Data from: Increased Soil Nitrogen Availability Suppresses Annual Soil Respiration in Mixed Temperate Forests Regardless of Acidification

In 2011, an experimental nitrogen x pH manipulation study was initiated in mixed temperate forests in central New York, USA to disentangle the often-confounded roles of nitrogen (N) and soil pH in driving various ecosystem processes. This data publication includes data from a study investigating how soil N availability and acidity affect soil respiration and its plant- and decomposer-driven component fluxes. The experiment includes three separate sites that each contain two co-located forest stand types: primary forests that were never cleared for agriculture and had limited harvest history; and secondary, post-agricultural forests that were approximately 90 years old at the beginning of the experiment. Experimental fertilizer additions were initiated in 2011 in three plots within each stand and paired with an unfertilized control (24 plots total). Plots are 40 m x 40 m for measurements, with an additional 10 m perimeter buffer treated to ensure fertilization of the majority of root systems of in-plot trees. Treatments consist of sodium nitrate (NaNO₃), ammonium sulfate ((NH₄)₂SO₄), and elemental sulfur (S), with N application rates of 50 kg N ha^-1 yr^-1 for both N treatments and S application rates of 54 kg S ha^-1 yr^-1 for both S treatments. Treatments were selected for their abilities to increase (NaNO₃) or decrease ((NH₄)₂SO₄, S) soil pH. Soil respiration data included in the data publication are: (1) measurements collected from five fixed collars per plot using a LI-COR 6400 Portable Photosynthesis System equipped with a 6400-09 soil chamber (LI-COR Biosciences, Lincoln, Nebraska, USA); and (2) plot-level annual soil respiration, estimated using the relationship between soil temperature and measured soil respiration. We measured soil respiration 5-6 times per plot during the snow-free season between October 2020 and October 2021, and annual fluxes are estimated for November 1, 2020 - October 31, 2021. The data publication also includes CO₂-C fluxes from 24-hour laboratory incubations of soils collected adjacent to soil respiration collars in 2022. Laboratory incubation carbon fluxes are reported per unit of dry soil mass, per gram of soil organic carbon, and on an areal basis, and we used them to operationally assess soil heterotrophic respiration. Soil physicochemical properties included in the data publication are: (1) pre-treatment (2009-2010) and post-treatment (2019 and 2022) soil pH; (2) soil nitrogen availability, assessed using ion exchange resins (summer of 2019); (3) soil temperature and volumetric water content (10 cm depth) measured concurrently with soil respiration measurements at each collar; and (4) continuous soil temperature measured at 10 cm depth in control plots in primary forest stands at each site (October 2020-October 2021).

Please see the linked Global Change Biology article (Frey et al., 2025) and the linked data package available at the Environmental Data Initiative (Frey et al., 2025) for detailed methods descriptions.