Atmospheric Deposition Outweighs Dryness in Regulating European Ecosystem Productivity

Ecosystem productivity across Europe is often assumed to be constrained primarily by water limitation in recent decades. Yet the influence of atmospheric deposition remains poorly quantified, even as Europe experiences the world’s fastest decline in nitrogen (N) and sulfur (S) inputs. Here we combine satellite-derived gross primary productivity (GPP) from a SIF-based product with gridded N and S deposition from EMEP and hydroclimate constraints represented by atmospheric dryness (vapor pressure deficit, VPD) and soil dryness (soil water potential, ψsoil) for 2000–2023. We assess how these drivers shape two functional components of productivity: maximum carbon uptake capacity (GPPmax) and the carbon uptake period (CUP). To disentangle the relative influence of deposition versus dryness, we use XGBoost to model spatiotemporal variability in GPPmax and CUP and identify the dominant controlling factor at both ecosystem and pixel scales. Across large parts of Europe, deposition emerges as a more spatially extensive and stronger influence on GPPmax and CUP than recent changes in VPD or ψsoil. Declining N deposition is consistently associated with reductions in GPPmax and a shorter CUP, indicating a shift towards stronger nutrient limitation. In contrast, declining S deposition is generally linked to increases in both metrics, consistent with ecosystem recovery from historical acidification. Dryness effects are more geographically confined, although VPD remains a strong functional constraint for most ecosystem types. Overall, our results suggest that changes in atmospheric nutrient supply can outweigh the influence of hydroclimate in shaping recent patterns of European ecosystem carbon uptake, with implications for projecting productivity as deposition regimes continue to evolve. Our study provides an early insight into how declining nutrient inputs may impact future productivity, as similar transitions emerge elsewhere.