Comparison of water-related physiological characteristics of Alnus maritima and A.incana growing in America
美国海滨桤木和薄叶桤木水分生理特性的比较

Aims Our goal was to compare basic physiological responses to water stress of Alnus maritima and A. incana in order to (a) explain why A. maritima occupies a small, patchy distribution in eastern U.S.A. while A. incana is broadly distributed and (b) further understand potential differences in adaptation to drought in these two species. Methods We compared stomatal conductance (Gs), leaf water potential (ψleaf) and basic osmotic regulation in A. maritima and A. incana under artificial soil irrigation. Important findings Alnus maritima kept a lower Gs and lower correlation coefficients with air temperature, vapor pressure deficit and relative humidity than A. incana under irrigation. During the dry-down period, A. maritima showed weaker ability to keep stomata open as influenced by the decrease of ψleaf. In the re-water experiment, Gs of A. maritima showed slower recovery than A. incana. Alnus maritima kept a higher ψleaf and also a higher threshold of ψleaf to close their stomata under well-watered conditions. The decline in ψleaf was larger under drought stress compared with A. incana. There was no significant difference in osmotic regulation between the two species under normal water conditions. However, under drought, both species showed: (a) a decrease in solute potential at full turgor (ψs sat), (b) a decline of maximum variation rate of turgor pressure against solute potential, (c) an increase in solute potential at turgor loss point (ψs tlp) and (d) a decrease in Dψs. The ψs tlp of A. maritima was higher and Dψs was lower than in A. incana. These results indicated that the small, patchy distribution of A. maritima may partly be attributed to the lower sensitivity of leaf stomata, higher leaf water potential and decrease in ability to adjust osmotically under drought stress.