水分浸泡过夜对刺槐枝条最大水分导度测定的影响及年龄差异

枝条最大水分导度是植物水分生理学研究中的核心指标之一,冲洗法是当前用来测定该指标最常用的方法,但在实验测定之前首先必须要找到获得稳定的最大水分导度的可靠方法。本研究中,我们以刺槐(Robinia pseudoacacia L.)不同年龄枝条为实验材料,通过枝条采集后立即用于实验测定和枝条经超纯水中浸泡过夜后再用于实验这两种不同处理方式对不同年龄枝条最大水分导度测定的影响,检测两种处理方式中枝条最大水分导度随冲洗时间的延长是否保持恒定来判断最大水分导度测定值的可靠性,探讨提高枝条最大水分导度测定结果稳定性的有效方法。结果显示:①未浸泡过夜的当年生枝条,经150 kPa压力冲洗达到最大导水率后,继续延长冲洗时间枝条导水率会呈近线性下降,而经超纯水浸泡过夜的当年生枝条以同样实验方法达到最大导水率后,继续延长冲洗时间枝条的导水率基本保持稳定。②二年生枝条无论是否经超纯水浸泡过夜处理,经150 kPa压力冲洗达到最大导水率后枝条的导水率都基本保持稳定,但经超纯水浸泡过夜后,二年生枝条达到最大导水率所需的冲洗时间明显比未浸泡处理短。③根据茎横截面上木质部面积所占百分比和枝条木质密度判断,实验期间当年生枝条的木质化程度明显比二年生枝条低。我们推测未经浸泡过夜的当年生枝条出现木质部水分导度随冲洗时间延长而下降是由于枝条遭受机械性损伤后产生的分泌物在冲洗过程中被引入导管堵塞导管腔所致,而超纯水浸泡枝条过夜可有效降低分泌物被引入导管的可能性。因此,我们认为超纯水浸泡枝条过夜,可提高枝条最大水分导度测定结果的稳定性。

Effect of Soak Stems Overnight with Deionized Water on Measuring Maximum Hydraulic Conductivity in Xylem of Stem Segments of Robinia pseudoacacia L. and Age-relate Difference

The maximum hydraulic conductivity in xylem of branches is one of the core indexes in plant water physiology research. The method of flush the stem by perfusing solution at higher pressure which dissolves and expels the emboli is the most commonly used method which be used to measure the hydraulic conductivity in xylem of stem segments. However, it is necessary to find a reliable method to obtain stable maximum hydraulic conductivity prior to experiment.In this study, the differentyears branches of Robinia pseudoacacia L. was used as the experimental materials, and we compared the effect of two different sample treatment methods on measuring hydraulic conductivity in xylem of stem segments(i.e., without soaked stem segments overnight with deionized water and soaked stem segments overnight with deionized water prior to experiment), the reliability of the maximum hydraulic conductivity determination was determined by test whether the maximum hydraulic conductivity in xylem of stem segments can be kept constant with increasing flushing time, and explore the effective method to improve the stability of measuring maximum hydraulic conductivity of branches. Our results demonstrated that:①the water conductivity of the branches that had not been soaked overnight with deionized water decreased linearly with increasing flushing time after the maximum hydraulic conductivity was reached by 150 kPa pressure flushing, while the hydraulic conductivity of the branches that had been soaked overnight with deionized water prior to experiment kept constant by the same experimental method. ②The hydraulic conductivity of two-year-old branches kept constant after 150 kPa pressure flushing, regardless of whether they were soaked overnight with deionized water or not. However, after soaking stems overnight with deionized water, the time required for two-year-old branches to reach the maximum hydraulic conductivity was significantly shorter than that of non-soaking treatment. ③According to the percentage of xylem area on the cross section of stem and the wood density of branches, the lignification degree of current-year branches was significantly lower than that of biennial branches during the experiment. We speculate that the decrease with increasing flushing time of hydraulic conductivity in the current-year's branches without soaked overnight is due to the blockage of vessel lumen caused by the secretion produced by mechanical injury of branches, and that soaked stem segments overnight with deionized water prior to experiment can effectively reduce the possibility of secretion being introduced into vessel lumen. Therefore, the soaking stem segments overnight with deionized water prior to experiment can improve the stability of maximum hydraulic conductivity measuring.