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. 热带森林林下层（understory）具有显著的时空异质性，栖息于此的植物往往演化出相应适应策略（例如性状可塑性（trait plasticity）），借此利用环境波动以获取生存优势。本研究依托为期两年的荫棚（shade-house）实验，验证了如下假说：两种广布的林下层草本植物，在可变环境与恒定环境中的生长表现无显著差异。
2. 本研究测定了Heliconia tortuosa与Calathea crotalifera的种群统计性状（demographic traits，包括生长与存活）、生理性状中的最大光合能力（maximum photosynthetic capacity），以及生活史性状（life history traits，包括叶寿命（leaf lifespan）与生物量分配（biomass allocation））。本研究探究了幼苗阶段的光照可获得性、降水量，以及植株所处的光照环境类型（恒定/可变）对上述性状的影响。
3. 可变光照环境对植物是否有利，取决于降水量与植株的早期生长环境。在低降水量条件下，仅当植株在幼苗阶段经历弱光照环境时，可变光照环境下的植物生长量才显著高于恒定光照环境；而在高降水量条件下，无论早期生长环境如何，恒定光照环境下的植物生长量均显著高于可变光照环境。低降水量条件下，可变光照环境中植株的存活率更低；高降水量条件下，该存活率降幅更为显著。当幼苗阶段经历强光照环境时，可变光照环境下植株的最大光合能力显著低于恒定光照环境下的植株。
4. 无论实验处理如何，Calathea的生长速率均显著高于Heliconia，但其存活率更低。高降水量条件下Calathea的生长量高于低降水量条件，而Heliconia的生长量则在低降水量条件下更高。不同实验处理间，植株的叶寿命与生物量分配均无显著差异，但Calathea的地上生物量占总生物量的比例显著高于Heliconia。
5. 综合分析：环境波动对两种植物的生物量分配、光合能力与叶寿命均无显著负面影响，甚至存在积极作用。存活率是唯一在可变光照环境中始终更低的性状。环境波动的影响同时依赖于植株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率为代价维持高生长速率，在森林环境愈发波动的背景下保持较高的适合度（fitness）。