不同冲洗液对毛白杨和油松枝条水力导度和抵抗空穴化能力测定值的影响

植物通过木质部管道系统进行水分运输, 木质部的水分运输效率和抗空穴化能力等水力结构特征对于植物物种的分布、抗逆能力等方面起关键性作用。目前, 国内外学者一般采用“冲洗法”进行木质部水力结构研究, 然而在该方法中使用的不同冲洗溶质可能对植物木质部水力结构等产生较大影响, 因此该文研究了3种溶质的冲洗溶液对毛白杨(Populus tomentosa)和油松(Pinus tabulaeformis)枝条的水力导度和抵抗空穴化能力的影响。实验结果表明: 相对于去离子水, 用0.01 mol·L^-1的草酸和0.03 mol·L^-1KCl溶液作为冲洗溶液, 均导致毛白杨木质部导管和油松管胞的水力导度测定值的增大。KCl导致毛白杨和油松木质部抵抗空穴化能力测定值的提高, 草酸导致杨树抵抗空穴化能力测定值增强, 但导致油松抗空穴化能力显著(p<0.01)减弱。小枝水平上, 毛白杨和油松的水分运输效率和抗空穴化能力之间没有显著相关性。另外, 在截枝实验中发现, 毛白杨小枝木质部水力导度随长度增加变化不大, 而油松枝条的木质部水力导度有逐渐增大的趋势。以上的实验结果表明不同溶质下毛白杨和油松枝条的木质部水力导度和抵抗空穴化能力不同, 草酸和KCl可能对木质部管道系统及纹孔处的果胶等产生作用, 从而使毛白杨和油松的水力结构发生变化。毛白杨与油松水力结构在去离子水、草酸和KCl的作用下的不同结果及两物种截枝试验下水力导度的不同变化趋势表明, 导管运输系统和管胞运输系统可能具有不同的水分运输影响因素。

EFFECTS OF DIFFERENT FLUSH SOLUTIONS ON VALUES OF HYDRAULIC CONDUCTIVITIES AND CAVITATION RESISTANCE ABILITIES OF TRESS OF POPULUS TOMENTOSA AND PINUS TABULAEFORMIS

Aims Xylem hydraulic structure of water transport plays a key role in plants’ distribution, resistance to stress, etc. However, the current “flushing method” for studying characteristics of xylem hydraulic structure takes different solutions as the flushing solution, which may lead to different values of xylem hydraulic conductivity and cavitation resistance ability. Methods We used deionized water (pH=7), the solution of 10 mmol&#8226;L^–1 oxalic acid (pH=2) and 30 mmol&#8226;L^–1 KCl (pH=7) as flush solutions to measure the hydraulic characteristics of tress of Populus tomentosa and Pinus tabulaeformis, which are the specific conductivities (Ks), leaf specific conductivities (Kl), xylem vulnerability curves and cavitation resistance ability (Ψ₅₀) . Important findings Compared with deionized water, oxalic acid and KCl as flushing solutions led to higher xylem hydraulic conductivities (Ks, Kl) in both species. With KCl flushing, the cavitation resistance abilities (–Ψ₅₀) slightly increased in P. tomentosa and significantly increased (p<0.01) in P. tabulaeformis. However, oxalic acid led an increase in cavitation resistance in P. tomentosa but a significant decrease (p<0.01) in P. tabulaeformis. Furthermore, there was no significant linear correlation between xylem hydraulic conductivity and cavitation resistance ability for both species, measured under the same flush solution. The hydraulic conductivity with different tress length (in a range of 5–20 cm) showed that the hydraulic conductivity was stable with trees length in P. tomentosa, but greatly increased with tress length in P. tabulaeformis. Different flush solutions have different effects on xylem hydraulic structure. Furthermore, the hydraulic conductivities and cavitation resistance abilities measured with different flush solutions show a species-specific response. Thus, dynamic adjustment of components and concentration of sap in xylem conduit may facilitate a flexible response of plant hydraulic structure to changing environmental conditions.