Compensatory Growth and Physiological Protective Mechanisms of Populus talassica Kom. × Populus euphratica Oliv. in Response to Leaf Damage

Abstract

The compensatory growth and defensive capabilities of woody plants after damage are crucial to their large-scale promotion and economic value. Here, Populus talassica × Populus euphratica were subjected to artificial defoliation treatments that simulated leaf damage [25% (D25), 50% (D50), and 75% (D75) leaf removal] to study the growth, anatomical, and physiological characteristics. The results showed that D25 and D50 treatments significantly increased the growth parameters, such as leaf length, leaf area, and specific leaf area, but did not affect the distributions of root and stem biomasses compared with the CK. However, the D75 treatment significantly decreased most growth parameters. The time required for the chlorophyll content to recover increased along with the damage intensity as follows: D25, high-flat-high; D50, low-high-flat; and D75, low-flat-high. Furthermore, leaf damage significantly reduced stomatal density, whereas the stomatal width, area, opening, and Pn significantly increased by 8.59%, 8.40%, 23.27%, and 31.22%, respectively, under the D50 treatment, generating a photosynthetic compensation response. The leaf anatomical parameters increased along with damage intensity, except spongy tissue thickness, which decreased, while the stem anatomical parameters showed trends of first increasing and then decreasing, reaching maxima under the D50 treatment. The enzymes showed an increasing and then decreasing trend as the damage time increased. After 1 d of treatment, CAT, POD, and PAL activities peak at D75, in contrast to a peak of SOD activity at D50. Overall, these findings indicate that it is advisable to keep the amount of leaf damage within 50%. The leaf damage can have an impact on the growth of P. talassica × P. euphratica. They adjusted their resource allocation strategy and physiological defense capacity by increasing the chlorophyll content, improving photosynthetic capacity, changing stem and leaf anatomy, and increasing defense enzyme activity levels, thereby improving their damage tolerance and adaptability.