Abstract:

To explore the effect and mechanism of 6-BA and planting density on leaf senescence of Nitraria tangutorum, after spraying 6-BA of different concentrations (0, 10, 20, and 30 mg·L^-1) on Nitraria tangutorum under two planting densities (low density plant spacing: 1.2 m × 1.5 m, high density plant spacing: 0.8 m × 1.0 m), we studied the dynamic changes and variation in leaf photosynthetic parameters (Pn, Tr, Gs, and Ci), chlorophyll, leaf osmoregulation substance content (Pro and SP), active oxygen metabolism, and antioxidant enzyme activity. Results showed that under 20 mg·L^-1 6-BA treatment, the Pn, Tr, and Gs of Nitraria tangutorum planted at low density were significantly higher than those without 6-BA treatment by 37.72%, 117.94%, and 83.18%, respectively, and Ci was significantly lower by 32.29% than that of the control. Compared with the physiological indices related to leaf senescence under the two planting densities of other 6-BA treatments, the 20 mg·L^-1 6-BA treatment of Nitraria tangutorum planted at low density can effectively promote the synthesis of Chl and SP in the early stage of leaf development (period t₁ to t₃); effectively alleviate the degradation of Chl, SP, and Pro; and inhibit the increase in malondialdehyde and H₂O₂ content in the later stage (period t₄ to t₅). Under the treatment of 10 and 20 mg·L^-1 6-BA, the antioxidant enzymes in the early growth stage of Nitraria tangutorum can be promoted, or their peroxidase, superoxide dismutase, and catalase activities can be increased. In addition, the decline in enzyme activities in the later growth stage of Nitraria tangutorum can be slowed down. The activities of the three enzymes treated with the same concentration of 6-BA showed low density > high density. The analysis of principal components and membership functions revealed that the anti-senescence ability of leaves under low density planting was the strongest when the leaves were treated with 20 mg·L^-1 6-BA every 10 days (eight times in total) from flower budding to fruit shedding. Spraying of 6-BA and reduced planting density can be used as important technical measures to alleviate leaf senescence and realize efficient planting and effective resource exploitation.

Key words: Nitraria tangutorum, 6-Benzyl adenine (6-BA), planting density, physiological characteristics of leaf senescence