Submergence Causes Similar Carbohydrate Starvation but Faster Post-Stress Recovery than Darkness in Alternanthera philoxeroides Plants

Carbon assimilation by submerged plants is greatly reduced due to low light levels. It is hypothesized that submergence reduces carbohydrate contents and that plants recover from submergence in the same way as darkness-treated plants. To test this hypothesis, the responses of plants to submergence and darkness were studied and compared. Plants of a submergence-tolerant species, Alternanthera philoxeroides, were exposed to well drained and illuminated conditions, complete submergence conditions or darkness conditions followed by a recovery growth period in a controlled experiment. The biomass maintenance and accumulation, carbohydrate content dynamics and respiration rate in the plants were assessed to quantify the carbohydrate utilization rate and regrowth. The submerged plants maintained higher chlorophyll contents, more green leaf tissue and more biomass; recovered more quickly; and accumulated more carbohydrates and biomass than darkness-treated plants. The respiration rate was continuously reduced in the same pattern under both stress conditions but was maintained at a significantly lower level in the submerged plants; the total soluble sugar and total fructan contents were decreased at approximately the same rate of decrease, reaching similar low levels, in the two stress treatments. The A. philoxeroides plants were more tolerant of submergence than darkness. The faster recovery of desubmerged plants could not be explained by the similar carbohydrate contents at the start of recovery. Other types of carbon reserves besides carbohydrates or other mechanisms such as higher post-stress photosynthetic performance might be involved.

受淹植物的碳素同化作用因光照不足而大幅降低。本研究提出假说：淹水胁迫会降低植物体内碳水化合物含量，且淹水后的植株恢复过程与黑暗处理植株一致。为验证该假说，我们对植物在淹水与黑暗条件下的响应开展了对比研究。本对照实验选取淹水耐受物种喜旱莲子草（Alternanthera philoxeroides）的植株，设置了排水良好且光照充足、完全淹水、黑暗三种处理组，随后均设置恢复生长阶段。通过测定植株的生物量维持与积累情况、碳水化合物含量动态变化以及呼吸速率，以量化碳水化合物利用效率与再生生长能力。结果显示，与黑暗处理植株相比，淹水植株的叶绿素含量更高、绿叶组织更多、生物量更大，恢复速度更快，且碳水化合物与生物量积累更多。两种胁迫条件下，植株呼吸速率均呈相同模式持续下降，但淹水植株的呼吸速率始终维持在显著更低的水平；两种胁迫处理下，植株的总可溶性糖与总果聚糖含量均以近似速率下降，最终降至相近的低水平。喜旱莲子草对淹水胁迫的耐受性强于黑暗胁迫。淹水解除后植株恢复更快这一现象，无法通过恢复初期二者碳水化合物含量相近这一点来解释。推测可能存在碳水化合物以外的其他碳素储备形式，或是胁迫后光合性能提升等其他作用机制。