Population Differentiation along a Flood Frequency Gradient: Physiological Adaptations to Flooding in Nyssa sylvatica
Population Differentiation along a Flood Frequency Gradient: Physiological Adaptations to Flooding in Nyssa sylvatica
复制标题
沿洪水频率梯度的种群分化：Nyssa sylvatica 对洪水的生理适应
DOI：
--
复制
发表时间：
1979
期刊：
影响因子：
--
通讯作者：
J. Keeley
中科院分区：
文献类型：
--
作者：
J. Keeley
在整个美国东南部，硬木Nyssa sylvatica（sensu lato）沿着土壤湿度梯度分布，从从未被洪水淹没的高地到定期被洪水和排水的洪泛区，再到永久被洪水淹没的沼泽地。使用沿该梯度收集的种子在温室中生长的一岁幼苗，研究了关于洪水耐受性和相关生理属性的群体分化。高地植物非常不耐水淹的土壤。它们的根系恶化，根系呼吸速率下降，在这种条件下一年后，它们的存活率很差，而那些留下来的则严重发育不良，并积累了高浓度的许多营养元素。相比之下，沼泽植物对淹没的土壤相当耐受。洪水过后，部分原始根系消失，但新根开始生长，酒精发酵能力增强。许多这些新根比排水的根更肉质、直径更大、分枝更少。然而，这种多汁的根只是对短期洪水的暂时反应。被洪水淹没一年的植物没有这样的根，而是根系表面上类似于排水的根。与这种类似排水状根的恢复相伴的是，向根部内部氧气输送的增加和酒精发酵的减少。在排水条件下，洪泛区植物分配给根的生物量少于分配给芽的生物量，并且具有高呼吸速率，其特征与旱地植物相似。在淹没条件下，它们以中等呼吸速率启动新根，分配给根的生物量比分配给芽的生物量少，显着增加了向根的氧气输送，并且具有高成活率，其特征与沼泽植物相似。因此，洪泛区种群产生了明显的耐洪表型。但对洪水条件的耐受性不如沼泽表型。漫滩植物与沼泽植物的不同之处在于，在排水条件下，向根部输送较少的氧气，在洪水时引发较少的肉质型根，并且不加速酒精发酵，并且在淹没条件下一年后，总生物量较少，向根部输送的氧气较少，并且根部中铁和锰的积累较多。洪泛区植物显然被选择为类似于排水条件下的高地植物和洪水条件下的沼泽植物，其结果之一是它们对洪水条件的耐受性是中等的。有人认为，适应淹没条件的更重要的权衡之一是，在水胁迫条件下，高内部氧气运输会带来过度失水的“成本”。
Throughout the southeastern United States the hardwood Nyssa sylvatica (sensu lato) is distributed along a soil moisture gradient from upland sites, which are never flooded, to floodplains, which are periodically flooded and drained, to permanently flooded swamps. Population differentiation with respect to flood tolerance and related physiological attributes was investigated using 1-year-old seedlings grown in a greenhouse from seed collected along this gradient. Upland plants were very intolerant of flooded soils. Their root systems deteriorated, root respi- ration rates dropped and, after a year under such conditions, survival was poor and those that did remain were greatly stunted and had accumulated large concentrations of many nutrient elements. In contrast swamp plants were quite tolerant of flooded soils. Upon flooding, parts of the original root system were lost but new roots were initiated which had an increased capacity for alcoholic fermentation. Many of these new roots were more succulent, larger in diameter, and less branched than drained roots. Such succulent roots however were only a temporary response to short-term flooding; plants flooded for a year did not have such roots, rather the root system superficially resembled drained roots. Concomitant with this return to drained-like roots was an increase in internal oxygen transport to the roots and a drop in alcoholic fermentation. Floodplain plants under drained conditions allocated less biomass to roots than to shoots and had high respiration rates, traits similar to upland plants. Under flooded conditions they initiated new roots with medium respiration rates, allocated less biomass to roots than to shoots, significantly increased oxygen transport to the roots and had high survival, traits similar to swamp plants. Thus, the floodplain population produced a distinctly flood-tolerant phenotype; but not nearly as tolerant of flooded conditions as the swamp phenotype. Floodplain plants differed from swamp plants in transporting less oxygen to the roots under drained conditions, initiating fewer succulent-type roots and not accelerating alcoholic fermentation upon flooding and after a year under flooded conditions having less total biomass, less oxygen transport to the roots and a greater accumulation of Fe and Mn in the roots. The floodplain plants apparently have been selected to be similar to upland plants under drained conditions and swamp plants under flooding and one consequence of this is that their tolerance of flooded conditions is intermediate. It is argued that one of the more important trade-offs in adapting to flooded conditions is that high internal oxygen transport carries with it a "cost" in terms of excessive water loss under water stress conditions.