Graduate School of Environmental Science, Okayama University, Tsushima-naka 1-1-1, Kita-ku, Okayama, 700-8530, Japan.
Tree Physiol. 2010 May;30(5):608-17. doi: 10.1093/treephys/tpq011. Epub 2010 Apr 5.
Xylem cavitation and its recovery were studied in 1-year-old stems of ring-porous Quercus serrata Thunb. and diffuse-porous Betula platyphylla var. japonica Hara. The Q. serrata had 5-100 microm vessel diameter in the functional current xylem and 5-75 microm in nonconducting 1-year-old xylem; B. platyphylla had a narrower range of vessel diameters of 5-55 microm and more than double the number of vessels in both functional growth rings. Although hydraulic conductivity of Q. serrata appeared to decrease after release of moderate water stress of a half loss of native hydraulic conductivity--about -2 MPa in xylem water potential--no significant recovery of hydraulic conductivity was observed, probably because of intraspecific variation in vessel diameter distribution, which induced variable vulnerability to cavitation. Furthermore, in terms of xylem anatomy, larger and more efficient vessels of the current xylem did not show obvious refilling. In B. platyphylla, after release of water stress, rapid (1 h) recoveries of both hydraulic conductivity and water potential were apparent after rewatering: so-called 'novel refilling'. During that time, a high degree of vessel refilling was observed in both xylems. At 12 h after rewatering, embolized vessels of the current xylem had refilled completely, although about 20% of vessels were still embolized in 1-year-old xylem. This different pattern of vessel refilling in relation to xylem age for B. platyphylla might be attributable to structural faults in the 1-year-old xylem, such as pit degradation or perhaps xylem aging itself. Results show that Q. serrata performs water conduction using highly efficient large vessels instead of unclear vessel refilling. In contrast, B. platyphylla transports water via less efficient but numerous vessels. If cavitation occurs, B. platyphylla improves water conduction by increasing the degree of vessel refilling.
对 1 年生的环孔材栓皮栎和散孔材白桦的木质部空穴化及其恢复进行了研究。栓皮栎功能木质部的导管直径为 5-100 微米，非传导性 1 年生木质部的导管直径为 5-75 微米；白桦的导管直径范围更窄，为 5-55 微米，且功能生长轮中的导管数量是栓皮栎的两倍多。尽管栓皮栎的水力传导率在释放中度水分胁迫（木质部水势下降约-2 MPa，丧失其原生水力传导率的一半）后似乎有所下降，但并未观察到水力传导率的显著恢复，这可能是由于导管直径分布的种内变异导致对空穴化的易感性不同。此外，就木质部解剖结构而言，当前木质部较大且效率较高的导管并没有明显的再填充现象。在白桦中，在释放水分胁迫后，重新浇水后，水力传导率和水势都迅速（1 小时）恢复：所谓的“新型再填充”。在此期间，两个木质部都观察到导管高度再填充。重新浇水 12 小时后，当前木质部栓塞导管已完全填充，但在 1 年生木质部中仍有约 20%的导管栓塞。白桦木质部年龄与导管再填充模式的这种差异可能归因于 1 年生木质部的结构缺陷，如纹孔退化，或者可能是木质部老化本身。研究结果表明，栓皮栎通过使用高效的大导管进行水分传导，而不是通过不明确的导管再填充。相比之下，白桦通过效率较低但数量众多的导管来输送水分。如果发生空穴化，白桦会通过增加导管再填充程度来提高水分传导能力。
