Figures (6)  Tables (7)

    • Figure 1. 

      SLA of Q. mongolica seedlings. SLA indicates the specific leaf area of the plant, while Roman numerals (I, II, III) represent different age classes. Different upper case letters indicate significant differences in indicators between different light environments at the same age (p < 0.05); different lower case letters indicate significant differences in indicators between age classes at the same light environment (p < 0.05).

    • Figure 2. 

      S/R ratio of seedlings of Q. mongolica. The S/R ratio indicates the ratio of shoot to root of the plant, while Roman numerals (I, II, III) represent different age classes. Different upper case letters indicate significant differences in indicators between different light environments at the same age (p < 0.05); different lower case letters indicate significant differences in indicators between age classes at the same light environment (p < 0.05).

    • Figure 3. 

      Pattern of biomass allocation in Q. mongolica seedlings. (RMF) represents root mass fraction, (SMF) represents stem mass fraction, and (LMF) represents leaf mass fraction. (I, II, and III) stand for different age classes. Light environments include US (forest understory) and FE (forest edge). Different capital letters indicate significant differences in the indicators between different light environments at the same age (p < 0.05); different lower case letters indicate significant differences in the indicators between age classes at the same light environment (p < 0.05).

    • Figure 4. 

      NSC concentration of the individual organs in Q. mongolica seedlings. (a) Soluble sugar concentration in the leaves, (b) soluble sugar concentration in the stems, (c) soluble sugar concentration in the roots, (d) starch concentration in the leaves, (e) starch concentration in the stems, (f) starch concentration in the roots, (g) TNC concentration in the leaves, (h) TNC concentration in the stems, (i) TNC concentration in the roots. I, II, and III represent age classes. * stands for significance at a level of 0.05; **stands for significance at a level of 0.01.

    • Figure 5. 

      Correlation analysis between the NSC concentrations of Q. mongolica seedlings in different age classes (Pearson). (a) 1−2 years old, (b) 3−4 years old, (c) 5−6 years old. Red stands for a positive correlation and blue for a negative correlation. The darker the colour, the higher the correlation. * stands for significance at a level of 0.05; ** stands for significance at a level of 0.01.

    • Figure 6. 

      The correlation relationships between the relative light intensity and the (a) TNC concentration in the leaves, (b) the soluble sugar concentration in the leaves and (c) the starch concentration in the roots. The equation of the linear regression, the r-square and the p-values are also shown in the graph.

    • PlantationArea
      (hm2)      		Average
      DBH (cm)      		Average tree
      height (m)      		Stand density
      (plant/hm2)
      Q. mongolica1.252615.0312.992,050
      F. chinensis0.890425.1617.33375
      B. platyphylla1.27229.8810.261,675
      P. sylvestris1.225914.7413.101,600
      Species included Quercus mongolica Fisch. ex Ledeb., Fraxinus chinensis subsp. rhynchophylla (Hance) E. Murray, Betula platyphylla Sukaczev and Pinus sylvestris var. mongholica Litv.

      Table 1. 

      Plantations from which seedlings were collected, the area of each plantation, the average tree height and the average diameter at breast height (DBH).

    • PlantationLight environmentAge classHeight
      (cm) ± SD      		Basal diameter
      (mm) ± SD
      F. chinensisUnderstory1−2a20.83 ± 3.132.99 ± 0.52
      3−4a41.51 ± 4.084.87 ± 0.69
      5−6a66.33 ± 1.696.82 ± 0.49
      Forest edge1−2a16.15 ± 1.632.52 ± 0.29
      3−4a43.13 ± 5.784.95 ± 0.65
      5−6a66.29 ± 3.556.93 ± 0.86
      P. sylvestrisUnderstory1−2a20.58 ± 4.532.98 ± 0.61
      3−4a39.56 ± 4.915.06 ± 0.42
      5−6a62.33 ± 5.396.94 ± 0.11
      Forest edge1−2a21.67 ± 2.192.94 ± 0.30
      3−4a42.75 ± 4.764.48 ± 0.42
      5−6a65.71 ± 2.946.63 ± 0.44
      B. platyphyllaUnderstory1−2a26.53 ± 3.983.31 ± 0.36
      3−4a45.09 ± 4.525.21 ± 0.56
      5−6a65.26 ± 3.406.23 ± 0.19
      Forest edge1−2a23.16 ± 5.633.52 ± 0.22
      3−4a37.52 ± 2.534.89 ± 0.45
      5-6a61.73 ± 1.796.61 ± 0.44
      Q. mongolicaUnderstory1−2a20.16 ± 4.742.94 ± 0.56
      3−4a40.75 ± 6.644.94 ± 0.73
      5−6a——
      Forest edge1−2a19.16 ± 2.732.86 ± 0.59
      3−4a40.01 ± 4.944.47 ± 0.26
      5−6a——
      Species included Quercus mongolica Fisch. ex Ledeb., Fraxinus chinensis subsp. rhynchophylla (Hance) E. Murray, Betula platyphylla Sukaczev and Pinus sylvestris var. mongholica Litv.

      Table 2. 

      Average height and basal diameter (± SD) of Q. mongolica seedlings of all age classes in the forest understory and at the forest edge in four plantations.

    • PlantationRelative light intensity (%)
      Forest understoryForest edge
      Q. mongolica1.410.2
      F. chinensis2.030.5
      B. platyphylla2.814.1
      P. sylvestris6.327.0

      Table 3. 

      Relative light intensity of the sample plot.

    • AbbreviationFull nameDefinitionUnits
      USForest understoryUnder the forest canopy, beyond 10 meters from the boundary, the canopy closure is around 80%.−
      FEForest edgeAt the edge of the forest, within 10 meters from the boundary, the canopy closure is around 50%.−
      RLIRelative light intensityThe light intensity at the observation point / full light intensity.g/g
      SLASpecific leaf areaSpecific leaf area / leaf dry mass.cm2/g
      LMFLeaf mass fractionLeaf dry mass / total plant dry mass.g/g
      SMFStem mass fractionStem dry mass / total plant dry mass.mg/g
      RMFRoot mass fractionRoot dry mass / total plant dry mass.g/g
      S/R ratioShoot to root ratio(leaf + stem dry mass) / root dry mass.g/g
      SSSoluble sugar−g/g
      STStarch−mg/g
      TNCTotal non-structural carbohydratesStartch +Soluble sugar concentration.mg/g

      Table 4. 

      Abbreviations used in this article together with their definitions and units.

    • Functional traitsSeedling
      age      		Light environmentLight environment
      * seedling age      		Marginal R2/
      Conditional R2
      SLA0.11<0.01**<0.01**0.081/0.123
      RMF<0.01**0.120.870.095/0.324
      SMF<0.01**0.850.540.167/0.224
      LMF<0.01**0.090.630.233/0.398
      S/R ratio<0.01**0.10.920.086/0.296
      SLA (specific leaf area), RMF (root mass fraction), SMF (stem mass fraction), LMF (leaf mass fraction) and S/R ratio (shoot-to-root ratio). Significance levels: * p < 0.05, ** p < 0.01.

      Table 5. 

      p-values of linear mixed-effects models assessing the significance of fixed and interaction effects of light environment and seedling age on the functional traits of Q. mongolica seedlings, as well as the model conditional R2 and the marginal R2 of the model.

    • OrgansNSCSeedling ageLight environmentLight environment * seedling ageMarginal R2/
      Conditional R2
      RootSS0.282<0.01**<0.01**0.221/0.414
      ST<0.01**<0.01**<0.01**0.362/0.458
      TNC<0.01**0.08<0.01**0.288/0.414
      StemSS0.380.50.970.028/0.186
      ST0.330.150.610.069/0.133
      TNC0.240.280.70.058/0.175
      LeafSS0.33<0.01**0.310.373/0.609
      ST0.080.86<0.01**0.143/0.419
      TNC0.12<0.01**0.080.262/0.402
      SS (soluble sugars), ST (starch), TNC (total non-structural carbohydrates). Significance levels: * p < 0.05, ** p < 0.01.

      Table 6. 

      p-values of the linear mixed-effects models assessing the significance of the fixed and interaction effects of light environment and seedling age on NSC in Q. mongolica seedlings, as well as the model conditional R2 and the marginal R2 of the model.

    • IndicatorsAge class IMarginal R2/
      Conditional R2      		Age class IIMarginal R2/
      Conditional R2      		Age class IIIMarginal R2/
      Conditional R2
      SLA<0.01**0.208/0.2290.420.003/0.0180.770.006/0.206
      RMF0.350.011/0.1570.430.011/0.4020.740.001/0.659
      SMF0.610.003/0.2620.570.006/0.2810.280.048/0.148
      LMF0.730.001/0.3380.100.051/0.3710.790.001/0.461
      S/R ratio0.290.013/0.1430.360.015/0.3730.610.005/0.496
      Root SS0.02*0.132/0.4430.070.248/0.7040.03*0.216/0.216
      Root ST0.140.128/0.458<0.01**0.106/0.3540.04*0.137/0.477
      Root TNC0.100.053/0.5780.03*0.021/0.2820.120.093/0.336
      Stem SS0.770.026/0.3340.570.011/0.2150.390.024/0.422
      Stem ST0.060.131/0.3620.460.023/0.0230.860.001/0.288
      Stem TNC0.140.064/0.3850.580.013/0.0560.850.001/0.335
      Leaf SS0.04*0.202/0.698<0.01**0.532/0.5900.03*0.395/0.841
      Leaf ST0.180.076/0.0760.100.091/0.2980.150.015/0.876
      Leaf TNC0.02*0.214/0.395<0.01**0.462/0.4620.01*0.061/0.855
      SLA (specific leaf area), RMF (root mass fraction), SMF (stem mass fraction), LMF (leaf mass fraction), S/R ratio (shoot-to-root ratio), SS (soluble sugars), ST (starch) and TNC (total non-structural carbohydrates). Significance levels: * p < 0.05, ** p < 0.01.

      Table 7. 

      p-values for linear mixed-effects models measuring the effects of light environment on functional traits and NSC concentrations in seedlings of different age classes, and conditional R2 and marginal R2 for the models.