Figures (4)  Tables (4)
    • Figure 1. 

      Location of experimental sites and layout of treatment plots at each site and photos of canopy nitrogen and water increase.

    • Figure 2. 

      Effect of nitrogen (N) and water addition on leaf functional traits. Treatments included a control (CK), canopy addition N at 25 kg·ha−1·yr−1 (N), canopy water addition at 30% of the local precipitation (W), canopy N addition at 25 kg·ha−1·yr−1 and water addition at 30% of the local precipitation (N + W). Different lowercase letters above the error bar (standard error) indicate differences of statistical significance.

    • Figure 3. 

      Effect of nitrogen (N) and water addition on leaf chemical properties. Treatments included a control (CK), canopy addition N at 25 kg·ha−1·yr−1 (N), canopy water addition at 30% of the local precipitation (W), canopy N addition at 25 kg·ha−1·yr−1 and water addition at 30% of the local precipitation (N + W). Different lowercase letters above the error bar (standard error) indicate differences of statistical significance.

    • Figure 4. 

      Results of the structural equation model. The arrows represent the hypothesized causal relationships between the variables: N, canopy nitrogen addition at 25 kg·ha−1·yr−1; W, canopy water addition at 30% of the local precipitation; *, p < 0.05; **, p < 0.01; ***, p < 0.001. Black arrows represent positive effects, and the red arrows represent negative effects. The values next to the arrows are the standardized path coefficients. The values of R2 represent the percentage of the response variations explained by the observed variables.

    • Life formSpecies namesFamilyGeneraAbundance
      TreeLiquidambar formosana HanceHamamelidaceaeLiquidambar84
      Quercus acutissima CarruthFagaceaeChestnut464
      Quercus variabilis BlFagaceaeChestnut100
      ShrubsCeltis sinensis PersUlmaceaeCeltis212
      Lindera glauca (Sieb. et Zucc.) BlLauraceaeLindera212
      Acer buergerianum MiqAceraceaeAcer441

      Table 1. 

      Sampled dominant tree species in canopy and shrub layers in the warm temperate zone.

    • NWN + W
      FPFPFP
      LDMC
      Quercus acutissima0.3920.5421.0430.3261.2340.287
      Quercus variabilis0.320.5821.8240.2020.1450.71
      Liquidambar formosana2.8550.0982.4930.1210.8650.357
      Celtis sinensis0.310.5812.3710.1316.1870.017
      Lindera glauca2.1330.1510.0210.8860.5480.463
      Acer buergerianum1.4840.230.6140.4380.520.475
      SLA
      Quercus acutissima0.2580.620.0180.8950.3370.571
      Quercus variabilis0.0860.7740.0220.8843.6380.081
      Liquidambar formosana3.5750.0650.0160.9011.1340.293
      Celtis sinensis0.9040.3470.2660.6090.0410.841
      Lindera glauca0.0030.964.7150.0350.0640.801
      Acer buergerianum0.4850.490.0250.8750.8820.353
      EWT
      Quercus acutissima0.0460.8331.3870.260.9190.355
      Quercus variabilis0.1160.742.2910.1562.480.141
      Liquidambar formosana00.9972.5830.1150.2280.635
      Celtis sinensis0.1770.6760.8660.3583.4150.072
      Lindera glauca2.7880.1022.9950.0910.3980.531
      Acer buergerianum1.360.251.5410.2210.0290.865
      LDMC, leaf dry matter content; SLA, specific leaf area; EWT, equivalent water thickness; bold characters indicate significant differences.

      Table 2. 

      The effects of nitrogen (N), water (W) and the interaction (N + W) of the two on the functional traits of the leaves.

    • NWN + W
      FPFPFP
      LNC1.8540.19819.8420.00110.1160.008
      LPC0.0270.8720.4750.5040.4350.522
      C/N0.8560.3733.030.1072.7790.121
      N/P5.2180.04112.6130.0042.4010.147
      LNC, leaf nitrogen content; LPC, Leaf phosphorus content; bold characters indicate significant differences.

      Table 3. 

      The effects of nitrogen (N), water (W) and the interaction (N + W) of the two on leaf chemical properties.

    • TreatmentMoisture (%)NH4-N (mg·kg–1)NO3-N (mg·kg–1)
      CK29.01 ± 1.21 b4.41 ± 0.21 b17.97 ± 2.92 b
      N28.23 ± 1.04 b5.11 ± 0.62 ab21.37 ± 1.64 ab
      W36.98 ± 3.13 a4.4 ± 0.08 b15.73 ± 2.92 b
      N+W33.65 ± 2.09 ab7.61 ± 0.16 a30.28 ± 3.71 a
      CK, control; N, canopy N addition at 25 kg·ha−1·yr−1; W, canopy water addition at 30% of the local precipitation; N + W, canopy N addition at 25 kg·ha−1·yr−1 and water addition at 30% of the local precipitation.

      Table 4. 

      Soil moisture content and available N (NH4-N, and NO3-N) content.