Trade-off relationship between leaf number and leaf size on current-year twigs of Populus euphratica Oliv. in response to groundwater gradients in extreme arid area of northwestern China

In this paper, Populus euphratica Oliv. was selected as the research object, and standardized major axis regression was used to determine the allometric relationship between leaf size (individual leaf mass and leaf area) and leafing intensity (based onstem mass, volume, and twig mass) on current-year twigs under different groundwater depths (GWD) and to explore the effects of GWD on the scaling relationship between individual leaf size and leafing intensity. Results showed:(1) Leaf number of current-year twigs increased significantly (P < 0.05), while tree height, specific leaf area, leaf area ratio, leaf/stem mass ratio, and individual leaf area and lamina mass decreased with GWD increase. (2) A negative and isometric relationship was found between leaf size and leafing intensity (based-mass), whereas a negative and allometric relationship was found between leaf size and leafing intensity (based-volume) along the GWD gradient. (3) GWD significantly affected the trade-off relationship between leafing intensity and leaf size. (4) P. euphratica compensated for the loss of limited leaf size by increasing the number of leaves with GWD increase. In brief, P. euphratica tended to have relatively few large leaves in habitats with better water conditions, but tended to have many small leaves on current-year twigs in arid and barren habitats.