Data from: Above and belowground responses of four tundra plant functional types to deep soil heating and surface soil fertilization

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 1) accelerated nutrient mobilization in the
surface soil layers, and 2) 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 belowground responses of four plant
functional types (grasses, sedges, deciduous shrubs and evergreen shrubs).
Seasonal thawing was accelerated with heating cables at ~15 cm depth
without warming the surface soil, whereas nutrient availability was
increased in the surface soil by adding slow-release NPK fertilizer at ~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 aboveground 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 aboveground biomass
of the two dwarf shrub functional types, which both had very shallow root
systems. Grasses showed the strongest response to fertilization, both
above and belowground. 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.

1.北极地区气候变暖速率高于全球平均水平。冻土带土壤的养分有效性预计将因气候变暖而提升，其途径包括：1）表层土壤养分活化加速；2）生长季解冻深度增加，从而提高深层土壤养分的可及性。这两个过程均可能引发冻土带植被组成的转变。理解这两个过程对冻土带植物功能型（plant functional types）的影响至关重要。
2.我们在东北西伯利亚冻土带研究站点调控土壤解冻深度与养分有效性，以探究其对四种植物功能型（禾草、莎草、落叶灌木及常绿灌木）地上及地下响应的影响。季节性解冻通过埋置于约15 cm深度的加热电缆加速，同时避免加热表层土壤；而养分有效性则通过在约5 cm深度施加缓释NPK肥料来提高。此外，还设置了两种处理的组合。本研究是首个专门针对冻土带生态系统中解冻加速效应开展的田间试验。
3.深层土壤加热显著增加了莎草的地上生物量——莎草是本研究中根系最深的植物功能型——但对其他植物功能型的生物量无显著影响。相反，施肥处理提高了两种矮灌木功能型的地上生物量，这两种灌木均具有极浅的根系。禾草对施肥的响应最为强烈，涵盖地上与地下部分。禾草为深根植物，且在垂直根分布方面表现出最高的根可塑性（root plasticity）：其根系分布会分别响应深层土壤加热与表层土壤施肥，向深层或表层土壤转移。
4.综合分析——本研究结果表明，解冻深度增加仅能使深根性莎草受益，而浅根性矮灌木及根系适应性强的禾草则可利用上层土壤养分有效性的提升。结果提示，禾草具有最高的根可塑性，这使其在快速变化的环境中更具竞争优势。我们得出结论：根系垂直分布策略是北极冻土带植被响应气候诱导型土壤养分有效性提升的关键因素，未来植被组成的转变将取决于解冻深度变化与表层土壤养分有效性变化之间的平衡。