Developmental control of xylem hydraulic resistances and vulnerability to embolism in Fraxinus excelsior L: Impacts on water relations
Developmental control of xylem hydraulic resistances and vulnerability to embolism in Fraxinus excelsior L: Impacts on water relations
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DOI：
10.1093/jxb/48.3.655
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发表时间：
1997-03-01
影响因子：
6.9
通讯作者：
Granier, A
中科院分区：
文献类型：
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作者：
Cochard, H;Peiffer, M;Granier, A
比较了不同树龄和垂直树冠位置的黄曲柳（Fraxinus excelsior L.）枝条在相同环境空气条件（蒸汽压差和总辐射）下的水力特性和叶片气体交换。同一冠不同分枝间小叶水势psi、小叶气孔导度和蒸腾速率E的差异较小。采用高压流量计测定全枝水力阻力（r（枝））和叶片阻力（r（叶））与木质部阻力（r（木质部））之间的分配，其中r（叶）分别占上冠和下冠枝r（枝）的90%和10%。这种变化主要是由于短枝节间的形成导致r（木质部）的增加，而短枝节间主要位于次生轴。然而，整个树冠的叶面积比枝阻力（r（枝）*=r（枝）× LA）几乎是恒定的。这与psi（小叶）的垂直变化一致，因为r（枝）* x E表示从树干到叶片的水势下降。由于r（木质部）较高，预计下冠枝的psi（木质部）值较低。然而，下冠枝的茎比上枝的茎更不容易栓塞（栓塞开始时的psi（木质部），psi（cav）分别为-3和-2 MPa）。r（木质部）随枝龄的增加而增加，但r（枝）*因LA的降低而保持不变。结果，E最大化，且psi（木质部）保持在psi（cav）以上。这表明，在曲霉中，叶片气体交换和叶面积与木质部水力能力可能是通过控制芽活性来耦合的。
The hydraulic properties and leaf gas exchanges of Fraxinus excelsior L. branches differing by their age and their vertical crown position, but in comparable ambient air conditions (vapour pressure deficit and global radiation) were compared. The variations in leaflet water potential psi(leaflet), leaflet stomatal conductance and transpiration rate, E, were small between different branches of the same crown. Whole branch hydraulic resistances (r(branch)), and partitioning between leaf (r(leaf)) and xylem resistance (r(xylem)) were assessed with a high pressure flowmeter, r(leaf) represented 90% and 10% of r(branch) for upper and lower crown branches, respectively. The changes resulted from increases in r(xylem) caused by the formation of short shoot internodes mostly located in secondary axes. However, leaf area-specific branch resistances (r(branch)*=r(branch) x LA) were nearly constant throughout the crown. This was consistent with the vertical variations in psi(leaflet) because r(branch)* x E represents the water potential drop from the trunk to the leaves. Because r(xylem) was higher, lower psi(xylem) values were predicted in lower crown rachises However, rachises from lower crown branches were less vulnerable to embolism than in upper branches (psi(xylem) at onset of embolism, psi(cav), were -3 and -2 MPa, respectively). It was concluded that r(xylem) increased with branch age, but r(branch)* remained constant because LA decreased. As a consequence, E was maximized and psi(xylem) remained above psi(cav). This suggested that, in Fraxinus, leaf gas exchanges and leaf areas were coupled with xylem hydraulic capacities probably through a control of bud activity.