Schmid College of Science and Technology, Chapman University, CA, USA.
Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.
Ann Bot. 2021 Mar 24;127(4):495-503. doi: 10.1093/aob/mcaa106.
Leaf functional traits are strongly tied to growth strategies and ecological processes across species, but few efforts have linked intraspecific trait variation to performance across ontogenetic and environmental gradients. Plants are believed to shift towards more resource-conservative traits in stressful environments and as they age. However, uncertainty as to how intraspecific trait variation aligns with plant age and performance in the context of environmental variation may limit our ability to use traits to infer ecological processes at larger scales.
We measured leaf physiological and morphological traits, canopy volume and flowering effort for Artemisia californica (California sagebrush), a dominant shrub species in the coastal sage scrub community, under conditions of 50, 100 and 150 % ambient precipitation for 3 years.
Plant age was a stronger driver of variation in traits and performance than water availability. Older plants demonstrated trait values consistent with a more conservative resource-use strategy, and trait values were less sensitive to drought. Several trait correlations were consistent across years and treatments; for example, plants with high photosynthetic rates tended to have high stomatal conductance, leaf nitrogen concentration and light-use efficiency. However, the trade-off between leaf construction and leaf nitrogen evident in older plants was absent for first-year plants. While few traits correlated with plant growth and flowering effort, we observed a positive correlation between leaf mass per area and performance in some groups of older plants.
Overall, our results suggest that trait sensitivity to the environment is most visible during earlier stages of development, after which intraspecific trait variation and relationships may stabilize. While plant age plays a major role in intraspecific trait variation and sensitivity (and thus trait-based inferences), the direct influence of environment on growth and fecundity is just as critical to predicting plant performance in a changing environment.
叶片功能性状与物种间的生长策略和生态过程密切相关，但很少有人将种内性状变异与个体发育和环境梯度上的表现联系起来。人们认为，植物在胁迫环境中和随着年龄的增长，会向更具资源保守性的性状转变。然而，由于种内性状变异与植物年龄以及在环境变化背景下的表现如何一致存在不确定性，这可能限制了我们使用性状在更大尺度上推断生态过程的能力。
我们在 3 年内，以加利福尼亚旱生蒿（Artemisia californica）为研究对象，在环境条件下测量了叶片生理和形态性状、冠层体积和开花量，处理条件为 50%、100%和 150%的环境水分。
植物年龄是性状和表现变异的比水分可用性更强的驱动因素。较老的植物表现出更具资源保守性策略的性状值，且对干旱的敏感性较低。在不同年份和处理条件下，一些性状的相关性是一致的；例如，具有高光合速率的植物往往具有高气孔导度、叶片氮浓度和光能利用效率。然而，在较老的植物中，叶片构建和叶片氮之间的权衡关系在第一年植物中并不存在。尽管很少有性状与植物生长和开花量相关，但我们观察到一些较老植物群体中，叶面积与性能呈正相关。
总的来说，我们的结果表明，性状对环境的敏感性在发育的早期阶段最为明显，此后种内性状变异和关系可能趋于稳定。虽然植物年龄在种内性状变异和敏感性方面起着重要作用（因此也是基于性状的推断），但环境对生长和繁殖力的直接影响对于预测植物在变化环境中的表现同样至关重要。
