热浪频次及间隔时间对闽楠和木荷苗木水力结构和非结构性碳水化合物的影响

近年来亚热带地区极端气候事件热浪发生频率增加,热浪频次及间隔时间的变化使热浪发生的模式及其对植物的胁迫方式更加多样化。高频热浪不仅通过热胁迫影响植物的碳固持速率,还会间接形成水分胁迫造成植物水力结构发生障碍,影响碳水化合物的运输。然而,目前亚热带树木水力结构和非结构性碳水化合物(NSC)对复杂热浪的模式的响应仍不明确。以亚热带主要阔叶树种闽楠(Phoebe bournei)和木荷(Schima superba)苗木为研究对象进行了热浪模拟试验,关注不同热浪频次(单次,两次)及重复热浪间隔时间(短间隔、中间隔、长间隔)对苗木茎部水力结构特征及NSC的影响,使用冲洗法测定水力结构中的导水率(K_h)、最大导水率(K_max)、比导率(K_s)、木质部栓塞百分数(PLC),使用蒽酮-硫酸比色法测定茎段非结构性碳水化合物含量。结果表明,(1)闽楠和木荷的水力结构和非结构性碳水化合物在树种间存在显著差异;(2)不同热浪频次对闽楠和木荷的K_max和PLC影响存在显著差异;(3)重复热浪间隔时间变长,木荷茎栓塞减轻,而闽楠茎栓塞增加,且植株栓塞越严重,茎NSC含量越少。总体上,闽楠的水力传输系统对热浪抗性较弱,在热浪后栓塞严重,导水率下降且无法完全恢复,且NSC含量与栓塞程度相关性较弱;而木荷水力传输系统抗性较强,在热浪后导水能力可能恢复至未受干扰水平,且其恢复程度与NSC含量紧密相关。该研究结果表明,高频热浪的发生会显著影响闽楠和木荷苗木茎部的导水能力,且不同间隔时间的重复热浪事件对植物水力结构的影响存在差异性,并且两个亚热带阔叶树种对热浪伴随的高温和水分胁迫的耐受性和耐受机制存在差异。

Effects of heat wave frequency and interval on the hydraulic structure characteristics and non-structural carbohydrates of Phoebe bournei and Schima superba seedlings

In recent years, the frequency of extreme climate events in subtropical regions has increased, and changes in the frequency and interval of heat waves have made the patterns of heat waves and their stress on plants more diverse. High frequency heat waves not only affected the carbon sequestration rate of plants through heat stress, but also hindered the hydraulic structure of plants through water stress, affecting the transportation of carbohydrates. However, the response of subtropical tree hydraulic structures and non-structural carbohydrates (NSCs) to complex heat wave patterns is still unclear. This study conducted a heat wave simulation experiment on the seedlings of the main subtropical broad-leaved tree species Phoebe bournei and Schima superba, focusing on the effects of different heat wave frequencies (once or twice) and different interval times between multiple heat waves (short interval, medium interval, and long interval) on the hydraulic structure characteristics and NSCs of the stems of the seedlings. The hydraulic conductivity (K_h), maximum hydraulic conductivity (K_max), specific hydraulic conductivity (K_s), percentage loss of hydraulic conductivity (PLC) in the hydraulic structure were measured using a flushing method, and the content of non-structural carbohydrates in the stems was determined using an anthrone sulfuric acid colorimetric method. The results showed that (1) there were significant differences in the hydraulic structure and non-structural carbohydrates between Phoebe bournei and Schima superba in tree species. (2) The frequency of heat waves had significant impact on the K_max and PLC of Phoebe bournei and Schima superba. (3) The interval between repeated heatwaves became longer, and the embolism of Schima superba stems decreased, while the embolism of Phoebe bournei stems increased. The more severe the embolism, the less NSC content in the stems. Overall, the water conductivity of the stem of Phoebe bournei seedlings was relatively fragile, with severe embolism and decrease in water conductivity after heat waves, and NSC had little effect in alleviating embolism function. However, Schima superba had strong water conductivity. If sufficient recovery time is obtained after a heat wave, its water conductivity can be fully restored, and its recovery degree is closely related to NSC content. The results of this study indicate that the occurrence of high frequency heat waves significantly affects the hydraulic conductivity of the stems of Phoebe bournei and Schima superba seedlings, and there are differences in the effects of repeated heat wave intervals on the hydraulic structure of plants. Additionally, there are differences in the tolerance and tolerance mechanisms of the two subtropical broad-leaved tree species to high temperature and water stress associated with heat waves.