Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan Province, 666303, China.
Physiol Plant. 2013 May;148(1):74-86. doi: 10.1111/j.1399-3054.2012.01694.x. Epub 2012 Oct 10.
The epiphytic growth habit in many Ficus species during their juvenile stages has commonly been hypothesized to be an adaptation for avoiding deep shade in the forest understory, but this has never been tested experimentally. We examined growth and ecophysiology in seedlings of three hemiepiphytic (Hs) and three non-hemiepiphytic (NHs) Ficus species grown under different irradiance levels. Both Hs and NHs exhibited characteristics of high light requiring species, such as high plasticity to growth irradiance and relatively high maximum photosynthetic assimilation rates. Diurnal measurements of leaf gas exchange showed that Hs have much shorter active photosynthetic periods than NHs; moreover, leaves of Hs have lower xylem hydraulic conductivity but stronger drought tolerance as indicated by much lower rates of leaf diebacks during the drought treatment. Seedlings of NHs had 3.3- and 13.3-fold greater height and biomass than those of Hs species after growing in the nursery for 5 months, indicating a trade-off between growth and drought tolerance due to the conflicting requirements for xylem conductivity and cavitation resistance. This study does not support the shade-avoidance hypothesis; rather, it suggests that the canopy regeneration in Hs is an adaptation to avoid alternative terrestrial growth-related risks imposed to tiny Ficus seedlings. The NHs with terrestrial regeneration reduce these risks by having an initial burst of growth to rapidly gain relatively large seedling sizes, while in Hs seedlings more conservative water use and greater drought tolerance for surviving the canopy environment are intrinsically associated with slow growth.
在许多榕属植物的幼年期，其附生的生长习性通常被假设为是一种避免在森林林下深荫中生长的适应策略，但这从未经过实验验证。我们研究了在不同光照水平下生长的三种半附生（Hs）和三种非半附生（NHs）榕属植物幼苗的生长和生理生态特征。Hs 和 NHs 都表现出喜光物种的特征，例如对生长光照具有高度的可塑性，以及相对较高的最大光合同化率。叶片气体交换的日变化测量表明，Hs 的有效光合时间比 NHs 短得多；此外，Hs 的叶片具有较低的木质部导水率，但耐旱性更强，这表明在干旱处理期间叶片凋落率较低。NHs 幼苗在苗圃中生长 5 个月后，其高度和生物量比 Hs 种增加了 3.3 倍和 13.3 倍，这表明由于木质部导水率和空穴阻力的冲突要求，生长和耐旱性之间存在权衡。本研究不支持避荫假说；相反，它表明 Hs 中的树冠再生是一种适应策略，以避免对微小榕属幼苗造成的替代陆地生长相关风险。具有陆地再生能力的 NHs 通过初始的生长爆发迅速获得相对较大的幼苗大小，从而降低了这些风险，而在 Hs 幼苗中，为了在树冠环境中生存，更加保守的水分利用和更强的耐旱性与缓慢的生长密切相关。
