Nutrient dynamics in ecosystems under sulphur deficient scenarios For clearcut forest, meadow and recultivated systems

Sulphur (S) is an essential element for plant growth, and S availability plays a key role in crop yield and quality in soil. Its global significance has been highlighted under soil S deficiency scenarios. However, soil S cycling and its stoichiometric relationships with other elements, e.g., carbon (C), nitrogen N (N) and phosphorus (P) are still poorly under-documented in many ecosystems. Therefore, we mainly focused on the spatial-temporal response of S dynamics in concurrence with that of C, N, and P to anthropogenic disturbances in three different ecosystems. Specifically, we explored sulphate and DOC dynamics in stream water of a deforested catchment (Wüestebach, Germany) using wavelet transform coherence analysis (Chapter 2). Based on novel isotope approaches, we quantified the microbial depletion of S-containing amino acids in recultivated agricultural soils (Inden, Germany; Chapter 3) and in a grassland meadow (Rengen, Germany; Chapter 4 and 5). Our results emphasise the significance of soil S for ecosystem functioning. It is particularly striking for the European cultivated systems with low S input and other ecosystems susceptible to S deficiency (Chapter 3). It also highlighted the importance of other nutrients for S cycling, specifically the novel finding of the importance of P availability to S cycling in N-saturated grassland (Chapter 4 and 5). In conclusion, our work reconfirmed the key role of S for plants and addressed knowledge gaps (i.e. anthropogenic disturbance, organic S decomposition, stoichiometric elemental relationship) within crucial ecosystems, thereby enriching our comprehension of the global S cycle.