美国海滨桤木和薄叶桤木水分生理特性的比较

采取盆栽、人工控水的方式, 研究并比较了美国本土海滨桤木(Alnus maritima)和薄叶桤木(A. incana)的气孔导度(G_s)、叶片水势(ψ_leaf)以及渗透调节能力对土壤水分条件的响应, 以探讨引起两种桤木生态分布差异巨大的生理生态原因。结果表明: 1)正常水分条件下, 海滨桤木的G_s低于薄叶桤木, 其与大气温度、相对湿度和水蒸气亏缺等气象因子的相关性低于薄叶桤木; 干旱胁迫下, 海滨桤木的G_s对其自身ψ_leaf下降信号的敏感度低于薄叶桤木; 复水后, 其G_s恢复更为缓慢。2)正常水分条件下, 海滨桤木的ψ_leaf高于薄叶桤木, 且引起气孔关闭的ψ_leaf临界值较高; 干旱胁迫下, 海滨桤木的ψ_leaf下降幅度高于薄叶桤木。3)正常水分条件下, 海滨桤木和薄叶桤木的渗透调节能力无显著差异; 干旱胁迫下, 尽管两种桤木均表现出饱和状态渗透势(ψ_s^sat)下降、膨压与水势关系的最大变化率降低、初始失膨点渗透势(ψ_s^tlp)增加、细胞渗透调节能力范围(ψ_s^sat-ψ_s^tlp, Dψ_s)减小的趋势, 但与薄叶桤木相比, 海滨桤木的ψ_s^tlp较高, Dψ_s较小。从以上生理生态指标可以看出, 较高的叶片水势、较低的气孔调节能力、干旱下较低的渗透调节能力是造成海滨桤木分布范围狭小的重要原因。

Comparison of water-related physiological characteristics of Alnus maritima and A.incana growing in America

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 (G_s), leaf water potential (ψ_leaf) and basic osmotic regulation in A. maritima and A. incana under artificial soil irrigation. Important findings Alnus maritima kept a lower G_s 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 ψ_leaf. In the re-water experiment, G_s of A. maritima showed slower recovery than A. incana. Alnus maritima kept a higher ψ_leaf and also a higher threshold of ψ_leaf to close their stomata under well-watered conditions. The decline in ψ_leaf 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 (ψ_s ^sat), (b) a decline of maximum variation rate of turgor pressure against solute potential, (c) an increase in solute potential at turgor loss point (ψ_s ^tlp) and (d) a decrease in Dψ_s. The ψ_s ^tlp of A. maritima was higher and Dψ_s 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.