ABSTRACT
New plant functions in the exchange of greenhouse gases between ecosystems and atmosphere have recently been discovered. We tested whether photosynthetic activity has an effect on N2O emission rates from incubated plant-soil systems.Two laboratory experiments were performed. One to unravel possible effect of photosynthetic activity on the net N2O ecosystem exchange for two species (beech and ash saplings). The other to account for possible effects from rhizosphere and aboveground plant parts separately (ash sapling only).Total N2O emissions from both plant and plant-soil systems were significantly lower under light than in darkness (31%-65%). The photosynthetic effect only applied to the aboveground plant parts.Underlying processes have now to be unraveled to improve our understanding of ecosystem functioning. This will improve modeling and budgeting of greenhouse gas exchanges between ecosystems and the atmosphere.
ABSTRACT
Salinization of surface waters is a global environmental issue that can pose a regional risk to freshwater organisms, potentially leading to high environmental and economic costs. Global environmental change including climate and land use change can increase the transport of ions into surface waters. We fit both multiple linear regression (LR) and random forest (RF) models on a large spatial dataset to predict Ca2+ (266 sites), Mg2+ (266 sites), and [Formula: see text] (357 sites) ion concentrations as well as electrical conductivity (EC-a proxy for total dissolved solids with 410 sites) in German running water bodies. Predictions in both types of models were driven by the major factors controlling salinity including geologic and soil properties, climate, vegetation and topography. The predictive power of the two types of models was very similar, with RF explaining 71-76% of the spatial variation in ion concentrations and LR explaining 70-75% of the variance. Mean squared errors for predictions were all smaller than 0.06. The factors most strongly associated with stream ion concentrations varied among models but rock chemistry and climate were the most dominant. The RF model was subsequently used to forecast the changes in EC that were likely to occur for the period of 2070 to 2100 in response to just climate change-i.e. no additional effects of other anthropogenic activities. The future forecasting shows approximately 10% and 15% increases in mean EC for representative concentration pathways 2.6 and 8.5 (RCP2.6 and RCP8.5) scenarios, respectively.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.
