Data from: Trait patterns of epiphytes compared to other plant life forms along a tropical elevation gradient

Compared to other plant life forms, epiphytes remain understudied. Understanding the responses of epiphytes to changing environmental conditions is necessary to predict changes in ecosystem functioning especially in subtropical and tropical regions. We investigated the functional traits of epiphytes along a large elevation gradient on Mount Kilimanjaro, Tanzania. We measured traits of co-occurring trees and terrestrial non-tree life forms, and compared changes in community-weighted means of traits (CWM) and trait spread, the range of observed trait values. We chose traits linked to growth and persistence: leaf area, specific leaf area, leaf dry matter content, stem specific density, plant height, leaf carbon, leaf nitrogen, and leaf phosphorus. For most traits, differences in community-weighted means between life forms exceeded differences within life forms along the elevation gradient. Many CWM showed linear changes with elevation, but no response and unimodal patterns were also frequent. This was best explained by temperature, or a combination of temperature with precipitation or humidity, indicating effects of these factors on the distribution of epiphytic and non-epiphytic species. Trait spread did not change with elevation in nearly half of the traits, but hump-shaped patterns were also common, probably a result of weaker environmental filtering in the gradient center. The magnitude of trait spread, i.e. the variability between species of the same life form within communities, was highest for terrestrial non-trees. Excluding ferns from the analyses lead to marked differences in trait patterns for epiphytes, as ferns made up 59 % of the epiphytic species, while playing a minor role in the other groups. The observed differences can be explained by a dichotomy in epiphytic life strategies, with tough-leaved xero-tolerant species on one side and succulent soft-leaved species on the other. However, the influence of phylogeny was lower than expected from the taxonomic composition of the three life form groups. Our results emphasize that environmental constraints act upon functional traits of epiphytes, trees and terrestrial non-trees. The differences in trait expressions, arguably adaptations of the different life forms, need to be taken into account in conservation contexts as well as when modeling the effects of global change on ecosystems.

与其他植物生活型相比，附生植物（epiphytes）的研究仍相对不足。理解附生植物对环境变化的响应，是预测生态系统功能变化的必要前提，尤其在亚热带与热带区域。本研究针对坦桑尼亚乞力马扎罗山沿大海拔梯度分布的附生植物展开功能性状调查，同时测定了伴生木本植物与陆生非木本植物的性状，并对比了沿海拔梯度的群落加权性状均值（community-weighted means of traits, CWM）与性状离散度（即观测性状值的分布范围）的变化。本研究选取与生长及存活相关的性状：叶面积（leaf area）、比叶面积（specific leaf area）、叶干物质含量（leaf dry matter content）、茎比密度（stem specific density）、植株高度（plant height）、叶碳含量（leaf carbon）、叶氮含量（leaf nitrogen）与叶磷含量（leaf phosphorus）。在多数性状上，沿海拔梯度的不同生活型间的群落加权性状均值差异，均大于同一生活型内部的差异。多数CWM随海拔呈线性变化，但无响应与单峰模式也较为常见。这一现象最可由温度，或温度与降水、湿度的协同作用解释，表明上述因素对附生与非附生物种分布的调控作用。近半数性状的性状离散度未随海拔发生变化，但驼峰型模式也较为普遍，这或源于梯度中部较弱的环境过滤作用。性状离散度的大小，即群落内同一生活型物种间的性状变异程度，在陆生非木本植物中最高。将蕨类植物从分析中剔除后，附生植物的性状模式出现显著差异——蕨类占附生植物物种总数的59%，但在其他类群中占比极低。上述差异可归因于附生植物生活策略的二分性：一类为硬叶耐旱物种，另一类为肉质软叶物种。但相较于三个生活型类群的分类组成所预期的结果，系统发育的影响相对较弱。本研究结果表明，环境约束对附生植物、木本植物与陆生非木本植物的功能性状均存在调控作用。性状表达的差异（可视为不同生活型的适应性特征），在生态保护研究以及全球变化对生态系统影响的模拟工作中均需纳入考量。