LEAF DEMOGRAPHY OF A NEOTROPICAL RAIN-FOREST CYCAD, ZAMIA-SKINNERI (ZAMIACEAE)
LEAF DEMOGRAPHY OF A NEOTROPICAL RAIN-FOREST CYCAD, ZAMIA-SKINNERI (ZAMIACEAE)
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DOI：
10.2307/2445193
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发表时间：
1992-01-01
影响因子：
3
通讯作者：
GRAYUM, MH
中科院分区：
文献类型：
--
作者：
CLARK, DB;CLARK, DA;GRAYUM, MH
热带雨林林下环境是光照极其有限的环境。人们对这些栖息地树叶的人口统计知之甚少。为了确定新热带雨林林下物种的叶子寿命和死亡原因，我们在哥斯达黎加 La Selva 生物站对 173 株苏铁灌木 Zamia Skinneri 的 634 片叶子进行了 10 年的研究。对五个不同季节的叶子进行了跟踪。各队列之间的中位叶片寿命没有显着差异，但各队列在<1年至大于或等于6年的年间隔内死亡的叶片比例确实存在差异。所有叶子的中位最短存活时间为 4.6 年。昙花覆盖率从生命第一年的 0% 增加到第 4 年的 75%-100%。叶子死亡率可以通过两个独立的指数函数很好地描述，大约每年 10% 死亡率，直到第 4 年，然后突然增加到约 10%。 51%/年。在 625 片叶子死亡中，77.0% 是由于不明原因造成的，16.5% 是由于落叶造成的物理损坏，4.8% 是灰蝴蝶 Eumaeus minyas 幼虫的攻击，1.8% 是其他原因。叶片寿命与叶片大小呈正相关。 Z. Skinneri 个体经常在非常黑暗的林下条件下存活一个多世纪。我们认为，在这些情况下，叶子的寿命是由叶子老化和附生植物覆盖率增加导致的叶子碳平衡不可避免的恶化以及由于物理损伤和专科食草动物攻击造成的损失决定的。
Tropical rain forest understories are extremely light-limited environments. Little is known about the demography of leaves in these habitats. To determine leaf longevity and causes of mortality for a species in the understory of a neotropical rain forest, we studied 634 leaves on 173 individuals of the cycad shrub Zamia skinneri for 10 yr at the La Selva Biological Station, Costa Rica. Five different seasonal cohorts of leaves were followed. No significant differences among cohorts were found in median leaf longevity, but the cohorts did differ in the proportion of leaves dying in annual intervals from < 1 to greater-than-or-equal-to 6 yr. Median minimum time alive for all leaves was 4.6 yr. Epiphyll coverage increased from 0% in the first year of life to 75%-100% by year 4. Leaf mortality was well described by two separate exponential functions, approximately 10% mortality/yr until year 4, then abruptly increasing to ca. 51%/yr. Of 625 leaf deaths, 77.0% were due to unexplained causes, 16.5% to physical damage by falling litter, 4.8% to attacks by larvae of the lycaenid butterfly Eumaeus minyas, and 1.8% to other causes. Leaf longevity was positively correlated with leaf size. Individuals of Z. skinneri frequently survive more than a century in very dark understory conditions. We suggest that leaf longevity in these circumstances is determined by the inevitable deterioration in leaf carbon balance due to leaf aging and increasing epiphyll coverage, and by loss due to physical damage and attacks by the specialist herbivore.