Boorse G C, Ewers F W, Davis S D
Natural Science Division, Pepperdine University, Malibu, California 90263-4321; and.
Am J Bot. 1998 Sep;85(9):1224-30.
Leaf death due to freezing was examined for four, co-occurring species of chaparral shrubs from the Santa Monica Mountains of southern California, Rhus laurina (= Malosma laurina), R. ovata, Ceanothus megacarpus, and C. spinosus. Measurements were made on seedlings vs. adults for all species, and for Rhus spp. in winter vs. summer, and at a warm vs. a cold site. We used four methods to determine the temperature for 50% change in activity or cell death (LT(50)) of leaves: (1) electrical conductivity (electrolyte leakage into a bathing solution), (2) photosynthetic fluorescent capacity (Fv/Fm), (3) percentage of palisade mesophyll cells stained by fluorescein diacetate vital stain, and (4) visual score of leaf color (Munsell color chart). In all four species seedlings were found to be more sensitive to freezing temperatures than were adults by 1°-3°C. For adults the LT(50) ranged from -5°C for Rhus laurina in the summer to -16°C for Rhus ovata in the winter. The LT(50) of R. ovata located at a colder inland site was 4C lower than R. ovata at the warmer coastal site just 4 km apart, suggesting ecotypic differences between R. ovata at the two sites. Both R. laurina and R. ovata underwent significant winter hardening. At the cold site, R. ovata acclimated by 6°C on average, while R. laurina acclimated by only 3°C. These results were consistent with species distributions and with field observations of differential shoot dieback between these two congeneric species after a natural freeze-thaw event in the Santa Monica Mountains.
对来自南加州圣莫尼卡山脉的四种共生的丛林灌木进行了冻害导致叶片死亡的研究，这四种灌木分别是香叶漆树（= 劳氏漆树）、卵形漆树、大果鼠李和具刺鼠李。对所有物种的幼苗和成年植株进行了测量，对漆树属物种还在冬季和夏季以及温暖和寒冷的地点进行了测量。我们使用了四种方法来确定叶片活性或细胞死亡发生50%变化时的温度（LT(50)）：（1）电导率（电解质泄漏到浸泡溶液中），（2）光合荧光能力（Fv/Fm），（3）用荧光素二乙酸活体染色剂染色的栅栏叶肉细胞百分比，以及（4）叶片颜色的视觉评分（孟塞尔色卡）。在所有四个物种中，发现幼苗比成年植株对冷冻温度更敏感，敏感程度为1°C - 3°C。对于成年植株，LT(50)范围从夏季香叶漆树的-5°C到冬季卵形漆树的-16°C。位于较寒冷内陆地点的卵形漆树的LT(50)比相距仅4公里的较温暖沿海地点的卵形漆树低4°C，这表明这两个地点的卵形漆树存在生态型差异。香叶漆树和卵形漆树都经历了显著的冬季硬化。在寒冷地点，卵形漆树平均适应了6°C，而香叶漆树仅适应了3°C。这些结果与物种分布以及在圣莫尼卡山脉自然冻融事件后这两个同属物种之间不同枝条枯死的实地观察结果一致。
