College of Forestry, Northwest A&F University, Yangling, Shaanxi, 712100, China; Qinling National Forest Ecosystem Research Station, Yangling, Shaanxi, 712100, China.
Plant Cell Environ. 2014 Jan;37(1):35-44. doi: 10.1111/pce.12120. Epub 2013 Jun 12.
Vulnerability curves (VCs) generally can be fitted to the Weibull equation; however, a growing number of VCs appear to be recalcitrant, that is, deviate from a Weibull but seem to fit dual Weibull curves. We hypothesize that dual Weibull curves in Hippophae rhamnoides L. are due to different vessel diameter classes, inter-vessel hydraulic connections or vessels versus fibre tracheids. We used dye staining techniques, hydraulic measurements and quantitative anatomy measurements to test these hypotheses. The fibres contribute 1.3% of the total stem conductivity, which eliminates the hypothesis that fibre tracheids account for the second Weibull curve. Nevertheless, the staining pattern of vessels and fibre tracheids suggested that fibres might function as a hydraulic bridge between adjacent vessels. We also argue that fibre bridges are safer than vessel-to-vessel pits and put forward the concept as a new paradigm. Hence, we tentatively propose that the first Weibull curve may be accounted by vessels connected to each other directly by pit fields, while the second Weibull curve is associated with vessels that are connected almost exclusively by fibre bridges. Further research is needed to test the concept of fibre bridge safety in species that have recalcitrant or normal Weibull curves.
脆弱性曲线（VCs）通常可以拟合威布尔方程；然而，越来越多的 VCs 似乎难以拟合，即偏离威布尔分布，但似乎符合双威布尔曲线。我们假设双威布尔曲线在沙棘中是由于不同的血管直径类群、血管间水力连接或血管与纤维管胞之间的差异造成的。我们使用染色技术、水力测量和定量解剖学测量来检验这些假设。纤维占总茎导率的 1.3%，这排除了纤维管胞构成第二威布尔曲线的假设。然而，血管和纤维管胞的染色模式表明纤维可能在相邻血管之间充当水力桥。我们还认为纤维桥比血管到血管的坑更安全，并提出了这一概念作为一个新的范例。因此，我们初步提出，第一威布尔曲线可能是由通过坑场直接相互连接的血管来解释的，而第二威布尔曲线与几乎仅通过纤维桥连接的血管有关。需要进一步的研究来检验具有难治性或正常威布尔曲线的物种中纤维桥安全性的概念。
