Climate change may improve forest ecosystem’s capacity to retain excessive airborne Nitrogen

From the article: Historic nitrogen deposition determines future climate change effects on nitrogen retention in temperate forests.

Dirnböck, T., Foldal, C., Djukic, I., Kobler, J., Haas, E., Kiese, R., Kitzler, B. 2017. Historic nitrogen deposition determines future climate change effects on nitrogen retention in temperate forests. Climatic Change 144(2): 221-235. doi:10.1007/s10584-017-2024-y.

The intensively studied long-term monitoring plot at LTER Zöbelboden was used in this modelling study.

Too much Nitrogen emission from industrial activities, traffic, and agriculture is negatively impacting terrestrial ecosystems. Deposition of Nitrogen has caused increased nitrate leaching to the groundwater and gaseous Nitrogen efflux from the soils acting as greenhouse gases. We have a quite well-established knowledge about these effects but we do not know how ecosystems may react to Nitrogen deposition when climate is also changing. Yet, a variety of factors affecting Nitrogen cycling in terrestrial ecosystems are highly sensitive to temperature and soil moisture variations. Here, we evaluated the effect of future changes in climate and N deposition on ecosystem Nitrogen cycling using the model LandscapeDNDC forced with historical data from eight long-term forest ecosystem monitoring stations in Austria and downscaled future Nitrogen deposition and climate scenarios. If emission reductions according to current legislation are implemented, Nitrogen deposition will decrease positively affecting ecosystem retention but warming will add to this positive effects. We found that every 1 °C of warming resulted in up to 2 kg less Nitrogen leaching per hectare and year. This increased Nitrogen retention mostly came from enhanced tree growth due to warming. Changes in gaseous Nitrogen efflux due to warming were much more variable with no clear effect. Although the forest sites were quite variable with regard to their soils and climate, the magnitude of N deposition in the past was by far the most important determinant of the degree of improvement in Nitrogen retention. We argue that trees exposed to higher but not too high N deposition in the past might be less prone to nutrient limitation in the future. Our study shows that climate change will likely retention in many European forest ecosystems, and even more so at forest sites with elevated past N deposition.

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