A 'natural laboratory' in Iceland to clarify long-term global change effects on carbon dynamics
24 November 2016
On 14 November 2016, Niki Leblans defended her joint PhD between the University of Antwerp and the Agricultural University of Iceland.
Surface temperatures are rising as a consequence of anthropogenic greenhouse gas (GHG) emissions, but projections remain highly uncertain. Solid knowledge on potent feedback mechanisms from ecosystems to the climate system is limited. A potentially powerful feedback mechanism is the warming-induced degradation of soil organic carbon (SOC), exacerbating the warming, as CO2 and CH4 (two GHG) are transferred to the atmosphere. In this context, high northern latitude ecosystems are particularly important, as they store high amounts of SOC and experience pronounced warming.
Interactions with other anthropogenic pressures potentially interfere with this mechanism. Recent observations show that increased atmospheric nitrogen (N) deposition stimulates productivity at high northern latitudes, leading to increased C uptake, thereby mitigating global warming. The future evolution of these two antagonistic processes is highly uncertain, due to the scarcity of empirical observations, especially on the long-term.
In her thesis, Niki Leblans (Global Change Ecology Centre, research group Plant and Vegetation Ecology) made use of natural gradients to quantify the long-term warming and N input effects on the C balance of subarctic grasslands. Long-term warming effects were studied in natural (geothermal) soil warming gradients (+0 to +20 °C) in southwest Iceland. Niki compared these results with observations in more recently warmed soils, to separate permanent (long-term) responses and short-term transient changes. Long-term N input effects were studied on islands with different age (i.e. N accumulation time: 50 years vs. 1600 years) and different N inputs from seabird guano.
Niki: “The main conclusion of my thesis is that future warming can transform subarctic grassland soils rapidly into large C sources. While enhanced N deposition indeed increases SOC storage rate, the latter process will not be sufficient to offset the warming-induced C losses.”