遮荫对弗吉尼亚栎苗木生长及光合-荧光参数的影响

Effects of Shading on Growth, Photosynthesis and Chlorophyll Fluorescence Parameters in Leaves of Quercus virginiana Seedlings

[目的]揭示美国引进树种弗吉尼亚栎幼苗对光照强度的响应特征,为弗吉尼亚栎的引种驯化和高效栽培提供科学依据。[方法]采用人工遮荫法,研究3种光环境下(全光——100%自然光、中度遮荫——50%自然光和强度遮荫——25%自然光)弗吉尼亚栎苗木生长、光合作用以及叶绿素荧光参数的变化。[结果]表明:中度遮荫明显促进弗吉尼亚栎苗高生长(P<0.05),但对地径生长影响不明显;而强度遮荫条件下,地径生长受到明显抑制(P<0.05),苗高虽有所下降,但与对照相比差异不明显。对弗吉尼亚栎光响应曲线的观测表明:与全光条件相比,中度遮荫条件下,弗吉尼亚栎叶片暗呼吸速率(Rd)、光饱和点(LSP)以及光补偿点(LCP)均明显下降(P<0.05),说明适度的遮荫有助于提高弗吉尼亚栎对光的利用效率,促进干物质的积累;而强度遮荫条件下,光补偿点和光饱和点明显上升,暗呼吸速率明显增加(P<0.05)。遮荫并未对表观量子效率(α)和最大净光合速率(P_(max))产生明显的影响。进一步对叶绿素荧光参数分析发现,遮荫条件下,PSⅡ最大光化学量子产量(F_v/F_m)和实际光量子产量(Yield)有所增加,但均在正常范围,说明遮荫对PSⅡ活性并未产生胁迫。[结论]弗吉尼亚栎幼苗对遮荫均具有一定的耐受性,中度遮荫有利于苗高生长;而强度遮荫不利于干物质的积累。因此,建议在营林以及人工栽培过程中维持50%以上的自然光照。

[Objective] To discover the response to light intensity of Quercus virginiana, and the effects of different levels of shading on growth, photosynthesis and chlorophyll fluorescence parameters.[Method] Three light levels(full light-100% natural light, moderate shading-50% natural light and high shading-25% natural light) were set in greenhouse by covering different layers of shading net. The growth, chlorophyll content index, photosynthesis and chlorophyll fluorescence parameters were determined during the experiment.[Result] The results showed that the height growth of seedlings increased significantly(P<0.05) under moderate shading condition, while no obvious change was observed in the growth of basal diameter. Under high shading conditions, the height growth changed a little compared with control, whereas the growth of basal diameter was inhibited significantly(P<0.05). Under moderate shading, the dark respiration rate(R_d), light compensation point(LCP) and light saturation point(LSP) declined and whereas increased significantly under high shading, which showed that moderate shading might be helpful to improve the light use efficiency and increase the dry mass accumulation in leaves of Q. virginiana. There were no obvious changes in apparent quantum yield(α) and the maximum net photosynthetic rate(P_(max)). Further analysis of chlorophyll fluorescence parameters showed that PSII primary energy conversion efficiency(F_v/F_m) and photochemical efficiency of PSII in the light(Yield) remained a reasonable range under two light levels, which indicated that the PSII activity might be not damaged.[Conclusion] These results indicate that Q. virginiana could tolerate certain shading conditions, however, high shading was considered to be detrimental to the accumulation of dry matter, and light condition with more than 50% natural light would be recommended during the silviculture and nursery cultivation.