As radial root resistance (Rp) represents one of the key components of the soil-plant-atmosphere continuum resistance catena modulating water transport, understanding its control is essential for physiologists, modelers and breeders. Reports of Rp, however, are still scarce and scattered in the scientific literature. In this study, we assessed genetic variability in Rp and its dependence on temperature in five widely used olive cultivars. In a first experiment, cultivar differences in Rp at 25 °C were evaluated from flow-pressure measurements in excised roots and subsequent analysis of root traits. In a second experiment, similar determinations were performed continually over a 5-h period in which temperature was gradually increased from 12 to 32 °C, enabling the assessment of Rp response to changing temperature. Despite some variability, our results did not show statistical differences in Rp among cultivars in the first experiment. In the second, cultivar differences in Rp were not significant at 12 °C, but they became so as temperature increased. Furthermore, the changes in Rp between 12 and 32 °C were higher than those expected by the temperature-driven decrease in water viscosity, with the degree of that change differing among cultivars. Also, Rp at 25 °C reached momentarily in the second experiment was consistently higher than in the first at that same, but fixed, temperature. Overall, our results suggest that there is limited variability in Rp among the studied cultivars when plants have been exposed to a given temperature for sufficient time. Temperature-induced variation in Rp might thus be partly explained by changes in membrane permeability that occur slowly, which explains why our values at 25 °C differed between experiments. The observed cultivar differences in Rp with warming also indicate faster acclimation of Rp to temperature changes in some cultivars than others.

中文翻译：

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橄榄根水流径向抗性的基因型变异及其对温度变化的响应。

由于径向根抗性（Rp）代表着土壤-植物-大气连续性抗性调节水传输的关键组成部分之一，因此了解其控制对于生理学家，建模者和育种者至关重要。但是，Rp的报告在科学文献中仍然很少且分散。在这项研究中，我们评估了五个广泛使用的橄榄品种Rp的遗传变异性及其对温度的依赖性。在第一个实验中，从切离的根中的流压测量以及随后对根性状的分析中，评估了25°C下Rp的品种差异。在第二个实验中，在5小时内连续进行了类似的测定，其中温度逐渐从12℃升高到32℃，从而能够评估Rp对温度变化的响应。尽管有一些可变性，我们的结果在第一个实验中并未显示出品种之间Rp的统计差异。第二，Rp的品种差异在12°C时不显着，但随着温度升高而变大。此外，在12至32°C之间Rp的变化高于温度驱动的水粘度下降所预期的变化，不同品种之间变化的程度不同。同样，在相同但固定的温度下，第二个实验瞬间达到的25°C Rp始终高于第一个实验。总体而言，我们的结果表明，当植物暴露于给定温度足够长的时间后，所研究品种的Rp变异有限。因此，温度引起的Rp变化可能部分由缓慢发生的膜渗透率变化来解释，这解释了为什么我们的25°C值在实验之间会有所不同。随着温度的升高，观察到的Rp品种差异也表明Rp在某些品种中比其他品种更快适应温度变化。