Cleverly James R, Smith Stanley D, Sala Anna, Devitt Dale A
Department of Biological Sciences, University of Nevada, Las Vegas, Las Vegas, NV 89154-4004, USA fax: (702) 895-3956; e-mail:
Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA, , , , , , US.
Oecologia. 1997 Jun;111(1):12-18. doi: 10.1007/s004420050202.
Tamarix ramosissima (Tamaricaceae) is a woody phreatophyte that has invaded thousands of hectares of floodplain habitat in the southwestern U.S. In this study, we examined the response of gas exchange and stem sap flow of Tamarix and three co-occurring native phreatophytes (Pluchea sericea (Asteraceae), Prosopis pubescens (Fabaceae) and Salix exigua (Salicaceae)) to drought conditions in an early successional floodplain community in the Mojave Desert of southern Nevada. In an analysis of a size/age series of each species across the whole floodplain (both mature and successional stands), stem growth rate was lowest for Tamarix. However, along the same successional chronosequence, Tamarix came to dominate the 50+ year old stands with dense thickets of high stem density. Xylem sap flow, when expressed on a sapwood area basis, was highest in Tamarix under early drought conditions, but comparable between the four species toward the end of the summer dry season. Multivariate analysis of the gas exchange data indicated that the four species differentiated based on water use under early drought conditions and separated based on plant water potential and leaf temperature (indices of drought effects) at the end of the summer dry season. This analysis suggests that the invasive Tamarix is the most drought tolerant of the four species, whereas Salix transpires the most water per unit leaf surface area and is the least tolerant of seasonal water stress. Therefore, Salix appears to be well adapted to early successional communities. However, as floodplains in this arid region become more desiccated with age, Tamarix assumes greater dominance due to its superior drought tolerance relative to native phreatophytes and its ability to produce high density stands and high leaf area.
多枝柽柳（柽柳科）是一种木本深根植物，已入侵美国西南部数千公顷的洪泛区栖息地。在本研究中，我们调查了柽柳以及三种同时存在的本地深根植物（绢毛蓼（菊科）、柔毛豆（豆科）和矮柳（杨柳科））的气体交换和茎干液流对干旱条件的响应，该研究位于内华达州南部莫哈韦沙漠的一个早期演替洪泛区群落中。在对整个洪泛区（成熟林分和演替林分）中每个物种的大小/年龄序列进行分析时，柽柳的茎干生长速率最低。然而，沿着相同的演替时间序列，柽柳在50多年树龄的林分中占据主导地位，形成了高茎密度的茂密灌丛。在干旱初期，以边材面积为基础表示时，柽柳的木质部液流最高，但在夏季旱季末期，这四个物种的木质部液流相当。对气体交换数据的多变量分析表明，这四个物种在干旱初期根据水分利用情况有所区分，在夏季旱季末期根据植物水势和叶片温度（干旱影响指标）而分离。该分析表明，入侵的柽柳是这四个物种中最耐旱的，而矮柳每单位叶表面积的蒸腾水量最大，对季节性水分胁迫的耐受性最低。因此，矮柳似乎非常适合早期演替群落。然而，随着这个干旱地区的洪泛区随着时间推移变得更加干燥，柽柳由于其相对于本地深根植物具有更强的耐旱性以及能够形成高密度林分和高叶面积，而占据了更大的优势。
