Abstract:

In recent years, seasonal droughts have increasingly impacted subtropical regions, highlighting the potential significance of root morphological traits in shaping the drought resistance strategies of trees. To elucidate the adaptive mechanisms of tree species with varying root architectures in response to drought stress, this study focused on the seedlings of five subtropical species: the deep-rooted Camphora officinarum, Quercus variabilis, and Quercus glauca, and the shallow-rooted Cunninghamia lanceolata and Phyllostachys edulis. A 45−day drought stress was imposed using a natural water loss method to investigate responses in biomass allocation, organ water dynamics, and root morphological plasticity during the seedling stage. The results indicated that: 1) deep-rooted tree seedlings significantly enhanced drought resistance by optimizing root morphology and redistributing dry matter. Specifically, the root biomass and fine root proportion of Camphora officinarum increased by 28.7% and 44.3% (p<0.05) from the onset of the experiment under short-term drought conditions, with root length and tip numbers continuing to expand throughout the drought period, thereby maintaining water homeostasis in the stems and leaves. The root/shoot ratio and fine root proportion of Quercus variabilis increased by 20.4% and 13.3% (p<0.05), respectively, with a notable increase in root diameter following prolonged drought exposure. The leaf biomass ratio of Quercus glauca increased by 44.4% (p<0.05) during the later stages of drought stress, although its limited root plasticity restricted its adaptation to only medium-term drought. 2) In contrast, shallow-rooted tree seedlings predominantly rely on aboveground homeostatic mechanisms, with drought stress leading to root decline, thereby compromisings their drought resistance. The root biomass, root/shoot ratio, and overall water content of Cunninghamia lanceolata decreased by 22.0%, 29.0%, and 62.9% (p<0.05), respectively. Phyllostachys edulis mitigated drought effects through short-term water storage in stems; however, prolonged stress resulted in the continued deterioration of root traits, with a 36.4% reduction in the root biomass ratio, impairing survival under extended drought conditions. 3) Deep-rooted species effectively acquired resources through synergistic enhancements in root morphology and biomass allocation, whereas shallow-rooted species exhibited diminished absorption capacity owing to root shrinkage. In conclusion, deep-rooted species have adapted to prolonged drought conditions through active morphological plasticity and optimization of dry matter allocation within their root systems during the seedling stage. Conversely, shallow-rooted species adopt conservative aboveground homeostatic strategies that limit their ability to balance immediate survival and long-term drought resistance. Moreover, the drought resistance conferred by the root system depends not only on the depth of root architecture but also on the synergistic optimization of biomass distribution strategies and the functional plasticity of various organs.

Key words: drought, biomass, dry matter partitioning, water content, root plasticity

摘要：

近年来亚热带地区季节性干旱频发，根系形态特征可能主导树木抗旱策略形成。为揭示不同根型树种对干旱胁迫的适应性机制，以亚热带典型的深根型树种樟（Camphora officinarum）、栓皮栎（Quercus variabilis）、青冈（Quercus glauca）和浅根型树种杉木（Cunninghamia lanceolata）、毛竹（Phyllostachys edulis）5个树种幼苗为对象，采用持续45 d的自然失水法模拟干旱胁迫过程，研究不同根型树种幼苗时期生物量分配、器官水分动态及根系形态可塑性的响应规律。结果表明，1）深根型树种幼苗通过根系形态优化与干物质再分配显著提升抗旱性。樟在短期胁迫下根生物量和细根比例较试验开始时分别增加28.7%和44.3%（p<0.05），根长与根尖数量随胁迫时间持续增长，以维持茎叶水分稳态；栓皮栎经历长期干旱胁迫后根冠比和细根比例分别升高20.4%和13.3%（p<0.05），其根系直径明显增大；青冈干旱胁迫后期叶生物量比升高44.4%（p<0.05），但根系可塑性不足导致其仅能适应中期干旱。2）浅根型树种幼苗更多依赖地上稳态策略，干旱胁迫导致根系衰退，进而削弱其抗旱能力。杉木根生物量、根冠比、全株含水率分别降低22.0%、29.0%、62.9%（p<0.05）；毛竹通过茎部短期储水可短暂延缓干旱胁迫的影响，但随胁迫时间延长，根系性状持续退化，根生物量比降低36.4%，难以在长期干旱条件下存活。3）深根型树种通过根系形态优化与生物量分配的协同变化实现资源高效获取，而浅根型树种因根系收缩导致吸收能力下降。总体而言，深根型树种幼苗时期通过根系主动形态可塑性和干物质分配适应持续干旱，而浅根型树种依赖地上稳态的保守策略难以平衡短期生存与长期抗旱需求。同时根系抗旱优势不仅取决于构型深度，更依赖于生物量分配策略与器官功能可塑性的协同优化。

关键词: 干旱, 生物量, 干物质分配, 含水率, 根系可塑性