Wu Angelica, Anderegg Leander D L, Dawson Todd E, Trugman Anna T
Department of Integrative Biology, 3040 Valley Life Sciences Building, University of California, Berkeley, CA 94720, USA.
Department of Ecology, Evolution, and Marine Biology, Noble Hall, University of California, Santa Barbara, CA 93106, USA.
Tree Physiol. 2023 Dec 12;43(12):2098-2108. doi: 10.1093/treephys/tpad127.
Trees are arguably the most diverse and complex macro-organisms on Earth. The equally diverse functions of trees directly impact fluxes of carbon, water and energy from the land surface. A number of recent studies have shed light on the substantial within-species variability across plant traits, including aspects of leaf morphology and plant allocation of photosynthates to leaf biomass. Yet, within-tree variability in leaf traits due to microclimatic variations, leaf hydraulic coordination across traits at different physiological scales and variations in leaf traits over a growing season remain poorly studied. This knowledge gap is stymieing the fundamental understanding of what drives trait variation and covariation from tissues to trees to landscapes. Here, we present an extensive dataset measuring within-tree heterogeneity in leaf traits in California's blue oak (Quercus douglasii) across an edaphic gradient and over the course of a growing season at an oak-grass savanna in Southern CA, USA. We found a high level of within-tree crown leaf area:sapwood area variation that was not attributable to sample height or aspect. We also found a higher level of trait integration at the tree level, rather than branch level, suggesting that trees optimize water use at the organismal level. Despite the large variance in traits within a tree crown and across trees, we did not find strong evidence for adaptive plasticity or acclimation in leaf morphological traits (e.g., changes to phenotype which increased fitness) across temporal and spatial water availability gradients. Collectively, our results highlight strong variation in drought-related physiology, but limited evidence for adaptive trait plasticity over shorter time scales.
树木可以说是地球上最多样化和最复杂的宏观生物。树木同样多样的功能直接影响着陆地表面碳、水和能量的通量。最近的一些研究揭示了植物性状在物种内部存在显著变异性，包括叶片形态以及光合产物在叶片生物量中的分配等方面。然而，由于微气候差异导致的树木内部叶片性状变异性、不同生理尺度下叶片性状间的水力协调性以及生长季节内叶片性状的变化，目前仍研究不足。这一知识空白阻碍了我们从组织到树木再到景观层面，对驱动性状变异和协变因素的基本理解。在此，我们展示了一个广泛的数据集，该数据集测量了美国加利福尼亚州南部橡木 - 草地稀树草原上，蓝橡树（Quercus douglasii）在土壤梯度上以及生长季节内树木内部叶片性状的异质性。我们发现树冠内叶面积与边材面积的变化程度很高，且这并非由采样高度或方向所致。我们还发现，在树木层面而非分支层面存在更高水平的性状整合，这表明树木在生物体层面优化了水分利用。尽管树冠内以及不同树木间性状存在很大差异，但我们并未找到有力证据表明叶片形态性状（例如，增加适应性的表型变化）在时间和空间水分可利用性梯度上具有适应性可塑性或驯化现象。总体而言，我们的研究结果凸显了干旱相关生理过程中的强烈变异性，但在较短时间尺度上适应性性状可塑性的证据有限。
