Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, 55108, USA.
Department of Botany, Plant Anatomy Laboratory, São Paulo University (USP), São Paulo, Brazil.
Ecology. 2019 Nov;100(11):e02827. doi: 10.1002/ecy.2827. Epub 2019 Aug 14.
Lianas are more abundant in seasonal forests than in wetter forests and are thought to perform better than trees when light is abundant and water is limited. We tested the hypothesis that lianas perform better than trees during seasonal drought using a common garden experiment with 12 taxonomically diverse species (six liana and six tree species) in 12 replicated plots. We irrigated six of the plots during the dry season for four years, while the remaining six control plots received only ambient rainfall. In year 5, we measured stem diameters for all individuals and harvested above- and belowground biomass for a subset of individuals to quantify absolute growth and biomass allocation to roots, stems, and leaves, as well as total root length and maximum rooting depth. We also measured rate of photosynthesis, intrinsic water use efficiency (iWUE), pre-dawn and midday water potential, and a set of functional and hydraulic traits. During the peak of the dry season, lianas in control plots had 54% higher predawn leaf water potentials (Ψ ), and 45% higher photosynthetic rates than trees in control plots. By contrast, during the peak of the wet season, these physiological differences between lianas and trees become less pronounced and, in some cases, even disappeared. Trees had higher specific leaf area (SLA) than lianas; however, no other functional trait differed between growth forms. Trees responded to the irrigation treatment with 15% larger diameters and 119% greater biomass than trees in control plots. Liana growth, however, did not respond to irrigation; liana diameter and biomass were similar in control and irrigation plots, suggesting that lianas were far less limited by soil moisture than were trees. Contrary to previous hypotheses, lianas did not have deeper roots than trees; however, lianas had longer roots per stem diameter than did trees. Our results support the hypothesis that lianas perform better and experience less physiological stress than trees during seasonal drought, suggesting clear differences between growth forms in response to altered rainfall regimes. Ultimately, better dry-season performance may explain why liana abundance peaks in seasonal forests compared to trees, which peak in abundance in less seasonal, wetter forests.
藤本植物在季节性森林中的丰度高于湿润森林，并且当光照充足而水分有限时，它们的表现被认为优于树木。我们通过在 12 个重复样地中使用 12 种具有不同分类学的物种（6 种藤本植物和 6 种树木）的通用花园实验来测试这样一个假设，即在季节性干旱期间，藤本植物的表现优于树木。我们在四个旱季对六个样地进行灌溉，而其余六个对照样地仅接受自然降雨。在第五年，我们测量了所有个体的茎直径，并收获了一部分个体的地上和地下生物量，以量化绝对生长和生物量分配给根、茎和叶，以及总根长和最大根深度。我们还测量了光合作用速率、内在水分利用效率（iWUE）、晨始和中午水势以及一组功能和水力特性。在旱季高峰期，对照样地中的藤本植物的晨始叶片水势（Ψ ）比对照样地中的树木高 54%，光合作用速率高 45%。相比之下，在雨季高峰期，藤本植物和树木之间的这些生理差异变得不那么明显，在某些情况下甚至消失了。树木的比叶面积（SLA）高于藤本植物；然而，生长形式之间没有其他功能特征存在差异。与对照样地中的树木相比，灌溉处理的树木的直径增加了 15%，生物量增加了 119%。然而，藤本植物的生长并未对灌溉做出响应；对照样地和灌溉样地的藤本植物的直径和生物量相似，这表明藤本植物受土壤水分的限制远小于树木。与先前的假设相反，藤本植物的根没有树木深；然而，藤本植物的每茎直径的根比树木长。我们的结果支持这样一个假设，即在季节性干旱期间，藤本植物的表现优于树木，并且经历的生理压力较小，这表明在应对改变的降雨模式时，生长形式之间存在明显差异。最终，更好的旱季表现可能解释了为什么与树木相比，藤本植物的丰度在季节性森林中达到峰值，而树木的丰度在季节性较弱、湿润的森林中达到峰值。
