Morphological, structural and physiological differences in heteromorphic leaves of Euphrates poplar during development stages and at crown scales

Abstract

Euphrates poplar (Populus euphratica Oliv.) has heteromorphic leaves including strip, lanceolate, ovate, and broad-ovate leaves from base to top in the mature canopy. To clarify how diameter at breast height (DBH) and tree height affect the functional characteristics of all kinds of heteromorphic leaves, we measured the morphological anatomical structure and physiological indices of five crown heteromorphic leaves of P. euphratica at 2, 4, 6, 8, 10, and 12 m from the same site. We also analysed the relationships between morphological structures and physiological characteristics of heteromorphic leaves and DBH and the height of heteromorphic leaves. The results showed that the number of abnormalities regarding blade width, leaf area, leaf thickness, leaf mass per area, cuticle layer thickness, palisade tissue thickness, and palisade tissue/sponge tissue ratio increased with size order and sampling height gradient. Net photosynthetic rate, transpiration rate, stomatal conductance, instantaneous water use efficiency, stable delta carbon isotope ratio, proline and malondialdehyde (MDA) content increased with DBH and sampling height. By contrast, blade length, leaf shape index, and intercellular CO2 concentration decreased with the increase in path order and sampling height gradient. Although MDA content and leaf sponge thickness were not correlated with DBH or sampling height, other morphological structure and physiological parameters were significantly correlated with these variables. In addition, correlations were found among leaf morphology, anatomical structure, and physiological index parameters indicating that they changed with path order and tree height gradient. The differences in the morphology, anatomic structure and physiological characteristics of the heteromorphic leaves ofP. euphratica are related to ontogenesis stage and coronal position.

Keywords: Heteromorphic leaf; Populus euphratica Oliv; morphological anatomy; osmotic regulation; photosynthetic water physiology.

Figure 1

Changes in leaf index (LI) across diameter class and sampling height scales on P. euphratica. Black dots indicate sampling height at 2 m, blue dots indicate 4 m, red dots indicate 6 m, green dots indicate 8 m, yellow dots indicate 10 m, purple dots indicate 12 m.

Figure 2

Changes in leaf mass per area (LMA) across diameter class and sampling height scales on P. euphratica. Black dots indicate sampling height at 2 m, blue dots indicate 4 m, red dots indicate 6 m, green dots indicate 8 m, yellow dots indicate 10 m, purple dots indicate 12 m.

Figure 3

Changes in leaf palisade tissue/spongy tissue ratio (PSR) across diameter class and sampling height scales in P. euphratica. Black dots indicate sampling height at 2 m, blue dots indicate 4 m, red dots indicate 6 m, green dots indicate 8 m, yellow dots indicate 10 m, purple dots indicate 12 m.

Figure 4

Changes in leaf cuticle thickness (CT) across diameter class and sampling height scales in P. euphratica. Black dots indicate sampling height at 2 m, blue dots indicate 4 m, red dots indicate 6 m, green dots indicate 8 m, yellow dots indicate 10 m, purple dots indicate 12 m.

Figure 5

Changes in leaf net photosynthesis rate (A) across diameter class and sampling height scales in P. euphratica. Black dots indicate sampling height at 2 m, blue dots indicate 4 m, red dots indicate 6 m, green dots indicate 8 m, yellow dots indicate 10 m, purple dots indicate 12 m.

Figure 6

Changes in leaf carbon isotope value (δ¹³C) across diameter class and sampling height scales in P. euphratica. Black dots indicate sampling height at 2 m, blue dots indicate 4 m, red dots indicate 6 m, green dots indicate 8 m, yellow dots indicate 10 m, purple dots indicate 12 m.

Figure 7

Changes in leaf proline (Pro) concentration across diameter class and sampling height scales in P. euphratica. Black dots indicate sampling height at 2 m, blue dots indicate 4 m, red dots indicate 6 m, green dots indicate 8 m, yellow dots indicate 10 m, purple dots indicate 12 m.