Based on a six year long experiment, a team of researchers from the Federal Institute for Forest, Snow and Landscape Research (WSL) has concluded that climate warming will alter the composition of the fungal community in the soil, especially in colder locations like at the tree line. As a consequence, nutrient cycles in the ecosystem are likely to change.
If climate change leads to warmer temperatures, the soil will get warmer too – which will affect the fungal community. WSL researchers conducted a six-year long experiment at the Stillberg research site in Davos (Canton of Graubünden) to determine how fungi will be affected. They laid heating cables on the soil surface under larch and mountain pine forests at a total of 20 test plots at the tree line, which enabled them to heat the uppermost organic soil layer by 4°C – equivalent to the expected warming in 2070.
DNA analysis of soil samples and monitoring of the fungi's fruiting bodies revealed that warming has altered the species composition of fungi. One species of fungus, the larch waxy cap (Hygrophorus speciosus Peck), almost completely disappeared, while some other species appeared to benefit from the warming, like the rufous milkcap (Lactarius rufus) and the milking bonnet (Mycena galopus): they became more abundant. Researchers observed no changes in the fungi on the 20 control sites that were not artificially warmed.
The changes in the fungal community are most likely related to an increase in available nitrogen associated with higher temperatures, rather than to the higher temperatures themselves. Soil warming led to an increased microbial activity which in turn enhanced the decomposition of humus and released twice as much nitrogen as at the unheated sites. This change promoted the abundance of nitrogen-favouring fungi like the rufous milkcap. The speed at which the soil conditions changed took the researchers by surprise. "We did not expect warming to have such a marked effect on the fungal community in such a relatively short time," says Frank Hagedorn, WSL geoecologist and leader of the study. "Our results show that fungi are extremely sensitive to changes in the environment."
The changes were more pronounced in soils under larches than in soils under mountain pines. There are two reasons for this: on the one hand, each tree species has its own fungal community, while on the other hand, the composition of organic soil material under larches and pines is different too.
The results indicate that a further, climate-change-induced rise in temperatures is likely to alter soil processes and nutrient cycling. This is especially true for cold locations, like at the tree line, where trees experienced a low nitrogen availability so far. Rising temperatures, however, will also dry the soil, so while there will be more nitrogen for plants, fungi and soil organisms, there will also be less water. This, too, will change the interactions between trees, fungi and the soil.
The Stillberg research site near Davos (GR) is one of the best-studied test sites run by the Federal Institute for Forest, Snow and Landscape Research (WSL). The sloped site was systematically planted with Swiss stone pines, mountain pines and larches in 1975 and has been providing information about the long-term effects of various environmental factors at the alpine tree line ever since. Besides, for a number of years now, researchers have been heating individual trees and exposing them to higher concentrations of CO2. As such, the Stillberg site is increasingly becoming a testing ground for answering questions about climate change.