Hydraulic constraints determine the distribution of heteromorphic leaves along plant vertical height

Abstract

As an interesting and important trait of some drought-tolerant species, heteromorphic leaves are distributed differentially along plant vertical heights. However, the underpinning mechanism for the formation of heteromorphic leaves remains unclear. We hypothesize that heteromorphic leaves are caused by the hydraulic constraints possibly due to the compensation of the changes in functional traits in response to water transport capacity or the reduction of ineffective water loss. In this study, differences in water transport capacity, morphological traits, anatomical structures, and cellular water relations among three typical types of heteromorphic leaves (i.e., lanceolate, ovate, and broad-ovate) of Populus euphratica Oliv. (a dominant species of desert riparian forest in Central and West Asia) and their relationships were analyzed in order to explore the forming mechanism of heteromorphic leaves. The results showed that the lanceolate, ovate, and broad-ovate leaves were growing in the lower, intermediate, and higher positions from the ground, respectively. Morphological traits, anatomical structures, cellular water relations, and water transport capacity significantly varied among the three types of heteromorphic leaves (P< 0.01). Drought stress in broad-ovate leaves was significantly higher than that in ovate and lanceolate leaves (P< 0.01). Water transport capacity has significant correlations with morphological traits, anatomical structures, and cellular water relations (R2 ≥ 0.30; P< 0.01). Our results indicated that heteromorphic leaves were used as an important adaptive strategy for P. euphratica to alleviate the increase of hydraulic constraints along vertical heights.

Drought stress-induced the formation of heteromorphic leaves of Populus euphratica Oliv: evidence from gene transcriptome

“…This is because plants in these areas are prone to hydraulic failure and drought-induced death due to the fact that they are suffered drought stress ( Körner, 2019 ; Garcia et al., 2021 ). Yang et al. (2022a) has confirmed this speculation that, with the plant development, the progressive increases of gravitational potential between soil and plant canopy and the frictional resistance of water flow in xylem increases xylem tension, which in turn triggers hydraulics dysfunction through embolization.…”

“…Midday water potential and the contents of malondialdehyde (MDA), proline, and soluble sugar of leaves were used as the proxies to reflect the drought stress ( Cao et al., 2020 ; Yang et al., 2022a ). Since the young leaves collected in mid-April were too small to meet the experimental measurement requirements, we collected leaves from each selected individual in the peak season of plant growth (early July), and then measured the proxies of drought stress in the laboratory.…”

“…Since the young leaves collected in mid-April were too small to meet the experimental measurement requirements, we collected leaves from each selected individual in the peak season of plant growth (early July), and then measured the proxies of drought stress in the laboratory. To be specific, the heteromorphic leaves were collected from local 12:00 p.m. to 2:00 p.m, as suggested by Yang et al. (2022a) .…”

The Euphrates Poplar Responses to Abiotic Stress and Its Unique Traits in Dry Regions of China (Xinjiang and Inner Mongolia): What Should We Know?

“…The P. euphratica tree, a dominant species of the desert, is one tree species in the terrestrial ecosystem that develops strong leaves in the face of environmental changes, which subjects it to long-term drought and salt stress tolerance. Many researchers have found that P. euphratica has a significant strategy to alleviate the increase in hydraulic constraints along vertical heights [178]. Importantly, poplar saplings exhibit a high degree of phenotypic plasticity in response to water-deficit growing conditions, with reductions in hydraulic stem sensitivity and leaf area being particularly important in postponing the onset of hydraulic failure during an induced drought event.…”