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gcb12063-sup-0001-FigureS1-S4.docxWord document432K

Figure S1. Soil temperature at (a) 2 cm below the soil surface and (b) 10 cm below the soil surface from October 2008 to 2010 with sampling periods highlighted in gray. Values represent the average of the daily soil temperature within each sampling period (= 9 for each warming treatment during each sampling period) ±SE. Open circles and dotted lines represent unwarmed plots, light grey circles and dashed lines represent low warmed plots, dark grey circles and thin solid lines represent medium warmed plots, and black circles and thick solid lines represent high warmed plots.

Figure S2. The (a) total number of freeze-thaw cycles in each warming treatment at both 2 cm and 10 cm below the soil surface across all winter sampling periods (October 2008–January 2009, October 2009–January 2010, January–April 2010). Values represent means (= 27 for each warming treatment) ±SE. The (b) average snow depth, and (c) cumulative soil freezing depth in each warming treatment across winter sampling periods in 2009–2010 (October 2009–January 2010, January–April 2010). Values represent means (= 18 for each warming treatment) ±SE. Letters a through d represent a significant difference (Tukey's HSD, α = 0.05) between the warming treatments.

Figure S3. The (a) average snow depth and (b) cumulative soil freezing depth in each precipitation treatment across winter sampling periods in 2009–2010 (October 2009–January 2010, January–April 2010). Values represent means (= 24 for each warming treatment) ±SE. Letters a and b represent a significant difference (Tukey's HSD, α = 0.05) between the precipitation treatments.

Figure S4. Interactive effects of precipitation and warming on N mineralization or N nitrification during April to June 2010. Values represent means (= 3 for each treatment, except for the unwarmed, wet treatment in April to June 2010 where = 2) ±SE. Open circles represent dry plots, gray circles represent ambient plots, and black circles represent wet plots.

gcb12063-sup-0002-TableS1-S4.docxWord document39K

Table S1. A summary of the P-values and numerator and denominator degrees of freedom, respectively (in parentheses), from a repeated measures mixed model anova testing for the treatment effects on the gravimetric and volumetric soil moisture and soil temperature across all sampling periods. Significant effects are in bold (P < 0.05). The gravimetric and volumetric soil moisture (in %) and soil temperature (in °C) within each of the warming treatments and each of the precipitation treatments across all sampling dates is also summarized. Values are means ±SE (= 9 for the warming treatments, = 12 for the precipitation treatments).

Table S2. A summary of the P-values and denominator degrees of freedom (‘DDF’) from a mixed model split-plot anova testing for the main and interactive effects of precipitation (‘P’) and warming (‘W’) on net N mineralization (‘Min.’) and net nitrification (‘Nit.’) within each sampling period from 2008–2010, the ratio of C mineralization to net N mineralization (‘Cmin : Nmin’) within each sampling period from 2008 to 2010, and the annual rates of net N mineralization and net nitrification from October 2009 to 2010. The numerator degrees of freedom are: 2 (precipitation), 3 (warming), and 6 (precipitation × warming). Significant effects are in bold (P < 0.05) and marginally significant effects are in italics (0.05 ≤ P < 0.1). For significant effects, a positive response of net N mineralization or net nitrification to increased precipitation or warming was indicated with an upward pointing arrow ([UPWARDS ARROW]) and a negative response was indicated with a downward pointing arrow ([DOWNWARDS ARROW]).

Table S3. A summary of the P-values and denominator degrees of freedom (‘DDF’) from a mixed model split-plot anova testing for the main and interactive effects of precipitation (‘P’) and warming (‘W’) on potential nitrification rates within each sampling period. The numerator degrees of freedom are: 2 (precipitation), 3 (warming), and 6 (precipitation × warming). Significant effects are in bold (P < 0.05) and marginally significant effects are in italics (0.05 ≤ P < 0.1). For significant or marginally significant effects, a positive response of potential nitrification to increased precipitation or warming was indicated with an upward pointing arrow ([UPWARDS ARROW]).

Table S4. Exponential model of (a) net N mineralization, (b) net nitrification, (c) C mineralization as a function of soil temperature within each treatment across all sampling periods from August 2009 to October 2010 and apparent Q10 values.

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