Although the Earth is accustomed to cycles of warmer and cooler periods, we human beings – and the human society as it is – do not have experience from any other climate than the one we currently have. Studying soil can help us estimate the magnitude of future changes in climate and provide tools to mitigate climate warming.
The ongoing climate warming raises concern and the world’s governments have agreed to limit the warming below 2 °C compared to pre-industrial levels. Yet, even this degree of warming is likely to have severe consequences for the living conditions on Earth. The temperatures and rainfall patterns are likely to change, extreme events are likely to become more frequent and the ocean surface is likely to rise. Some of these changes could alter processes in the Earth system that are essential for maintaining the current atmospheric composition. These include changes in the capacity of oceans and land areas to bind and release carbon dioxide and other greenhouse gases. If carbon release is stimulated more than the uptake of carbon, global warming becomes amplified – the phenomenon is referred to as the carbon–climate feedback. Yet, the magnitude of this feedback is extremely complicated to model and current predictions contain large variation. This is reflected on government policies, since the magnitude of nature’s feedback determines the amount of feasible anthropogenic emissions. Therefore, there is a crucial need for better understanding of the controls of natural carbon cycle. This would improve predictions of the future carbon cycle and reduce the risk of irreversible feedbacks.
Changes in subarctic soil carbon reservoirs are of global interest
My research delves into the controls of climate feedbacks in subarctic areas. In these areas, the cold and wet conditions have limited the activity of the bacteria and fungi inhabiting the soils and therefore, decomposition rates have been slower than the fixation of carbon by plants. Within the past centuries or even millennia, this has resulted in the accumulation of dead plant tissue – and thus carbon – to soils. The accumulation of carbon may change now that temperatures in high latitudes are rising at a particularly fast pace: In warmer soils, fungi and bacteria can increase their activity and thereby accelerate the release of carbon to the atmosphere. However, microbial activity is not the only control of changes in soil carbon, as there are many chemical and physical processes controlling the stability and carbon storage of soils – and these also interact with each other. Additionally, soil carbon cycling is tightly coupled with the life on top of the soil. Plants determine the amount and quality of dead material entering soils and their root growth and water intake physically alter soil environment. Moreover, plants may release a variety of beneficial or toxic compounds either directly to the soil or to the root-inhabiting fungi – and thereby interfere with soil carbon cycling.
The central role of plants in controlling processes below the soil surface indicate that aboveground changes matter for soil carbon cycling and for the net release of carbon. These include northward shifts of plants, the occurrence of invasive species, changes in fire frequency and altered land use. An improved understanding on the consequences of these would not only improve predictions of the climate feedback, but it could also be used to guide land use decisions to aim at carbon friendliness.
Also animals shape carbon cycling
In my PhD project that was done jointly for the University of Oulu and the University of Lapland, me and my collaborators studied the role of aboveground animals in shaping subarctic carbon storage and its feedbacks to warming. The studies were focused on the effects of reindeer grazing, the most common large animal in Scandinavia and across the Arctic. As reindeer selectively feed on plants, trample and bring nutrients in the form of faeces, they can alter the occurrence of plant species and induce drastic changes in tundra landscape. The reindeer effect on vegetation can be seen when driving or hiking in Lapland, where fences create straight lines in the landscape due to the vegetation differences between the two sides of the fence. In our newest publication, we show that the reindeer impact on vegetation can be reflected on the amount of carbon stored in soil (Ylänne, H., Olofsson, J., Oksanen, L. & Stark, S.: “Consequences of grazer-induced vegetation transitions on ecosystem carbon storage in the tundra”, in press in Functional Ecology. A summary of the findings can be read here). This gives reason to doubt that the areas could also differ in their response to warmer temperatures. Yet, the current climate change models do not account for such animal effect on the carbon cycle projections. Me and my colleagues believe that animals could be the missing link towards a more comprehensive understanding of carbon cycle and its responses to climate change – and that there are several, animal-mediated links waiting to be discovered in the Arctic.
Last updated: 14.12.2017