Data compilation of soil respiration, moisture, and temperature measurements from global warming experiments from 1994-2014

A literature search, which was conducted on September 22, 2014 using Web of Science, produced five publications presenting non-aggregated instantaneous data that were extractable. Unpublished values make up the majority of the data in the dataset. We obtained unpublished data by first creating a list of all known experimental warming studies globally and asking the principal investigators to supply soil respiration data with corresponding soil temperature and moisture values. All individual fluxes were calculated by individual PIs. The experiments generally had several replicate plots for each treatment. We averaged all plot-scale values for each sampling event to obtain one average (± SD) for each treatment for each sampling event (‘sampling events’ typically refer to a single day of sampling, although several studies complete full suites of sampling (i.e., ‘sampling events’) from all plots in both morning and afternoon). Only soil respiration values with corresponding soil moisture and soil temperature values from experimental warming studies were included in our analysis. Only observations from single-factor treatments (i.e., warming) were used, excluding values that combined warming with other treatments (e.g., precipitation or nitrogen manipulation). Four studies included more than one level of warming treatment (e.g., both 1.5 and 3 degrees Celsius warming treatments); in these cases, data from all levels of warming were used. All data were reported as instantaneous change in CO2 efflux over a fixed area, with belowground (i.e., roots and rhizomes), but not aboveground vegetation, included. Only biomes with at least 100 data points are analyzed individually, which prevented Meadow and Tundra from being analyzed in isolation, as these did not have at least 100 data points each. Therefore they are found in the dataset but not in the publication, Carey et al. 2016.
The following are the published sources of data:
Reynolds LL, Johnson BR, Pfeifer-Meister L, Bridgham SD (2015) Soil respiration response to climate change in Pacific Northwest prairies is mediated by a regional Mediterranean climate gradient. Glob Chang Biol 21(1):487–500.
Lellei-Kovács E, et al. (2008) Experimental warming does not enhance soil respiration in a semiarid temperate forest-steppe ecosystem. Community Ecol 9(1):29–37.
de Dato GD, De Angelis P, Sirca C, Beier C (2009) Impact of drought and increasing temperatures on soil CO2 emissions in a Mediterranean shrubland (gariga). Plant Soil 327(1-2):153–166.
Saleska SR, Harte J, Torn MS (1999) The effect of experimental ecosystem warming on CO2 fluxes in a montane meadow. Glob Chang Biol 5(2):125–141.
Flanagan LB, Sharp EJ, Letts MG (2013) Response of plant biomass and soil respiration to experimental warming and precipitation manipulation in a Northern Great Plains grassland. Agric For Meteorol 173:40–52.
Jarvi MP, Burton AJ (2013) Acclimation and soil moisture constrain sugar maple root respiration in experimentally warmed soil. Tree Physiol 33(9):949–959.
Suseela V, Conant RT, Wallenstein MD, Dukes JS (2012) Effects of soil moisture on the temperature sensitivity of heterotrophic respiration vary seasonally in an old-field climate change experiment. Glob Chang Biol 18(1):336–348.
Allison SD, Treseder KK (2008) Warming and drying suppress microbial activity and carbon cycling in boreal forest soils. Glob Chang Biol 14(12):2898–2909.
Allison SD, McGuire KL, Treseder KK (2010) Resistance of microbial and soil properties to warming treatment seven years after boreal fire. Soil Biol Biochem 42(10):1872–1878.
Poll C, Marhan S, Back F, Niklaus PA, Kandeler E (2013) Field-scale manipulation of soil temperature and precipitation change soil CO2 flux in a temperate agricultural ecosystem. Agric Ecosyst Environ 165:88–97.
Johnson LC, et al. (2000) Plant carbon - nutrient interactions control CO2 exchange in Alaskan wet sedge tundra ecosystems. Ecology 81(2):453–469.
Reinsch, S., Sowerby, A., Emmett, B.A. (2016) Fortnightly soil respiration data from Climoor fieldsite in Clocaenog Forest 1999 – 2015. DOI: 10.5285/[2]c0822023-0ec2-425f-8bf9-a546ce281ee0
Reinsch, S., Sowerby, A., Emmett, B.A. (2016) Daily plot level (micro meteorological) data at Climoor field site in Clocaenog Forest 1998-2015. DOI: http://doi.org/10.5285/afb994e5-b33d-48b4-ad29-d374b1f9f3c8

Meta-analysis using log response ratios, standardized mean difference. We used methods from Hedges et al. 1999. We used a log-quadratic temperature response function, as this was the best supported model for most biomes. ln(R)=y0 +y1T+y2T^2 where R is soil respiration (micro mol C m^-2 s-1) and T is soil temperature (Celsius). Using this basic model, we further included warming treatment as an interaction term in order to evaluate differences in the temperature response between warmed versus control plots. We used this model for all biomes, except the boreal forest and northern shrublands, where a log-linear model (ln(R) = y0 + y1T) was the better fit. We evaluated two specific features of the temperature response function: (i) the temperature sensitivity (i.e., the shape of the curve denoted by the first derivative of Eq. 1: (= d ln(R)/dT, Table 1) and (ii) the magnitude of the respiration response when T = 0. More information can be found in the methods section of the paper Carey et al. 2016.

Standard methods for grain size analysis were used by individual PIs in the original studies.

Added keywords section with USGS persistent identifier as theme keyword.