The great decoupling: Evidence for a fundamental breakdown in terrestrial carbon-nitrogen cycles.

We provide information on the follwing: Article ID: A unique study ID First Author: The name of the first author Year (soil collected): Year of collection (whenever available) of the soil. This can differ from the publication year lat: latitude long: longitude: C mg/g: soil organic carbon N mg/g: soil total nitrogen δ13C: carbon stable isotope of soil δ15N: nitrogen stable isotope of soil Forest type: type of forest n: replication number pH: soil pH Data collection On September 20, 2024, we carried out a systematic literature search in the Web of Science Core Collection using the search string "(delta or 15N or 13C) and soil and forest". The initial search yielded 9917 non-review articles. We carried out the initial filtering based on titles and abstracts, which filtered out a total of 9499 articles. We subsequently checked the main text of the remaining articles, which resulted in a set of 236 papers that met our inclusion criteria (Fig. S1). Our inclusion criteria were that (a) at least one isotopic value (δ¹³C or δ¹⁵N); (b) the observations were taken from forest mineral soils. Over the literature search phase, we preserved entries that only contained one of the two isotopes but for subsequent analyses we worked on the subset of entries for which we had both soil δ¹³C and δ¹⁵N values. For each selected paper, we extracted the following variables: the mean values and standard deviation of δ¹³C, δ¹⁵N, soil sample replicates (n), total nitrogen (TN), total carbon (TC), total phosphorus (TP), soil pH, sampling depth, geographic coordinates (latitude and longitude) of sampling locations, year of soil collection, forest succession stage (classified as primary forest, secondary forest, or plantation), forest type (categorized as evergreen broadleaf, deciduous broadleaf, coniferous forest or a mix of the above). Data were obtained directly from published tables or, when necessary, extracted from figures using PlotDigitizer (https://plotdigitizer.com). The forest type classification was based on either explicit descriptions or the dominant species of the forest. The forest succession stage was determined through textual information regarding: the presence of anthropogenic or natural disturbances, natural growth history, and evidence of management. We further extracted information, based on coordinates on the mean annual temperature and mean annual precipitation (WorldClim(Hijmans et al., 2005)), total, dry and wet deposition(Ackerman et al., 2018), aridity index and evaporotranspiration(Zomer et al., 2022) and Köppen climate(Beck et al., 2018).