Long-term low-level nutrient additions significantly impact a low arctic mesic tundra plant community, but species responses differ from high-level fertilization: Implications for predicting climate warming impacts
Data files
Dec 19, 2025 version files 194.98 KB
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ActiveLayerDepths_DaringLake_LNLP_ArcticScience2025.xlsx
10.43 KB
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Biomass_DaringLake_LNLP_ArcticScience2025.xlsx
15.32 KB
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BirchMeasurements_DaringLake_LNLP_ArcticScience2025.xlsx
134.68 KB
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README_(Arctic_Science_2025).docx
16.50 KB
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README.md
6.03 KB
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SoilMeasures_DaringLake_LNLP_ArcticScience2025.xlsx
12.01 KB
Abstract
Arctic climate warming is expected to enhance the soil’s supply of growth-limiting nutrients, resulting in changes in plant community composition. Much of our understanding of nutrient influences on tundra plants is derived from experiments with very high levels of fertilization. Here, aboveground biomass of all species in a mesic birch hummock community, and shoot extension of Betula glandulosa, were measured in response to 11-19 years of factorial annual low-level nitrogen (N) and phosphorus (P) additions that simulate climatically realistic anticipated increases in soil fertility. Only the low N addition treatment had significant effects, enhancing the mosses and some infrequent vascular species’ biomass, reducing others, while the dominant shrubs were unaffected. Hence, overall community composition was altered, but in markedly different ways than classic high-level fertilization responses. By contrast, when measured in much larger sampling areas (9 m2), birch shrub new shoot extension was clearly stimulated by the separate low-level N and P additions, and even more so by their combination, indicating that its growth was NP co-limited. Overall, our results demonstrate that this tundra plant community is sensitive to low-level (climatically-realistic) increases in nutrient availability, and suggest that changes will be slow (multiple decades), and likely to favour species whose growth is primarily N-limited.
Dataset DOI: 10.5061/dryad.wstqjq310
Description of the data and file structure
Birch shoot length measurements
At the end of the 2022 growing season, we measured total shoot length and current year’s new shoot extension of all individual birch stems in centrally located 3 m x 3 m sampling areas within 3 replicates of each of the low N and low P factorial experimental plots at Daring Lake, NWT. For each birch individual ramet within the sampling area, the lengths of all stems arising from the soil surface and their associated branches were measured. Concurrently, any new shoot apical extension (i.e. current year’s primary growth) was identified and measured for each stem. Since a very considerable time was required to identify all Betula glandulosa individual ramets within each of the 3 m x 3 m plots, and then to measure all total and new shoot growth of each individual shoot and its branches, we were logistically restricted to measuring only three randomly selected plots from the five experimental replicates in each treatment.
Biomass sample collection
Aboveground plant biomass was harvested in 1 m x 1 m sampling areas of all five replicate plots of each treatment in the factorial low N x P experiment in late summer of 2023. For sorting, each live shoot of all vascular plants was followed down to the first adventitious root or where the shoot met the rhizome - whichever occurred first, at which point the shoot was clipped and sorted by species. Lichen pieces > 1 cm diameter were plucked from the top soil/moss surface and all lichen species were grouped together for biomass. For mosses, the green-brown boundary was used to differentiate above- from belowground growth, and all green moss tissue for all species was clipped and grouped together. Standing dead biomass of vascular species, leaf litter, and dead moss were discarded (i.e. not included in the sorted sample components). For birch, live leaves were separated from stems to separately quantify each component of aboveground biomass. Finally, all sorted biomass components were dried at 65 °C in a fan-assisted oven for ~7 days and weighed immediately afterwards.
Soil measurements
We returned to the site to measure multiple soil variables in the treatment plots a year later (August 25th, 2024) at points directly adjacent to each plot’s harvested area that were covered by comparable intact vegetation to the harvested community. The active layer (i.e. late August soil thaw depth) was measured 15 cm away from each of the four corners of the harvest area and averaged. Soil bulk density and late August gravimetric soil moisture content were determined by using a serrated breadknife to cut out a 20 cm x 20 cm block of soil that was carefully extracted to prevent disturbance of soil structure/volume. The density and soil moisture properties were then determined on carefully measured subsamples (~5 x ~5 x ~10 cm) cut from the outermost side of the main block (furthest from the harvested sample area) by measuring first the fresh weight, and then the dry weight after oven-drying samples at 65 °C for 5 days. Finally, the transition from organic to mineral soil was identified in the 20 cm x 20 cm excavated hole, and its depth from the soil surface (i.e. the green-brown transition in the moss layer) was measured to quantify the organic layer depth.
Files and variables:
File: BirchMeasurements_DaringLake_LNLP_ArcticScience2025.csv
Plot - unique numeric/letter plot identifier also denoting treatment
Treatment - C = Control, LN = low nitrogen addition, LP = low phosphorus addition, LNLP = low nitrogen and phosphorus addition
Birch Individual - code ascribed to birch individuals in a given plot
Shoot Length - Measurements of birch individuals’ shoot length and of all associated branches in cm
New Shoot Extension - Measurements of a birch individuals’ current year’s growth in cm
File: Biomass_DaringLake_LNLP_ArcticScience205
Plot - unique numeric/letter plot identifier also denoting treatment
Treatment - C = Control, LN = low nitrogen addition, LP = low phosphorus addition, LNLP = low nitrogen and phosphorus addition
Species - Species name or name of growth form
Biomass - Total dry weight of biomass from a given species in a given plot (g)
File: ActiveLayerDepths_DaringLake_LNLP_ArcticScience2025.csv
Plot - unique numeric/letter plot identifier also denoting treatment
Treatment - C = Control, LN = low nitrogen addition, LP = low phosphorus addition, LNLP = low nitrogen and phosphorus addition
Active Layer Depth - Measurements of active layer depth using a metal probe (cm)
File: SoilMeasures_DaringLake_LNLP_ArcticScience2025.csv
Plot - unique numeric/letter plot identifier also denoting treatment
Treatment - C = Control, LN = low nitrogen addition, LP = low phosphorus addition, LNLP = low nitrogen and phosphorus addition
active_layer_avg - the mean active layer depth across four measurements for a given plot (cm)
org_layer - soil depth at the transition from organic to mineral soil (cm)
soil_fresh_weight - weight of soil subsamples (5 x 5 x 10 cm) directly after harvest (g)
soil_dry_weight - weight of soil subsamples following oven drying (g)
bulk_density - mass of dry soil per unit volume (g/cm^3)
soil_moisture - gravimetric water content obtained by (fresh weight - dry weight) / dry weight x 100%
Data Files:
- ActiveLayerDepths_DaringLake_LNLP_ArcticScience2025.xlsx
- Biomass_DaringLake_LNLP_ArcticScience2025.xlsx
- BirchMeasurements_DaringLake_LNLP_ArcticScience2025.xlsx
- README_(Arctic_Science_2025).docx
- Description: a word file copy of this README.
- SoilMeasures_DaringLake_LNLP_ArcticScience2025.xlsx