Differences in the Functional Traits of Populus pruinosa Leaves in Different Developmental Stages

Abstract

Populus pruinosa Schrenk has the biological characteristics of heteromorphic leaves and is a pioneer species for wind prevention and sand fixation. The functions of heteromorphic leaves at different developmental stages and canopy heights of P. pruinosa are unclear. To clarify how developmental stages and canopy height affect the functional characteristics of leaves, this study evaluated the morphological anatomical structures and the physiological indicators of leaves at 2, 4, 6, 8, 10, and 12 m. The relationships of functional traits to the developmental stages and canopy heights of leaves were also analyzed. The results showed that blade length (BL), blade width (BW), leaf area (LA), leaf dry weight (LDW), leaf thickness (LT), palisade tissue thickness (PT), net photosynthetic rate (Pn), stomatal conductance (Gs), proline (Pro), and malondialdehyde (MDA) content increased with progressing developmental stages. BL, BW, LA, leaf dry weight, LT, PT, Pn, Gs, Pro, and the contents of MDA, indoleacetic acid, and zeatin riboside had significant positive correlations with canopy heights of leaves and their developmental stages. The morphological structures and physiological characteristics of P. pruinosa leaves showed more evident xeric structural characteristics and higher photosynthetic capacity with increasing canopy height and progressive developmental stages. Resource utilization efficiency and the defense ability against environmental stresses were improved through mutual regulation of each functional trait.

Keywords: Populus pruinosa; canopy height; developmental stage; functional traits; leaf.

Figure 1

Changes in leaves’ morphological characteristics in different diameter classes of P. pruinosa. Note: (a) blade length; (b) blade width; (c) leaf area; (d) leaf index; (e) leaf dry weight; (f) specific leaf area. The lowercase letters and the uppercase letters represent the significance of the differences between different leaf heights and different diameter classes of P. pruinosa (p < 0.05). Two-factor analyses of variance (ANOVA) were applied to evaluate the effects of different factors and interactions. FH, leaf height effect; FDC, diameter class effect; FH×DC, leaf height × diameter class effect (p < 0.001: ***; 0.001 < p < 0.01: **).

Figure 2

Changes in leaves’ anatomical structure characteristics in different diameter classes of P. pruinosa. Note: (a) main vein vascular bundle area; (b) main vein xylem area; (c) leaf thickness; (d) palisade tissue thickness. The lowercase letters and the uppercase letters represent the significance of the differences between different leaf heights and different diameter classes of P. pruinosa (p < 0.05). Two-factor analyses of variance (ANOVA) were applied to evaluate the effects of different factors and interactions. FH, leaf height effect; FDC, diameter class effect; FH×DC, leaf height × diameter class effect (p < 0.001: ***).

Figure 3

Changes in leaves’ photosynthetic physiological parameters in different diameter classes of P. pruinosa. Note: (a) photosynthetic rate; (b) transpiration rate; (c) stomatal conductance; (d) intercellular CO₂ concentration. The lowercase letters and the uppercase letters represent the significance of the differences between different leaf heights and different diameter classes of P. pruinosa (p < 0.05). Two-factor analyses of variance (ANOVA) were applied to evaluate the effects of different factors and interactions. FH, leaf height effect; FDC, diameter class effect; FH×DC, leaf height × diameter class effect (p < 0.001: ***; 0.001 < p < 0.01: **).

Figure 4

Changes in leaves’ water use efficiency in different diameter classes of P. pruinosa. Note: (a) stable carbon isotope value; (b) instantaneous water use efficiency. The lowercase letters and the uppercase letters represent the significance of the differences between different leaf heights and different diameter classes of P. pruinosa (p < 0.05). Two-factor analyses of variance (ANOVA) were applied to evaluate the effects of different factors and interactions. FH, leaf height effect; FDC, diameter class effect; FH×DC, leaf height × diameter class effect (p < 0.01: **; p > 0.05: ns).

Figure 5

Changes in leaves’ physiological characteristics in different diameter classes of P. pruinosa. Note: (a) proline content; (b) malondialdehyde content. The lowercase letters and the uppercase letters represent the significance of the differences between different leaf heights and different diameter classes of P. pruinosa (p < 0.05). Two-factor analyses of variance (ANOVA) were applied to evaluate the effects of different factors and interactions. FH, leaf height effect; FDC, diameter class effect; FH×DC, leaf height × diameter class effect (p < 0.001: ***; p > 0.05: ns).

Figure 6

Changes in leaves’ endogenous hormone content in different diameter classes of P. pruinosa. Note: (a) abscisic acid content; (b) gibberellin content; (c) indoleacetic acid content; (d) zeatin riboside content. The lowercase letters and the uppercase letters represent the significance of the differences between different leaf heights and different diameter classes of P. pruinosa (p < 0.05). Two-factor analyses of variance (ANOVA) were applied to evaluate the effects of different factors and interactions. FH, leaf height effect; FDC, diameter class effect; FH×DC, leaf height × diameter class effect (p < 0.001: ***).

Figure 7

Linear fitting of leaf morphology characteristics of different diameter classes (8/12/16/20) with leaf height of P. pruinosa. (p < 0.01: **; p > 0.05: NS). Note: (a) BL, blade length; (b) BW, blade width; (c) LA, leaf area; (d) LI, leaf index; (e) LDW, leaf dry weight; (f) SLA, specific leaf area.

Figure 8

Linear fitting of leaf anatomical structure characteristics of different diameter classes (8/12/16/20) with leaf height of P. pruinosa. (p < 0.01: **; p > 0.05: NS) Note: (a) MVBA, main vein vascular bundle area; (b) MXA, main vein xylem area; (c) LT, leaf thickness; (d) PT, palisade tissue thickness.

Figure 9

Linear fitting of leaf physiological and biochemical characteristics of different diameter classes (8/12/16/20) with leaf height of P. pruinosa. (p < 0.01: **; 0.01 < p < 0.05: *; p > 0.05: NS) Note: (a) Pro, proline; (b) MDA, malondialdehyde; (c) ABA, abscisic acid; (d) GA₃, gibberellin; (e) IAA, indoleacetic acid; (f) ZR, zeatin riboside.

Figure 10

Principal component analysis (PCA) based on leaf traits in P. pruinosa at different heights across four diameter classes. The diamond, upper triangle, right triangle, and left triangle represent the tree heights of 2, 4, 6, 8, 10, and 12 m, respectively; the light blue, dark blue, green, and red represent diameter classes 8, 12, 16, and 20, respectively. BL, blade length; BW, blade width; LA, leaf area; LI, leaf index; LDW, leaf dry weight; SLA, specific leaf area; MVBA, main vein vascular bundle area; MXA, main vein xylem area; LT, leaf thickness; PT, palisade tissue thickness; Pn, photosynthetic rate; Tr, transpiration rate; Gs, stomatal conductance; Ci, intercellular CO₂ concentration; δ¹³C, stable carbon isotope value; WUEi, instantaneous water use efficiency; Pro, proline; MDA, malondialdehyde; ABA, abscisic acid; GA₃, gibberellin; IAA, indoleacetic acid; ZR, zeatin riboside.