低养分基质下沙地柏和樟子松苗木对遮荫的响应

Responses of Juniperus sabina and Pinus sylvestris var. mongolica seedlings to shading in low nutrient conditions

为了研究遮荫对贫瘠土壤上生长的植物存活率、相对生长率(RGR)、生物量分配模式及光合特性的影响,本文以耐荫的沙地柏和不耐荫的樟子松苗木为试材,进行全光和不同遮荫处理(35%、65%和95%),遮荫处理时间为2个生长季。结果表明,随着光照强度减弱,沙地柏的存活率和生长量没有明显变化,总生物量和RGR均呈先上升后下降的趋势,且RGR指标均为正值,茎根比显著提高;而樟子松存活率和生长量显著降低,总生物量和RGR一直呈下降趋势,且95%遮荫率下RGR为负值,茎根比显著降低。沙地柏的最大光化学效率(Fv/Fm)对遮荫更加敏感,在35%遮荫率下就显著增加,而樟子松在65%遮荫率时才开始显著增加。JIP-测定进一步表明,遮荫下沙地柏标准化荧光值(Vt)从O相到接近P相的过程中均明显低于全光照(CK),电子越过QA的能量占反应中心捕获能量的比例(ψo)、用于电子传递的量子比率(ψEo)均提高,且质体醌库(Sm)变大,质体醌库还原速率(Sm/Tfm)提高、初级醌受体被还原的次数(N)增多,单位激发态面积用于电子传递的能量(ET_o/CS_o)增加、反应中心数目(RC/CS_o)增多,单位反应中心电子传递的能量(ET_o/RC)增加,同时单位激发态面积(DIo/CS_o)和单位反应中心(DIo/RC)的热耗散的能量均降低,最终导致其性能指数(PIABS,PICS_o,PICSm)明显高于全光照。遮荫下樟子松标准化荧光值从O相到接近P相的过程中均明显高于CK,除热耗散指标外以上这些荧光参数与CK没有明显差异,甚至更低,而DIo/RC指标保持不变,最终导致其性能指数(PIABS,PICS_o,PICSm)与CK没有明显差异。以上结果暗示,沙地柏在较低的光强下能维持较高的生长量,通过维持正向碳平衡保持了较高的存活率,增加了地上生物量的比例,提高了光反应阶段电子传递的能量水平;而樟子松碳收支失衡导致了较低的存活率,地上生物量比例下降,电子传递的能量水平降低。

To determine the effects of shade on survival rate,relative growth rate（RGR）,biomass allocation and photosynthesis characteristics,potted seedlings of shade-tolerant Juniperus sabina and shade-intolerant Pinus sylvestris var.mongolica in low-nutrient substrate were grown without shade or under a 35%,65% or 95% reduction of full sunlight over two growing seasons.The results showed that,with decreased light availability,J.sabina growth and survival did not change significantly.Total biomass and RGR increased and then decreased;RGR indicators were positive;and the shoot/root ratio increased significantly.In contrast,the survival rate and growth of P.sylvestris var.mongolica decreased significantly.Total biomass and RGR decreased;the RGR was negative under 95% shade;and the shoot/root ratio decreased significantly.The maximum photochemical efficiency（Fv/Fm） of J.sabina was more sensitive to shade and increased significantly under 35% shade,while the Fv/Fmof P.sylvestris var.mongolica increased significantly until 65% shade.A JIP-test showed that the standardized fluorescence values（Vt） of J.sabina under shade were lower than those under the non-shading treatment（CK） from initial O phase to final P phase.Furthermore,the proportion of electron energy across the QAreaction center to the whole energy captured（ψo）,quantum yield of electron transfer（ψE o）,size of plastoquinone pool（Sm）,plastoquinone pool reduction rate（Sm/Tfm）,number of reduced primary quinone acceptors（N）,and energy for electron transfer per excited cross-section（ETo/CSo） all increased.The density of reaction centers（RC/CSo） increased,while dissipation per excited cross-section（DIo/CSo） and per reaction center（DIo/RC） decreased,leading to significantly higher performance indexes（PIABS,PICSo,PICSm） under shade than under CK.The Vtof P.sylvestris var.mongolica under shade was higher than under CK from O phase to P phase;however,the above fluorescence parameters were lower or were not significantly different under shade except for the heat dissipation indexes.DIo/RC remained unchanged in P.sylvestris var.mongolica under shade,and the performance indexes（PIABS,PICSoand PICSm） also remained unchanged.The above results indicated that J.sabina was able to maintain high growth and survival under low light intensity by maintaining a positive carbon balance and increasing the proportion of aboveground biomass and electron transfer energy levels during the light-reaction stage.In contrast,P.sylvestris var.mongolica had a low survival rate due to a carbon budget imbalance,and the decreases in proportion of aboveground biomass and electron transfer energy level under shading conditions.