Abstract
BackgroundUnderstanding how grasslands are affected by a long-term increase in temperature is crucial to predict the future impact of global climate change on terrestrial ecosystems. Additionally, it is not clear how the effects of global warming on grassland productivity are going to be altered by increased N deposition and N addition.Methodology/Principal FindingsIn-situ canopy CO2 exchange rates were measured in a meadow steppe subjected to 4-year warming and nitrogen addition treatments. Warming treatment reduced net ecosystem CO2 exchange (NEE) and increased ecosystem respiration (ER); but had no significant impacts on gross ecosystem productivity (GEP). N addition increased NEE, ER and GEP. However, there were no significant interactions between N addition and warming. The variation of NEE during the four experimental years was correlated with soil water content, particularly during early spring, suggesting that water availability is a primary driver of carbon fluxes in the studied semi-arid grassland.Conclusion/SignificanceEcosystem carbon fluxes in grassland ecosystems are sensitive to warming and N addition. In the studied water-limited grassland, both warming and N addition influence ecosystem carbon fluxes by affecting water availability, which is the primary driver in many arid and semiarid ecosystems. It remains unknown to what extent the long-term N addition would affect the turn-over of soil organic matter and the C sink size of this grassland.
Highlights
Due to rising atmospheric concentrations of CO2 and other greenhouse gases, global mean air temperatures increased by
The specific questions we addressed in this study included: (1) to what extent do warming and N addition affect gross ecosystem productivity (GEP) and ecosystem respiration (ER) and (2) what are the interactive effects between warming and N addition on ecosystem carbon fluxes in the Songnen grassland?
Seasonal Variation in Ecosystem C Fluxes Temporal dynamics of net ecosystem CO2 exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP) during the vegetation growth period followed the seasonal patterns of air temperature in the four experimental years with higher values of CO2 exchange being observed in summer and lower values in both spring and autumn
Summary
Due to rising atmospheric concentrations of CO2 and other greenhouse gases, global mean air temperatures increased by
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