确定P-V曲线中质壁分离点的方法比较

质壁分离渗透势(Ψ_tlp)与质壁分离相对含水量(C_RW,tlp)作为重要的水分生理参数,被认为是衡量树木耐旱性强弱的重要指标。为了验证不同方法确定质壁分离点的差异,笔者对比了Ⅰ型与Ⅱ型标绘P-V曲线类型,采用Ⅱ型标绘方式,利用常见的数学法、图形法和程序法分析了东北东部山区主要树种的Ψ_tlp和C_RW,tlp。结果表明:Ⅰ型8个树种Ψ_tlp和C_RW,tlp平均值分别较Ⅱ型高出0.20 MPa和3.17%。其中两种标绘类型对针叶树兴安落叶松和红松参数求解影响大于阔叶树。不同标绘类型改变了树种间参数的对比关系。Ⅱ型中除了程序法求解春榆Ψ_tlp显著高于数学法外(P<0.05),其他树种3种方法求解Ψ_tlp及C_RW,tlp均无显著性差异(P>0.05)。3种方法求解的同一参数间的线性方程决定系数在0.63～0.90之间(P<0.01)。其中,数学法与图形法线性关系最好,数学法与程序法、图形法与程序法线性关系次之。Ⅱ型标绘P-V曲线图形变化平缓,曲线部分与直线部分分界明显,可较好地估计水分参数。图形法在适用性上具有优势。

Comparison of different methods for determining the turgor loss point in pressure-volume curves

Water potential at turgor loss point(Ψ_tlp)and relative water content at turgor loss point(C_RW,tlp)have been considered important measurements of the drought tolerance of trees. This study compared Ψ_tlp and C_RW,tlp by two types of P-V curves(typeⅠ: Ψ versus C^-1_RW; typeⅡ:Ψ^-1 versus 1-C_RW)and with three common calculation methods(mathematical method, graphical method, and PV computer program)in type Ⅱ for major tree species in the eastern mountain region of Northeast China. The results showed that average values of Ψ_tlp and C_RW,tlp of eight species calculated from type Ⅰ were 0.20 MPa and 3.17% higher than those calculated from type Ⅱ. Especially parameters for the coniferous species Larix gmelinii and Pinus koraiensis were more significantly affected by two types of transformations than those of the broad-leaved species. In addition, the difference among species changed with different types of transformations. Ψ_tlp and C_RW,tlp calculated by three methods for the same species were similar except that Ψ_tlp for Ulmus japonica calculated by the computer program was significantly higher than the value calculated by the mathematical method(P<0.05). The determination coefficients(R²)between values of Ψ_tlp or C_RW,tlp calculated by the three methods were in the range of 0.63-0.90(P<0.01), and the values of R² of the mathematical method and graphical method were the highest. Compared with the typeⅠcurve, the shape of typeⅡ P-V curve had the advantages of being smooth and the obvious boundary between the curve part and the straight portion, making the turgor loss point easily detectable via plots of the data. Meanwhile, the graphical method had the advantage of easily applied, which can make it being used widely in the future.