Figures (4)  Tables (3)

    • Figure 1. 

      (a) The gross mineralization rates, (b) nitrification rates, and (c) immobilization rates in the acid and calcareous soil-wheat systems. Differences between the soil-wheat systems are indicated by *, * p < 0.05, ** p < 0.01, and *** p < 0.001.

    • Figure 2. 

      The 15NH4+ and 15NO3− uptake rates of (a) wheat and (b) soil microorganisms with time-varying conditions in calcareous and acid soil-wheat systems. Differences between 15NH4+ and 15NO3− uptake/assimilation rates are indicated by *, * p < 0.05, ** p < 0.01, and *** p < 0.001.

    • Figure 3. 

      The % 15N recovery of (a) wheat and (b) soil microorganisms of calcareous and acid soil-wheat systems. The values at the top represent the ratios of total 15N recovery (15NH4+ + 15NO3−) in calcareous soil and that of acid soil at each time point.

    • Figure 4. 

      The regression analyses of N assimilation rates of wheat and soil microorganisms of calcareous and acid soil-wheat systems under (a) 15NH4+ and (b) 15NO3− labelling.

    • Properties Soil types
      Calcareous soil Acid soil
      pH 8.17 4.83
      SOC (g kg−1) 10.72 15.82
      TN (g kg−1) 0.89 1.14
      C/N 12.04 13.87
      NH4+-N (mg kg−1) 1.01 4.90
      NO3−-N (mg kg−1) 28.55 33.58
      < 2 μm clay (%) 20.13 12.03

      Table 1. 

      The soil physicochemical properties of calcareous and acid soils

    • Calcareous soil-wheat system Acid soil-wheat system
      0 h 4 h 24 h 48 h 0 h 4 h 24 h 48 h
      NH4+-N 30.93 22.34 ± 1.00a 14.00 ± 0.66b 5.92 ± 0.73c 31.02 33.62 ± 1.32a 32.53 ± 1.04a 19.94 ± 0.58b
      NO3−-N 61.40 60.06 ± 3.64a 67.72 ± 2.22a 70.15 ± 3.99a 66.50 65.87 ± 0.65a 74.17 ± 0.92a 71.50 ± 2.81a
      15NH4+ 9.71 8.42 ± 0.24a 7.88 ± 0.10a 4.21 ± 0.25b 9.68 8.28 ± 0.21a 8.24 ± 0.08a 8.25 ± 0.06a
      15NO3− 5.12 4.62 ± 0.14a 4.10 ± 0.08a 3.64 ± 0.13a 4.15 3.83 ± 0.15a 3.58 ± 0.15a 3.48 ± 0.06a
      Lowercase letters represent differences between the calcareous and acid soil-wheat systems at different labeling times. p < 0.05.

      Table 2. 

      The concentration and 15N abundance of NH4+/NO3− in the calcareous and acid soil-wheat systems

    • Gross mineralization
      rate (µg g−1 d−1)      		 Gross nitrification rate (µg g−1 d−1) 15N uptake
      rate of wheat
      (µg g−1 d−1)      		 15N assimilation rate of microbes
      (µg g−1 d−1)      		 Ratios of microbial 15N uptake to wheat 15N uptake rates (%) 15N recovery
      of wheat (%)      		 15N recovery of microbes (%)
      Calcareous soil-wheat 3.63 ± 0.6a 9.44 ± 1.6a 0.46 ± 0.00a 0.19 ± 0.04b 41.30% 30.23 ± 0.4 10.55 ± 3.5
      Acid soil-wheat 0.40 ± 0.1b 4.63 ± 1.2b 0.42 ± 0.01a 0.40 ± 0.12a 95.23% 27.99 ± 0.7 23.42 ± 6.8

      Table 3. 

      The time-weighted average gross mineralization rates, gross nitrification rates, 15N uptake (15NH4+ + 15NO3−) of wheats, 15N assimilation rate of microbes, ratios of microbial 15N uptake to wheat 15N uptake rates, and total 15N recovery (15NH4+ + 15NO3−) at 48 h in the calcareous and acid soil-wheat systems