The Hydraulic Architecture And Physiological Traits Of Machilus Species

Comparative study using congeneric species from different functional groups is an effective way for investigating adaptation and evolution of plant functional traits. Basal angiosperms include ANITA group, Chloranthaceae and Magnolids. We have a certain understanding of phylogenetic relationships of basal angiosperms. However, we have little knowledge on the species specific ecophysiological traits and their responses to various environmental stressors. We studied structural features of leaves, xylem structure of nine Machilus species, compared with Persea americana and Phoebe puwenensis planted at Xishuangbanna Tropical Botanical Garden in Southwest China. We wanted to find the correlation between the structural characteristics and physiological functions of these plants. The results showed that:1) leaf specific conductivity(Ks) and sapwood hydraulic conductivity(KL) of 9 Machilus species are at a relatively low level, and the low efficiency of water transport in these basal angiosperms is related to their relatively primitive vessel anatomy, which is consistent with their growth habitats in wet and dark forest understory.2) The xylem density and size of these plants are associated with specific leaf hydraulic conductance (KL), but there is no correlation between KL and the vessel diameter and vessel diameter and hydraulic conductivity is positively correlated. The vessel wall reinforcement is significantly correlated with the maximum length of the conduit and also significantly and positively correlated with maximum hydraulic conductivity (Kh). The maximum length of the vessel and the vessel diameter is positivelycorrelated. Thus, Machilus species could maintain the balance between hydraulic efficiency and safety.3) Palisade thickness has a negative correlation with Huber value and stomata density. The correlations are found between leaf RWC and vessel diameter, turgor loss point, and between stomata size and leaf thickness and spongy tissue thickness, indicating that Machilus species have the balance in leafwater supply and leaf transpiration. The correlation between vein density and stomata density is not significant, and Machilus species have relatively high stomata quantity, but a low vein density, which are suitable to their lives in habitats with plenty of water and low light.4) Compered to Machilus species with widespread distribution, widespread distribution species have a low turgor loss point, high reinforced conduct wall and small size of the vessel. Besides, the specific leaf weight have little relevance with distribution. Our study suggests that hydraulic traits can be used to explain the evolution and geographical distribution of basal angiosperm.