Plant cover changes drive plant and soil carbon pool responses in High Arctic dry heath exposed to decades of experimentally increased summer rain and nutrient addition

With accelerating climate change, higher summer rainfall and warmer soils are expected for high Arctic ecosystems. Yet, how increased inputs of moisture and nutrients to soils will affect plant composition and ecosystem C storage in these arid, low-productivity ecosystems remains unclear. We utilised a long-term experiment in a dry shrub heath tundra in Zackenberg, NE Greenland, in which N and P availability was increased and precipitation doubled experimentally every summer for 25 years. We determined soil and vegetation C pools, plant cover and leaf chemistry, and ecosystem CO2 fluxes were measured over three weeks in peak growing season. Watering increased the cover of graminoids, which likely drove a moderate increase in upper soil carbon stocks. Soil respiration was consistently stimulated in watered plots, confirming the high sensitivity of soil microbes to moisture in dry tundra environments. As aboveground biomass and plant C uptake were not equivalently enhanced by watering, we..., Fieldwork was facilitated by the Zackenberg Ecological Research Operations station in July 2022. Plants and organic materials were collected and analysed in accordance with the non-exclusive licence G22-053 for utilization of Greenland genetic resources.
The experimental work was conducted in 2022 in the Zackenberg valley, NE Greenland (74°30’N, 21°00’ W).
The experiment consists of a fully factorial setup, with 48 plots of 0.5m × 0.5m dimensions in 6 blocks. To study the effects of increased summer precipitation and moderately increased nutrient availability, the full factorial block design includes 3 factors: Water (W), nitrogen (N) and phosphorus (P) additions, applied in all combinations within each block, hence with eight treatment combinations including controls in each block.
To analyse soil C pool changes >25 years after initiation of the experiment, four 10 cm-deep soil cores were taken from each of the 48 plots under the main vegetation types/species which were: Dryas,..., , # Data from: Plant cover changes drive plant and soil carbon pool responses in High Arctic dry heath exposed to decades of experimentally increased summer rain and nutrient addition

[https://doi.org/10.5061/dryad.95x69p8vm](https://doi.org/10.5061/dryad.95x69p8vm)

## Description of the data and file structure

Fieldwork was facilitated by the Zackenberg Ecological Research Operations station in July 2022. Plants and organic materials were collected and analysed in accordance with the non-exclusive licence G22-053 for utilization of Greenland genetic resources.

The experimental work was conducted in 2022 in the Zackenberg valley, NE Greenland (74°30’N, 21°00’ W).

The experiment consists of a fully factorial setup, with 48 plots of 0.5m × 0.5m dimensions in 6 blocks. To study the effects of increased summer precipitation and moderately increased nutrient availability, the full factorial block design includes 3 factors: Water (W), nitrogen (N) and phosphorus (P) additions, applied** **...,