Data from: Dry-season decline in tree sapflux is correlated with leaf turgor loss point in a tropical rainforest

1. Water availability is a key determinant of forest ecosystem function and tree species distributions. While droughts are increasing in frequency in many ecosystems, including in the tropics, plant responses to water supply vary with species and drought intensity, and are therefore difficult to model. Based on physiological first principles, we hypothesized that trees with a lower turgor loss point (πtlp), i.e., a more negative leaf water potential at wilting, would maintain water transport for longer into a dry season. 2. We measured sapflux density of 22 mature trees of 10 species during a dry season in an Amazonian rainforest, quantified sapflux decline as soil water content decreased, and tested its relationship to tree πtlp, size, and leaf predawn and midday water potentials measured after the onset of the dry season. 3. The measured trees varied strongly in the response of water use to the seasonal drought, with sapflux at the end of the dry season ranging from 37 to 117% (on average 83 ± 5 %) of that at the beginning of the dry season. The decline of water transport as soil dried was correlated with tree πtlp (Spearman ρ≥0.63), but not with tree size or predawn and midday water potentials. Thus, trees with more drought-tolerant leaves better maintained water transport during the seasonal drought. 4. Our study provides an explicit correlation between a trait, measurable at the leaf level, and whole-plant performance under drying conditions. Physiological traits such as πtlp can be used to assess and model higher-scale processes in response to drying conditions.1. 水分可利用性是森林生态系统功能与树种分布的关键决定因素。当前，包括热带生态系统在内的众多生境中，干旱事件的发生频率正持续上升；但植物对水分供应的响应因物种及干旱强度而异，相关建模工作因此极具挑战性。基于生理学第一性原理，我们提出假说：膨压丧失点(turgor loss point, πtlp)更低的树木（即萎蔫时的叶水势更负），其水分运输过程可在旱季维持更长时间。 2. 我们在亚马孙雨林(Amazonian rainforest)的一个旱季期间，对10个物种共计22棵成熟受试树木的树干液流密度(sapflux density)开展了测定；量化了随土壤含水量(soil water content)下降时树干液流的衰减幅度，并检验了该衰减与树木πtlp、树木个体大小，以及旱季发生后测得的黎明前与正午叶水势之间的相关性。 3. 供试树木的水分利用对季节性干旱的响应差异显著：旱季末期的树干液流占旱季初期的比例介于37%至117%之间（平均为83±5%）。土壤干燥过程中水分运输的衰减与树木πtlp呈显著相关（斯皮尔曼秩相关系数(Spearman ρ)≥0.63），但与树木个体大小、黎明前与正午叶水势均无显著关联。由此可见，叶片耐旱性更强的树木，在季节性干旱期间的水分运输维持能力更为出色。 4. 本研究明确建立了可在叶片层面测定的功能性状与干燥条件下整株植物性能之间的直接关联。诸如πtlp这类生理学性状，可用于评估并建模干旱响应相关的更高层级生态过程。