Methodology:

Gathering and processing of species composition and foliar nutrient concentration data is described in doi/10.1111/nph.13265/full

Gathering and processing of data for nutrient and carbon stocks in vegetation and soil were as follows:

Two plant/soil turves (10 x 5 cm, to below the organic horizon) were collected from each plot; the location of each turf was randomly selected to capture small scale within-plot variability. The depth of the moss (green and brown intact moss tissue) and soil organic layers were measured on each side of each turf in the field. The interface between intact mosses (green and brown parts) and the soil organic horizon was well-defined. Turfs were stored at 4 °C and within one week were sorted into aboveground vascular plant biomass, green moss, litter (comprising the lower, brown part of the moss and a small amount of vascular plant litter), organic soil and mineral soil. Each fraction was immediately dried (70 °C, 48 h) and weighed. One 4.2 cm diameter soil core was also taken from each plot (after removing the moss layer) and the soil organic horizon and top 0-3 cm of the mineral horizon were separated and used to calculate bulk density. Mass and volume of stones, where they occurred (in c. 20 % of samples) were accounted for in bulk density measurements. Soil and litter samples, which were too large to mill in their entirety, were coarsely ground using a laboratory blender to ensure thorough mixing before being subsampled for fine milling. All material was steel ball milled (F.Kurt Retsch GMbH & Co. KG, MM200, Germany) prior to CN analysis (Carlo-Erba NA 1500 Series 2, USA) and total P determination by hydrogen peroxide/sulphuric acid digestion and Flow Injection Analysis (Technicon autoanalyser, Sterilin Instruments, Herts, UK). Total carbon stocks are reported for the vegetation and soil organic layers only. The depth of the mineral soil layer above frost-shattered parent material was extremely variable (range 2.8 - 10.0 cm), making treatment effects on total carbon stocks in mineral soils difficult to detect with the available replication (n = 5). We therefore only sampled the top 3 cm of the mineral horizon to quantify potential changes in soil carbon content and bulk density in the surface mineral layers.

Data collection:

Instrumentation:

Basic low-tech field equipment

Steel ball mill (F.Kurt Retsch GMbH & Co. KG, MM200, Germany

CN analyser (Carlo-Erba NA 1500 Series 2, USA)

Flow Injection Analyser (Technicon autoanalyser, Sterilin Instruments, Herts, UK)

Data quality:

Standard analytical laboratory quality control procedures followed (eg inclusion of appropriate blanks and standards at intervals throughout sample analysis runs).

No significant data losses or cleaning of data required.

Species composition, foliar nutrient concentrations and NDVI were measured for all treatments on both heath types. Other parameters were measured in control, phosphorus, high nitrogen and high nitrogen plus phosphorus plots only.