Ecosystems

Ecosystems are widely interconnected by spatial flows of material, but the overall importance of these flows relative to local ecosystem functioning remains unclear. Here we provide a quantitative synthesis on spatial flows of carbon connecting ecosystems worldwide. Cross-ecosystem flows range over eight orders of magnitude, bringing between 10⁻³ and 10⁵ gC m⁻² year⁻¹ to recipient ecosystems. Magnitudes are similar to local fluxes in freshwater and benthic ecosystems, but two to three orders of magnitude lower in terrestrial systems, demonstrating different dependencies on spatial flows among ecosystem types. The strong spatial couplings also indicate that ecosystems are vulnerable to alterations of cross-ecosystem flows. Thus, a reconsideration of ecosystem functioning, including a spatial perspective, is urgently needed.

Dissolution of Fe(III) (hydr)oxide minerals by siderophores(i.e., Fe-specific, biogenic ligands) is an important step in Fe acquisition inenvironments where Fe availability is low. The observed coexudation ofreductants and ligands has raised the question of how redox reactions mightaffect ligand-controlled (hydr)oxide dissolution and Fe acquisition. Weexamined this effect in batch dissolution experiments using two structurallydistinct ligands (desferrioxamine B (DFOB) and N,N′-di(2-hydroxybenzyl)-ethylene-diamine-N,N′-diacetic acid (HBED)) and four Fe(III) (hydr)oxideminerals (lepidocrocite, 2-line ferrihydrite, goethite and hematite) over anenvironmentally relevant pH range (4-8.5). The experiments were conductedunder anaerobic conditions with varying concentrations of (adsorbed) Fe(II) as the reductant. We observed a catalytic effect ofFe(II) on ligand-controlled dissolution even at submicromolar Fe(II) concentrations with up to a 13-fold increase in dissolutionrate. The effect was larger for HBED than for DFOB. It was observed for all four Fe(III) (hydr)oxide minerals, but it was mostpronounced for goethite in the presence of HBED. It was observed over the entire pH range with the largest effect at pH 7 and8.5, where Fe deficiency typically occurs. The occurrence of this catalytic effect over a range of environmentally relevantconditions and at very low Fe(II) concentrations suggests that redox-catalyzed, ligand-controlled dissolution may be significantin biological Fe acquisition and in redox transition zones.

Increasing demand for food is driving a worldwidetrend of agricultural input intensification. However, there is nocomprehensive knowledge about the interrelations betweenpotential yield gains and environmental trade-offs that wouldenable the identification of regions where input-driven intensificationcould achieve higher yields, yet with minimal environmentalimpacts. We explore ways of enhancing global yields, while avoidingsignificant nitrogen (N) emissions (N_e) by exploring a range of Nand irrigation management scenarios. The simulated responses ofyields and N_e to increased N inputs (N_in) and irrigation show highspatial variations due to differences in current agricultural inputsand agro-climatic conditions. Nitrogen use efficiency (NUE) ofyield gains is negatively correlated with incremental N_e due to N_in additions. Avoiding further intensification in regions wherehigh fractions of climatic yield potentials, ≥ 80%, are already achieved is key to maintain good NUE. Depending on theintensification scenarios, relative increases in N_e could be reduced by 0.3−29.6% of the baseline N_e with this intensificationstrategy as compared to indiscriminate further intensification, at the cost of a loss of yield increases by 0.2−16.7% of the baselineyields. In addition, irrigation water requirements and N_in would dramatically decrease by considering this intensificationstrategy.

Hydrological variables are among the most influential when analyzing or modeling stream ecosystems.However, available hydrological data are often limited in their spatiotemporal scale and resolution for usein ecological applications such as predictive modeling of species distributions. To overcome this limitation, aregression model was applied to a 1 km gridded stream network of Germany to obtain estimated dailystream flow data (m³ s⁻¹) spanning 64 years (1950–2013). The data are used as input to calculatehydrological indices characterizing stream flow regimes. Both temporal and spatial validations wereperformed. In addition, GLMs using both the calculated and observed hydrological indices were compared,suggesting that the predicted flow data are adequate for use in predictive ecological models. Accordingly,we provide estimated stream flow as well as a set of 53 hydrological metrics at 1 km grid for the streamnetwork of Germany. In addition, we provide an R script where the presented methodology is implemented,that uses globally available data and can be directly applied to any other geographical region.

Fertilization, crop uptake followed by plant harvest, runoff and erosion, and transformations ofphosphorus (P) in soil are the major factors influencing the P balance of croplands. It is important to integrateplant-soil-management interactions into consistent modeling systems to determine the effect of Pfertilization conditions on yields and to quantify P losses. Previous assessment of P losses on large scales didnot consider the interactions among these factors. Here we applied a grid-based crop model to estimateglobal P losses from three most produced crops: maize, rice, and wheat. The model was forced by detailed Pinput data sets over the period 1998–2002. According to our simulations, global P losses from the threecrops reached 1.2 Tg P/year, and about 44% of it was due to soil erosion. The global total P losses weredominated by contributions from a few hot spot regions. Reducing P fertilizer in regions experiencingexcessive P uses and hence losses, especially in China and India, could achieve the same yields as today andsave about two thirds of global total P inputs, with the cobenefits of declining global total P losses by 41%and downstream water quality improvement. Reducing soil erosion and retaining more crop residues oncroplands could further save P inputs and alleviate P losses. This study is of significance to determine themajor factors influencing P balance across regions of the world and help policy makers to propose efficientstrategies for tackling P-driven environmental problems.