干旱胁迫对桢楠幼树生长及光合特性的影响

Effects of drought stress on photosynthetic characteristics and growth of Phoebe zhennan seedlings

【目的】探讨桢楠幼树对干旱胁迫的响应机制,为桢楠幼树栽培的立地条件选择和水分管理提供参考。【方法】以2年生桢楠(Phoebe zhennan S.Lee)幼树为研究对象,采用盆栽控水的方法,对桢楠幼树进行干旱胁迫试验,试验共设7组处理,每隔5d依次对其中1组处理停止浇水,即分别持续干旱0(正常供水,对照),5,10,15,20,25,30d,30d后形成了不同土壤水分梯度,之后测定桢楠幼树在不同干旱胁迫处理下的生长和光合生理指标,并分析其变化规律。【结果】持续干旱0,5,10,15,20,25,30d后,土壤体积含水量(SWC)分别为20.50%,9.26%,7.55%,5.34%,3.86%,2.80%,2.57%。与对照相比,干旱胁迫下,土壤体积含水量显著降低(P<0.05)。干旱胁迫程度较轻(处理0～20d)时,桢楠幼树的叶片相对含水量(LRWC)无显著变化;重度干旱胁迫(处理20～30d)时,LRWC显著降低(P<0.05)。随着干旱胁迫强度的增加,桢楠幼树的树高生长量和地径生长量均显著降低(P<0.05),桢楠幼树叶片的叶绿素总量和类胡萝卜素含量均呈先升高后降低的趋势。干旱胁迫前期(干旱时间≤15d),桢楠叶片的净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)和胞间二氧化碳浓度(Ci)均显著降低(P<0.05);干旱胁迫后期(干旱时间>15d),Pn、Gs和Tr继续降低,而Ci显著升高,光合活性下降。干旱胁迫下桢楠幼树的表观量子效率、光饱和点、RuBP羧化速率、CO2饱和点均减小,对光能和CO2的利用能力减弱。【结论】干旱胁迫显著降低了土壤体积含水量,从而使桢楠幼树叶片的相对含水量减少,导致气孔关闭,阻碍了桢楠叶片光合色素的合成,减弱了其对光能和CO2的利用能力,进而抑制了桢楠幼树树高和地径的生长,当土壤体积含水量降至3.0%以下时,植株处于枯死状态。

【Objective】This study explored the response mechanism and adaptive capacity of nanmu(Phoebe zhennan)seedling to drought stress to provide basis for the rational management of young nanmu plantation.【Method】A pot experiment was conducted to study the growth and photosynthetic characteristics of two-year-old nanmu seedlings.A series of drought stresses with 7 treatments were formed by watering all treatments and then stopped watering for 30,25,20,15,10,5 and 0 d(CK),respectively.Then,the growth and photosynthetic physiological indicators of seedlings in different treatments were determined and analyzed.【Result】After continuous drought of 0,5,10,15,20,25,30 d,soil volumetric water contents(SWC)were 20.50%,9.26%,7.55%,5.34%,3.86%,2.80%and 2.57%,respectively.It is indicated that SWC decreased significantly(P<0.05)under drought stress.When the stress was moderate(0-20 d),there was no significant difference in leaf relative water content(LRWC)of seedlings between treatments,but LRWC was significantly decreased(P<0.05)after 20-30 d.The diameter and height increment of seedlings decreased significantly(P<0.05)with the increase of drought stress.The total amount of photosynthetic pigments increased first and then decreased with the intensifying drought stress.In the early stage of drought stress(drought time≤15 d),The Pn,Gs,Tr and Ci of seedling decreased significantly(P<0.05).While in the late stage of drought stress(drought time>15 d),Pn,Gs and Tr continuously decresased but Ci increased significantly(P<0.05),and photosynthetic activity declined.The apparent quantum yield(AQY),light saturation point(LSP),carboxylation rate of enzyme RuBP(CE),and CO2 saturation point(CSP)declined gradually with the increase of drought stress.【Conclusion】The drought stress significantly decreased SWC and LRWC,which resulted in stomatal closure and reduction of synthesis of photosynthetic pigments.Then,the ability of using light energy and carbon dioxide of seedlings was reduced and the growth of nanmu seedling was inhibited.When soil volumetric water content decreased to<3.0%,the stressed plant was in death state.