A warmer climate gives more carbon in forest soils

During a period of 20 years, SLU researchers have placed litterbags containing Scots pine needles in coniferous forests throughout Sweden. The results indicate that litter formed in southern Sweden become more recalcitrant to decomposition in the third year.

One explanation may be that the nitrogen deposition is higher in southern Sweden. Nitrogen appears to stimulate decomposition in the early stages of the decomposition process and inhibits it in later stages. Another possibility is that a higher temperature generates more recalcitrant humus.

The researchers have also studied the potential for microbial decomposer activity in humus layers. Humus layer samples from northern Sweden showed the highest respiration, when measured in a standardised laboratory setting; the respiration steadily declining in samples from northern to southern Sweden (see figure below).

Map: Jakob Nisell/SLU. Figure: Ewa Bringmark/SLU and Lars Sonesten/SLU

Low respiration indicates a more recalcitrant litter. This slowed down litter decomposition may move northward, if the climate in northern Sweden becomes more like the climate in the southern parts of the country. In a warmer climate the coniferous forest will also produce more needles, which will also affects the amount of organic material on the ground and in the soil.