Background and AimsPrescribed burning is a widely used management technique, often employed to restore grasslands affected by woody plants encroachment. However, its interaction with pre-existing plant species in influencing soil properties remains unclear.MethodsWe conducted a diachronic soil survey to assess the evolution of several soil properties in the mid-term (up to 18 months) after burning, including physico-chemical parameters and microbial biomass carbon on soils under vegetation patches of different plant functional types and life forms. Vegetation patches included Ericaceae and legume shrubs, ferns, and biocrusts dominated by lichens. Soil samples were taken pre-burning, immediately after burning and 9 and 18 months after.ResultsOur findings indicate that while some soil properties returned to pre-burning levels in the mid-term (i. e., soil cations and NH4+), others, such as available phosphorous (P Olsen), exhibited a significant decline that persisted even 18 months later. Furthermore, soils under legumes initially displayed higher levels of soil carbon and nitrogen compared to other vegetation patches, but this distinction diminished over time. This was likely due to legumes' susceptibility to fire damage, in contrast to the greater resilience of Ericaceae shrubs.ConclusionOur study highlights the complex vegetation patch-dependent effects of prescribed burning on soil properties. While legumes initially enhance soil carbon and nitrogen, their contribution decreases over time due to fire sensitivity. Some soil parameters recover in the mid-term, but nutrients like available phosphorus continue to decline. Fire management strategies should consider plant diversity and recovery time to mitigate soil fertility loss.

1. Climate warming is faster in the Arctic than the global average. Nutrient availability in the tundra soil is expected to increase by climate warming through (i) accelerated nutrient mobilization in the surface soil layers, and (ii) increased thawing depths during the growing season which increases accessibility of nutrients in the deeper soil layers. Both processes may initiate shifts in tundra vegetation composition. It is important to understand the effects of these two processes on tundra plant functional types. 2. We manipulated soil thawing depth and nutrient availability at a Northeast-Siberian tundra site to investigate their effects on above- and below-ground responses of four plant functional types (grasses, sedges, deciduous shrubs and evergreen shrubs). Seasonal thawing was accelerated with heating cables at c. 15 cm depth without warming the surface soil, whereas nutrient availability was increased in the surface soil by adding slow-release NPK fertilizer at c. 5 cm depth. A combination of these two treatments was also included. This is the first field experiment specifically investigating the effects of accelerated thawing in tundra ecosystems. 3. Deep soil heating increased the above-ground biomass of sedges, the deepest rooted plant functional type in our study, but did not affect biomass of the other plant functional types. In contrast, fertilization increased above-ground biomass of the two dwarf shrub functional types, both of which had very shallow root systems. Grasses showed the strongest response to fertilization, both above-and below-ground. Grasses were deep-rooted, and they showed the highest plasticity in terms of vertical root distribution, as grass root distribution shifted to deep and surface soil in response to deep soil heating and surface soil fertilization respectively. 4. Synthesis. Our results indicate that increased thawing depth can only benefit deep-rooted sedges, while the shallow-rooted dwarf shrubs, as well as flexible-rooted grasses, take advantage of increased nutrient availability in the upper soil layers. Our results suggest that grasses have the highest root plasticity, which enables them to be more competitive in rapidly changing environments. We conclude that root vertical distribution strategies are important for vegetation responses to climate-induced increases in soil nutrient availability in Arctic tundra, and that future shifts in vegetation composition will depend on the balance between changes in thawing depth and nutrient availability in the surface soil.