Effects of boron on the growth, physiology and photosynthetic characteristics of Cunninghamia lanceolata under aluminum stress
In order to reveal the regulatory mechanism of boron(B)-mediated aluminum (Al) tolerance in Cun-ninghamia lanceolata, and provide a reference for reducing Al toxicity of C. lanceolata by nutrient management, the effects of B on the growth, physiological and photosynthetic characteristics of C. lanceolata under Al stress were investigated in this study. A total of four treatments with control (CK), B deficiency (-B), B deficiency plus Al (-B+Al) and B plus Al (+B+Al) were set by using three-month old of C. lanceolata seedlings to investigate the dif-ferent responses of growth, photosynthetic physiology and resistant physiology of C.lanceolata among different treatments. The results showed: (1) The growth of the seedlings height was significantly inhibited under different stress treatments as compared with CK, and which was decreased by 31.83％- 55.56％, moreover, under Al stress,exogenous application of boron (+B+Al) significantly alleviated the boron deficiency (-B+Al)-induced growth inhibi-tion of the seedlings, and the decreased of malondialdehyde, hydrogen peroxide (H2O2) and photosynthetic pigment contents in leaves of C. lanceolata, the seedling height, the contents of MDA, H2O2, chlorophyll and carotenoid in (+B+Al) treatment were increased by 48.02％, 24.18％, 16.39％, 17.16％ and 17.78％, respectively, as compared with (-B+Al) treatment. (2) The activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase in the leaves of C. lanceolata were significantly higher under different stress treatments as compared with CK, and the se-quential order of antioxidant enzyme activities was +B+Al>-B+Al>-B>CK, the increasing amplitude of these en-zyme activities in different stress conditions ranged from 17.10％- 128.87％, 15.19％- 152.10％, 37.39％- 412.11％ and 44.07％- 271.66％, respectively. (3) The net photosynthetic rate, water use efficiency, the maximal fluorescence, variable fluorescence, PSⅡ potential photochemical activity, PSⅡ maximum photochemical efficiency, potochemi-cal quenching coefficient and actual maximum quantum yields in the leaves of C. lanceolata all displayed decreasing tendency under different stress conditions as compared with CK, and their decreasing amplitude were in the ranges of 51.06％- 59.50％, 2.43％- 16.71％, 7.07％- 20.45％, 7.80％- 29.93％, 27.16％- 54.07％, 2.53％- 13.53％, 4.66％- 12.61％ and 4.25％- 13.77％, respectively, moreover, the decreasing amplitude in -B+Al treatment was significantly higher than that in +B+Al treatment. In conclusion, under Al stress, as compared with boron deficiency, exogenous application of boron could significantly decreased the accumulation of H2O2 and MDA by increasing antioxidant en-zyme activities in the leaves, thus alleviated H2O2-induced oxidative damage and degradation of photosynthetic pig-ment, which enhanced the photosynthetic efficiency and light energy utilization in the leaves, and promoting the syn-thesis of carbon assimilation product, and ultimately ameliorated Al-induced growth inhibition.
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