Hydraulic Traits in Populus simonii Carr. at Stands of Categorized Ages in a Semi-Arid Area of Western Liaoning, Northeast China

Abstract

Poplar plantations can acclimate to drought stress in semi-arid areas, where the variation of stand age may result in varied water adaptation strategies presented as hydrodynamic performance. In this study, nine mature Populus simonii Carr. individuals were targeted as sampling objects in plantations characterized to three stand ages: young (9 yr), middle-aged (17 yr), and near-mature (29 yr) stages in a semi-arid area of western Liaoning, Northeast China. Hydraulic traits were investigated as parameters of leaf pressure-volume curves, xylem embolism vulnerability curves, hydraulic structure, and wood density (WD). Results showed that osmotic potential (Ψtlp) and relative water content at the turgor loss point and cell-wall bulk elastic modulus were lowest in middle-aged stands (−2.19 MPa; 86.71%; 13.75 MPa). Stem and leaf-specific hydraulic conductivity (Ks and LSC) were all the highest in middle-aged stands. Xylem embolism vulnerability (P50) and lethal water potential of trees (P88) increased with the growth of stand age. Young stands faced minimal risk of hydraulic failure according to the stomatal safety margin (SSMtlp, Ψtlp minus P50), which was consistent with the comprehensive evaluation results of the principal component analysis. WD was related to P88 (R2= 0.51; p < 0.05). P50 was related to drought avoidance traits Ψtlp (r = 0.76; p < 0.05) but not to xylem efficiency (Ks). Overall, WD can be an excellent proxy for hydraulic safety monitoring. Young and middle-aged Populus simonii populations are more adaptable to drought conditions than near-mature populations, and near-mature stands should receive intermediate cuttings to avoid exposure to drought stress.