Data from: Annual species’ experimental germination responses to light and temperature do not correspond with their microhabitat associations in the field

Annual species have evolved sets of germination cues that are thought to
be predictive of the post-germination environment. In naturally patchy
environments, germination microsites often vary considerably in the amount
of light they receive and in the diurnal temperature fluctuations they
experience. However, whether species’ differential germination responses
to light and temperature are associated with their spatial patterns of
occurrence remains largely untested. We surveyed species’ occurrences in
annual plant communities in 150 quadrats across gradients of canopy cover
and litter cover. Nineteen species recorded in this survey were then
included in a germination experiment that manipulated (1) Light vs. Dark
(12h light or continuous dark) approximating seeds near the soil surface
versus those covered by litter and (2) Cold vs. Warm temperature regimes
(7/18 °C and 7/24 °C) approximating diurnal fluctuations experienced in
shaded versus sun-exposed microsites, respectively. In the germination
experiment, six species had highest germination probabilities in the Light
treatment (regardless of temperature), five in Cold + Light, one in Warm +
Light, two were indifferent to the treatments, and four did not germinate
at all. Binomial linear mixed-effects models showed that species’ maximum
responses to light and temperature did not explain their spatial
distributions along canopy cover and litter cover gradients, contrary to
theoretical expectations of germination being a strong driver of species’
occurrences. Despite variation in species’ responses to experimental
treatments, no association was found with their field microsite
associations. Germination strategies in our system were wider than
expected for Mediterranean systems. Our results support that germination
cues are not strong drivers of microhabitat associations in this system.

一年生植物已演化出一套萌发线索（germination cues），据信这些线索可有效预测萌发后的生长环境。在自然异质生境中，不同萌发微生境所接收的光照量以及所经历的昼夜温度波动往往存在显著差异。然而，物种对光照与温度的差异化萌发响应是否与其空间分布格局相关，目前仍未得到充分验证。
我们在横跨冠层覆盖度与枯落物覆盖度梯度的150个样方（quadrats）中，对一年生植物群落的物种分布开展了调查。本次调查共记录到19个物种，随后将其纳入一项萌发实验，该实验设置了两组操控变量：其一为光照与黑暗处理（12小时光照或持续黑暗），分别模拟土壤表层种子与被枯落物覆盖的种子；其二为低温与高温温度模式（7/18℃与7/24℃），分别对应遮阴与向阳微生境所经历的昼夜温度波动。
在该萌发实验中，6个物种在光照处理组（无论温度条件如何）的萌发概率最高，5个物种在低温+光照组合下表现最优，1个物种在高温+光照组合下萌发效果最佳，2个物种对实验处理无显著响应，另有4个物种完全未萌发。
二项式线性混合效应模型（binomial linear mixed-effects models）分析结果显示，物种对光照与温度的最大响应，并不能解释其沿冠层覆盖度与枯落物覆盖度梯度的空间分布格局，这与“萌发是驱动物种分布的关键因素”这一理论预期相悖。
尽管不同物种对实验处理的响应存在差异，但未发现其与野外微生境偏好存在关联。本研究系统中的萌发策略范围较地中海生态系统的预期更广。我们的研究结果表明，在该系统中，萌发线索并非驱动微生境偏好的核心因素。