Department of Biotechnology and Life Science, University of Insubria, Varese, Italy.
Physiol Plant. 2023 May-Jun;175(3):e13934. doi: 10.1111/ppl.13934.
How temperate trees respond to drier summers strongly depends on the drought susceptibility and the starch reserve of the very-fine roots (<0.5 mm in diameter). We performed morphological, physiological, chemical, and proteomic analyses on very-fine roots of Fagus sylvatica seedlings grown under moderate- and severe drought conditions. Moreover, to reveal the role of the starch reserves, a girdling approach was adopted to interrupt the flux of photosynthates toward the downstream sinks. Results show a seasonal sigmoidal growth pattern without evident mortality under moderate drought. After the severe-drought period, intact plants showed lower starch concentration and higher growth than those subjected to moderate drought, highlighting that very-fine roots rely on their starch reserves to resume growth. This behavior caused them to die with the onset of autumn, which was not observed under moderate drought. These findings indicated that extreme dry soil conditions are needed for significant root death in beech seedlings and that mortality mechanisms are defined within individual compartments. The girdling treatment showed that the physiological responses of very-fine roots to severe drought stress are critically related to the altered load or the reduced transport velocity of the phloem and that the changes in starch allocation critically alter the distribution of biomass. Proteomic evidence revealed that the phloem flux-dependent response was characterized by the decrease of carbon enzymes and the establishment of mechanisms to avoid the reduction of the osmotic potential. The response independent from the aboveground mainly involved the alteration of primary metabolic processes and cell wall-related enzymes.
温和气候树木对干旱夏季的响应在很大程度上取决于非常细根（<0.5mm 直径）的耐旱性和淀粉储备。我们对在中度和重度干旱条件下生长的欧洲山毛榉幼苗的非常细根进行了形态学、生理学、化学和蛋白质组学分析。此外，为了揭示淀粉储备的作用，我们采用了环割方法来中断光合产物向下游库的流动。结果表明，在中度干旱条件下，根呈现出季节性的 S 形生长模式，没有明显的死亡率。在严重干旱期后，完整的植株表现出比中度干旱条件下更低的淀粉浓度和更高的生长速度，这表明非常细根依赖于它们的淀粉储备来恢复生长。这种行为导致它们在秋季开始时死亡，而在中度干旱条件下则没有观察到这种情况。这些发现表明，极端干燥的土壤条件是山毛榉幼苗中显著根死亡所必需的，并且死亡率机制在个体隔室中确定。环割处理表明，非常细根对严重干旱胁迫的生理响应与韧皮部改变的负荷或减少的运输速度密切相关，而淀粉分配的变化则极大地改变了生物量的分布。蛋白质组学证据表明，韧皮部依赖性响应的特征是碳酶的减少和建立避免渗透势降低的机制。与地上部分无关的响应主要涉及初级代谢过程和细胞壁相关酶的改变。
