Divergent adaptations of leaf functional traits to light intensity across common urban plant species in Lanzhou, northwestern China

Abstract

Leaves are the most important photosynthetic organs in plants. Understanding the growth strategy of leaves in different habitats is crucial for elucidating the mechanisms underlying plant response and adaptation to the environment change. This study investigated the scaling relationships of the laminar area (LA), leaf fresh mass (LFM), leaf dry mass (LDM), and explored leaf nitrogen (N) and phosphorus (P) content in leaves, and the relative benefits of these pairwise traits in three common urban plants (Yulania denudata, Parthenocissus quinquefolia, and Wisteria sinensis) under different light conditions, including (full-sun and canopy-shade). The results showed that: the scaling exponent of LDM vs LA (> 1, p < 0.05) meant that the LDM increased faster than LA, and supported the hypothesis of diminishing returns. The LFM and LDM had isometric relationships in all the three species, suggesting that the leaf water content of the leaves was nearly unaltered during laminar growth. Y. denudata and W. sinensis had higher relative benefit in full-sun habitats, while the reverse was observed in P. quinquefolia. The N and P content and the N:P ratio in full-sun leaves were generally higher than those of canopy-shade leaves. The leaves of the three urban plants exhibited a shift in strategy during transfer from the canopy shaded to the sunny habitat for adapting to the lower light conditions. The response of plant leaves to the environment shapes the rich variations at the leaf level, and quantification of the relative benefits of plants in different habitats provides novel insights into the response and adaptation strategies of plants.

Keywords: light environment; phenotypic plasticity; relative benefit; scaling relationship; stoichiometry; urban plants.

Figure 1

Scaling relationships between leaf traits in different urban plants. (A–C) represent the fitting relationship between LDM with LFM, LFM with LA, and LDM with LA of Y. denudata leaves, respectively. (D–F) represent the fitting relationship between LDM with LFM, LFM with LA, and LDM with LA of P. quinquefolia leaves, respectively. (G–I) represent the fitting relationship between LDM with LFM, LFM with LA, and LDM with LA of W. sinensis leaves, respectively. Circles represent the observed values; the blue and red solid lines represent SMA fitting lines between leaf traits under low and high light habitats, respectively; and dotted lines represent 1:1 line. Some 1:1 lines are not shown due to the proportional value of the axes.

Figure 2

Relative benefits between paired leaf traits of different urban plant. (A–C) represent the relative benefit between LDM with LFM, LFM with LA, and LDM with LA of Y. denudata leaves, respectively. (D–F) represent the relative benefit between LDM with LFM, LFM with LA, and LDM with LA of P. quinquefolia leaves, respectively. (G–I) represent the relative benefit between LDM with LFM, LFM with LA, and LDM with LA of W. sinensis leaves, respectively. The blue and red points indicate low light and high light habitats, respectively. The relative benefit is represented by the RMSE of paired traits. The RMSE represents the distance from the coordinate of the paired traits to the diagonal 1:1 line where the trade-off is zero. The farther the distance, the larger the relative benefit.

Figure 3

The N and P contents and N:P ratios under conditions of different light habitats. (A–C) represent the N, P content and N:P of Y. denudata leaves under different light habitats, respectively. (D–F) represent the N, P content and N:P of P. quinquefolia leaves under different light habitats, respectively. (G–I) represent the N, P content and N:P of W. sinensis leaves under different light habitats, respectively. The blue and red circles represent low light and high light, respectively. The numerical values in the figures represent the mean ± SD. p < 0.05 indicates a significant difference between the two light environments.

Figure 4

PCA analysis of leaf traits of urban plants in different light habitats. (A) Scree plot; (B) Loading plot; (C) Loadings of plant traits on the first and second axes; (D) Score plot and strategy shifts of the different plants under different light habitats.