Data from: Trade-offs in juvenile growth potential vs. shade tolerance among subtropical rainforest trees on soils of contrasting fertility

1. Plant adaptation to gradients of light availability involves a well-studied functional trade-off, as does adaptation to gradients of nutrient availability. However, little is known about how these two major trade-offs interact and thus it remains unclear whether and how the nature of the growth-shade tolerance trade-off differs on soils of contrasting fertility. 2. We asked if juvenile growth-shade tolerance trade-offs differed in slope and elevation between tree assemblages on nutrient-rich basalt and nutrient-poor rhyolite soils in an Australian subtropical rainforest. 3. We measured the growth of, and range of light environments occupied by, juveniles (40-120 cm tall) of eight basalt specialists, six rhyolite specialists, and one generalist that was common on both substrates. In situ minimum light requirements were estimated from the 5th percentile of the distribution of naturally regenerated juveniles in relation to daily light transmittance. Stem growth was measured for 12 to 16 months across a wide range of light environments to estimate the light compensation point of growth of each species. 4. Light compensation points of growth showed nearly a 1:1 correspondence with in situ minimum light requirements of species, indicating that whole-plant carbon balance is a key driver of ecological success in low light. Minimum light requirements were negatively correlated with relative growth rate in low light, but correlated positively with growth in high light. Soil type had no effect on either the slope or the elevation of this trade-off, all species aligning around a common growth-shade tolerance trade-off, but our results do show a wider range of growth rates and shade tolerance on the nutrient-rich basalt soil than on the nutrient-poor rhyolite. 5. Our results suggest that adaptation to light availability involves fundamentally similar trade-offs on these two substrates of differing fertility. However, a wider range of growth rates and shade tolerance on the nutrient-rich basalt soil than on the nutrient-poor rhyolite may help to explain the higher species richness and greater structural complexity of forest stands on the former substrate.1. 植物对光照有效性（light availability）梯度的适应涉及一种被广泛研究的功能权衡（functional trade-off），对养分有效性（nutrient availability）梯度的适应亦是如此。然而，目前对这两种主要权衡如何相互作用的认知仍十分有限，因此尚不清楚生长-耐荫权衡（growth-shade tolerance trade-off）的本质在肥力迥异的土壤上是否存在差异，以及具体差异如何。 2. 本研究旨在探究澳大利亚亚热带雨林中，生长在养分丰富的玄武岩（basalt）土壤与养分贫瘠的流纹岩（rhyolite）土壤上的树木群落，其幼树的生长-耐荫权衡在斜率与截距上是否存在差异。 3. 我们测定了8种玄武岩专性物种、6种流纹岩专性物种以及1种在两类基质（substrates）上均常见的广适物种的幼树（株高40~120 cm）的生长状况及其所占据的光照环境范围。通过自然更新幼树的分布与每日光照透过率（daily light transmittance）的关系的第5百分位数，估算出各物种的原位最低光照需求。在广泛的光照环境中开展为期12至16个月的茎生长测定，以估算各物种生长的光补偿点（light compensation point of growth）。 4. 物种生长的光补偿点与原位最低光照需求近乎呈1:1对应关系，这表明整株碳平衡（whole-plant carbon balance）是弱光环境下生态成功的关键驱动因子。原位最低光照需求与弱光下的相对生长速率（relative growth rate）呈负相关，却与强光下的生长呈正相关。土壤类型对该生长-耐荫权衡的斜率与截距均无影响，所有物种均围绕一条共通的生长-耐荫权衡轴分布，但研究结果同时显示，相较于养分贫瘠的流纹岩土壤，养分丰富的玄武岩土壤上的生长速率与耐荫性的分布范围更广。 5. 本研究结果表明，在这两类肥力迥异的基质上，植物对光照有效性的适应所涉及的权衡本质上是相似的。然而，相较于养分贫瘠的流纹岩土壤，养分丰富的玄武岩土壤上更广的生长速率与耐荫性分布范围，或可解释该基质上林分更高的物种丰富度与更复杂的群落结构。