turnover rates of soil carbon (C) and nitrogen (N), 2) which factors influence productivity and diversity of plant communities, and 3) how different processes of SOM turnover and plant growth influence the long-term development of soil and plant in dune succession. We combined field measurements in Amsterdamse Waterleidingduinen (AWD) (for the research aim 1 and 2) and modeling study of dune soil development (for the research aim 3). We selected 40 plots in AWD, including both lime-rich and lime-poor sites from four different successional stages, which were established in 2012 by the previous DPW project [Aggenbach et al., 2013]. The empirical study included measurements of soil and plant variables, as well as lab incubation experiments of the soils to determine process rates of SOM decomposition. For the modelling study, we modified the internationally-used SOM- hydrology-plant model, CENTURY, to include several important processes in Dutch Grey dune ecosystems. With this modified model, we simulated dune succession, starting from bare sand, using the historical data of atmospheric N deposition and climate. The model output was validated with the observed data in AWD.

Effectief beheer en herstel van droge duingraslanden is van groot belang voor duinwaterbedrijven in het kader van nationale maatregelen (Programmatische Aanpak Stikstof) en EU regelgeving (Natura 2000). De biodiversiteit van duingraslanden is in de afgelopen decennia flink afgenomen door vergrassing en struweelvorming, die werden versneld door de hoge stikstofdepositie en daarmee gepaard gaande accumulatie van organische stof. Om beter inzicht te krijgen in het mechanisme van de snelheid van organischestofaccumulatie en diens effecten op de biodiversiteit, onderzochten wij de factoren die invloed hebben op de mineralisatiesnelheid van koolstof en stikstof, en op de productiviteit en biodiversiteit van kalkrijke en kalkarme duingraslanden. Tevens bestudeerden wij de effecten van verschillende bodem-processen en biomassaproductie op de ontwikkeling van duinecosystemen op de lange termijn. Het onderzoek bestond uit veldmetingen en een modelstudie in de Amsterdamse Waterleidingduinen.