巨桉根系分解对菊苣生长及光合特性的影响

巨桉是我国退耕还林过程中采用的重要速生树种之一,被广泛用于人工造林。采用盆栽试验,研究了巨桉根系分解初期对菊苣幼苗生长和光合生理特性的影响。试验设置A1(50 g/盆)、A2(100 g/盆)和对照(CK)3个根系水平,将各处理的根系分别与10 kg土壤混合后装盆,播种菊苣。待A2处理植株的第3片真叶完全展开后测定菊苣光合生理指标及相关生长指标。结果表明:在巨桉根系分解初期,明显抑制了菊苣高生长、根生长、生物量积累、叶面积扩展及光合色素的合成,且随着根系添加量的增加抑制作用加大;菊苣叶片胞间CO2浓度(Ci)增加,而净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)均显著低于对照;随土壤中根系含量的增加,除CO2补偿点(CCP)呈增加趋势外,其他光响应和CO2响应的特征参数均呈明显的下降趋势,并与对照差异显著;各生长指标除与胞间CO2浓度呈现出负相关外,与其它光合特征参数、光合色素以及相应的响应曲线参数之间均呈现出显著或极显著的正相关关系;通过GC-MS检测表明,巨桉根系中含有2,6-二叔丁基对甲酚、N-甲基苯乙胺等多种具有化感潜力化学物质,在其分解过程中,这些化感物质逐步释放并作用于受体植物,抑制其光合色素合成和光合作用,降低其环境适应能力,从而抑制菊苣的生长。

Effects of decomposing Eucalyptus grandis root on the growth and photosynthetic characteristics of Cichorium intybus

In resent years, a large number of fast-growing exotic species had been introduced to south China for restoration and recon-struction of degraded ecosystem and economic development. Eucalyptus grandis, one of important tree species, was widely used in the Project of Returning Farmland to Forest and also used in afforestation in mountainous area. With the rapid development of E. grandis plantation, It has been not only brought tremendous economic benefits but also caused a series of ecological and environmental problems, such as soil degradation, the loss of soil nutrients, the decrease of soil productivity and the biological diversity shrinking, so its develop-ment has been attracted a great deal of controversy. It was reported that E. grandis could release certain chemical substances to inhibit the growth of the plants near and/or under the crown of E. grandis plantations. It is of great practical significance to explore the allelopathic effects and mechanisms of E. grandis litter(fallen leaves and dead roots) on some crops which were often intercropped with E. grandis in the system of agroforestry. Cichorium intybus was a kind of high-quality forage grass which was very common in south China, thus it was selected in this study.A pot experiment was conducted to study the effects of E. grandis root on the growth and the photosynthesis of C. intybus during its early stage of decomposition. Each pot contained 10 kg soil mixed with different amounts of E. grandis root (50 g/pot, A₁; 100 g/pot, A₂; and 0 g/pot, CK), and sowed with C. intybus. The growth indicators and the photosynthetic characteristics of C. intybus were measured after the third leaf of seedling fully expanded in treatment A₂. The results were as follows. At the early stage of E. grandis root decomposition, the height, root and leaf area growth, biomass accumulation, and the content of photosynthetic pigment of C. intybus were significantly inhibited, and the inhibition effect was getting stronger with the increasing amount of E. grandis root addition; The intercellular CO₂ concentration(C_i) of C. intybus was increased by root addition, while net photosynthetic rate(P_n), stomatal conduct-ance(G_s) and transpiration rate(T_r) were significantly lower than those of the control; With the increase of root addition, all parameters of light response and CO₂ response of C. intybus showed an obviously downward trend except CO₂ compensation point, and there existed significant differences between the treatments of root additions and the control; The growth indexes showed a negative correlation with the intercellular CO₂ concentration, while it showed significant or extremely significant positive correlation with other photosynthetic parameters, photosynthetic pigments, and the corresponding parameters of the response curve; Detection wtith GC-MS showed that E. grandis, roots contained chemical substances which had allelopathic potential, such as 2,6-Bis(1,1-dimethylethyl)-4-methylphenol and Benzeneeth-anamine, N-methl. It was indicated that, when E. grandis root decomposed, the allelopathic substances released gradually and acted on receptor plants, inhibited the synthesis of photosynthetic pigments and the photosynthesis of the receptors, decreased the adaptation ability of receptors to environment and accordingly, inhibited the growth of C. intybus.