College of Forestry, Northwest A&F University, 3 Taicheng Road, Yangling 712100, China.
College of Life, Northwest A&F University, 3 Taicheng Road, Yangling 712100, China.
Tree Physiol. 2024 Sep 3;44(9). doi: 10.1093/treephys/tpae109.
Seasonality in temperate regions is prominent during the era of increased climatic variability. A hydraulic trait that can adjust to seasonally changing climatic conditions is crucial for tree safety. However, little attention has been paid to the intraspecific seasonality of drought-related traits and hydraulic safety of keystone forest trees. We examined seasonal variations in the key morphological and physiological traits as well as multiple hydraulic safety margins (SMs) at the branch and leaf levels in oriental cork oak (Quercus variabilis Bl.), which is predominant in Chinese temperate forests. Pneumatic measurements indicated that, as seasons progressed, the water potential at which 50% of branch embolisms occur (P50_branch) decreased from -3.34 to -4.23 MPa, with a coefficient of variation (CV) of 9.08%. Sapwood capacitance ranged from 48.19 to 248.08 kg m-3 MPa-1, peaking in autumn and reaching minimum in winter (CV 60.58%). Rehydration kinetics confirmed higher leaf embolism vulnerability (P50_leaf) in spring and autumn than those in summer, with values ranging from -1.06 to -3.02 MPa (CV 39.85%). All leaf pressure-volume (PV) traits shifted with growth, with CVs ranging from 6.95% to 46.69%. Sapwood density had significant negative correlations with P50_branch and hydraulic capacitance for elastic water storage, whereas leaf mass per area was linearly associated with PV traits but not with P50_leaf. Furthermore, the branch typical SMs (difference between branch midday water potential and P50_branch) were consistently >1.84 MPa, and vulnerability segmentation was prevalent throughout, implying a plausible hydraulic foundation for the dominance of Q. variabilis. Diverse hydraulic response patterns existed across seasons, leading to positive SMs mediated by the aforementioned physiological traits. Although Q. variabilis exhibits a high level of hydraulic safety, its susceptibility to sudden summer droughts may increase due to global climate change.
在气候变异性增加的时代，温带地区的季节性表现得尤为明显。树木具有适应季节性气候变化的水力特性对于其安全生长至关重要。然而，人们对与干旱相关的特性的种内季节性以及关键森林树木的水力安全问题关注甚少。我们研究了在中国温带森林中占主导地位的东方栓皮栎（Quercus variabilis Bl.）在树枝和叶片水平上的关键形态和生理特性以及多个水力安全裕度（SMs）的季节性变化。气动测量表明，随着季节的推进，发生 50%树枝栓塞时的水势（P50_branch）从-3.34 降至-4.23 MPa，变异性系数（CV）为 9.08%。边材电容范围为 48.19 至 248.08 kg m-3 MPa-1，在秋季达到峰值，在冬季达到最小值（CV 60.58%）。再水合动力学证实，春季和秋季的叶片栓塞脆弱性（P50_leaf）高于夏季，范围为-1.06 至-3.02 MPa（CV 39.85%）。所有叶片压力-体积（PV）特性都随生长而变化，CV 范围为 6.95%至 46.69%。边材密度与 P50_branch 和弹性储水的水力电容呈显著负相关，而叶面积与 PV 特性呈线性相关，但与 P50_leaf 无关。此外，树枝典型 SMs（树枝中午水势与 P50_branch 的差值）始终大于 1.84 MPa，且脆弱性分段普遍存在，这意味着 Q. variabilis 占主导地位可能具有合理的水力基础。整个季节存在不同的水力响应模式，导致上述生理特性介导的正 SMs。尽管 Q. variabilis 表现出较高的水力安全性，但由于全球气候变化，其对突发性夏季干旱的敏感性可能会增加。
