Data from: Tradeoff between physical and chemical defense in plant seeds is mediated by seed mass

Plants have evolved both physical and chemical defenses to make the nutrients of attacked organs difficult to access or more toxic to resist animal consumption or/and pathogen attack. Although it is intuitive that a tradeoff could exist between physical and chemical defenses because of finite defense resources, many studies have failed to detect this tradeoff. We hypothesized that tradeoff between physical and chemical defenses in individual organs was mediated by the total resource allocation to those organs. In this study, we tested whether a tradeoff between physical (i.e. fiber content, which has proved to be a good indicator of investment into seed coat) and chemical defenses (i.e. total phenolics, which are abundant chemical defenses in plant seeds) existed in plant seeds by using 163 common species collected from Xishuangbanna tropical forest, southwest China. Then we tested whether this tradeoff was mediated by seed mass which could be a potential proxy of total resource investment per seed. Among the 163 species, there was large interspecific variation in both total phenolics (from 0.01 to 20.52%) and fiber content (from 4.47 to 81.49%). Our results supported our hypothesis: negative relationships between physical and chemical defenses were much stronger among small seeds than among large seeds. Our study suggests that total resource acquisition must be considered when evaluating defense tradeoffs. However, it is usually extremely difficult to measure this resource acquisition variation, thus we suggest utilizing easily measured proxies of acquisition variation to quantify tradeoffs.

植物已演化出物理与化学双重防御策略，使受攻击器官的养分难以被获取，或提升其毒性，以此抵御动物取食及/或病原体侵染。尽管由于防御资源有限，物理与化学防御间可能存在防御权衡（tradeoff）这一推论符合直觉，但诸多研究均未能检测到该权衡现象。我们提出假说：单个器官的物理与化学防御间的权衡关系，由分配至该器官的总资源量所介导。本研究以采自中国西南西双版纳热带森林的163个常见物种为研究对象，检验植物种子中是否存在物理防御（即纤维含量——已有研究证实其为种皮投资的良好指标）与化学防御（即总酚类物质——植物种子中常见的化学防御成分）之间的权衡关系。随后，我们检验该权衡关系是否由种子质量介导——种子质量可作为单粒种子总资源投资的潜在替代指标。在这163个物种中，总酚类含量（0.01%~20.52%）与纤维含量（4.47%~81.49%）均存在较大的种间变异。研究结果支持我们的假说：相较于大种子物种，小种子物种间的物理与化学防御负相关关系更为显著。本研究表明，在评估防御权衡时必须考虑总资源获取量。然而，直接测量该资源获取变异通常极为困难，因此我们建议采用易于测定的资源获取变异替代指标来量化防御权衡。