盐生植物角果碱蓬种子二型性对环境的适应策略

角果碱蓬(Suaeda corniculata)是藜科一年生盐生植物, 在我国分布于北方盐碱滩涂和盐碱荒漠地区。角果碱蓬具有棕色和黑色两种异型体种子(简称棕色和黑色种子)。对采自内蒙古鄂托克前旗盐渍化生境的角果碱蓬二型种子的形态、休眠和萌发特性开展对比研究, 测定了二型种子休眠和萌发行为对温度、光照和盐分(NaCl)的响应, 以揭示盐生植物异型种子对温带盐漠生境的适应对策。结果表明: (1)二型性种子在大小、种皮特性和结实比例方面有显著差异。与黑色种子相比, 棕色种子个体较大, 种皮透水性强。黑色种子与棕色种子的结实比例约为5.6 : 1。(2)新成熟的棕色种子的萌发对各温度梯度和光照条件不敏感, 萌发率较高(84%-100%); 而新成熟的黑色种子萌发率较低(8%-78%), 萌发对光照敏感。(3)黑色种子具有浅度生理休眠, 种皮划破、赤霉素处理和低温层积均可有效地提高种子的萌发率。(4)二型种子萌发对土壤盐分的胁迫具有不同的响应。与黑色种子相比, 棕色种子对盐分胁迫不敏感, 在较高的盐分浓度下仍有较高的萌发率, 低温层积处理能够降低黑色种子对盐胁迫的敏感性, 有效地提高种子的初始萌发率、萌发恢复率和最终萌发率。角果碱蓬二型种子不同的形态、休眠和萌发特性, 提高了该物种在高度异质性生境中的适合度, 对种群成功地适应温带盐漠环境具有重要的意义。

Adaptive strategies of dimorphic seeds of the desert halophyte Suaeda corniculata in saline habitat

Aims Suaeda corniculata (Chenopodiaceae) is an annual halophyte in salt marshes and saline deserts of northern China. It produces two distinct types of seeds (brown and black). The primary aims of our study were to compare the morphology, dormancy and germination characteristics of dimorphic seeds of S. corniculata in order to elucidate adaptive strategies of the desert halophyte in stressful saline habitat. Methods Seeds were collected in saline habitats in Otog, Nei Mongol. The dimorphic seeds were incubated in different temperature regimes, light and salinity (NaCl) conditions to determine their germination responses. The effects of cold stratification and seed coat scarification on dormancy breaking of black seeds were also tested. Important findings Dimorphic seeds were different in seed mass and testa morphology. Brown seeds were bigger and more permeable to water than black seeds. Seed ratio was 5.6 : 1 (black seeds : brown seeds). Freshly matured brown seeds had a high germination percentage (84%–100%) in all temperature regimes and under either light or dark conditions. By contrast, black seeds had a lower germination percentage (8%–78%) than brown seeds in all temperature regimes, and germination was increased in light. Seed coat scarification, GA3 treatments and cold stratification significantly increased the germination of black seeds, suggesting that black seeds had non-deep physiological dormancy. Responses of dimorphic seeds to saline stress were different. Brown seeds were more salt-tolerant than black seeds and germinated at a high germination percentage in high salt concentrations. Cold stratification reduced the sensitivity of black seeds to salt stress and increased the initial germination percentage, recovery and final germination in salt solutions. The differences in morphology, dormancy and germination characteristics between dimorphic seeds of S. corniculata increased the species’ fitness to heterogeneous habitats and formed an ecological adaptive strategy that may allow S. corniculata to successfully adapt to the harsh desert habitat.