Characteristics and correlations of leaf stomata in different Aleurites montana provenances.

Stomata are important indexes in studies of plant origin, evolution, and classification and are important organs in plant phylogenetic relationship studies. Nine Aleurites montana provenances were used in this study to examine stomatal density, stomatal area, stomatal perimeter, long axis length, and short axis length. The correlation and cluster analyses were conducted among the morphological parameters of the pores. The results showed that there were significant differences in different A. Montana provenances in terms of stomatal morphology parameters. The average stomatal density, stomatal area, stomatal perimeter, stomatal long axis length, and stomatal short axis length of each provenance was between 224.16-307.10 stomata/mm2, 80.42-99.76 µm, 36.39-41.32 µm, 15.89-18.44 µm, and 6.53-7.46 µm, respectively, and the coefficient of variation was between 9.18%-20.15%, 17.57%-33.77%, 9.31%-18.79%, 9.71%-18.48%, and 10.26%-21.57%, respectively. Correlation analysis shows that there was a significant negative correlation between stomatal density and stomatal shape parameters (stomatal area, stomatal perimeter, stomatal long axis, stomatal short axis) and there was a significant positive correlation between stomatal parameters. There was no significant correlation between geographical environment factors and stomatal characteristics. There is a close relationship between stomatal morphology and stomatal conductance whereby dense small stomata can quickly adapt to changes in the environment; considering the characteristics A. montana stomata in terms of stomatal stability and ability to adapt to the environment, the Jianyang, Zhenghe, Fuding, Shaxian provenances were identified as being more suitable for planting at different sites. This study provides a theoretical basis for the genetic improvement and breeding of high quality A. montana provenances.

The contribution of vascular and extra-vascular water pathways to drought-induced decline of leaf hydraulic conductance.

Drought stress can impair leaf hydraulic conductance (Kleaf), but the relative contribution of changes in the efficiency of the vein xylem water pathway and in the mesophyll route outside the xylem in driving the decline of Kleaf is still debated. We report direct measurements of dehydration-induced changes in the hydraulic resistance (R=1/K) of whole leaf (Rleaf), as well as of the leaf xylem (Rx) and extra-vascular pathways (Rox) in four Angiosperm species. Rleaf, Rx, and Rox were measured using the vacuum chamber method (VCM). Rleaf values during progressive leaf dehydration were also validated with measurements performed using the rehydration kinetic method (RKM). We analysed correlations between changes in Rx or Rox and Rleaf, as well as between morpho-anatomical traits (including dehydration-induced leaf shrinkage), vulnerability to embolism, and leaf water relation parameters. Measurements revealed that the relative contribution of vascular and extra-vascular hydraulic properties in driving Kleaf decline during dehydration is species-specific. Whilst in two study species the progressive impairment of both vascular and extra-vascular pathways contributed to leaf hydraulic vulnerability, in the other two species the vascular pathway remained substantially unaltered during leaf dehydration, and Kleaf decline was apparently caused only by changes in the hydraulic properties of the extra-vascular compartment.

Diurnal and seasonal variations in leaf hydraulic conductance in evergreen and deciduous trees.

We studied changes in the hydraulic conductance of leaves (K(leaf)) between dawn and dusk during the growth period (July) and at midday at the beginning of autumn in four tree species. The main objectives of the study were to check the extent of diurnal and seasonal changes in K(leaf) and the relationships between K(leaf), irradiance and leaf gas exchange. Two evergreen (Aleurites moluccana and Persea americana) and two deciduous trees (Platanus orientalis and Quercus rubra) were studied. Leaf hydraulic conductance was measured every 2 h between 0700 and 1900 h in July and compared with values measured between 0900 and 1300 h in October. Other variables measured were photosynthetically active radiation (PAR), leaf conductance to water vapor (gL) and water potential (psiL). In July, K(leaf) varied by up to 75% in Pe. americana on a diurnal basis and by at least 44% in Q. rubra. The diurnal time course of K(leaf) showed a distinct increase between dawn and late morning (1100 h) and a subsequent decrease in the evening in A. moluccana and Pl. orientalis, whereas in the other two species, K(leaf) was highest just after dawn and lowest in the evening. In October, K(leaf) of all the species studied was lower than in July, with differences of 20 to 28% for A. moluccana and Pl. orientalis and of 66 to over 70% in Pe. americana and Q. rubra, respectively. Significant correlations were found between PAR and K(leaf) (in all species) as well as between gL and K(leaf) (in three out of four species). Leaf habit (evergreen or deciduous) did not influence absolute values of K(leaf) or its diurnal variation.