Data from: Early life conditions and precipitation influence the performance of widespread understory herbs in variable light environments

1. The understory of tropical forests is heterogeneous across time, and plants that inhabit this layer may exhibit adaptations (e.g. trait plasticity) that enable them to exploit this variability to their advantage. We tested the hypothesis that two widespread understory herbs would perform equally well in a variable as in a constant environment, using a two-year shade-house experiment. 2. We measured demographic traits (growth and survival), a physiological trait (maximum photosynthetic capacity), and life history traits (leaf lifespan and biomass allocation) of Heliconia tortuosa and Calathea crotalifera. We investigated how these traits were affected by light availability at the seedling stage, precipitation, and whether individuals experienced a constant or variable light environment. 3. Whether or not a variable environment was favorable for plants depended upon precipitation and the environment in which individuals started life. At low precipitation, plants in a variable light environment grew more than those in a constant environment, but only when individuals had lived as seedlings in low light. At high precipitation, plants in a constant environment grew more than those in a variable environment, regardless of early conditions. Survival was lower in a variable environment at low precipitation, and more so at high precipitation. Photosynthetic capacity was lower for individuals in a variable environment than in a constant environment when they had lived in high light as seedlings. 4. Calathea grew faster and survived more poorly than Heliconia, independently of the treatments. Calathea grew more at high than low precipitation while Heliconia grew more at low than high precipitation. Leaf lifespan and biomass allocation did not differ among treatments, although Calathea had a significantly greater proportion of its biomass aboveground versus that of Heliconia. 5. Synthesis Environmental variability had a neutral or positive effect on biomass allocation, photosynthetic capacity, and leaf lifespan for these species. Survival was the only trait that was always lower in a variable environment. The effect of environmental variability was dependent on early life conditions as well as precipitation, suggesting that generalist species may experience high fitness as forest environments become more variable by maintaining high growth at the expense of survival.1. 热带森林林下植被随时间呈现异质性，栖息于此层的植物可能演化出适应性特征（如性状可塑性（trait plasticity）），借此利用环境变异性以获益。本研究依托为期两年的人工遮棚实验，验证了如下假说：两种广布的林下草本植物在可变环境与恒定环境中的生长表现并无差异。2. 本研究测定了扭叶赫蕉（Heliconia tortuosa）和黄竹芋（Calathea crotalifera）的种群统计性状（生长与存活）、生理性状（最大光合能力（maximum photosynthetic capacity））以及生活史性状（叶寿命与生物量分配）。我们探究了幼苗阶段的光照有效性、降水量，以及植株所处光照环境为恒定或可变，如何对上述性状产生影响。3. 可变环境对植物是否有利，取决于降水量以及植株的初始生长环境。在低降水量条件下，仅当植株以幼苗阶段处于弱光环境时，可变光照环境中的植株生长量才高于恒定光照环境中的植株；而在高降水量条件下，无论早期生长环境如何，恒定光照环境中的植株生长量均高于可变光照环境中的植株。低降水量条件下，可变光照环境中的植株存活率更低，高降水量条件下该差异更为显著。当植株以幼苗阶段处于强光环境时，可变光照环境中的植株其光合能力低于恒定光照环境中的植株。4. 无论实验处理如何，黄竹芋的生长速率均快于扭叶赫蕉，但存活率更低。黄竹芋在高降水量条件下的生长量高于低降水量条件，而扭叶赫蕉则在低降水量条件下生长量更高。不同实验处理下，叶寿命与生物量分配均无显著差异，尽管黄竹芋的地上生物量占比显著高于扭叶赫蕉。5. 综合分析：环境变异性对本研究涉及物种的生物量分配、光合能力以及叶寿命具有中性或正向影响。存活是唯一在可变环境中始终更低的性状。环境变异性的效应同时取决于早期生长环境与降水量，这表明广适性物种可通过以牺牲存活为代价维持高生长速率，在森林环境愈发多变的背景下获得较高的适合度（fitness）。