Duncan Corrine, Schultz Nick L, Good Megan K, Lewandrowski Wolfgang, Cook Simon
School of Health and Life Sciences, Federation University, Mt Helen, VIC, Australia.
BioSciences, University of Melbourne, Parkville, VIC, Australia.
AoB Plants. 2019 Oct 10;11(6):plz066. doi: 10.1093/aobpla/plz066. eCollection 2019 Dec.
Water availability is a critical driver of population dynamics in arid zones, and plant recruitment is typically episodic in response to rainfall. Understanding species' germination thresholds is key for conservation and restoration initiatives. Thus, we investigated the role of water availability in the germination traits of keystone species in an arid ecosystem with stochastic rainfall. We measured seed germination responses of five arid species, along gradients of temperature and water potential under controlled laboratory conditions. We then identified the cardinal temperatures and base water potentials for seed germination, and applied the hydrotime model to assess germination responses to water stress. Optimum temperatures for germination ranged from 15 to 31 °C under saturated conditions (0 MPa), and three species had low minimum temperatures for germination (<3 °C). A small proportion of seeds of all species germinated under dry conditions (Ψ ≤ -1 MPa), although base water potential for germination (Ψ 50) ranged from -0.61 to -0.79 MPa. Species adhered to one of two germination traits: (i) the risk-takers which require less moisture availability for germination, and which can germinate over a wider range of temperatures irrespective of water availability ( and ), and (ii) the risk-avoiders which have greater moisture requirements, a preference for cold climate germination, and narrower temperature ranges for germination when water availability is low (, and ). High seed longevity under physiological stress in , combined with a risk-avoiding strategy, allows bet-hedging. The hydrotime model predicted lower base water potentials for germination than observed by the data, further supporting our assertion that these species have particular adaptations to avoid germination during drought. This study provides insights into the complex physiological responses of seeds to environmental stress, and relates seed germination traits to community dynamics and restoration in arid zones.
水资源可利用性是干旱地区种群动态的关键驱动因素，植物繁殖通常随降雨呈间歇性。了解物种的萌发阈值是保护和恢复计划的关键。因此，我们研究了水资源可利用性在一个降雨随机的干旱生态系统中对关键物种萌发特性的作用。在可控的实验室条件下，我们沿着温度和水势梯度测量了5种干旱物种的种子萌发反应。然后，我们确定了种子萌发的基础温度和基础水势，并应用水分时间模型评估对水分胁迫的萌发反应。在饱和条件（0兆帕）下，萌发的最适温度范围为15至31℃，有3个物种的最低萌发温度较低（<3℃）。所有物种的一小部分种子在干燥条件下（Ψ≤ -1兆帕）萌发，尽管萌发的基础水势（Ψ 50）范围为-0.61至-0.79兆帕。物种遵循两种萌发特性之一：（i）冒险型，萌发所需水分可利用性较低，且无论水分可利用性如何，都能在更宽的温度范围内萌发（ 和 ）；（ii）避险型，对水分需求更大，偏好寒冷气候下萌发，且在水分可利用性较低时萌发温度范围更窄（ 、 和 ）。 在生理胁迫下种子寿命长，再加上避险策略，实现了风险对冲。水分时间模型预测的萌发基础水势低于数据观测值，进一步支持了我们的观点，即这些物种具有特殊适应性以避免在干旱期间萌发。本研究深入了解了种子对环境胁迫的复杂生理反应，并将种子萌发特性与干旱地区的群落动态和恢复联系起来。
