Data from: Does soil moisture availability explain liana seedling distribution across a tropical rainfall gradient?

Liana density tends to increase with decreasing rainfall and increasing seasonality. However, the pattern of liana distribution may be due to differences in soil water retention capacity, not rainfall and seasonality per se. We tested the effect of rainfall and soil substrate with respect to the distribution of liana seedlings in six sites across a rainfall gradient from the wet Atlantic to the dry Pacific in central Panama. Soils were either limestone, with low water-holding capacity, or laterite, with higher water-holding capacity. We sampled liana seedlings at each site using three 1 × 100 m transect. We found that relative liana seedling density was higher on limestone soils compared to laterite soils regardless of the amount of rainfall. Furthermore, liana community composition on limestone soils was more similar to dry forest sites than to adjacent wet and moist forest sites. Liana seedling species diversity relative to trees was significantly higher in a low-fertility dry forest site compared to a high-fertility forest, but did not differ from the other sites. Thus, liana seedling density and community structure may be driven more by soil type and thus by soil moisture availability than strictly by mean annual rainfall and the seasonality of rainfall.

藤本植物（liana）的种群密度通常随降雨量减少、降水季节节律增强而升高。然而，藤本植物的分布格局可能由土壤持水能力的差异决定，而非降雨量与降水季节节律本身。我们在巴拿马中部沿降水梯度（从湿润的大西洋沿岸森林至干旱的太平洋沿岸森林）设置了6个样地，针对藤本幼苗的分布，检验了降雨量与土壤基质的影响效应。本次研究涉及的土壤分为两类：持水能力较低的石灰岩（limestone）土壤，以及持水能力较高的红土（laterite）土壤。我们在每个样地中布设3条1×100 m的样带（transect），对藤本幼苗开展取样调查。结果显示，无论降雨量多少，石灰岩土壤上的藤本幼苗相对密度均显著高于红土土壤。此外，石灰岩土壤上的藤本群落组成与干旱森林样地的相似度更高，而非邻近的湿润与半湿润森林。相较于高肥力森林样地，低肥力干旱森林样地中藤本幼苗相对于乔木的物种多样性显著更高，但该指标与其余样地并无显著差异。综上，藤本幼苗的密度与群落结构的驱动因素，更可能是土壤类型（进而关联土壤有效含水量），而非单纯的年平均降雨量与降水季节节律。