Cátedra de Ecología e IFEVA-CONICET, Universidad de Buenos Aires, Buenos Aires, Argentina.
Ann Bot. 2012 Sep;110(4):849-57. doi: 10.1093/aob/mcs147. Epub 2012 Jul 10.
Despite general agreement regarding the adaptive importance of plasticity, evidence for the role of environmental resource availability in plants is scarce. In arid and semi-arid environments, the persistence and dominance of perennial species depends on their capacity to tolerate drought: tolerance could be given on one extreme by fixed traits and, on the other, by plastic traits. To understand drought tolerance of species it is necessary to know the plasticity of their water economy-related traits, i.e. the position in the fixed-plastic continuum.
Three conspicuous co-existing perennial grasses from a Patagonian steppe were grown under controlled conditions with four levels of steady-state water availability. Evaluated traits were divided into two groups. The first was associated with potential plant performance and correlated with fitness, and included above-ground biomass, total biomass, tillering and tiller density at harvest. The second group consisted of traits associated with mechanisms of plant adjustment to environmental changes and included root biomass, shoot/root ratio, tiller biomass, length of total elongated leaf, length of yellow tissue divided by time and final length divided by the time taken to reach final length.
The most plastic species along this drought gradient was the most sensitive to drought, whereas the least plastic and slowest growing was the most tolerant. This negative relationship between tolerance and plasticity was true for fitness-related traits but was trait-dependent for underlying traits. Remarkably, the most tolerant species had the highest positive plasticity (i.e. opposite to the default response to stress) in an underlying trait, directly explaining its drought resistance: it increased absolute root biomass. The niche differentiation axis that allows the coexistence of species in this group of perennial dryland grasses, all limited by soil surface moisture, would be a functional one of fixed versus plastic responses.
尽管人们普遍认为可塑性具有适应性的重要性，但关于环境资源可利用性在植物中的作用的证据却很少。在干旱和半干旱环境中，多年生物种的持续存在和优势取决于它们耐受干旱的能力：这种耐受性可以通过固定特征在一个极端表现出来，也可以通过塑性特征在另一个极端表现出来。为了了解物种的耐旱性，有必要了解与其水分经济相关的特征的可塑性，即固定-塑性连续体中的位置。
在受控条件下，对来自巴塔哥尼亚草原的三种明显共存的多年生草本植物进行了研究，这些植物在四个稳定的水分供应水平下生长。评估的特征分为两组。第一组与植物潜在性能相关，与适应性相关，包括地上生物量、总生物量、分株和收获时的分株密度。第二组由与植物适应环境变化的机制相关的特征组成，包括根生物量、根冠比、分株生物量、总伸长叶片的总长度、黄色组织长度除以时间和最终长度除以达到最终长度的时间。
在这个干旱梯度上最具可塑性的物种对干旱最敏感，而最不具可塑性和生长最慢的物种则最耐受。这种对适应能力和可塑性之间的负相关关系对与适应性相关的特征是正确的，但对基础特征则是特征依赖性的。值得注意的是，最具耐受性的物种在一个基础特征上具有最高的正可塑性（即与对压力的默认反应相反），这直接解释了其耐旱性：它增加了绝对根生物量。允许该组多年生旱地草本植物共存的生态位分化轴将是固定与塑性反应的功能轴。
