Fig. 1. Dynamics of soil temperature and soil moisture for 0-20 cm surface soil and precipitation during the growing seasons of 2013 (a), 2014 (b), and 2015 (c).

Fig. 2. Soil variables with six N gradients and three years (n=3) Note: (a) Dissolved organic carbon; (b) Inorganic nitrogen; (c) Ph; (d) Total organic carbon; (e) Total nitrogen; (f) Aboveground biomass; (g) PLFAs; (h) Fungi to bacteria ratio; (i) Gram-positive bacteria to gram-negative bacteria ratio; (j) Soil respiration; (k) Q₁₀.

Fig. 3. Principal component analysis of microbial community composition in soil samples with six N gradients and three years (mean±SE) (n=3). Soil samples in the three years are presented by different colors, as black indicates 2013, white indicates 2014, and grey indicates 2015.

Fig. 4. Structural equation model for the effects of nitrogen addition, soil temperature and soil moisture on soil pH, C and N availability, aboveground biomass, total PLFAs, microbial composition, Rs and Q10. Note: Dashed, red, and blue paths indicate the effect is insignificant, positive, and negative, respectively. The width of the arrow indicates the magnitude of the standardized path coefficient. Bold and italic-typed values indicate the proportions of the variance explained for each variable. χ²—chi-square, df—degrees of freedom, P— P value, RMSEA—root mean square error of approximation, CFI—comparative fit index.