|Other Abstract||Leaf is considered as a critical hydraulic bottleneck in hydraulic plumbing system of plant, and the hydraulic conductance accounts for 30% of the whole-plant resistance. Leaf hydraulic traits (leaf hydraulic conductance, parameters of leaf anantomical, leaf hydraulic vulnerabilities e.g.) reflect the water transport of leaf. Efficient water transport inside leaves is a major determinant of plant function, especially in drought-stressed plants. This research made a supplement to the study of hydraulic traits in arid plant.
We selected Populus euphratica, a desert riparian forest vegetation, at the lower reaches of Tarim River as the research material. The hydraulic traits (leaf hydraulic conductance, leaf hydraulic vulnerabilities, parameters of leaf pressure-volume, leaf anatomical parameters) were measured; differences of the parameters among different groundwater depths were compared; and the effects of the groundwater depth on leaf hydraulic traits were analyzed. Meanwhile, the δ13C values of P. euphratica leaves were measured aiming to study the relationship between leaf hydraulic traits and water use efficiency. The main results are as follows:
1. We found that Kleaf-max of P. euphratica showed an increasing trend as the groundwater depth increased, while osmotic potential at full turgor (πft) and turgor loss point (Ψtlp) decreased, suggesting that tolerance to drought increased as the groundwater depth increased. There are some correlations among key leaf parameters calculated from P-V curves, but no clear relationship was found between P-V curve parameters and leaf hydraulic vulnerabilities. Leaf hydraulic safety margins showed negtive and postive varivations under different groundwater depths, wider margins occurred in good water conditions.
2. The results of leaf anatomical structure of P. euphratica, a constructive species in desert riparian forest, indicated that it had the typical characteristics of desert plants. In leaf anatomical parameters, differences were found in leaf anatomical structure parameters among different groundwater depth. The study showed that with the increase of groundwater depth, leaf thickness (LT), palisade tissue thickness (PT), leaf epidermal thickness (ET), leaf main-vein vessel diameter (MVD), stomata density (SD) and vein density (VD) increased; while leaf stomata anatomical structure parameters: stomatal guard cell length (SL), width (SW), stomatal area (SA) decreased. Significant correlations were found between vein density and stomatal anatomical parameters, suggesting that a positive relationship was formed between water transfer and water loss within P. euphratica leaves.
3. The δ13C values in P. euphratica leaves increased with the increasing in groundwater depth, indicating that water use efficiency increased with the enhanced drought stress.We also found a positive correlation between δ13C values and maximum hydraulic conductance; δ13C values and leaf anatomical parameters (LT, PT, ET, MVD, SD, VD) are positively correlated, while negative correlations were found between the stomata pore size parameters (SW, SL, SA) and δ13C values. No correlations were found among water use efficiency and water vulnerabilities.|