In the face of resource limitations, plants show plasticity in multiple trait categories, including biomass allocation, morphology, and anatomy, yet inevitably also grow less. The extent to which passive mass‐scaling plays a role in trait responses that contribute to increased potential for resource acquisition is poorly understood. Here, we assessed the role of mass‐scaling on the direction, magnitude, and coordination of trait plasticity to light and/or nutrient limitation in cultivated sunflower (Helianthus annuus). We grew seedlings of 10 sunflower genotypes for 3 weeks in a factorial of light (50% shade) and nutrient (10% supply) limitation in the greenhouse and measured a suite of allocational, morphological, and anatomical traits for leaves, stems, fine roots, and tap roots. Under resource limitation, plants were smaller and more biomass was allocated to the organ capturing the most limiting resource, as expected. Traits varied in the magnitude of plasticity and the extent to which the observed response was passive (scaled with plant mass) and/or had an additional active component. None of the allocational responses were primarily passive. Plastic changes to specific leaf area and specific root length were primarily active, and adjusted toward more acquisitive trait values under light and nutrient limitation, respectively. For many traits, the observed response was a mixture of active and passive components, and for some traits, the active adjustment was antagonistic to the direction of passive adjustment, for example, stem height, and tap root and stem theoretical hydraulic conductance. Passive scaling with size played a major role in the coordinated response to light, but correcting for mass clarified that the active responses to both limitations were more similar in magnitude, although still resource and organ specific. Our results demonstrate that both passive plasticity and active plasticity can contribute to increased uptake capacity for limiting resources in a manner that is resource, organ, and trait specific. Indeed, passive adjustments (scaling with mass) of traits due to resource stress extend well beyond just mass allocation traits. For a full understanding of plants’ response to environmental stress, both passive and active plasticity need to be taken into account.

中文翻译：

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栽培向日葵（Helianthus annuus L.）的可塑性以及质量尺度在分配、形态和解剖性状对地上和地下资源限制的反应中的作用


面对资源限制，植物在生物量分配、形态和解剖学等多个性状类别中表现出可塑性，但也不可避免地生长得较少。人们对被动大规模扩张在有助于增加资源获取潜力的特质反应中所发挥的作用程度知之甚少。在这里，我们评估了栽培向日葵（ Helianthus annuus ）中性状可塑性对光和/或养分限制的方向、幅度和协调的质量缩放的作用。我们在温室中将 10 种向日葵基因型的幼苗在光照（50% 遮荫）和养分（10% 供应）限制的条件下培育了 3 周，并测量了叶、茎、细根的一系列分配、形态和解剖特征，并主根。正如预期的那样，在资源有限的情况下，植物更小，更多的生物量被分配给捕获最有限资源的器官。性状在可塑性的大小以及观察到的反应的被动程度（随植物质量缩放）和/或具有额外的活性成分方面有所不同。没有一个分配反应主要是被动的。特定叶面积和特定根长的塑性变化主要是活跃的，并分别在光照和养分限制下向更具获取性的性状值进行调整。对于许多性状，观察到的响应是主动和被动成分的混合，并且对于某些性状，主动调节与被动调节的方向相反，例如茎高、主根和茎理论水导度。 被动的尺寸缩放在对光的协调响应中发挥了重要作用，但对质量的校正表明，对两种限制的主动响应在幅度上更相似，尽管仍然是资源和器官特定的。我们的结果表明，被动可塑性和主动可塑性都有助于提高以特定于资源、器官和性状的方式限制资源的吸收能力。事实上，由于资源压力而导致的特征被动调整（按质量缩放）远远超出了质量分配特征。为了充分了解植物对环境胁迫的反应，需要考虑被动和主动可塑性。