Woody plants constructing tundra soils

Abstract

26In tundra, woody plants are expanding towards higher latitudes and altitudes due to increasingly 27 favourable climatic conditions. Their expansion may also occur through increases in the coverage 28 and height of the plants. These shifts may cascade further across the ecosystem, such as in the 29 foundations of tundra: that is, in the soils. Yet, little is known about the effects woody plants have 30 on local soil conditions. Here, we examined if the coverage and height of woody plants affect the 31 growing-season soil moisture and temperature as well as soil organic carbon stocks. We carried out 32 a field observation study in a dwarf shrub-dominated tundra and built a hierarchical model. We 33 found that, after controlling for other possible factors influencing woody plants and soil conditions 34 (namely, topography, snow, and the overall plant coverage), the coverage of woody plants inversely 35 correlated with all three soil conditions. Yet, we found no link between the woody plant height to 36 the soil variables. This indicates that woody plants affect local soil conditions in various ways, 37 depending upon whether their expansion occurs though the growth of coverage or their height. 38Nevertheless, woody plants likely alter the very ground of the entire tundra system and feedback 39 into the global climate system through the water, energy, and carbon cycles of tundra. 40

Long-term warming manipulations reveal complex decomposition responses across different tundra vegetation types

“…The shift in plant growth-form composition, where forbs and bryophytes are replaced by deciduous shrubs, has been reported, or hypothesized, to contribute to increased carbon storage through various processes (Cahoon et al 2012;Myers-Smith and Hik 2013). For instance, increased production of shrub litter that is more recalcitrant than herbaceous litter (Cornelissen et al 2007), and changes in soil microclimate by increased shading and insulation (decreasing summer soil temperature) (Kemppinen et al 2019) may contribute to slower decomposition and increased soil carbon storage. However, this does not seem to be the case in the Betula heath in our study, where mass loss of the more labile tea was accelerated within the warming treatments in spite of increased shading by shrubs and colder August soil temperature.…”

“…These changes in plant community composition have the potential to alter the ecosystem carbon balance and nutrient dynamics by shifting the litter composition (Cornelissen et al 2007), altering the soils' microclimate (Kemppinen et al 2019) or by influencing the soils' mycorrhizosphere composition through priming (Parker et al 2015). Structural changes, such as changes in moss layer depth, could also alter ecosystem dynamics since mosses regulate soil thermal and hydrological regimes (Gornall et al 2007(Gornall et al , 2009 and thus greatly influence microbial activity in soils.…”