Prats Kyra A, Brodersen Craig R
School of the Environment, Yale University, New Haven, CT, USA.
AoB Plants. 2020 Sep 11;12(6):plaa048. doi: 10.1093/aobpla/plaa048. eCollection 2020 Dec.
Wintergreen fern has fronds that are photosynthetically active year-round, despite diurnal and seasonal changes in soil moisture, air temperature and light availability. This species can fix much of its annual carbon during periods when the deciduous canopy is open. Yet, remaining photosynthetically active year-round requires the maintenance of photosynthetic and hydraulic systems that are vulnerable to freeze-thaw cycles. We aimed to determine the anatomical and physiological strategies uses to maintain positive carbon gain, and the coordination between the hydraulic and photosynthetic systems. We found that the first night below 0 °C led to 25 % loss of conductivity (PLC) in stipes, suggesting that winter-induced embolism occurred. Maximum photosynthetic rate and chlorophyll fluorescence declined during winter but recovered by spring, despite PLC remaining high; the remaining hydraulic capacity was sufficient to supply the leaves with water. The onset of colder temperatures coincided with the development of a necrotic hinge zone at the stipe base, allowing fronds to overwinter lying prostrate and maintain a favourable leaf temperature. Our conductivity data show that the hinge zone did not affect leaf hydraulics because of the flexibility of the vasculature. Collectively, these strategies help to survive in northeastern forests.
冬青蕨的叶片全年都具有光合活性，尽管土壤湿度、气温和光照条件存在昼夜和季节性变化。该物种能够在落叶林冠层开放的时期固定其大部分年度碳。然而，全年保持光合活性需要维持易受冻融循环影响的光合和水力系统。我们旨在确定其用于维持正碳增益的解剖学和生理学策略，以及水力和光合系统之间的协调。我们发现，首次低于0°C的夜晚导致叶柄导水率损失25%（PLC），这表明发生了冬季诱导的栓塞。尽管PLC仍然很高，但冬季最大光合速率和叶绿素荧光下降，但到春季恢复；剩余的水力能力足以向叶片供水。气温下降与叶柄基部坏死铰链区的形成同时发生，使叶片能够平卧越冬并维持适宜的叶温。我们的导水率数据表明，由于脉管系统的柔韧性，铰链区不会影响叶片水力。总的来说，这些策略有助于其在东北森林中生存。
