Li Shubin, Huang Xiaoyan, Zheng Ruping, Zhang Maxiao, Zou Zhiguang, Heal Kate V, Zhou Lili
Forestry College, Fujian Agriculture and Forestry University, Fuzhou, China.
Chinese Fir Engineering Technology Research Center of the State Forestry and Grassland Administration, Fuzhou, China.
Front Plant Sci. 2024 Feb 19;15:1308360. doi: 10.3389/fpls.2024.1308360. eCollection 2024.
A better understanding of xylem hydraulic characteristics in trees is critical to elucidate the mechanisms of forest decline and tree mortality from water deficit. As well as temperate forests and forests growing in arid regions, subtropical and tropical forests are also predicted to experience an increased frequency and intensity of climate change-induced drought in the near future.
In this study, 1-year-old seedlings (a typical subtropical species in southern China) were selected for a continuous controlled drought pot experiment of 45 days duration. The experimental treatments were non-drought (control), light drought, moderate drought and severe drought stress, which were 80%, 60%, 50%, and 40%, respectively of soil field maximum moisture capacity.
The hydraulic conductivity, specific conductivity and water potential of roots, stems, and branches of all decreased with the prolonging of drought in the different drought intensities. The relative decrease in these hydraulic values were greater in roots than in stems and branches, indicating that roots are more sensitive to drought. Root tracheid diameters normally reduce to ensure security of water transport with prolonged drought, whilst the tracheid diameters of stems and branches expand initially to ensure water transport and then decrease to reduce the risk of embolism with continuing drought duration. The pit membrane diameter of roots, stems and branches generally increased to different extents during the 15-45 days drought duration, which is conducive to enhanced radial water transport ability. The tracheid density and pit density of stems generally decreased during drought stress, which decreased water transport efficiency and increased embolism occurrence. Correlation analysis indicated that anatomical plasticity greatly influenced the hydraulic properties, whilst the relationships varied among different organs. In roots, tracheid diameter decreased and tracheid density increased to enhance water transport security; stems and branches may increase tracheid diameter and pit membrane diameter to increase hydraulic conductivity ability, but may increase the occurrence of xylem embolism.
In summary, under drought stress, the xylem anatomical characteristics of organs were highly plastic to regulate water transport vertically and radially to maintain the trade-off between hydraulic conductivity efficiency and safety.
更好地了解树木木质部水力特性对于阐明水分亏缺导致森林衰退和树木死亡的机制至关重要。除了温带森林和干旱地区的森林外，亚热带和热带森林预计在不久的将来也会经历气候变化引发干旱的频率和强度增加的情况。
在本研究中，选用1年生幼苗（中国南方一种典型的亚热带物种）进行为期45天的连续控制干旱盆栽试验。试验处理为非干旱（对照）、轻度干旱、中度干旱和重度干旱胁迫，分别为土壤田间最大持水量的80%、60%、50%和40%。
在不同干旱强度下，随着干旱时间的延长，所有植株根、茎和枝的导水率、比导率和水势均下降。这些水力值的相对下降在根中比在茎和枝中更大，表明根对干旱更敏感。随着干旱时间延长，根导管直径通常会减小以确保水分运输安全，而茎和枝的导管直径最初会扩大以确保水分运输，然后随着干旱持续时间的延长而减小以降低栓塞风险。在干旱持续的15 - 45天内，根、茎和枝的纹孔膜直径普遍不同程度增大，这有利于增强径向水分运输能力。干旱胁迫期间，茎的导管密度和纹孔密度普遍下降，降低了水分运输效率，增加了栓塞发生率。相关性分析表明，解剖可塑性对水力特性有很大影响，而不同器官之间的关系各不相同。在根中，导管直径减小，导管密度增加以提高水分运输安全性；茎和枝可能会增加导管直径和纹孔膜直径以提高导水能力，但可能会增加木质部栓塞的发生。
总之，在干旱胁迫下，植株各器官的木质部解剖特征具有高度可塑性，可垂直和径向调节水分运输，以维持导水效率和安全性之间的平衡。
